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fluxia 12-06-2010 04:35 AM

crack fixing
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I need some advice on how to fix cracks please.

About 10 days ago I completed the insulation layer on my oven (4 inches of vermicrete). Prior to that I had fired the oven twice and it went well no cracks. So after leaving the insulation layer to dry for 10 days, on Saturday, I made a fairly big fire and it went ok. The oven went all white inside and was still steaming in the morning and warm on Sunday afternoon and again no cracks.

Last night I repeated the treatment but I think I have exaggerated. I got a crack on the top of the dome from the flue to the centre top - with smoke coming out of it. There is also a smaller crack from the centre top to the side but that looks less concerning as its smaller and it does not smoke. Please see pics. I have some more pics in my album :

I cant see any cracked bricks in the inside, so I suspect there is no structural damage, but as you can see from the pics I was not very good in properly filling the gaps between the bricks with mortar.

What it the best way to fix the crack and should I fill the gaps in between bricks with mortar in the inside?

Thank you


Tscarborough 12-06-2010 09:06 AM

Re: crack fixing
The best way would be to tuckpoint the inside, but I realize that is pretty hard to do.

fluxia 12-07-2010 01:28 PM

Re: crack fixing
Thanks for your reply

I will have to do it if necessary, do you kow if it's best to grind the crack and fill it with vermiculite or a mix of fireclay and cement (and sand) and patch it with another layer?

I know cracks tend to reoccur so I am unsure what material I should use. Presumably a flexible material, so probably vermicrete would be better.

Neil2 12-07-2010 01:38 PM

Re: crack fixing
"I got a crack on the top of the dome – from the flue to the centre top - with smoke coming out of it. "

Are you sure it is smoke and not steam ? Does it "smoke" initially or only after it has been fired for a while ? When first curing, or when firing after the inside gets damp, a lot of steam can be emitted.

"Presumably a flexible material, so probably vermicrete would be better."

Vermicrete is not flexible in that way. One of the acrylic caulks might be better.

david s 12-07-2010 02:35 PM

Re: crack fixing
Try placing a piece of plastic over the crack to determine if it's smoke or steam. If you can see steam being emitted then you are really going too hard at it, the expanding steam will create cracks.With 4" of vermicrete you will have added a lot of water in making the mix, probably one week of drying is insufficient and maybe your curing fires were progressed too quickly. Don't worry all is not lost. Don't use an acrylic product on the inside, it will burn, but it is ideal on the outside, get a product that has good elasticity. For the inside try squishing in some poor mans mortar.

fluxia 12-07-2010 02:53 PM

Re: crack fixing
Thanks; I 'll try to fire it again tomorrow and check, it was dark so I could well be wrong and I really hope so. In any case I will widen the crack a bit and patch it. I'll try to find acrylic caulk as you suggest.

Should I try and fire it again once I fixed the patch before attempting to tuckpoint the inside? How important is to do this job to prevent cracks in future?

Thanks for all your help, I was fairly desperate after seeing the dome cracked and "smoking" in that way :)

david s 12-07-2010 03:30 PM

Re: crack fixing
I've just returned from London, you poor thing! Don't worry too much about the crack at this stage, you would be better off to keep firing and cooking to ensure that all moisture has been removed, otherwise if you seal up the crack now you might just get more pressure build up and more cracking. At least now the steam has somewhere to escape through. It takes about 10 firings to get the oven totally dry.

fluxia 12-08-2010 08:51 AM

Re: crack fixing

Thanks David that's very helpful; I won't fix the crack untill the oven is competely dry . I din't fire the oven today as I noticed that some of the chimney bricks were coming off, so I decided to repair the chimney. I will fire the oven again in a few days when the chimney is a bit drier. However I think you are right: I inspected the crack and there is no sign of smoke around it; I should think the smoke would have left some black marks around the crack, but there is no trace of that. Anyway I will know for sure when I fire it, but I am a bit more optimistic now ....

It seems preatty hard to find acrylic stucco in England, I believe they call it acrylic mortar here but I have spoken with some builders suppliers and they don't even know what it is. I doubt that DIY shops will have it...

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