Slab on grade vapor barrier performance

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Author Message Dale Hurttgam, NCARB, AIA,LEED AP, CSI Senior Member Username: dwhurttgam Post Number: 55 Registered: 10-2005 Posted on Thursday, March 18, 2010 - 12:32 pm:    I have been asked to idenify the appropirate vapor barrier performance to comply with ACI 302.2R-06 that will satisfy flooring manufacturer's requirements. There would be many flooring manufacturers to contact in this regard - the common element is that almost all of them require the floor to pass testing at moisture content below 3 lb.per 1000 s.f.per 24 hour. The ASTM 302.2R-06 that I was given identifies: It should be determined whether a vapor retarder with 0.1 perm rating....is sufficient protection for flooring material to be installed. If not a vapor barrier with a perm rating oof 0.01 or less...should be specified. The above is from a synopsis of "Updated standards and expert recommendations" given to me by our structural engineering staff. I expect that if I start contacting floor manufacturers, they are going to tell me that they don't care how we achieve it - they just want the end result to test our per their requirements. In our office, we typically specify the vapor barrier to be directly below the slab with the sand cushion below. We have encountered projects where we have had difficulty meeting the moisture requirements and have had to go to costly remediation. We believe that a primary part of the problem is insufficient building enclosure and/or failure to wait long enough for the concrete to dry out. Although we have also encountered moisture problems when these two concerns did not appear to be part of the problem. Are there any floor manufacturer reps out there or underslab vapor barrier reps who may be able to address this. Comments from anyone with input on this concern will be welcome. Richard L Matteo, AIA, CSI, CCS Senior Member Username: rlmat Post Number: 370 Registered: 10-2003 Posted on Thursday, March 18, 2010 - 12:37 pm:    You also need to look at ACI 302.1R You might want to contact Stego Industries They are at the forefront of this There is also a CSI Green Sheet put out by the Phoenix, AZ CSI Chapter that may offer some insight Ralph Liebing, RA, CSI, CDT Senior Member Username: rliebing Post Number: 1153 Registered: 02-2003 Posted on Thursday, March 18, 2010 - 12:45 pm:    Might look at A-1030 and B-1030 docs on this site--http://www.conspectusinc.com/publications.htm And might try Tom Dudick, who is a very vocal manufacturer [his own company] of floor coatings-- www.dudick.com or tdudick@dudick.com Ronald L. Geren, AIA, CSI, CCS, CCCA, SCIP Senior Member Username: specman Post Number: 841 Registered: 03-2003 Posted on Thursday, March 18, 2010 - 12:55 pm:    Ditto Richard's suggestion on Stego. What have you used in the past? If you're meeting just the code minimum (6-mil poly) you're just wasting money. Ron Geren, AIA, CSI, CCS, CCCA, SCIP www.specsandcodes.com Nathan Woods, CCCA, LEED AP Senior Member Username: nwoods Post Number: 331 Registered: 08-2005 Posted on Thursday, March 18, 2010 - 01:20 pm:    Dale, if you happen to be in the LA area, there is a presentation TODAY at lunch on exactly this topic, presented by the ACI Southern California Chapter . Presentation includes: Moisture in Floors Presentation will include the following: California construction defect litigation past and present, particularly residential, involving concrete slab cracking and the presence of moisture related to the suitability for flooring installations; Senate Bill 800 and what it means for the stakeholders in the concrete industry, especially suppliers, subcontractors, and design professionals; degree of acceptance for, initial development of, changes in, and current uses for vapor emission and relative humidity tests of concrete before and after installation of flooring; the changing authority and requirements of flooring standards; discussions of concrete provided within resilient flooring guidelines. The changing risks and potential duties for those who design, specify, order, install and supply concrete especially foundations and interior slabs. Location: Luminarias Restaurant & Banquets 3500 West Ramona Boulevard, Monterey Park, CA 91754 For a good contact at Stego, try Mike McCarthy at (949) 412-3444 or mikemccarthy@stegoindustries.com (Mike is also a local CSI chapter Board Member) There are some excellent articles on moisture migration and related topics pertaining to concrete on Ken Bondy's website: http://kenbondy.com/professional.htm Dale Hurttgam, NCARB, AIA,LEED AP, CSI Senior Member Username: dwhurttgam Post Number: 56 Registered: 10-2005 Posted on Thursday, March 18, 2010 - 02:01 pm:    I am always amazed at how quick the responses come. Thank you for the info, I will be following up on the leads provided. Unfortunately I am not in the LA area - a couple thousand of miles away. We also recently had a seminar/meeting on slab moisture and curl problems at our local Building Envelope Council. The question reqarding specific perm ratings for the vapor barrier had not come up and did not get addressed there. J. Peter Jordan Senior Member Username: jpjordan Post Number: 407 Registered: 05-2004 Posted on Thursday, March 18, 2010 - 02:59 pm:    I have a chart that I would be willing to share (jpjordan@jordanconsultants.com). Although Stego almost invented this category of product, there are several manufacturers with products that are more durable and more impermeable. Although a good vapor retarder installed under a concrete slab on grade may prevent ground water in a vapor state from penetrating through the slab, the amount of water in the concrete may be problematic for floor coverings. This can be an issue for concrete floors over steel form deck since the moisture can't escape through the bottom. Steven Bruneel, AIA, CSI-CDT, LEED-AP Senior Member Username: redseca2 Post Number: 223 Registered: 12-2006 Posted on Thursday, March 