Ground Face Block Efflorescence

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Author Message Stephen Wilson Senior Member Username: swilson Post Number: 14 Registered: 02-2019 Posted on Thursday, August 12, 2021 - 11:33 am:    Hi all, thought I would wake up this forum with some questions about ground face CMU and efflorescence. We're working on a job where we have a masonry cavity wall: structural CMU backup with a drainage cavity and masonry veneer. The design architect wants to use ground face 4" CMU for the masonry veneer, but the CM we are working with is hesitant to do this, stating that masons he has worked with are hesitant to use ground face CMU for veneers. Apparently they have to do so much repeated cleaning to remove ongoing efflorescence that they prefer clay brick and will substitute it at no cost. It's worth noting that all the info on this issue has come from the CM via a major clay brick manufacturer that is promoting their oversize units as a substitute for the ground face CMU. (The plot thickens.) In this project, the design aesthetics are the reason for the ground face CMU veneer, and a clay brick veneer wouldn't match with the aesthetic the Owner or design wants. What is your experience out there with using ground face CMU as a veneer? Have you noticed excessive efflorescence or is this all a marketing push from the brick supplier? I don't doubt that in theory the argument makes some sense, but I wonder if these concerns could be addressed with proper specifications, detailing, and construction practices. (Such as specifying a integral water repellent ground face block and mortar, proper flashing and cap detailing, and covering wall cavities during construction.) Thoughts? David L. Heuring, AIA, CCCA Member Username: daveh Post Number: 3 Registered: 04-2020 Posted on Thursday, August 12, 2021 - 12:00 pm:    Architectural ground face CMU should be manufactured with an integral water repellant- i.e. have a factory applied acrylic resin sealer conforming to ASTM C-744 standards. You should spec a field coat of sealer be applied after final wash down to seal the entire wall. Also, integral water repellant mortar admixture must be added to the mortar by the mason at a rate of 1 quart bottle per 2 bags of mortar. Mortar admix must be purchased from the same block manufacturer which produced the block for the project. Installed along with the other practices for construction you mention, you should not have a problem. I never have. Also, remember any CMU (block or brick) shrinks and requires control joinsts, and clay brick will expand (requires expansion joints.) Consult your local NCMA rep and get their opinion on this. David L. Heuring, AIA, CCCA, LEED AP, NCARB Ronald L. Geren, FCSI Lifetime Member, AIA, CCS, CCCA, CSC, SCIP Senior Member Username: specman Post Number: 1595 Registered: 03-2003 Posted on Thursday, August 12, 2021 - 12:05 pm:    Brick can effloresce just as much as CMU. It all depends on the materials used to manufacture the masonry and the mortar, as well as the detailing of the wall assembly. Maybe conduct a simple wick test to see which material effloresces the least. Ron Geren, FCSI Lifetime Member, AIA, CCS, CCCA, CSC, SCIP ken hercenberg Senior Member Username: khercenberg Post Number: 1394 Registered: 12-2006 Posted on Thursday, August 12, 2021 - 01:18 pm:    Seems to me that ground face CMU would be easier to clean than split face and I've been successfully using both since the 80's. For exterior exposed block I prefer normal weight since it tends to be less absorptive. Insist on integral water repellent, ASTM E514, during manufacturer with the same product mixed in the mortar. It's a good start. Following NCMA TEK Notes - https://ncma.org/resources/tek-solutions-center/ is key. Protect materials during storage, handling, and installation. Proper detailing, flashing, and water management including drying potential is important. Proper protecting and cleaning during and after installation is critical. I advocate sealant joints at banding or at least provide continuous wire set in mortar at face shells to prevent cracking, especially when changing materials and plane. I don't seal CMU or brick unless it's exhibiting problems. Sealers can trap moisture that can lead to problems. Michael Chusid, RA FCSI CCS Senior Member Username: michael_chusid Post Number: 617 Registered: 10-2003 Posted on Thursday, August 12, 2021 - 04:05 pm:    The concrete mix (and mortar) can include pozzolans to reduce efflorescence. The pozzolan reacts with free lime created during cement hydration. Free lime is soluble and can migrate to the surface to effloresce. I am a fan of high reactivity metakaolin and have written about it for Construction Specifier. See https://www.monolithic.org/vault/pdf/metamax/bbw.pdf Other supplementary cementitious materials can also work. The mix design can be tested for effloresence potential Michael Chusid, RA FCSI CCS 1-818-219-4937 www.chusid.com www.buildingproduct.guru ken hercenberg Senior Member Username: khercenberg Post Number: 1396 Registered: 12-2006 Posted on Thursday, August 12, 2021 - 04:46 pm:    Great points Michael. I too have found that using replacement pozzolans in lieu of part of the Portland cement in your mix can add performance and environmental benefits. One caution is the use of some masonry cements vs. Portland cement-hydrated lime mortars as many masonry cements have "mystery ingredients" in addition to crushed lime as fillers. Make sure you know what is in your mix before allowing it on your Project. Beware of substitutions. Stephen Wilson Senior Member Username: swilson Post Number: 15 Registered: 02-2019 Posted on Friday, August 13, 2021 - 10:42 am:    Wonderful advice, all. Thanks for your input! Dennis C. Elrod, AIA, CSI Senior Member Username: delrodtn Post Number: 29 Registered: 04-2010 Posted on Friday, August 13, 2021 - 11:15 am:    When specifying CMU as a face veneer, I always specify a clear face silane/siloxane mix sealer, Section 07 19 00, to minimize the opportunity for efflorescence