Help! Cracks in newly cast homebrew oven

[Taz07]

Hi everyone. Was hoping I could get some advice for a problem I've encountered today.

I cast an 85cm diameter homebrew mix oven today. All was well until about 2 hours later I noticed cracks that appeared from the top of the dome an extended to the back in a 'Y' shape. I'm in the UK and it's been a rarely hot and sunny day. Luckily the mix was still malleable so I gently compressed through the cracks and immediately covered with wet towels.

I've been trying to see if anyone else has had similar issues and trying to figure out the cause.

I mixed in batches and the final two were for the top of the dome and were slightly wetter than the previous mixes. At the point I was doing this bit the sun was directly over. On looking further into the forums I've seen some people using SS needed and Polypropylene fibres. I haven't used either of these and was wondering how important they are?

Are these cracks going to be an issue? What's the best way of preventing or minimising the chances of them happening?

Thanks all

Taz

[NylandJim]

Hi Taz,

I just cast my homebrew dome today and have the same problem. I wonder what came of your oven?

[david s]

The polypropylene fibres are actually designed for use with concrete and their function is to reduce early set shrinkage cracking which, from your description is what you have. Thes fine fibres do not contribute strength like the stainless needles will. Hot weather exacerbates the early shrinkage cracking problem as well as the high proportion of clay in the mix.. Additionally, as the fibres melt at 160C they create a network of very fine pipes through which steam can pass. This quality provides a measure of steam spalling protection. You will have to be super careful with the drying fires to avoid this as your castable did not contain the fibres. Don’t worry too much as all ovens have some cracks and the dome is a self supporting structure so it won’t collapse.