18, 2010 - 03:36 pm:    Peter is correct. I have seen as many floor finish failures from slab moisture issues in raised slabs as I have seen in slab on grade. You certainly need a good vapor barrier under the slab on grade, but you also need to do moisture testing of the cured slab and be prepared with a remedial surface-applied moisture control product. I always enjoy relating that my first personal experience with a flooring failure was about 20 years ago when raised dot Pirelli rubber flooring started blistering like crazy on a high-end hotel restoration. The point of bringing this up was that particular concrete floor was several levels above grade and had been poured in 1908, more than 80 years before. Plenty of time to "cure". But enough moisture got into that concrete during the construction phase to delaminate the rubber flooring. Nathan Woods, CCCA, LEED AP Senior Member Username: nwoods Post Number: 332 Registered: 08-2005 Posted on Thursday, March 18, 2010 - 03:37 pm:    We specify .45 water/cement ratio for all floor slab concrete, whether it's on grade or elevated deck. Mark Gilligan SE, CSI Senior Member Username: mark_gilligan Post Number: 265 Registered: 10-2007 Posted on Thursday, March 18, 2010 - 03:51 pm:    The vapor barrier will have little to no impact on the time it takes to pass the moisture content test. Essentially the moisture being measured has to do with the moisture in the upper part of the slab. Transmission of moisture from the subgrade should be essentially nill in this short term. It has been reported that this 3 pound number may be difficult if not impossible to meet in many cases. In such circumstances the flooring manufacturer can deny all responsibility for the finished flooring. Recommendation to use concrete with a low water cement ratio and heat the space and provide normal air changes before performing the test. Also use the test devices with the courses sized salt particles acceptable under the standard to give you the lowest values. Dale Hurttgam, NCARB, AIA,LEED AP, CSI Senior Member Username: dwhurttgam Post Number: 57 Registered: 10-2005 Posted on Thursday, March 18, 2010 - 03:54 pm:    With respect to Ron's comment: Are current spec is for a 15 mil vapor barrier with several manufactures listed including some of those identified here. It is specified to comply with ASTM E 1745-95, Class A.1. I did also receive the chart from Peter - Thank you. David E Lorenzini Senior Member Username: deloren Post Number: 95 Registered: 04-2000 Posted on Thursday, March 18, 2010 - 05:35 pm:    The issue of vapor emission and alkalinity in slabs on grade is like "alchemy" (a medieval chemical science and speculative philosphy aiming to achieve the transmission of base metals into gold). Everyone has a solution but no one has produced the gold. However, there are several things you can do to minimize the problem: 1. any 15-mil vapor retarder 2. no sand layer between the retarder and the concrete!!! 3. water/cement ratio of 0.45 to 0.48 4. continuous water cure for 7 to 10 days In addition, you can ventilate the space above the slab to reduce the relative humidity. David Lorenzini, FCSI, CCS Architectural Resources Co. C. R. Mudgeon Senior Member Username: c_r_mudgeon Post Number: 62 Registered: 08-2002 Posted on Thursday, March 18, 2010 - 06:08 pm:    Or you could dig up some of the old high-VOC adhesives! JD Grafton New member Username: cc_solutions Post Number: 1 Registered: 03-2010 Posted on Thursday, March 18, 2010 - 06:47 pm:    Responding to the original question regarding the requirements for the sub slab vapor retarder, I believe ASTM E1745 (Standard Specification for Water Vapor Retarders Used In Contact With Soil or Granular Fill Under Concrete Slabs) calls for a product with a permeance of .1 or less. This specification is also called out in F710 (Standard Practice for Preparing Concrete Floors to Receive Resilient Flooring). Is that the type of information you were looking for? JD Grafton Junior Member Username: cc_solutions Post Number: 2 Registered: 03-2010 Posted on Thursday, March 18, 2010 - 07:01 pm:    David said: However, there are several things you can do to minimize the problem: 1. any 15-mil vapor retarder 2. no sand layer between the retarder and the concrete!!! 3. water/cement ratio of 0.45 to 0.48 4. continuous water cure for 7 to 10 days And those are excellent points! But I advise quite a bit more to increase the chances your slab will be ready for moisture sensitive flooring. 5. Limit the cement in the mix. Less cement means less water. If you can remove 100 pounds of cement by using a well graded aggregate and decreasing the required compressive strength (many slabs are coming in at 6,000psi and above) you can eliminate 50 pounds of water per yard of concrete. 6. Limit wet curing to 3-5 days. This is sufficient to achieve a hard cap on the concrete, yet it will begin the drying process earlier, and retain some of the porosity in the surface which promotes drying. 7. Minimize recurring wettings. Each time the slab is re-wet, the drying process is impacted significantly. Don't let sprinkler fitters flood the floors, or drywall mudders mix their products on drying slabs. 