Help: Stucco Flaking Off Dome

[John1133]

Hello. My home made WFO is now 3 years old. The stucco began flaking off after two years. Last fall I scrapped off all of the loose material and re-applied the stucco. That has not worked and it continues to flake off from the Matrilite mortar layer underneath. The Matrilite is smooth and it appears that the stucco is unable to really bond or adhere to the Matrilite. When I pull or scrape off the loose stucco the back side of the free piece of stucco is actually white as a very thin layer of the Matrilite has come off with the stucco. I'm not sure how to fix this problem. I am worried that the Matrilite is not intended to be exposed to water so is now absorbing water which likely makes the problem worse. We love our WFO and have prepared hundreds of meals in it but I'm worried that the the missing and flaking stucco is going to allow water to damage it. For reference, we made and posted a video on Youtube describing how we built the oven. Any ideas would be much appreciated. Thanks, John

[Toomulla]

have you talked to the manufacturer you may need a binder or primer

[Gulf]

What type stucco did you apply? Traditional stucco requires a a mesh layer for it to properly bind. It can't bind to a soft refractory insulation like "matrilite", vermicrete, or perlcrete. There are no binders that can be painted on to make that work.

There are newer stucco formulas which have reinforcement fibers that will help hold the stucco together as a shell. They are not a matrix like the mesh layer, but the fibers do help the stucco keep from cracking.

You are probably correct about the "matrilite" absorbing water and making the problem worse. No insulation can absorb water and still perform. Many will tell you that stucco needs to breath. That may be true on a vertical wall of a house which has an overhang. But on an igloo style oven, we are asking it to be a waterproof roofing material. No stucco will do that unless some type of waterproofing is added to it or applied as a finish coat. In Canada, freeze / thaw is a big problem. That may also be why your stucco is "flaking".

There are many things that you can do to help your stucco be a permanent roof for you oven. But, a roof over it will solve may problems and make your oven usable more days out of the year.