We are building a 6000sq castle type home out of nudura icf and covering the whole exterior with manufactured stone. One stone installer suggests using fiberglass mesh screwed to the webbing and placing the stone over this. The man made stone is lightweight and does not require a brick ledge. Another stone installer....the one that actually makes the stone states that mesh is not necessary and that a scratch coat can be applied directly to the icf and then put stone on this. I have given him a couple scrap pieces of form to stick some stone to so I can see it for myself. He states that the mortar binds so tightly to the EPS foam that you will tear chunks of foam off trying to remove the stone. We live in SE mississippi, so freezing should not be an issue. Has anyone used this method with success? I saw the article in June 2005 about applying stone directly to icf (without a scratch coat). I am just looking for some reassurance that this is ok before we make a huge mistake. Thanks, Larry

I've only built one ICF house, for myself, so I don't have a lot of experience, but here's what the stone mason did for me. He fastened metal lath to the block with screws and put the stone on with one coat of mortar, no scratch coat. The screwed on metal latch creates a solid mechanical bond to the wall. He argued that the single coat of mortar provided a more secure bond between the lath and the stone as you don't have the issue of bond quality between the scratch coat and second coat.

I'd be pretty leery of fiber mesh. The fiber mesh I used under synthetic stucco did not adhere well to the foam. It's also not mechanically strong and stiff. Why risk the security of the bond with direct application to foam when a good secure bond is so easily done? Of course, maybe experience shows otherwise.

It doesn't matter what the installer says.....what are the mfg' requirements????? Fiber Mesh may work, however, if the mfg doesn't approve, your warranty is out the window!

Here is a link to a project I did a few years ago
http://www.icfmag.com/back_issues/june-july_06.html#02

Pay attention to all the details with stone installations!

The guys that say direct application is the way to go are the ones that actually make the stone. They are the manufacturers. They use rubber molds and lightweight aggregate. Looks a lot like cultured stone. I will have to pin them down on warranty, but I really just want it to go on and work. If the adhesion between mortar and foam is strong, then direct application should pose no problem. Has anyone here done direct application, seen it done or heard either success or horror stories about this method? Thanks, Larry

hardhat,

maybe you need as system such as this:

http://www.suretouch.ca/e/4-a-galerie.htm

You should install stucco lathe and a scratch-coat. I bigger question is do we need weep screed and a moisture barrier behind the stone on ICFs?

Suretouch looks interesting, I would not want to be the first in the area to use it.

does anyone have any experience with direct application of stone to icf without the lathe? Any horror stories or success stories?

We have used real and faux stone on many projects and have seen many other projects with both products on them.  We have seen others contractors struggle with this and we have had our issues.  We currently have two projects using real stone and one project using Eldorado Stone.  Usually, I believe, the break point for using a corbel (brick ledge) or steel ledger is the product must be less than 12 pounds per square foot.  I know that Eldorado comes in just below this threshhold.

When we use real stone we use ledgers and corbels, use some type of drain plain such as a commercial rain screen, double layer felt ect..., integrate weep holes into the installation, and use a water repellant on the finished product.

When it comes to faux stones the people here are correct that you need to install it to at least the manufacture's recommendations or better.  Once you have settled on a method of install you need to have it approved in writing from the manufacturer that they will warrant the product with that install proceedure. 

Things to remember about an ICF install.  Some manufacturers don't require a drain plain behind, some do.  Some require a scratch coat with metal lathe, some don't.  Some require a water repellant applied after the application is finished, some don't.  If you apply stone only to the foam, you are now relying on the bond of the foam to itself as your only means of supporting the stone and there is no data that I have seen as to how long that will last.  Some manufacturers have never dealt with ICF and have no clue how to install their product to it.

My opinion and the stance our company takes is this.  We are building 100 year or longer homes, we never want to come back and fix a problem, we like doing things only once, hence we take a more conservative route to the finished product to ensure the job is right.  We install a drain plane, we apply metal lathe screwed off on a 8"x8" pattern with stainless steel screws and fender washers, use a portland cement bases scratch coat (let cure), install faux stone to the scratch coat.  Grout that lines.  Apply a water repellant.  This equals or exceeds any manufacturers recommendations and we don't have to return to repair anything.

Another thing to remember, the foam and concrete have provided you a tight water resistive building envelope that has moved the dew point from inside the wall, in a conventional frame home, to the outside just behind you exterior cladding be it siding, stone, stucco, or what ever.  Also your cladding probably won't be 100% water proof.  So you will get water in the space or potential space between your exterior surface and foam.  If you want your exterior to stand the test of time, you need to deal with this water.

ICF Contractor

I would place the metal mesh on with screws in the webs and place the scratch coat on that and proceed from there with my stone covering. I have done that on all of my jobs and do not have one call back due to stone falling off the wall. Better safe than sorry.

I think the article was a JLC on direct application? However, no mfg will warranty that application that I am aware of.

But, I would direct apply such as the article did, with limited hgts for something like a walk-out basement, but not for higher walls!

http://www.buildingsciencecorp.com/resources/presentations/Dallas_Zero_Energy_House.pdf was a project that used cultured stone directly over the Durisol ICF with no mesh. There was no problem and mfger did not have an issue with warranty

This was a non-polystyrene ICF that had a different type of bond between the cultured stone and ICF.

"This was a non-polystyrene ICF that had a different type of bond between the cultured stone and ICF."

Correct, and I don't think they'll have problems as long as the bedding mortar had sufficient moisture during the application!

With Durisol, trowelled on products should have a little more moisture in it than "normal" Even with a simple parge coat, when the parge is wetter than normal, it goes on so much smoother and easier. Dryer mixes tend to stick on and then fall off. It is fairly evident at the time of application whether this is an issue.

Even the concrete within the core is recommended to have a higher slump mix to account for the free drainiing Durisol material (it won't wick/suck moisture) that will allow the water in the concrete to drain with gravity. When you pour the walls, you can see the walls getting wet with the water from the concrete. Using an 8" slump concrete ends up as a 5" slump very quickly after it is poured in the wall.

Why don't you contact Permacrete directly, and talk to their experts.
I think their website (permacrete.com?) has contact info available.

Not associated with this company but have used the product in my current house build.

The product is called polyurestone. It's a polyurethane foam made to look like different stone.

I have applied directly to my Nudura ICF wall