8. Install RH probes early and keep all trades posted as to how you are coming along toward your goal. I have seen a real team spirit form when trades understand the goal and see the active pursuit of a dry slab. Dale Hurttgam, NCARB, AIA,LEED AP, CSI Senior Member Username: dwhurttgam Post Number: 58 Registered: 10-2005 Posted on Friday, March 19, 2010 - 01:14 pm:    Thank you JD. This is the type of info that I was looking for. I will check out F710. ken hercenberg Senior Member Username: khercenberg Post Number: 47 Registered: 12-2006 Posted on Wednesday, April 07, 2010 - 02:31 pm:    It seems that many flooring manufacturers are also moving away from re-emulsifiable acrylic adhesives in favor of epoxies and urethanes depending on application requirements. Still, as Dave and JD pointed out, if the water isn't there it isn't going to cause the problem. Oh, allow for the thickness of the concrete. An 8 inch thick concrete deck is going to take twice as long to dry as a 4 inch deck. Do not permit the Installer to heat the space to 'dry' it out. The heat will drive the moisture deeper into the concrete until the heat source is removed, one reason why RH testing is preferred to calcium chloride. Good luck. John Regener, AIA, CCS, CCCA, CSI, SCIP Senior Member Username: john_regener Post Number: 459 Registered: 04-2002 Posted on Wednesday, April 07, 2010 - 06:33 pm:    I'm with David Lorenzini on this subject of moisture mitigation. In fact, we share a client and have been fighting ignorance on this subject for literally years. The thickness of the vapor barrier under the slab on grade concrete is irrelevent. What is relevent is the performance of the vapor barrier. That is, how many perms (i.e., how much moisture vapor) will pass through the barrier. Roughly speaking, the perm rating should be 0.01. My understanding is that you can get this by using SaranWrap ("or equal"). But it isn't durable enough for construction use. THEREFORE, a vapor retarder of some thickness (8 mils, 10 mils, 15 mils?) get's specified. The 10 mil thickness is commonly specified because that's what's in the soils report's recommendations: the infamous 10 mil Visqueen. (Is unreinforced polyethylene Visqueen made and sold in the US anymore?) So, the vapor barrier stops moisture coming out from the soil under the building. But then there's the residual water in the concrete. Water in concrete GOOD for hydrating portland cement. Water in concrete BAD after hydrating all done. Gotta get rid of residual water in concrete or stop it from getting to slab surface. My understanding, after attending the seminars by SINAK Corporation at several CSI "Conventions", is that it isn't water that causes flooring adhesive failure but what's carried in the water: alkali. Alkali attacks the adhesive and causes it to stop bonding. Oh, and water provides a medium for growing mold, which can be a big NO-NO too. So, concrete gets tested before flooring gets installed. If minimizing moisture coming out of the concrete is the goal, expressed in vapor pressure (pounds per 1000 square feet of area in 24 hr period), then spec low value. 3 pounds is a nice low number but 5 pounds might be more reasonable. My understanding is that 5 pounds is the goal for adhesively-applied floor coverings. 3 pounds is the goal for coatings and products like epoxy terrazo. Getting 5 pounds is fairly common but takes serious work. Getting 3 pounds is difficult. Independent specifiers in Orange County, CA had a presentation by the president of Koester, a manufacturer of high-end moisture mitigation and other concrete remediation products. He's a true expert and he stated that 3 pounds is nearly impossible to achieve. But say the tests get done and the moisture vapor pressure is acceptable ... today. In weeks following, moisture comes up from inside the concrete. Remember, only the upper surface was tested. There's LOTS of water left in the concrete. Also remember that there was 2-inches of sand over top of the vapor barrier and it was soaked with water before the concrete was placed because the structural engineer insisted on it so the slab wouldn't curl. The structural engineer is responsible for slab curling but not flooring failures. The gobs of water in the concrete works its way to the surface over weeks and weeks or even years and years of time. Is it a wonder that any adhered flooring or floor coating doesn't fail? So ... here come the snake oil peddlars. "Our product is guaranteed (sort of) to not allow moisture vapor greater than (3) (5) pounds per 1000 square feet in 24 hours (as long as the concrete doesn't crack or get gouged during construction)." AND you get to save lots and lots of money compared to the cost of moist curing the concrete for 10 or 14 days. And you (contractor and/or CM) get a defined risk because they now have a set price for "moisture mitigation," especially compared to the high price of the undefined scope of topical remediation when the moisture vapor pressure gets tested just before the flooring is installed and fails. And if after you have used the topical treatment (snake oil, in my opinion) and there's a failure, it isn't the fault of the contractor or CM. They only followed the spec or deductive change order that the Architect-of-Record (LEED AP and all) said was okey-dokey. One final thought about the old, elevated concrete floor slab failing the moisture vapor test. A conscientious flooring contractor might have cleaned the floor slab before the flooring installation and might have even flooded the floor when washing it. This would send the moisture vapor pressure sky-high temporarily. I've heard of contractors who have an allowance in the contract for moisture vapor remediation purposely wetting the concrete surface to make it test high. After all this, I have to say I don't know what to do except specify 0.45 water:cement ratio, 14 day moist cure by sheet method and test the concrete floor before installing the flooring. If the test fails, fix it the way the flooring manufacturer says to do it so the flooring adhesive or coating won't fail. The Contractor and/or CM have control over this problem. They built the floor slab. Let them use their superior knowledge and experience to figure out how to fix their problem. Mark Gilligan SE, CSI Senior Member Username: mark_gilligan Post Number: 270 Registered: 10-2007 Posted on Wednesday, April 07, 2010 - 06:59 pm:    The thickness of the slab should not have a negative impact on the "drying" time. A couple of realities for dry slabs are the water that impacts the test is found near the surface of the slab and the interior of dry concrete will typically be saturated even many years afrter the slab has dried J. Peter Jordan Senior Member Username: jpjordan Post Number: 412 Registered: 05-2004 Posted on Thursday, April 08, 2010 - 11:27 am:    I tend to agree with Mr. Regener. I would say that when you build on a swamp (like in Houston) you probably will have more of a problem with ongoning vapor transmission; however, I believe that much of the initial problem is with unhydrated water in the concrete. I would also like emphasize that thickness doesn't have much to do with perm rating. 