Mesh Rainscreen Products and Stucco
My usual stucco guy has some major issues with mesh rainscreen products like Home Slicker and the like. (I haven’t known enough until recently to insist on using one.) He’s always done two layers of felt, staple up lathe, three coats of stucco, and paint.
I know the first suggestion I’ll get is to find another stucco guy, but hear him out. He has been called in to redo half a dozen jobs where a mesh rainscreen was used because the stucco was falling off the house. Like, all of it. He says the problem is the mesh pooches into the diamonds and prevents the stucco from pushing through the lathe enough to grab on.
He also reports the mesh causes the stucco to dry rather than cure. These guys start at 5:00AM so the stucco stays wet as long as possible. He’s quite the craftsman, so I’m loathe to argue unless someone gives me accurate ammunition. Also, if not mesh, than what? Thank you in advance.
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Replies
Johanna,
Traditional stucco installations just have too high a failure rate to use them today. https://www.greenbuildingadvisor.com/article/to-install-stucco-right-include-an-air-gap
I'm sure your stucco guy is a great craftsman, but that doesn't in any way change how the stucco will affect the wall behind. lf he is uncomfortable with mesh rain-screen backing it may be because he isn't using a paper backed lath which would avoid the mesh "pooch(ing) into the diamonds".
Here are three options you may consider:
- The gold standard of stucco walls would be one which has a rain-screen cavity formed by vertical strapping, a substrate of cement-board or DensGlass, lathe, and stucco.
- Paper backed lath can be fastened directly to vertical strapping with no backing, then the stucco applied.
- A mesh rain-screen used in conjunction with paper-backed lath.
It would be interesting to hear other posters and your stucco guy's opinions of these assemblies.
What part of the world are you building in? The assembly you described, without the rainscreen stucco is typically fine in desert parts of the country. It may not last for a hundred years but it can be ok if done right. If you are somewhere else then yeah, you probably want that rainscreen.
What it sounds like your stucco contractor is basically complaining about is that the mesh rainscreen is making it hard to install the lath normally. You need an extra deep furred lath so that the lath extends beyond the mesh. One possible thing that might help would be to put a layer of Grade D building paper (or cement board, which is more common in commercial) over the mesh, then put the lath on (again making sure it is furred out past the paper, you want the lath to be more in the middle of the scratch coat, not behind it). Something like structawire structalath may work well, it could make it easier. You can put together a sample with your proposed materials to make sure they are working together properly.
If you are looking for an alternative to the mesh, you could look into delta-dry & lath or Delta-Dry Stucco & stone. It is a dimple mat rain screen with built in lath. It is probably the simplest solution to your problem.
The nice thing about the rainscreen products is the reduction in labor costs. Furring and applying essentially a second layer of sheathing would be very labor intensive, and more expensive when I run the numbers. Commercial/deeper lathe has been discussed and adds quite a bit to the stucco cost. Of course, my guy hates paper backed lathe. What do you all think of something like mti’s Gravity Cavity with stucco? I’ve proposed that and now the dorken dry & lathe. Can’t wait to hear his opinion on those two. I’m in Asheville, NC where the folks don’t go for change much...
Johanna,
I can't be off much help. Both stucco and EIFS virtually disappeared here in the PNW once rain-screens came in about a decade ago.
The paper backed lath usually seems to have pretty much no furring. So that's why people tend to avoid it.
Gravity cavity looks similar to the delta dry products but it doesn't have an integrated lath so that necessitates an extra step. I can't imagine why either way wouldn't work just fine, just depends on what is optimal for you (availability, cost, ease of install etc).
Personally I've looked at using rainscreen products many times before but I've always decided against it due to cost. Then again I build in the desert and it's really not necessary.
It's hard getting contractors to do new things no matter where you are. And even with my own guys it can be an exercise in patience to teach them new techniques or ways to think about and approach things. Regardless, budget a bit of extra time and cost and material for your stucco guys to learn something new. Inspect it extra carefully.
In case anyone is interested in our solution… We opted to go with MTI’s gravity cavity product. This wasn’t without issue. The house has board sheathing, so we needed an advanced WRB. Unfortunately, we had already applied one that was not compatible with a million staple holes though our salesman originally claimed it was. Thank goodness we tested our assembly. We switched to a self-adhered membrane that seals around small penetrations, installed the MTI and got a new stucco guy.
Johanna,
Thanks for c0ming back. It's always interesting to hear how things turned out - and it sounds like they turned out well.
I thought I read that the 2018 IBC requires ventilation behind things like stucco. If it does say that (I don't know for sure), does the typical two layers of felt count (it seems like it shouldn't but I don't know)? My thinking even if it's not what's enforced in your region, the fact that it's there (again assuming I read it correctly) could be a data point for arguing for it.
I'll be in a similar situation in probably 6 months or so (in zone 2), so I'll also be interested in hearing the results. I've been trying to be as informed as I can be (hopefully so I can ask the right/good questions).