Dome Insulation and finish....

[fourlambs]

Hello all,
Well.... the dome and door are finished and drying out for a week before i start the curing process. I have the ceramic blanket ready...

I seek advise as to the best 'recipe' for the vermiculite [or perlite] insulation layer that goes over the blanket and any tips in appyling this layer, as i heard it can be a little tricky. How thick? How to apply? Use just portland cement? Add sand to mix too ?

Lastly the final render.... any tips for this?

Cheers
Phil

[BOOMERS WFO]

Re: Dome Insulation and finish....

Hi Phil,

The Forno instructions for the vermiculite layer work well. I think I did 10 parts perlite/Vermiculite to cement, mix dry and add water (not too much) just enough so that the cement coats the vermiculite. It is like a thick porridge.
I made a form tool out of ply about 60cm long by 20cm on a cut out thicker piece of ply. This I held in place and shovelled the mix behind applying pressure toward the dome while compacting it into place from above. There is a photo of a similar tool on one of the Australia posts.
I worked around the dome in 200 mm strips allowing the lower course to cure a bit to support the upperlayers. As height increased I allowed the lower layers to fully dry before continuing to avoid a collapse.

Most of this layer I did at about 75 mm on top of the 50mm blanket. I did two layers of render, only two small cracks.

This insulation prevents a large amount of heat loss. The inside of the top of my dome can be at 500C+ after a few hours and the outside only at 28C.

Good luck

Craig

[Les]

Re: Dome Insulation and finish....

Insulation over the blanket (which is obviously insulation) is not required. It does no harm but you could just apply a stucco render and be done with it, assuming you are building a dome.

[david s]

Re: Dome Insulation and finish....

The advantage of using a vermicrete layer over the blanket is that it enables you to get a nice shape. There are lots of lumps and bumps where the blanket folds or overlaps. If you don't do a vermicrete layer you end up having to make the outside shell much thicker in an effort to get the hemispherical form. The vermicrete layer also insulates of course.

[cobblerdave]

Re: Dome Insulation and finish....

Insulation over the blanket (which is obviously insulation) is not required. It does no harm but you could just apply a stucco render and be done with it, assuming you are building a dome.

Gudday
I agree render over the blanket it not only quicker than dealing with a layer of pearlite/cement. Time is also saved waiting for that pearlite to dry.
Downside is that the pearlite/ cement is cheaper than an extra inch of ceramic.
Decision ultimately is yours fourlambs you can't wrong either way.
Regards dave

[UtahBeehiver]

Re: Dome Insulation and finish....

Based on your original question, I did install a perlcrete layer over a ceramic fiber blanket. Used a 5 perlite to 1 portland mix. I wanted it a little more robust since I was going to stucco next and then drill in fasteners for copper singles (BTW which I have not done yet). I wanted a fairly consistent shape for the shingle base. Attached is pic of a curve trowel I made to pack and form the pcrete. Also Ignore the foil covering on the CF blanket. General consenseus is not to use. My CF blanket came that way so I punched hundreds of holes in foil so moisture could migrate out.

[deejayoh]

Re: Dome Insulation and finish....

Snow is coming soon Russell! Gotta see that copper. I might get down to SLC this winter for some boarding. I'll have to come check on you.