10 mil polyethylene only has a perm rating of 0.1400, far above the 0.01 Mr. Regener recommends. Stego's 15 mil product has a perm rating of 0.0084. There are, however, at least two 10 mil products on the market with a lower perm rating and better puncture resistance. There are some reps out there who are claiming that a product with a perm rating of 0.01 or less can be called a "vapor barrier"; I have yet to see any standard (ASTM, ANSI, etc.) cited for this statement. It is my suspicion that when the perm ratings get below 0.02, the difference this makes in the field is negligible, but I don't know that for a fact, and the 0.02 cutoff line is purely arbitrary. JD Grafton Member Username: cc_solutions Post Number: 3 Registered: 03-2010 Posted on Sunday, April 11, 2010 - 11:32 pm:    The thickness of the slab has a huge impact on drying time. Much of the water of convenience will be a very long time coming out from the deep horizons of the concrete when it is allowed to dry in only one direction. One very confusing aspect of the CaCl test is that it only reads the moisture being emitted from the top half-inch or so of the concrete. On a well cured slab, the top can be forced dry while the interior of the slab is very wet. Examining a failure and finding high vapor emissions at a later date is readily explained by moisture redistribution or equilibration through the slab. For this reason I always use RH readings carefully harvested from several locations to get a good picture of the true 'potential' of the concrete slab to cause problems later on. In my former life I trouble-shot (shooted?) flooring failures for a medical facility builder that provided a lifetime warranty on their buildings. You can imagine the importance placed on finding the causes and cures for flooring failures when you have a lifetime warranty on those floors. Oh the stories I can tell.... Now I am a consultant and mitigation contractor. I am Koester certified, and I cringe at all those spray and pray systems. LOL Oh, I recommend a two to three day moist cure. Longer than that and the cement matrix begins sealing the pores of the concrete so thoroughly that the drying process is impeded, less than that and the concrete surface may be left weak. With a low water/cement ratio and the use of less cement and a well graded aggregate, we can get strong concrete that will dry to required RH and MVER in a very short time, say 3-4 months for a 4" slab. ken hercenberg Senior Member Username: khercenberg Post Number: 48 Registered: 12-2006 Posted on Monday, April 12, 2010 - 09:49 am:    Excellent thread. So now we know to limit the cement content and the water-cement ratio, use a good vapor retarder with no blotter course, wet cure for 2 to 3 days, and test using Relative Humidity, not just calcium chloride. Now let's continue... With LEED, we have the inclusion of fly ash, granulated slag, etc as replacement pozzolans to offset the amount of Portland cement in our mix. How does this affect our efforts to decrease the amount of cement in the mix? Regarding curing, sealing, densifying, etc., what happens after the initial 2-to-3 days of wet cure? Do we opt for silicate technologies for concrete being left exposed (no floor coatings or coverings)? What about at floors with finishes? There is a whole industry (see http://www.4specs.com/s/09/09-6105.html) of manufacturers of systems, including reputable systems, that claim to be able to reach that elusive 3 pound threshold. Do we give up and just include it in the project or do we include a square foot allowance and require unit prices, or do we approach this in some other manner (like make it the Contractor's problem)? As an aside, I prefer to have an independent agency test the floor specifically to prevent the probability of having the wolf guard the henhouse. I too have heard of contractors who have made sure the concrete 'failed' just to ensure extensive remediation. Surface prep: How important is the inclusion of light shot-blasting in the spec to remove the fracture plane that is often a problem even if the pH and moisture content are okay? Obviously I have my bias; curious to hear from each of you. John Bunzick, CCS, CCCA, LEED AP Senior Member Username: bunzick Post Number: 1194 Registered: 03-2002 Posted on Tuesday, April 13, 2010 - 12:23 pm:    The best publication for this issue is ACI 302.2R "Guide for Concrete Slabs that Receive Mosture-Sensitive Flooring Materials." That document references reseach that found that a 6-inch slab takes twice as long to dry as a 4-inch slab, and an 8 inch slab 2.8 times as long as 4-inch. In addition, slabs drying in two directions take about twice as long as those drying in one direction. W/C ratios also affect drying time, though less dramatically than other factors. Finally, keeping the slab dry after curing by keeping rain and other sources of construction water off the slab is critical, as the drying time needs to "restart" after re-wetting. Though it will dry faster after a rewetting event, overall progress is significantly slowed. We are specifying significant levels of control of the environment that the contractor must use, specifically for the purpose of promoting drying. We will be trying a method where the contractor must a provide moisture mitigation membrane if the drying does not reach the necessary levels by the time finish flooring is installed. A matter of 2 to 4 months of properly protected concrete should be enough according to research studies cited in the ACI document. I do not believe that making the flooring contractor "own" the mitigation membrane is the correct