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Old 01-17-2009, 11:17 AM   #1
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Synthetic Stucco over XPS foam


Has anyone here had experience applying synthetic stucco (acrylic based - the kind used with EIFS) over XPS foam? I'm getting ready to do this and I'm concerned about several issues.

  1. Can the XPS foam (not the traditional EPS) be rasped using 12-grit sandpaper? (I've been told by the company rep that I'll need a power rasper, but we only have about 460 SF to do so I think it can be done by hand, albeit slower). I'd appreciate detailed info on how to rasp the boards from anyone with experience.
  2. The Styrofoam will be installed over 10" poured concrete walls that have been waterproofed with Bituthene sheet membrane (a self-adhesive rubberized asphalt membrane). I've been told by Grace (the waterproofing manufacturer) that the styrofoam can be adhered to the waterproofing with adhesive, but I want to secure it with mechanical fasterners per instruction for the stucco. Tapcon screws w/ 1 1/2" conical washers have been recommended. My question concerns predrilling the holes. Can one drill through the styrofoam into the concrete wall so that the holes will be aligned? (My idea is to glue the foam up temperarily and then drill and install the fasterners.)
  3. The instructions from Parex (who makes the stucco) say to "interlock" the foam at the corners of the building. We purchased our foam before deciding on the stucco so we already have 2" XPS tongue and groove (Dow blueboard) My plan is to have flat edges at the corners but have one edge stick out 2" past the edge of the wall so that the perpendicular edge can butt against it, thus forming the corner. I have no idea what the company means by interlock unless they are using foam that is specially made to specs to have this can of edge. Does anyone know what this means?
Thanks for the help.
Tech


Last edited by techinstructor; 01-17-2009 at 11:19 AM.
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Old 01-18-2009, 02:03 PM   #2
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Synthetic Stucco over XPS foam


bump -- Anyone?

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Old 07-09-2009, 08:34 PM   #3
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Synthetic Stucco over XPS foam


Interesting.

I'm wondering something similar myself, I intend to use XPS on my entire foundation and all the way up to the attic vents.

Now my siding isn't going to go all the way to the ground.

But i certainly don't want to have blue foam sticking out and call it good.

So what do you cover it with?

One guy i read about did an entire condo complex by just applying the lath and then the stucco right on the xps apparently. I have no idea what stucco even is, or how it is applied, but I did read that here; http://www.xpsa.com/comm/belowgrade/index.html

I'm wondering if you could also just cover it with fiber cement board, if cement board can endure contact with the ground and a few inches under for a few decades?

I'm curious about a definitive answer to your question about boring holes as well, what effect would it have on the housewrap etc, or below grade on the weatherproofing?

I also read that you should always weatherproof xps when used below grade, but with what?
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Old 07-09-2009, 08:36 PM   #4
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Synthetic Stucco over XPS foam


I'm also wondering if you drilled holes in that butyl stuff and put screws in, would that be an issue for the waterproofing? and if so, how would you alleviate that problem?

(sorry for the thread hijack, i think I'll go make my own now, lol. I have a zillion questions, this ought to be good...)
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Old 07-10-2009, 10:01 AM   #5
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Synthetic Stucco over XPS foam


You have to cover any of the foam that is above grade to protect it from UV from the sun. You can use any siding material, brick, stucco, cement boards etc, though I think the cement boards recommend staying 2" above the soil. So you either have to leave a gap or use a material that can go all the way to the ground.

As for screws through the waterproofing, time will tell, but it isn't supposed to cause any problems. The XPS foam is more water resistant than EPS foam but I really don't think you ave to waterproof either of them for below grade use. Water isn't going to go through the foam and it isn't going to hurt it. The tapcon screws will have Wind Devil washers on them which are supposed to create somewhat of a seal when they are installed into the foam. (There are some other brands that are a little cheaper but Windlock makes the ones that are recommended by Parex (who makes the stucco).

If you do decide to use synthetic stucco, do your research well, and get it approved by your inspector before you make purchases. Because of all the law suits over synthetic stucco that was installed (sometimes improperly) over wood that got invested with termites, inspectors are real picky about how it is installed. It can be done and I finally got approval for my plan but I had to PROVE that it would work before he would approve it.

The companies that make the materials have good tech support departments and they are more than willing to help you with documentation.

I haven't done my wall yet... we're behind schedule but when I do I'll let you know how it turns out.
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Old 07-10-2009, 04:21 PM   #6
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Synthetic Stucco over XPS foam


well i know that xps is supposed to be very resistant to water infiltration, but not impervious, otherwise it would probably be used as a waterproofing in and of itself with something to seal the edges only, i've never heard of that though, and likely because it is not actually water proof. Being that it is not waterproof, if it gets saturated with water, it will lose some of it's insulation qualities, and a constantly soaked piece of insulation would be pretty useless. Therefore, it is likely wise to waterproof the insulation as well, however, how best to accomplish this, i have no idea...

although I think i might have just cooked up a good idea, but I'm not so sure, a plastic sheet would accumulate condensation, and there would be absolutely no where for it to go, this would be the case if any air gap existed, which it would be nigh impossible to elimate ALL air from such a method. With that in mind, a painted or some other similar application type of waterproofing is likely what would be best, however, I don't know what that is?
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Old 07-12-2009, 09:23 AM   #7
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Synthetic Stucco over XPS foam


The foam is not 100% waterproof but unless you have it SITTING in water, you shouldn't have a problem. The action most critical to having a dry basement is the drainage system that is around the perimeter. You need adequate drain lines and your backfill material needs to be porous enough to carry the water away. Gravel is ideal, but course sand will work too. If you do this then there won't be enough water sitting on the foam to ever cause a problem.

BTW, the reason the foam has to be rasped before applying the stucco is because it is coated on the outside with polyethylene....plastic.

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