Sirs;We have 4″ of extruded polystyrene (pink board insulation)over masonry block.We need to now stucco over this.using traditional site mixed stucco.Do we have to use metal lath over the polystyrene before the stucco layer? We see that the EIFS systems only use fiberglass mesh over the polystyrene and this is for reinforcement only.Also the Canadian Building web site says mortar may be used as an adhesive for polystyrene to masonry block.This leads us to believe that stucco/mortar readily adheres to the polystyrene without using metal lath.Does anyone have experience with these questions.Thanks,Don Lauer
Replies
EIFS systems don't use traditional stucco, so the analogy doesn't hold. The mesh is applied with an acrylic base coat.
you should apply the stucco directly to the block. It will be failsafe then. stucco and block will bond indefinitly due to same makeup of material.
Stucco doesn't quite insulate as well as polystyrene though.Kevin Halliburton
"I believe that architecture is a pragmatic art. To become art it must be built on a foundation of necessity." - I.M. Pei -
They make special "nails" that you epoxy to the block, point out, then you push the foam down over the "nails".
The "nails" sticking out of the foam allow you to fasten the stucco mesh directly to the block, then you stucco normally. Depending on the water permeability of the foam you may want to paper under the stucco.
You can use cement to bond foam to block, but how much does foam weigh?
Stucco should be well fastened to the structural material underneath it.
At this point you may have to anchor some hefty furring thru the foam to the block.
SamT