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Stucco on the exterior of my 36 inch dome work ok?

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  • Stucco on the exterior of my 36 inch dome work ok?

    I did 3 layers of ceramic insulation, chicken wire, 2 layers (around 2 inches) or 5-1 perolite cement insulation which is now drying. Planning on finishing the exterior of the dome with 2-3 layers of stucco to finish but was nervous regarding the possibility of it cracking? Any helpful advise would be greatly appreciated on this next step ...

  • #2
    Not sure how much perlite you used but a third of its volume would be the approx amount of water that you would have added. As the water deep in the layer will take longer to evaporate the outside may appear dry whilst deeper inside it won't be. If a significant amount of water remains in the insulation space at best it will reduce its insulating capacity as the water conducts heat. At worst it can make the perlcrete swell and crack and possibly crack the outer rendered shell. So it is prudent to eliminate the water before rendering over it. A 5:1 perlcrete is nowhere near as good an insulator as a 10:1 mix, but is far easier to apply. Unfortunately the amount of cement in a 5:1 brew tends to fill nearly all the spaces between the grains of perlite which make drying even slower. As you have 3 layers of (presumably 25mm thick) insulation you probably don't need the higher performance of the leaner brew. You can feel the moisture coming of the perlcrete layer during firing with your hand, but a better indicator is a sheet of plastic thrown over the oven during the drying fires where moisture present will condense on the underside. Alternatively a cheap garden moisture meter can be inserted into the perlcrete layer.
    Kindled with zeal and fired with passion.


    • #3
      Thank you !!! Very helpful and appreciated advise. Luckily (or not) we live in a pretty dry and warm climate in Atascadero, CA which will be far easier than doing this in (say) Florida. My wife and I have had a blast (mostly) building this project BTW. I think I'll let it breath for a week before any stucco goes on. Cheers!