Bacterium's 2nd build

[david s]

Re: Bacterium's 2nd build

Shirilite Is Commercial Product, Perlite Vermiculite, Refractory Cement Fire Clay.
Just Add water.

And some high temperature aggregate and fibres in the mix too IIRC.

[oasiscdm]

Re: Bacterium's 2nd build

Shirilite Is Commercial Product, Perlite Vermiculite, Refractory Cement Fire Clay.
Just Add water.

[david s]

Re: Bacterium's 2nd build

If you research Shiralite I think you'll find that although it is classed as insulating it's pretty dense. That of course makes it stronger but less insulating. It is a fancier version of vermicrete or perlcrete and able to withstand much higher temperatures because it contains calcium aluminate cement.

[Bacterium]

Re: Bacterium's 2nd build

Crack minimisation .......sounds like another oven mantra

Can someone enlighten me on the shiralite stuff pls.

[david s]

Re: Bacterium's 2nd build

The pathway for the steam, through the insulatin layer is fairly restricted before it even reaches the vent so a lot of water can still crack the outer shell. A vent works pretty well but can't release large volumes if they suddenly turn to steam. Especially if you have a thick vermicrete layer, that whole layer can expand considerably. It is better to eliminate the water as much as possible before rendering the outer shell, otherwise you tend to lock in moisture.

[oasiscdm]

Re: Bacterium's 2nd build

With a small vent like cobblerdave and others have used would that not prevent that? Thus Creating a point of least resistance for steam to escape thus protecting the outer shell.

[david s]

Re: Bacterium's 2nd build

Ok, I take your point. It is possible that some fibres could find their way through cracks in the dome with all the expansion and contraction going on there could be some abrasion to the blankets surface. I don't use blanket at all, mainly because of the cloud over its safety. I work in a school and we are not allowed to use ceramic blanket any more because of its greater risk to young people.the water soluble stuff is safe, but more expensive. I stick to perlite and vermiculite which I can obtain locally and it's relatively safe.

My comment re safer to drive out the water prior to rendering relates to steam pressure causing outer shell cracks.

[oasiscdm]

Re: Bacterium's 2nd build

Why?

David am only reporting what I was told by a commercial refractory builder. Same source re using the shirilite first prior to blanket. One of the points in doing this first revolves around ceramic blanket fibers getting through cracks, as I believe in Europe they have banned ceramic blanket due to carcinogenic issues now using superwool.

[david s]

Re: Bacterium's 2nd build

It's actually safer to drive out the moisture before rendering it.

[oasiscdm]

Re: Bacterium's 2nd build

hi

here here Alan, I was talking to a Furnace builder [30years in industry]today and he confirmed what you posted.

Comments made were along the lines of - Every oven is unique and not having cracks is what is rare. But the tips were - complete your oven without sealing it i.e. cement based render not acrylic, Then cure it very slowly. this will give you the best chance toward crack minimization.

[brickie in oz]

Re: Bacterium's 2nd build

All ovens crack to some degree.

[Wayne73]

Re: Bacterium's 2nd build

Are hair line cracks a big deal? And won't most ovens get them? Or not?

[brickie in oz]

Re: Bacterium's 2nd build

Ouch....
The crack fairy visited last night.....

Ya probably need a totally new description for cracks appearing in the oven........

[Bacterium]

Re: Bacterium's 2nd build

Cheers Colin.....I struggle with that on the iPad as its different to android on my phone.

David thanks, after more reading last night this confirms my direction. .....might stick some remaining heat proof mortar on the cracks then chicken wire then this smoothing and thermal mass layer.......you would think it would help keep the dome integral/strong.

[david s]

Re: Bacterium's 2nd build

Better to use a dense mix over the dome that will provide some extra thermal mass and strength IMO. Shiralite is an insulator. You are better to use your best insulator closest to the heat. For that cladding layer I use aggregate, sand, cement, lime and steel fibres for strength, but chicken wire will do too.