approach, unless the owner wants to pay for it whether needed or not. This is because the flooring contractor has zero control over the drying before they arrive. Making the moisture mitigation membrane a requirement only if the floor slab is not dry when needed gives a financial incentive to take the appropriate steps to get the slab dry. We'll see if it flies. Paul Gerber New member Username: paulgerber Post Number: 1 Registered: 04-2010 Posted on Wednesday, April 14, 2010 - 01:49 pm:    OK I'm jumping into the fray as a first time poster, but a "lurker" on the forum for the last couple of months...and to top it all off I'm Canadian, not American so there are some differences in our respective construction environments. A couple of things have struck me from reading through this post (and I will admit I skimmed a few of the responses rather quickly) so I will offer them up as points of consideration: 1. If the project is has a high water table or high moisture content within the native soil conditions then, as mentioned earlier, there are sheet vapour (yes, I know; there is no "u" in vapor...what can I say I'm a Crazy Canuck) retarders on the market that offer much high perm ratings than off the shelf clear poly (8, 10, or 15mil). Although the costs for these products (such as Vapor-Mat by W.R. Meadows or Perminator by Grace Construction Products) is significantly higher than clear poly, there performance is generally much better and offer the benefit of a reinforced polyester scrim to reduce the likelihood of punctures during concrete placement. Also, with any underslab sheet vapour retarder a key to the overall efficacy of the product is the treatment of the joints. 2. I don't believe anyone has discussed the inclusion of a water reducing admixture to the concrete design mix which allows the workability required during placement, but aids in removing the (as identified) "troublesome" water trapped in the slab after placement and during the curing stage in an accelerated fashion. These are common place in our area. Euclid has different products available to assist in the regard. 3. Including the provision for dehumidification during the curing stage prior to placement of floor coverings. This is also commonplace in my area and greatly assists in getting the "troublesome" water out of the slab. 4. If you happen to be in an area where the fall/winter/spring is less than conducive to construction activities such as curing concrete (yeah I mean copious amounts of COLD and SNOW eh?) then you may also want to address the type of temporary heaters the Contractor uses. Although most Contractors like to use direct-fired propane-powered unit heaters (affectionately called Salamanders in my area; no I have no idea why), these operationally cost-effective devices also spew large amounts of water vapour into the air, which makes the removal of "troublesome" water in concrete slabs more difficult to remove without the use of dehumidification. A combination of the above generally works quite well for our projects, a lot of which are institutional projects (schools, long term care facilities etc) which tend to have a lot of resilient floor finishes. John Bunzick, CCS, CCCA, LEED AP Senior Member Username: bunzick Post Number: 1196 Registered: 03-2002 Posted on Wednesday, April 14, 2010 - 04:15 pm:    Paul, Don't worry, I think we can handle some stray 'u's here and there! We don't have as much cold in Massachusetts as much of Canada, but we nevertheless prohibit salamanders due to the moisture given off, as well the fact that they send other noxious combustion gas products into the space. Also, one of the requirements of our Division 01 for controlling the environmental moisture is to use desicant drying, if necessary, to accelerate the drying process. Paul Gerber Member Username: paulgerber Post Number: 3 Registered: 04-2010 Posted on Wednesday, April 14, 2010 - 05:03 pm:    Jouhn - thaunks for the waurm welcoume!! I can be a bit of a smarta$$ sometimes. After 20 years in a couple of architecture practices (maybe if we practice enough we will eventually get it right??) and some retail design & construction experience one could almost say I have become significantly jaded and "curmudgeonly" to fit in well (hopefully) on this forum! You can also expect to hear some bad jokes (?) and potentially wry comments from me as well. But in our line of work, how else would we maintain our sanity??? I wasn't worried to much about being accepted because I am a Canadian as it seems ya'll have accepted at least one other Canadian, albeit ex-pat, (Wayne Yancey) around here...which also gave me hope as he is also a fellow rider (I dislike the term biker as it usually conjures up negative stereotypes of the less-than-savoury type). Do any other current or former Canucks hang out here? I'm sure you will all be pleased to know my current choice of ride is American, so I did my part to support your economy! Ride it like you stole it!!! (Unregistered Guest) Unregistered guest Posted on Wednesday, April 14, 2010 - 12:45 pm:    We specify a 15 mil "vapor barrier", recognizing that moisture from the ground takes years to make itself manifest in the slab. We currently use 2" sand under the slab, but that cannot be saturated or problems will arise. That is the hard one - keeping the sand at the proper moisture level for working but not too wet. Contractors here don't seem to want to eliminate the sand claiming an impact on bleed off time and finishing. We reduce water/cement ratio to 0.48 with a 14 day wet cure, or 0.42 with a 7 day wet cure. We have been specifying 4,000 psi for interior slabs as a way to densify the concrete, but have experienced curl, likely as a result of this. We may back that down to 3,000 psi. We will not specify spray-on or in-mix silicate products to reduce vapor emissions. We do specify topical vapor emission products as a matter of course, usually as an allowance so that the money and time is in the project to deal with potential