Oven Base

[stef]

Hello. I took the plunge today and finished the first stage of the build.

I've completed the base, which is a 'C' chaped wall, made from 100mm concrete block on decent concrete footings.

I will be adding two concrete lintels from wall to wall, on which I plan to add two off the shelf, standard concrete paving stones measuring approx 50mm in height. I then plan to make a 50mm vermiculite concrete or fire cement screed (made from watered down ready mixed fire cement).

I'll then build the walls out of fire bricks that I acquired with a brick flue.

My question is will a 50mm vermiculite concrete or fire cement screed be sufficient and would I risk cracking the paving stones underneath?

[curlygirl]

I'm not an expert Stef, just a newbie like yourself and I may stand to be corrected, but when I read up about it the suggestion was 100mm of vermiculite concrete. It's really light stuff so won't cause any problems weight wise and at 10cm the concrete underneath will hardly heat up at all. I mixed mine 5 parts vermiculite to 1 part Portland cement. It does take a long time to dry though. I let mine dry for a fortnight and I'm still not sure if that was enough. Post pictures! I love seeing other peoples builds!
Nikki

[downunderdave]

Vermicrete insulating slab.doc (84.26 KB)


Yes, the usual under floor thickness is 100 mm if using 5:1 vermicrete. If you cast 50mm, allow it to dry for a week then cast another 50 mm on top, that should work ok. attached is an experiment I did to test the drying of the stuff, although much will depend on your weather conditions. It will eventually dry from the fires anyhow, but may take a long time.

[stef]

Sept 18, 2016 20:51:34 GMT downunderdave said:

View Attachment


Yes, the usual under floor thickness is 100 mm if using 5:1 vermicrete. If you cast 50mm, allow it to dry for a week then cast another 50 mm on top, that should work ok. attached is an experiment I did to test the drying of the stuff, although much will depend on your weather conditions. It will eventually dry from the fires anyhow, but may take a long time.

Wow. That's really useful. I will post some pics. Already taken a few and will post them all in due course.

[stef]

Thanks again for this. Will the vermiculite screed be hard and set solid or will it be flexible? Would I need to add a layer of firebricks for the base of the fire? I've read that it can be soft even when set.

[oblertone]

Sept 19, 2016 8:51:34 GMT stef said:

Thanks again for this. Will the vermiculite screed be hard and set solid or will it be flexible? Would I need to add a layer of firebricks for the base of the fire? I've read that it can be soft even when set.

Vermicrete is an insulating layer but will not provide a viable working surface; you'll need to lay a layer of firebricks/tiles/heater blocks to retain the heat needed for cooking. I prefer heater blocks because they're the cheapest option, but the choice is yours; you'll probably need to use a layer of fine sand to bed them evenly but there's no need to cement them down.

[jennabean]

I am also at the stage of setting the fire bricks for my oven, and I have read conflicting opinions of how to do this. Some people say that you need to lay the fire bricks on a thin layer of sand, others say no.

My base is made up of a 75mm thick 5:1 perlite/cement mix which I made very flat, so I could lay the bricks flat onto this surface, but need some advise. Thanks

[cobblerdave]

G'day
If the pearl Crete layer is flat... So much the better. Just lay your Heath bricks. If you have a a few lumps and bumps use house brick. The ones with the holes, rubbed over the surface will take away the minor imperfections.
Regards dave