|Robin (Unregistered Guest)|
|Posted on Thursday, June 03, 2004 - 07:28 pm: |
What do you typically do on parking garages? In the southwest, many of them are not sealed. A standard sealer seems like it won't help much anything over time. Membrane sealers may eventually leak. Some contractor's like to add an shrink-reducing admixture to help prevent cracks. I'd like to hear what others usually do.
|Anne Whitacre, CCS CSI
Post Number: 91
|Posted on Monday, June 07, 2004 - 04:29 pm: |
Robin: my understanding is that there are two reasons to use a sealer on concrete parking decks:
1) is if the Owner really wants it to look "pretty " -- something to seal out the oil drips and other possible stains. We do some retail garages here, and seal them for that reason only.
2) the other reason, used in other parts of the country east of the Cascades/Sierras is that the salt/sand used on icy roads will seep into the wet concrete and corrode the reinforcing. We have some structural engineers in Seattle who claim that there is enough natural salt used in the sanding sand (we don't use salt or ice-melters much here) that they will corrode the rebar as well, but in most cases in the Seattle area, the sealer is left off due to cost. When I've done work in the midwest, its typically used, at least on the top deck.
Post Number: 75
|Posted on Monday, June 07, 2004 - 04:48 pm: |
It really is an owner decision, based on 'pay me now or pay me later".
On a couple of recent projects, we have specified epoxy-coated rebar for the garage (usually for top bars only, not bottom bars) and also a penetrating sealer. These sealers need to be re-applied every few years.
We occasionally have had an alternate for a corrosion-inhibiting admixture (eg DCI by Grace), in lieu of or sometimes in addition to, epoxy-coated rebar.
We have rarely used traffic-bearing waterproofing for parking garages due to cost. When we have specified them, it is typically only for ramps down to the first below-grade level.
|Bill Buchholz, AIA, CCS (Unregistered Guest)|
|Posted on Monday, June 07, 2004 - 05:37 pm: |
In California we do not generally have a problem with salt from roads. If you have rusting rebar problems, maybe a concrete admixture would help, but we've found the additives are generally not worth the added cost.
We use a good quality urethane deck coating above occupied spaces, elevator equipment rooms, mechanical rooms, etc., but generally not anywhere else. There is a legal as well as a cost reason for this. We don't want to claim that we've prevented all water (and lime) from coming thru the slab (from now to eternity) and dripping onto that expensive Mercedes on the level below. We'd rather say that the structure is not designed to prevent water from coming thru the slabs.
We always have an allowance with an associated unit price for concrete crack repair using a urethane sealant to handle the inevitable shrinkage cracking that occurs during the curing process (especially in post-tensioned slabs).
Post Number: 108
|Posted on Monday, June 07, 2004 - 05:49 pm: |
Serendipitiously, I'm working at this very moment on a parking garage in the upper midwest. Any recommended products for traffic deck coatings? Or conversely, any to stay away from?
Post Number: 7
|Posted on Monday, June 07, 2004 - 06:13 pm: |
Unfortunately I worked in the coatings business for awhile. There is a lot of messed up stuff out there from people who should know better (nobody here of course)
There are three manufacturers who do coatings reliably time after time, and even these have problems.
In the midwest and east you will find garages with an asphalt paving overlay. These are effectively recycleable, and do allow some resurfacing via the relatively cheap asphalt business. Not so in the west.
Unless the garage is totally enclosed, a urethane coating is essentially required - in specific areas, not throughout. Ramps and turn radiuses need special attention. Joints and edges require bond breaking details to extend the life of the coating. The urethane systems are highly evolved.
Under no circumstances should a garage coating be specified for the first time without a meeting with a coatings expert. This goes double for a repair job.
I heard a lot of complaining about the cost of coatings, and honestly I don't think there is a better place to spend some money on waterproofing than in a parking garage. It is not uncommon to get a responsive material bid at $1.15 per square foot (subcontractor price). The most important thing is to properly assess and make allowances for concrete preparation.
|Bill Buchholz, AIA, CCS (Unregistered Guest)|
|Posted on Monday, June 07, 2004 - 06:30 pm: |
In my humble opinion, 3M is a good place to start. Neogard is also good. I'm sure there are other good companies out there. Total dry film thickness is important. I specify: 50 mils minimum overall; base coat minimum 20 mils DFT, with good tensile and elongation numbers written into the spec; UV resistant top and wear coat minimum 30 mils DFT.
You could play games with thicker systems on ramps and drive lanes, and lighter systems at parking stalls, but a front tire can tear a coating when leaving a parking stall just as easily as turning in a drive lane or ramp. And who's going to watch the applicator that closely to verify mill thickness?
If you care about the environment, these manufacturers also have low-VOC, low-odor formulations that I'm told are just as durable.
Post Number: 8
|Posted on Monday, June 07, 2004 - 08:07 pm: |
The issue with ramps and turns is primarily those areas are subject to repeated wear under heavy loads, day in and day out.
That's not to say other areas arne;t subject to heavy loads, but instead these are variable and happen 'all over'.
There are a few people in the country who have spent their careers developing these kinds of systems. I found out in 15 months that we specifiers can get half way there, but an experienced person is necessary to get the job done.
I found the subcontractors generally were not stable enough year in and year out to perform on a consulting or advisory basis, and also 'everyone is an expert'.
Post Number: 9
|Posted on Monday, June 07, 2004 - 08:30 pm: |
For abrasion, the company I worked for tested an SUV tire, 1200 pound loading, stationary, applied directly onto parking deck samples in the warehouse. Without moving the vehicle, it required over 200 turns lock to lock to tear out walnut shell granules, and another 150 to show through the coating.
Using mineral aggregate under the other wheel, the material came apart and the concrete showed through under less than 150 turns total. Both coatings were mixed and applied by an experienced chemist in a controlled environment.
There are marketplace issues in that business. Use gaco, neogard or 3M. The first priority should be how well you are supported by the representative. The next should be your representative's effectiveness with the subcontractor. Price should be low on your list of selection criteria because this is a commodity business and the highest percentage of the project dollar is going to concrete preparation. Money is saved by decreasing the preparation because all the coating salesmen know what the market will bear in terms of material cost.
|Richard Howard, AIA CSI CCS
Post Number: 25
|Posted on Tuesday, June 08, 2004 - 09:28 am: |
There is a monograph on this topic at the NRC (Canada) through this link http://irc.nrc-cnrc.gc.ca/ctus/29.html