| Author |
Message |
Robert E. Woodburn
Senior Member
Username: bob_woodburn
Post Number: 36
Registered: 11-2010
| | Posted on Tuesday, February 26, 2013 - 04:11 pm: |    |
We're looking for an interior coating for tilt-up panels that can serve a dual purpose as a vapor barrier coating and finish. Apparently there are several new products on the market made just for that purpose. I just inquired about a Sherwin Williams product, but it has been tested as a vapor barrier only on drywall, not concrete, so it isn't 's a proven vb on tilt-up. Any suggestions or comments? |
Wayne Yancey
Senior Member
Username: wayne_yancey
Post Number: 570
Registered: 01-2008
| | Posted on Tuesday, February 26, 2013 - 04:25 pm: | |
Robert,
Go to Building Science.com for Building Science Digest 106, "Understanding Vapor Barriers: 2006-10-24 by Joseph Lstiburek. Scroll down to figures 14, 15 and 16. There you will find three assemblies with precast concrete exterior walls.
Or sent me an e-mail at wayne.yancey@callison.com
for a copy. |
ken hercenberg
Senior Member
Username: khercenberg
Post Number: 442
Registered: 12-2006
| | Posted on Tuesday, February 26, 2013 - 04:53 pm: | |
If you've already determined that dewpoint is not an issue and just want a low-perm coating that can be applied to concrete (either before or after tilting) you may want to give your local Tnemec or Carboline rep a call. Most epoxy coatings have low vapor permeability. Carboline used to have a very good tile-like coating that was very vapor impermeable and as smooth as paint on gyp board. My guess is that any coating you put on the concrete before tilting it into place will get banged up. Patching never looks as good.
Lately there seems to be a push for acrylics instead of epoxies. You'd have to beef up the mil thickness to increase the vapor impermeability but again, Tnemec has a couple good products if you want to go that route. |
Robert E. Woodburn
Senior Member
Username: bob_woodburn
Post Number: 37
Registered: 11-2010
| | Posted on Tuesday, February 26, 2013 - 05:28 pm: | |
Wayne, coincidentally I had found and printed out that very report (found on a Google search) shortly before posting my question. Though I hadn't read it yet (it's 29 pages), I have the highest respect for Joe Lstiburek and anything he writes. Problem is, those 3 tiltwall assemblies all have the exposed concrete face on the exterior, but in our case, we'd like to put the vb on an exposed interior face. It's a tilt-up sandwich - out to in, it's 3-1/2 to 5 inches of exterior concrete (with Thorocoat or equal exterior finish coating), 4 inches of polystyrene or polyiso insulation (penetrated by tiltwall ties), and 8 inches of structural concrete on the interior. The vb must go on the interior side of the insulation, and we'd like an interior finish paint that doubles as the vb, saving a material and the labor to apply it.
Intuitively, I'd think that 8 inches of structural concrete is as good a vb as a few mils of coating. In fact, under figure 14, Joe writes, "The vapor barrier in this assembly is the precast concrete itself." (It's an exterior vb, in this case.) However, the RFP apparently requires a vapor barrier on the inside of the insulation, and we'd like to be able to point to a finish coating we can say doubles as a vapor barrier.
Ken, dew point likely is, in fact, the issue. I hadn't occurred to me that it would be applied before tilting. There's a lot of this, and we'd like to avoid expensive epoxies etc. if possible. The person who is proficient in our dew point software is out of the office today and we'd like to have a solution in mind, if possible, before he can run the numbers. |
Wayne Yancey
Senior Member
Username: wayne_yancey
Post Number: 571
Registered: 01-2008
| | Posted on Tuesday, February 26, 2013 - 05:50 pm: | |
Robert,
Your wall assembly is discussed and illustrated in BSC INSIGHT-054, Figure 7 on last page. I think the vapor retarder is still the precast concrete, in your case the inner wythe.
I had a similar requirement for an interior finish on insulated precast. Stud/gypsum board furring was in to hid the precast then out. I specified Protective Coatings Technologies (800-846-30200 "Clear Seal W-100 with PROBAN", 8 wet mils.
I cannot confirm this was actually done but that is where I left it in an ASI. It's purpose was to mitigate concrete dusting.
You may want to talk to "ThermoMass" Insulation System. |
ken hercenberg
Senior Member
Username: khercenberg
Post Number: 443
Registered: 12-2006
| | Posted on Wednesday, February 27, 2013 - 09:26 am: | |
Thoroseal/TexCote/Miracote type exterior coatings are good in this instance since they are vapor permeable.
Concrete may work as a vapor retarder, but it cracks and has micro-fissures that can cause problems.
Keep in mind that enough of just about any film-forming finish material will eventually become vapor impermeable, even latex paint. You might experience problems with cohesive strength by the time you get there. Still, perhaps with enough 100% acrylic coating thickness, you may get what you're looking for. Your client just needs to decide what amount of maintenance cost is acceptable (pay me now or pay me later). I have heard that there are some acrylic and urethane systems that can provide good vapor impermeability that are less expensive than traditional epoxies. They also have better appearance in that they don't tend to yellow.
Maybe check with the Scuffmaster/Master Coating Technology folks and see what they have on the low end. |
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