Interesting... could clay be applied directly over ICFs?

Traditionally plaster would be applied over wood lath (you know, thin narrow strips of wood nailed horizontally to the vertical framing members), or later to diamond mesh metal lath.

I am building a house with rewards ICF.  we are very happy with it and now I am doing the inside.  I want to use earthen plaster on the walls.  I am slightly experienced with cob--love it.  I would like to have built a whole cob house, but we live in temporate rain forest, in a county with difficult building codes and I am doing alot of the work myself and did not have a team of twenty people to cob.

I would love to hear more peoples' thoughts on earthen plaster on ICF.  what I have read from the manufacturers on line is that you have to use some sort of lath or cement to make it stick.  However this differs from what I read with natural plaster books.  They claim that any sort of lath even chicken wire types leave room for trapped air under the plaster which causes it to come off.  They reccommend various sorts of reciepes of adhesives-- such as homemade wall paper paste with sand in it.

I would love to hear from someone who had actually earthen plastered over ICF

I am not a builder (just a homeowner), but the American Clay site does say you can use ICF if you prepare it properly: "If the surface material of the ICF is foam or a soft material, it will need to be sheathed or brown-coated, following manufacturers’ directions for  adhering a hard, durable surface to the ICF."

Regarding applying to wood or diamond mesh lath, I don't think that is going to work since the clay plaster is just a skim coat: "American Clay earth plaster is a veneer coat, a total of 1/16” for the two thin layers; as such, it
needs a hard substrate." Again, I'm not a construction guy, but I would think if you use lath you would have to use some sort of plaster coat as an intermediary, such as lime plaster. I would like that idea if that weren't such a labor-intensive (expensive) method.

American clay has a lot of answers regarding specific surface substrates on their site.

John
Condemnation Plantation

John, after having read more about, I see the clay finish is really just cosmetic. I guess you're going to have to bite the bullet and use gypsum or something like it. There is lots of discussion elsewhere in this forum about magnesium oxide board as an alternative to gypsum, of course it's more expensive and the jury is still out on the carbon footprint since most of it is made in China. Your initial idea of recycled gypsum sounds like a good one, given it's not too expensive. Keep us posted on what you decide.

I would say it is a little more than cosmetic. It is a completely natural product made with little environmental damage. It has no danger of off-gassing. Mold is unable to grow on it, and it will observe and slowly release moisture in the air, which is one of the reasons I think it will make a good surface for the bathroom. On the cosmetic side, I do think it is a handsome finish, and it will not fade. It can be touched up and cared for fairly easily, although not in comparison with certain other surfaces. I have found an apparent source for recycled gypsum board (Lafarge) manufactured not too far away, so I am hoping that will pan out. I'm waiting to hear back from Lafarge to learn more about their product. One of the interesting things I discovered is that my local Lowe's did not even know it was a recycled product. Lafarge is missing a marketing opportunity.

Yes, the clay does look like a nice product. When I said cosmetic I was just referring to its need for a substrate, as opposed to a thicker plaster or adobe, which is what I initially thought it was.

We did our entire home in American Clay back in early 2005. We were told that we were the first new home in Dallas to do so.  Croft, the founder, come out to do a demo and explain techniques to some painters (who wanted to learn it) and other builders, in our garage.

We applied it over sheetrock, that was applied directly to the ICF forms.  At that time, it was the only recommended way.  To have a brown coat applied over ICF foam, in order to do Am. Clay, seems like an awful lot of cost and labor to me, and not any more efficient than drywall.

You can see our results here.

You also should read this article in ICF Builder magazine about ICF interior finishes. PlasterMax can be applied directly over the ICF EPS.  Also, that's me they quote in the Am. Clay section.

How does the cost of PlasterMax compare to installation and finishing of drywall?

I do not remember ever seeing PlasterMax or GigaCrete at product shows.

I know nothing about PlasterMax. 

Drywall does not have to be taped and bedded before Am. Clay application.  When we did it, the only way was a base coat of clay (no color), then your finish coat.  The seams were taped with fireglass mesh tape and a glue they sold before doing the base coat.  Corners were covered with glue only so the clay would stick to the metal.

They obviously have some other methods now.

Hello Alton,

GigaCrete's PlasterMax-ICF [u]base coat[/u] is the fire rated coating directly applied over ICF no mesh.  This has recently evolved to a final finish without a second coat of PlasterMax finish coat by using a roller textured sleeve over a paint roller, very very fast and cost effective at 3/8" versus 1/2" minimum gypsum board.  Hand troweled is fastest on a small installation, takes on a few minutes to mix and apply and finish with a roller and looks awesome. Kentucky schools have selected this as a finish over ICF walls.  Photos available just email me.  Can be stained or painted or faux finished. 4,000 psi indent resistant finish is superior to VHI and all known abuse resistant wallboard and will not support mold or mildew.  Cost parity with abuse resistant wallboard. High recycled materials content.

curious what you found out about interior finish for ICF's.......

Whatever you use, you probably don't want clay -- it will be too expensive for your application. I don't know if your objection is to sheetrock specifically, or to wallboard in general. There are environmentally sensitive options for wallboard now, if that is your concern. It is probably going to be hard to find something as inexpensive in terms of both product and application.

Posted By faeriegrove on 12 Dec 2011 12:38 PM
curious what you found out about interior finish for ICF's.......

 We have built an underground root cellar 16' x 8'out of ICF's and want a simple product to coat the inside that would be safe for our food storage.

An acrylic modified cement parge coating is what I would recommend.  Google [eps acrylic modified cement parge coat] for more info.  Below are a couple of many products available:

http://www.wrmeadows.com/wrm0825.htm

http://www.homedepot.ca/product/b20...ems/964143

Stick with code approved and well tested finishes or risk having to remove the coatings for fire safety violations.  Gypsum board and PlasterMax have passed the fire codes testing which is severe. The only known fire rated coating to replace drywall over ICF foam is PlasterMax by GigaCrete.  Technically or legally you should not apply anything that does not meet IBC and NFPA fire codes.  PlasterMax is also based on all natural ingredients using limestone as the type of sand, not silica sand which has known carcinogens. PlasterMax is over 8,500 psi and scratch and impact resistant well beyond drywall or even high impact gypsum board. PlasterMax will not support mold or mildew either and has no food source (paper) like drywall. Application is made directly over the ICF foam by sprayer or hand trowel.  The ideal thickness is 3/16" and includes a fiberglass mesh the similar to EIFS finishes.  Material costs for 3/16" thick with mesh are about $1.68 sq ft from the factory.  A bit higher than drywall but then a Mercedes costs more than a Yugo ;)