after CMU installation, cleaning and drying. While specifying a factory face sealed CMU is good, it doesn't protect the joints, which usually show the first signs of efflorescence. Another critical component to a successful installation is weep holes at 32" OC top and bottom to make sure any moisture that gets in the cavity is evacuated via natural convection. Dennis C. Elrod, AIA Dave Metzger Senior Member Username: davemetzger Post Number: 803 Registered: 07-2001 Posted on Friday, August 13, 2021 - 01:51 pm:    This question is for those contributors to this thread who know more about the topic than I do. I've preferred to use a spray-applied breathable water repellent after the wall is constructed, rather than an integral water repellent in the CMU mix and the mortar mix. This is because I'm antsy that the integral WR will inhibit bond between the mortar and CMU. Is there anything to this concern, or is it a non-issue in your experience? ken hercenberg Senior Member Username: khercenberg Post Number: 1398 Registered: 12-2006 Posted on Friday, August 13, 2021 - 02:51 pm:    Hi Dave. Three-part answer from a biased source: 1. From what I understand CMU manufacturers prefer to include some amounts of the integral water repellent in the mix as it helps release the block from the form. Greater amounts are added when specified for water repellent performance. 2. From investigating the same question I was told that using the same brand admixture in the mortar as used in the block mix, bond should actually be promoted as opposed to inhibited. I have not tested this but that is according to the major manufacturers of the admixtures I spoke with (technical folks, not reps). 3. As I noted above I'm not big on sealing anything unless it's a problem as sealers can inhibit drying. Brick and block get wet and then they dry. If materials and completed work are properly protected and cleaned during and after installation none of this should be an issue. In fact I've been called in on projects that had efflorescence after sealing and that posed an even bigger problem as a result. Hope everyone is having a wonderful Friday the 13th. Michael Chusid, RA FCSI CCS Senior Member Username: michael_chusid Post Number: 618 Registered: 10-2003 Posted on Friday, August 13, 2021 - 03:11 pm:    Dennis - Weep holes at the TOP? I am unfamiliar with this practice. Liquid would not accumulate there, and I thought vapor can usually vent through the masonry veneer. Any guidance you can offer will be appreciated. Michael Chusid, RA FCSI CCS 1-818-219-4937 www.chusid.com www.buildingproduct.guru David L. Heuring, AIA, CCCA Intermediate Member Username: daveh Post Number: 4 Registered: 04-2020 Posted on Friday, August 13, 2021 - 03:31 pm:    I have heard of weeps at the top, though typically weeps are above flashings to allow water out. Otherwise, weeps only at the bottom and with a clear air space is enough for a wall to vent and dry. From NCMA: Vents can also be installed at the top of other masonry veneer walls to provide natural convective air flow within the cavity to facilitate drying. For vented cavities, it is prudent to create baffles in the cavity at the building corners to isolate the cavities from each other. This helps prevent suction being formed in the leeward cavities. David L. Heuring, AIA, CCCA, LEED AP, NCARB Greta Eckhardt (Unregistered Guest) Unregistered guest Posted on Friday, August 13, 2021 - 05:41 pm:    It is my understanding that efflorescence can result from moisture (water vapor or liquid water) accumulating behind the masonry cladding, diffusing into the pores of the masonry units and mortar, sitting in those pores long enough to dissolve some salts, after which the moisture migrates to the outer surface and evaporates, leaving the salts behind. I am not sure how a surface-applied water repellent will solve this situation since the moisture is coming from behind it, but if there is one, it should be vapor-permeable. I am glad to see comments emphasizing proper detailing including making sure that there are top and bottom vents (the bottom ones can also serve as weeps) for venting of the airspace behind the masonry cladding. The venting will help prevent excess moisture from accumulating in the airspace. In addition, a continuous air barrier assembly that prevents exfiltration of moist interior air into the airspace, and a waterproof barrier (may be the same membrane as the air barrier) sealed and lapped properly with adequate flashing - all these are critical to avoiding efflorescence. George A. Everding, FCSI, CCS, CCCA, AIA Senior Member Username: geverding Post Number: 929 Registered: 11-2004 Posted on Friday, August 13, 2021 - 05:56 pm:    Weeps at the top are really air vents, right? Brian E. Trimble, CDT Senior Member Username: brian_e_trimble_cdt Post Number: 127 Registered: 08-2005 Posted on Monday, August 16, 2021 - 12:57 pm:    Since efflorescence needs a source of soluble material and copious amounts of water, reducing those two things makes sense. Good discussion on reducing the amount of free lime in the materials (CMU has more cement so there is a higher "chance" of efflorescing, but not guaranteed). As David and Greta mentioned drying out the wall will aid in keeping efflorescence to a minimum. Don't get too hung up on the term weeps or weep holes. Weeps are doing double duty these days by weeping water out of the wall as well as allowing some air flow into the cavity (assuming you are using the vent-type weeps and not tubes or ropes). I often use the term "weep vent" to denote the kind I like and what they do. The weep vents at the bottom of the wall or compartment aid in getting the water out and allow air movement into the air space. Weep vents at the top of the wall or compartment may allow convective currents which could aid in the drying of the wall. Which brings us to the overused term rainscreen. Having a ventilated cavity provides for a rainscreen wall system. Designers seem to like rainscreens and you can get that with a masonry cavity wall. How about that?