Stucco/Render over insulating Perlite/Vermiculite layer.

[slainte]

It has been about 3 weeks since I placed the Vermiculite/Perlite layer over my homebrew cast dome. This includes a week of firing.
I am ready to add my stucco/render layer on.

My plan is to use a 1-1-4 (portland cement, lime, sand) mix, with polypropylene fibers and acrylic fortifier. I plan to make the layer 20mm (3/4 inch.) thick.
I will sponge some water on the dry vermiculite/perlite layer first.
I do not plan on using chicken wire.
I will cover the stucco/render layer with cling wrap for at least a week to damp cure it.

Any suggestion on this plan? I could use the chicken wire if it is worth the work.

I am a little bit worried about the water loss into the vermiculite/perlite layer, but not sure much could be done about it, I don't think it would be wise to really soak that insulation layer after purging all that water out of it.

Any thoughts are appreciated!

[david s]

Yes, that's what I do. The fine polypropylene fibres will do little to increase strength, but will improve workability and reduce any slump cracks. AR fibreglass fibres (12 x 0.5 mm) are a more suitable reinforcing fibre for a render of 3/4” thickness. I usually only do around 1/2”. Wrap the finished render layer by wrapping the whole oven in cling wrap as soon as you've finished and gone over the finished surface with a wet sponge, to remove tooling marks. This will hold the moisture in the outer layer and compensate for the moisture loss to the dry perlcrete. I've done many ovens using this technique with great results and no failures.