problems. Testing determines the outcome. Sometimes we see low test levels, sometimes we don't. We make the Owner choose whether or not to accept the risk of not installing the vapor emission product. This is our current "best guess" as to how to handle the problem. Scott Parish John Bunzick, CCS, CCCA, LEED AP Senior Member Username: bunzick Post Number: 1199 Registered: 03-2002 Posted on Thursday, April 15, 2010 - 02:19 pm:    Scott, I'm curious as to your location, since you mention common use of sand beds by contractors. I think that including an allowance is making the owner take the risk of excess slab vapor emissions, because she is being asked to pay for it (if needed) regardless of whether the contractor met contractual obligations to properly schedule the project, protect the slab from moisture, use appropriate concrete mixes and curing methods, or other steps within their control. Contractor's should make provisions to deal with slab moisture based upon available research into the subject, contract requirements, and their own experience. They are in the best position to know what the most cost-effective methods are to meet the project conditions. If the schedule allows a slow dry--great. If some dessicant drying is needed in a few areas, they can plan for it. If they know that the schedule is aggressive and neither of these will work, they can forget all the other stuff and go with the epoxy membrane. (In that case, maybe they use a cheaper concrete finish, too, knowing they'll shot-blast anyhow.) I do not believe that excess concrete slab moisture is an unforeseen condition. (Unregistered Guest) Unregistered guest Posted on Friday, April 30, 2010 - 02:29 pm:    John: We are in Visalia, CA. We tried the tack you are suggesting...making the contractor responsible...but without real success. Why? Because when the contractors did everything we asked them, they still could not achieve the 3 pounds needed, most of the time. This is just not an exact science with a cause/effect relationship that can be counted on every time. And if we are going to place all the risk on the contractor and force it down their throats, then the owner will pay a premium. And...the finger will get pointed at the designer as well...and we've had enough of that. So yes, the owner should pay for it and if they don't want to pay for it, they should take the risk - not the designer or contractor. Dennis C. Elrod, AIA Intermediate Member Username: delrodtn Post Number: 4 Registered: 04-2010 Posted on Tuesday, June 22, 2010 - 12:17 pm:    I received a message from our local Stego rep, Lance Escue, about a week ago. As I attempt updating our Office Masters from MF95 to MF04, and being currently in Div 07, I sought his advice on the subject. Here is what he sent me. Dennis, Thank you for speaking with me last week about the most current under slab vapor barrier specifications. Please consider updating your master specification to include (editable word copies of 11 mil, 16 mil, and 31 mil composite attached for your use). Sorry about all the attachments – but I wanted you to have the documents on file we ask that all your specified vapor barrier manufacturers provide. When you specify true ISO 9001 certified manufacturers they will be able to provide all of these. We look forward to the opportunity of presenting the AIA/Sustainable Design Seminar when convenient for you. AIA Program # 91188 - Controlling Water Vapor Moisture Intrusion through Concrete Slab-On-Grade – 1 CEU – Sustainable Design M W Escue Company, manufacturers' representative for Inteplast Group, would like to ensure that you have our updated specifications for “under slab on-grade vapor retarders”, and we, respectfully, request your consideration to be included in your Master Office Specifications. The attached specifications (VB250 & VB350) each include a total of six (6) true manufacturers of vapor retarder products designed for "under slab on grade" use. These specifications offer everyone a broad selection of excellent quality, well-known and recognized, and readily available manufacturers' products in our industry; and allows for competitive bidding. We are pleased to announce that the ASTM committee updated their ASTM E 1745 standard this year for Under Slab Vapor Retarders. The updated listing is ASTM E 1745-09 and the major change was the minimum water vapor permeance (WVP) changed from 0.3 to 0.1 We, respectfully, request that the specifications include the updated reference to ASTM E 1745-09, Class A (the highest level of protection) and reference 03300 and 07260 (which many manufacturers of underslab vapor retarders have adopted). Attached is a copy of our suggested "under slab on grade vapor retarder" specification(s) and they are in “word format” so you can edit as needed: Barrier-Bac VB-250 (11 mil) Membrane - 11 mil (over the 10 mil minimum per ACI-302) – WVP 0.020 / WVT 0.006 Barrier-Bac VB-350 (16 mil) Membrane - 16 mil (over the 10 mil minimum per ACI-302) – WVP 0.009 / WVT 0.003 Barrier-Bac VBC-350 (31 mil) Composite Membrane - 31 mil (for project conditions which require greater concrete adhesion to the membrane) Included in the Guide Specifications (except the VBC 350 Composite Membrane) are six (6) manufacturers in the products section – we have limited the products to companies that actually manufacture vapor retarder products in the USA. Entities which out-source and/or import and function only as marketers to the industry have NOT been listed. By using this specification, your firm will not only protect itself from liability by meeting current governing standards and industry recommendations, but you will also be providing a high level of protection for your clients and the people who will occupy the buildings you design. The most important aspect of this specification is the performance based characteristics. The (Water Vapor Permeance) WVP-0.020 / (Water Vapor Transmission) WVT-0.006 (gr/hr-ft2) for Barrier Bac VB250 11 mil vapor retarder and WVP- 0.009 / WVT-0.003 (gr/hr-ft2) for Barrier Bac VB350 16 mil vapor retarder defines the low WVP permeance and the reference to ASTM E 1745-09, Class A emphasizes the puncture and tensile strength characteristics of products. The Inteplast Group Barrier-Bac product characteristics meet and/or exceed certain other competitive vapor retarder products on the market today. (WVT is not listed in or part of ASTM E 1745-09; however, several entities do state this data; so, we have elected to do so as well). Barrier-Bac vapor retarder membranes exceed ASTM E 1745-09, Class A. It is important to remember that Inteplast Group is the manufacturer and their Barrier-Bac manufacturing facility in Lolita, TX is an ISO 9001:2008 registered/certified facility. (Just one aspect of having this certification is the manufacturer must produce the same consistent/continual quality assurance stated in their Product Data Information with each and every production). There are several entities that market, private label, out source plastic membrane for below slab application and they have no manufacturing facilities. It is believed some even import into the U.S. Likely, importers have no true means to verify the proper quality control/assurance of the products they are promoting and selling? Recommend that you always specify that material be manufactured in the United States and accept no "marketers" products. (If you have concerns, simply ask for a "Certificate of Origin"). If you have any questions regarding the suggested specification, Inteplast Group, Ltd - Barrier-Bac and its supplementary products, the ISO 9001:2008 Certification, or any information in general about below-slab moisture protection, please do not hesitate to contact M. W. Escue Company, Inc: You can request anytime by contacting us at 901-861-5502, barrierbac@mwescue.com, or underslab@mwescue.com Lance Escue lance@mwescue.com Cell: 901-277-9077 Office: 901-861-5502 Fax: 901-861-5510 Dennis C. Elrod, AIA Nathan Woods, CCCA, LEED AP Senior Member Username: nwoods Post Number: 337 Registered: 08-2005 Posted on Tuesday, June 22, 2010 - 12:27 pm:    Hmmm.. by specifying 11 mil, 16 mil, and 31 mil, aren't you eliminating Stego? Anne Whitacre, FCSI CCS Senior Member Username: awhitacre Post Number: 967 Registered: 07-2002 Posted on Tuesday, June 22, 2010 - 12:54 pm:    about ten posts up, there is a comment about using fly ash as an additive for LEED points. Fly ash in concrete will slow the curing time (and the more fly ash the slower); in the northwest there isn't a note in the building code that allows for slower break strengths just because you use fly ash. Therefore, in fly ash mixes, most of the time it isn't substituted for cement (the point of the LEED credit) but is used along with the same cement content. For the most part, if you want to have the slab workable, you don't want to use more than 25%fly ash in the mix, or the mix will be too "sticky" to trowel. I have typically used a 12 or 15 mil crosslaminated barrier, with absolutely NO sand course (the SoCal engineers still want that, as do the Arizona ones); and appropriate protection and saw cuts and haven't had any moisture problems in slabs -- ground level or elevated -- except once when there was a plumbing leak and the contractor was complaining about the dampness of the slab and how it was ruining his schedule. After he discovered the leak, he had a lot more problems than just his schedule. Mark Gilligan SE, Senior Member Username: mark_gilligan Post Number: 285 Registered: 10-2007 Posted on Tuesday, June 22, 2010 - 01:01 pm:    I believe that the emphasis on ISO 9001 is inappropriate. ISO 9001 simply means that the manufacturer has adopted a number of practices and standards related to manufacturing of the product and has been audited to verify that they are being followed. It does not guarantee that the product will be perfect nor should it be inferred that non-ISO 9001 firms do not produce a quality product. My perception is that if ISO 9001 were to be specified as a requirement the competition would not be able to comply. The focus should be on the reputation of the manufacturer supplemented by testing of product delivered to the project if there is a significant concern. Mark Gilligan SE, Senior Member Username: mark_gilligan Post Number: 286 Registered: 10-2007 Posted on Tuesday, June 22, 2010 - 01:12 pm:    Regarding the statement that there isn't a provision in the code that allows slower strength if fly ash is used: ACI 318-05 Section 5.1.2 States "... If other than 28 days, test age for f'c shall be indicated in design drawings or specifications" A 56 day test age is regularly specified when using slag and fly ash as well as when very high strength concrete is used in highrise buildings. The down side is that you wait longer to find out if you had a bad batch of concrete. Never the less there is no reason not to specify the longer periods. Richard L Matteo, AIA, CSI, CCS Senior Member Username: rlmat Post Number: 387 Registered: 10-2003 Posted on Tuesday, June 22, 2010 - 01:39 pm:    I've had success with convincing the soils & structural engineers on my projects in SoCal not to use sand. I specify a minimum 15 mil Stego or equivalent product. I just tell them this is what I'm doing and send them the references from ACI 302.1R Arizona engineers need to read the Green Sheet on MVE published by the Phoenix CSI chapter a few years ago. They're the reason it was created. The Stego rep was in my office a while back with the same line presented to Dennis - the problem the way I see it, is, if we specify it their way, no one else can comply Dennis C. Elrod, AIA Advanced Member Username: delrodtn Post Number: 5 Registered: 04-2010 Posted on Tuesday, June 22, 2010 - 03:01 pm:    To Nathans' comment...I posed the question back to Lance...His response is as follows... All of the other approved manufacturers listed are 10 or 15 mil products. The minimum stated in spec is 10 mil or 15 mil - its just that Barrier Bac is made to 11 mil