I will be using Gigacrete's gigapanels (http://gigacrete.com/) as the shell of my house. It will have 8" of EPS with steel studs embedded inside(appx 3" foam on the outside and 1" on the inside. The system uses a coat of stuccomax on the outside and a coat plastermax on the inside. The quotes for plastermax(material+labor) are making it cost prohibitive for me to use it. For this reason I am investigating ways to use drywall while keeping the studs where they are inside the foam to minimize the thermal bridging. I would also prefer something stiffer than just the drywall. I have considered mgo board but it would also get spendy considering I would want to use it on the interior walls and ceilings as well just for the uniformity. The other option is installing 1/2" plywood first and then drywall over it. What would be the the best way to attached the plywood to the panels if I were to go that route? Anyway, I would love to get some ideas from the members. Thanks

You want something stiffer than drywall inside? If the drywall is screwed directly on to the foam, it will be plenty stiff. I dare you to punch my ICF walls!

Posted By jdebree on 09 Apr 2014 05:49 PM
You want something stiffer than drywall inside? If the drywall is screwed directly on to the foam, it will be plenty stiff. I dare you to punch my ICF walls!

ICFs have typically only 2.5" of 1.5 lbs/cu ft density eps backed by concrete while gigapanels are 8" of 1 lb density EPS with steel studs at 24" OC. I would think there would be a pretty decent difference between the 2 if one were to punch both walls. Anyways, my main question is how to best attach drywall or plywood/osb + drywall to gigapanels.

Why do you want more than drywall??

Just standard 1/2" drywall seems fine to me, screwed every 2'. I suppose you could glue in addition to screwing. Because of the foam backing between the studs, it should be pretty tough. Get some abuse-resistant or VHI (very high impact) drywall if you want more strength (adding plywood seems like overkill).

Too bad plastermax is priced out of range. Do you care to share your plastermax (and stuccomax) quote? I want to use it too on my next project. I thought it goes for around $3-4 sq ft turnkey (materials, labor and painted). However, I don't think drywall is much less, probably $2-$3 sq ft turnkey (materials, hang, tape, texture, paint) and perhaps significantly more if you get better quality drywall (both on materials and probably labor, as I'm told the stuff is harder to work with). There is some cost savings in the painting of plastermax vs drywall, as it only requires one coat and no primer.

Sharter,

Sorry for the late reply. The turnkey cost of palstermax/stuccomax depends on the local labor rates, and as you know it can really vary. Mine is coming out to well over $5/sq ft on average not including painting, only one bid is close to $5. It maybe different in your area.

By the way, the plastermax material cost is $1.44/sqft for the coating+mesh at 3/16" thickness.

As far as installing drywall over EPS is concerned, I have read about issues with foam compression, screw popping, cracks etc. I guess I will have to run it by my drywall contractor.

Posted By timberwolf78 on 14 Apr 2014 10:18 AM
As far as installing drywall over EPS is concerned, I have read about issues with foam compression, screw popping, cracks etc. I guess I will have to run it by my drywall contractor.

It all comes down to installation. If the drywall person/people know what they are doing, there will not be any problems.

Installing drywall over wood framing (16 or 24 oc) will cause problems if they don't do it right. I've seen plenty of nail pops, cracks, bulging drywall, when installed on wood framed walls.

Once again, it's all about the technique. Just don't overdrive the screw into the wall when installing into ICF EPS. Also, set the screw gun on a lower speed setting so as to not "overheat" the plastic furring strip which can cause it to melt. This isn't rocket science and to be honest, installing drywall over ICF EPS is actually easier than wood framing spaced at 16" or 24" oc. The reason is that with ICF EPS you have a furring strip every 8" oc and you are installing over a continuous solid rigid surface.

Don't see any reason for foam to cause screw pops. I have seen some pops in ICF home if the drywall goes on to soon and absorbs moisture from the ICF.

Use EnerBond foam to glue the drywall with limited screws.

http://www.bing.com/search?q=icf+and+sheetrock+problems&qs=HS&pq=icf+and+sheetrock+problems&sc=1-26&sp=1&FORM=QBLH&cvid=4b2347f36cb24e31b9b6b966a4bbd44f

If rates are going for $5+ sq ft and plastermax is $1.44 then that means $3.50+ for labor per sq ft. That's about $1850 for a 12x12 room including ceiling, just for labor. Ouch.

Even at $100\hour including two people, I doubt it takes 18.5 hours to prep, install and clean up a single room. Probably more like 4 hours, although I suppose that depends quite a bit on skill. I'd rent or buy the spray machine and do a room myself along with a couple decent hard-working helpers willing to learn (and familiar with plastering and texturing) and train eachother, and then let them do the rest of the house. If the test room turns out to be a PITA, then plan B.

IMHO around $1.50 \ sq ft for labor sounds like a fair price, especially given it's a simpler one coat, two pass method. That's $800 for a 12x12 room, which seems fair assuming 4 hours @ 2 people.