Stucco question

[Patrick.S]

I’m in the process of curing my oven now and then I’m planning on stuccoing the dome when it is all done. The classic recipe for cement stucco from my research is 3-1-.5 sand-Portland-lime. Should I go with that. I actually have some homebrew dry mixed. Any reason that wouldn’t work? Any other suggestions from someone with stucco experience? Thanks!

[lventi]

Hmmmm timely question (for me)...I've been looking into this and have seen a 4:1:1 ratio all. Can anybody confirm? We have the 6" of vermicrete over our dome and it's fully cured. Sounds like David S (who I trust, follow, admire) sees no need for chicken wire if AR fibers are used in the stucco mix. But I'm not sure of the ratio when adding the fibers. One site said 3%, and somebody else said to use 50% more than recommended. Can it be sort of random I hope? And then does one have to add another layer without the fibers over that so there are no fibers sticking up? I ask because it sounded like David S simply used the one layer with AR fibers, then the waterproofing seal coat. (I have SealKrete for this final layer.) David S, are you out there??

[david s]

The normal procedure is two or three coats of render about 5 mm thick each. Because of time constraints I do it in one go of around 12 -15 mm thick, then to enhance strength wrap the whole thing in cling wrap and leave it for a week.
Regarding the fibres, I add 1 litre to every 25 litres of dry render. They are fairly soft to work with and any sticking out can be easily sanded off before the waterproofing coat is applied. There are many different ways to do it, but this is the approach that suits me.

[Patrick.S]

I found a local source for the fibers but they say there are several sizes. Is there a size you recommend for this application David?

[david s]

The ones I use are around 17 mm long.
You must get AR (alkaline resistant) fibreglass fibres. They are coated with zirconium to protect them from reaction with the highly alkaline cement. Used a lot by the concrete countertop guys.

[Patrick.S]

Thanks David. They’re from the local redimix concrete supplier so they should be the right stuff.