Parging Foundation Insulation

[keegs]

I'm looking for suggestions/experiences on coating/coverinng methods and products for the extruded foam board foundation insulation that's exposed above grade.

The exposure runs about 24" around the house. The sill plate extends 2" over the foundation wall and the foam board (blue board) butts right up to it. I've been thinking about nailing up some lathe at the sill and then to some PT furring strips screwed into the foundation wall running horizontally and parallel to the sill plate and then do the two or three coats of mortar/mason's lime mix over the lathe.

There are some products available designed for this but I'm hearing they don't last.

Anyone have ideas/experiences with any of this?

 

[2manyrocks]

I only took a class in synthetic stucco. Have never done it in real life.


My recollection is that you put up the board and wood like you say and then cover it with a net like material. It gets covered with a base, and then there's a topcoat. The tricky part is in getting the top coat applied in a more or less uniform way, and then we were warned that we could end up with something that didn't look right if we applied part of it in the sun and part in the shade or even allowed scaffolding to shade the sun over part of it. The class wasn't very good at addressing water penetration problems and how to prevent water from getting trapped inside the materials and rotting the structure later. At ground level, a weed eater or a rock thrown by a lawnmower is going to punch a hole in it is what we were told. We kept asking the instructor how long it would last and he would only say, "it will outlast vinyl siding." His words--not mine.

Someone who has done it in real life can tell you better and how it compares to a real mortar job.

If nothing else, there are some articles in Fine Homebuilding that discuss how to do what you are asking about. One thing that comes to mind is that you may want to install a good drip edge on the ledger to get moisture out and away from your backing material and your mortar job. In theory, I'd think a drip edge on the bottom also makes sense so you don't have water destroying your bottom rail over time.

I would like to know how the insulation board and expanded lath gets attached to the building and if any tar paper should also be used to further protect the insulation board when you're using real mortar.

 

[PILOON]

I don't know brand names, but there is a system whereby you adhere a fiberglass mesh onto the foam with a simple trowel and then add a finishing resin based stucco over the top.
It is a pattented product and used in many commercial applications.
It wants the rigid blue foam as a base.
Properly applied it will resist even hammer blows.
I do know that it is rather pricy but very permanant.

 

[keegs]

I hadn't thought about a drip edge. Thanks.

I found a textured coating product at a local (Northern Maine) home center chain. If I recall the instructions were to scratch the surface with a rasp, tape the foam board seams with a mesh tape and then apply a few coats of this textured coating. It was moderately priced. Maybe the whole job for $200. US. But the mason who did the chimney for us said he used it and it didn't last.

Lowes had a more expensive system that involved a mesh material that covered the surface and then several coats of a textured finish over that. It was pricey but looked doable.

I've done a few jobs around the house here using the galvanized steel lathe and mortar. Its cheap, sturdy and seems to hold up well.

 

[dave1949]

I don't know brand names, but there is a system whereby you adhere a fiberglass mesh onto the foam with a simple trowel and then add a finishing resin based stucco over the top.
It is a pattented product and used in many commercial applications.
It wants the rigid blue foam as a base.
Properly applied it will resist even hammer blows.
I do know that it is rather pricy but very permanant.

That resin based stucco really holds up to moist and rainy weather in Germany. They get long stretches of it. Not affected by freezing either.
Dave.

 

[2manyrocks]

Now that you mention it, I do recall having to rough up the foam board and taping the seams, but I had forgotten it. One thing I haven't forgotten is that the synthetic stucco had a strong smell to it until it dried.

You might want to do some searching on this. A quick search turned up this discussion where they discuss parging and also bring up the issue of termites: Exterior Foundation Insulation - JLC-Online Forums

 

[magicheater]

I'm looking for suggestions/experiences on coating/coverinng methods and products for the extruded foam board foundation insulation that's exposed above grade.

The exposure runs about 24" around the house. The sill plate extends 2" over the foundation wall and the foam board (blue board) butts right up to it. I've been thinking about nailing up some lathe at the sill and then to some PT furring strips screwed into the foundation wall running horizontally and parallel to the sill plate and then do the two or three coats of mortar/mason's lime mix over the lathe.

There are some products available designed for this but I'm hearing they don't last.

Anyone have ideas/experiences with any of this?

I have experimented with this extensively. Here is what I do: I use expanded metal lathe which would be nailed to your sill. To anchor the foam to the foundation, I use plastic concrete anchors which are inserted into a drilled hole of the correct size but have a foam nail(with the large plastic washer and of the correct length for the foam thickness) stuck in a bit first. a few taps with the hammer sets the anchor in the hole and cinches the foam nail to the anchor. To keep the lathe tight to the foam in areas not pinched with the before mentioned combo I use 3" shingle nails put in at a severe angle so not to contact the foundation and not all in the same direction. This works on the 1.5" and 2" foam, I then cover with a mixture of masons sand/cement/lime/fiberglas fibers. 60/40 on the sand/cement, enough lime to make it sticky and enough fibers to give it strength. Put on thick so you can't see the lathe pattern in your mud. When applying don't let it dry fast, keep wet as long as possible. Also try to extend this at least 4" below grade. Had good luck so far. The previous experiments have not done as well but are holding their own.

 

[keegs]

I have experimented with this extensively. Here is what I do: I use expanded metal lathe which would be nailed to your sill. To anchor the foam to the foundation, I use plastic concrete anchors which are inserted into a drilled hole of the correct size but have a foam nail(with the large plastic washer and of the correct length for the foam thickness) stuck in a bit first. a few taps with the hammer sets the anchor in the hole and cinches the foam nail to the anchor. To keep the lathe tight to the foam in areas not pinched with the before mentioned combo I use 3" shingle nails put in at a severe angle so not to contact the foundation and not all in the same direction. This works on the 1.5" and 2" foam, I then cover with a mixture of masons sand/cement/lime/fiberglas fibers. 60/40 on the sand/cement, enough lime to make it sticky and enough fibers to give it strength. Put on thick so you can't see the lathe pattern in your mud. When applying don't let it dry fast, keep wet as long as possible. Also try to extend this at least 4" below grade. Had good luck so far. The previous experiments have not done as well but are holding their own.

Thanks !