or 16 mil (price is still the same as, or in many cases, lower to distributor than the 10 or 15 - explained later). Only TRUE manufacturers are listed. Since Inteplast Barrier-Bac is a total vertically integrated manufacturer (wells in the gulf - 3 of their own (not leaking), resin plant - Baton Rouge, and film manufacturing plant - Lolita, TX) they are probably the most competitive of all the products listed and less than Stego to the Distributors. Stego is not a manufacturer - they are a marketing company that purchases film stock from a bag manufacturer in Yakima, WA - they do a great job on specifications; however, they do not actually own any plants or equipment nor do they actually manufacturer any products. The 31 mil (membrane + geotextile fabric) product has few competitors; however is priced lower than the known available products. The 31 mil is for job specific needs - shifting soils, under gym floors, post-tension concrete, polished concrete, terrazzo floors, etc. I know the spec is demanding but it just covers true manufacturers of the under slab vapor barriers. If you need to keep Stego in the spec - please just add Barrier-Bac VB-250 (11 mil) and Barrier-Bac VB-350 (16 mil) as others listed. You could remove all of the references to ISO Certification, Certificate of Origin, Current Testing Data, etc. Dennis C. Elrod, AIA Anne Whitacre, FCSI CCS Senior Member Username: awhitacre Post Number: 969 Registered: 07-2002 Posted on Wednesday, June 23, 2010 - 12:08 pm:    The allowance of a longer curing time in the ACI does not mean that the all local building codes (AHJ) will allow a longer curing time. I've worked in many jurisdictions that have set break times and do not allow longer curing times with the exception of very high strength concrete. I also had success in calling out the lack of sand barrier in SoCal, Arizona and Florida, but it took a number of terse conversations along the lines of "we have the license and you don't" before they got the message. Mark Gilligan SE, Senior Member Username: mark_gilligan Post Number: 287 Registered: 10-2007 Posted on Wednesday, June 23, 2010 - 02:27 pm:    Anne I would suggest that when the AHJ is not allowing the longer test age that they are not enforcing the building code as adopted but rather are enforcing what they are used to doing. The code is clear that this is an option given to the applicant. ACI 318 is a reference standard in the IBC and thus is a code requirement. There is an endemic problem with building officials and plan checkers who do not understand that they have an obligation to enforce the code and cannot enforce requirements that were not legally adopted. In these situations you could force their hand but generally the decision is made to accommodate them. The result is that the building official and staff think they have a right to impose their preferences and the design professionals come to accept this as normal. Mark Gilligan SE, Senior Member Username: mark_gilligan Post Number: 289 Registered: 10-2007 Posted on Friday, June 25, 2010 - 02:26 am:    For slabs on grade the default capillary break in the new 2010 "California Green Building Standards Code" consists of a vapor barrier in direct contact with the slab and on top of a 4" aggregate base. (Section 4.505.2) You can download the document from http://www.documents.dgs.ca.gov/bsc/documents/2010/Draft-2010-CALGreenCode.pdf.  ICC will shortly be publishing the code. Robin E. Snyder Senior Member Username: robin Post Number: 320 Registered: 08-2004 Posted on Wednesday, June 30, 2010 - 10:55 pm:    Let's say an Architect wants to eliminate the vapor barrier altogether and use a surface applied product intended to block or reduce MVT. Does anyone know if these products are acceptable to IBC as an "other approved equivalent method" for retarding vapor transmission? don't ask me why... I have sent them ACI publications and recommended against ommitting the barrier, but that is what they want to do (per the structural engineer's recommendation) Ronald L. Geren, AIA, CSI, CCS, CCCA, SCIP Senior Member Username: specman Post Number: 863 Registered: 03-2003 Posted on Wednesday, June 30, 2010 - 11:25 pm:    It should be quite easy to prove that anything is more effective than 6-mil polyethylene sheet. Even a surface-applied treatment with a modest resistance to vapor transmission pressure will out-perform the code-required minimum--especially over time. However, using a Class A below-slab vapor retarder costs much, much, much less than the surface applied treatments. Ron Geren, AIA, CSI, CCS, CCCA, SCIP www.specsandcodes.com Mark Gilligan SE, Senior Member Username: mark_gilligan Post Number: 291 Registered: 10-2007 Posted on Wednesday, June 30, 2010 - 11:57 pm:    Legaly there is no such thing as a general approval of an alternate means of compliance. Each use must be approved by the local building department. The building official's approval does not relieve the applicant of any liability. If the building official does not specifically approve this alternate then this deviation could be considered a code violation. I am not aware of anybody who is recommending such a system for new construction. The structural engineer should consider that if he uses an alternate means of compliance and something goes wrong that he will have more liability exposure. He is actively promoting this system as opposed to implementing a code requirement. It is not clear what is driving the SE. Many structural engineers would consider the vapor retarder a part of the building membrane system and thus outside of their scope of work and thus happy to defer to the architect. What is the opinion of the Architect? Does he not consider the building membrane and issues related to moisture and water to be part of his primary scope? At a certain point this is a place for a specification consultant to provide factual information to the licensed professionals signing the documents and let them accept the liability for their actions.