Outer Render Question

[CapePizza]

Can type S mortar be the final render coat over the perlcrete layer? Or if I put the type S mortar over the perlcrete layer is it then also necessary to put a stucco over the type S mortar? My oven is exposed and not covered by a “dog house”.
thanks!

[rsandler]

Type S mortar is 2:1:9 portland cement:hydrated lime:sand. There are many recipes out there for a stucco mix, but none are exactly that. Making your own stucco mix also gives you the opportunity to introduce additives like fibers to help with cracking, bonding agents etc., which would not be in a bag of mortar. Some of these additives, fibers especially, can be found in bagged commercial stucco mixes.

On the whole, I suspect that if you just used mortar you'd get some kind of hard shell, but it might not stand up to the weather the way you want.

[CapePizza]

Thanks for the reply. I understand your comments about the mix recipe and the addition of adding fibers...... are you saying to skip the mortar Type S altogether and just put the stucco over the perlcrete, or put the Type S mortar on over the perlcrete and then over that mortar layer put on the stucco layer (with the possible addition of fibers)? Thanks again for the help.

[rsandler]

Just put stucco on your perlcrete layer. Type S mortar is intended to stick bricks together, not as a coating. While as I indicated it's not that different a mix from stucco, there's no reason to use it as a base layer.

[david s]

Commercial render/stucco mixes do not usually provide exact proportions of their ingredients, but will contain partial waterproofing which reduces porosity but still allows some breathability. Some products also contain acrylic fortification which improves strength and ease of application. This product is falsely labeled, in our country as Acrylic Render although it is a cement based dry product in a bag, not to be confused with the much more expensive100% acrylic wet render in a bucket.