Fine Treated Perlite

[fourlambs]

Hi All,

For my 50mm outer layer (after blanket) a local company here in Melbourne has recommended 'FINE TREATED PERLITE' with a 1 - 2mm particle size for the Perlicrete coating. I am unsure as i have read elsewhere that a MEDIUM grade is better? What do the experts think?

The dome is ready, covered in blanket and chicken wire, I will be mixing at 10:1 Perlite: Portland Cement. Also, i have some refractory cement left over, could i use this up for the Perlicrete?

How far does a 100lt of Perlite go?

Thanks and regards...
Phil

[david s]

Re: Fine Treated Perlite

There is a product used in the building industry that treats perlite with silicon which prevents water being absorbed into the perlite grains. Not sure if this is what your product is, but I would like to use it if it's available as the water absorbency is a problem, or getting rid of the water is at least. Most of the perlite and vermiculite used is for agricultural use and the grains ability to hold water is a desirable quality. I've never come across the silicon treated stuff in Australia, but believe it would suit our purposes better. Perlite tends to have a lot of fine dust which is quite irritating to breathe whereas vermiculite is less of a problem in this regard. The small grain size means that you will require more water when mixing rather than the larger grains. You don't say how big your oven is but you can work out the volume and add around 20% because you will lose some volume on mixing.

[Toomulla]

Re: Fine Treated Perlite

Why not just buy silicone waterproofing liquid and work that through the perlite

[david s]

Re: Fine Treated Perlite

Why not just buy silicone waterproofing liquid and work that through the perlite

That could well work. I haven't pursued that idea because I figured you'd need a lot of it and in a small batch would be not economic. Try it and report back.

[fourlambs]

Re: Fine Treated Perlite

Thanks all, I have purchased the silicon coated perlite (from Exfoiliators, Melbourne) and will let you know how it goes.

Phil

[tonybaker]

Re: Fine Treated Perlite

why not put a layer of ordinary mortar over the insulating layer? Mortar has some degree of water resistance, or you could paint it or treat it with silicon sealer....

[brickie in oz]

Re: Fine Treated Perlite

Mortar has some degree of water resistance

Not in the real world it hasnt, its like a sponge and sucks up moisture readily.

[fourlambs]

Re: Fine Treated Perlite

Ok.... Yesterday I made a few batches of the perlicrete (10:3:1 perlite, Water, Portland) and managed to get it onto the dome around 2" thick, this morning it has firmed up but still appears quite crumbly, is this normal? What should the dry perlicrete be like? Will it get harder still over time or is crumbly normal?

Thanks
Phil

[david s]

Re: Fine Treated Perlite

Phil,
The stuff only needs to strong enough for you to render over. Making it stronger by adding more cement just decreases its insulation capacity. Give it around a week to dry then start some fires (read the curing thread) After all the water has been driven out you can do the top render coating.Because you have the treated perlite you should not need to use so much water in the mix. I would guess 10:1.5:1 would be adequate, because the perlite grains are not sucking up the excess water.

[fourlambs]

Re: Fine Treated Perlite

Hopefully the final question, then its all over....

After some searching i am planning to use this product as the sealer/waterproofer over the final render coat;

Brick & Render Sealer: Sealers: Crommelin
Does anybody have any thoughts on this? Is there a better way?

Cooked 7 loaves and 2 steaks on the weekend!


Phil

[david s]

Re: Fine Treated Perlite

Phil,
That product looks as though it will be quite suitable, both waterproof and elastic. Take your time and eliminate all the water on your perlite layer before doing the outside render. Throwing some plastic over the dome will tell you if water is still present in that layer and condensing on the underside of the plastic. Failure to eliminate this water can lead to the cracking of the outer shell. After your render has been finished and cured (wrap it for a week) you need to do about 10 decent cooking fires to make sure that the render itself is also totally dry or your waterproofing layer may bubble.This procedure may sound tedious in terms of time and short cuts can be made, but it eliminates most problems that can arise.Because you have used the treated perlite then there is less water to eliminate so things should be easier for you.
Good luck,

Dave