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talisker63 03-15-2008 05:53 PM

External crack
2 Attachment(s)
Oh no! :eek:

Fired the oven last night (see pizza photos in photo bragging section) but just as the fire was finished and burning down the oven render cracked. The crack is only in the final waterproofing render that i put on last weekend (7 days ago). So I guess I fired too hot - too soon :(

Also thought that maybe the render was too thin, only about 1-1.5".

The crack started at the flue and then slowly worked its way all the way down to the arch. It is only hairline down by the arch but about 1/16" up by the flue.

Any advice on how to repair?
Do I need to render the entire oven again or just the front section?\
If I leave the crack and tile the front would that work?

Help! :confused:


Dutchoven 03-15-2008 09:25 PM

Re: External crack
I might suggest using the oven for a while...maybe crack will stabilize...mark it with a pencil to see if there is any movement and watch it when the oven is firing and when it gets hot to see what it does...any widening and where etc...then you will have a better idea of what to do.

gjbingham 03-15-2008 10:28 PM

Re: External crack
I agree with Dutch. Did you add stain to the rendering material or did you paint afterwards?

If it doesn't get worse, I might be tempted to take a grinder and open the crack up and refill it again. I forget. What's the insulation like below this layer?

Xabia Jim 03-16-2008 12:30 AM

Re: External crack
Those pesky cracks:mad:

I think we're still looking for a dome that has not cracked. I would also be interested in hearing of someone has had good success with grinding out a crack and filling it.

With the continued expansion and contraction of these ovens and fireplaces, are cracks just a part of life?

I had an indoor fireplace and never was able to successfully fill an exterior crack on that one. (never ground it out though) And I do have two exterior cracks on my oven now. I've filled them a few times and painted over. Recently I tried an arcrylic caulk (more flexible).

Reminds me of a song....

Oh, the crack came back
It wouldn't stay away
The crack came back
The very next day

Dutch has it right too, give it time to grow (if it's going to) and stabilize

Xabia Jim 03-16-2008 12:46 AM

Re: External crack
Then I read Frances post on her Ostrich......

No bacon today,
the bacon's gone away,
sad as it is to say,
the bacon's gone away

...sorry, I was out on the oven today and seem to to have got stuck in singing mode. Let me know what you think if you try it!


Frances, this is too funny.....

I think we were both humming the same tune!!

.....another FB cosmic connection

Frances 03-16-2008 01:36 AM

Re: External crack
Thats so funny, Jim! :D Great minds and all that, eh?

About the crack: this subject interests me greatly, as my render will be covered with mosaics which means I probably won't see the cracks if/when they form...

So is a crack in the outside render very serious? If some of you say you left the cracks as is? I thought that even a small crack could wick up enormous amounts of water every time it rains. What about tiling over the top, does that help at all?

Great pizzas btw, talisker!

talisker63 03-16-2008 05:34 AM

Re: External crack
Thanks appreciate your support in these difficult times:(

The insulation material is vermiculite mixed with sand/cement over a blanket.

The top coat is tinted with oxide.

I think the top coat is too thin over the arch, this bit was hard to do and I may have skimped a bit on the thickness :o

I am having a big pizza party next weekend for Easter. Will report after that.


CanuckJim 03-16-2008 05:44 AM

Re: External crack

I don't think hairline cracks are much of an issue. BUT, exterior cracks on an igloo will allow moisture infiltration, and that is not a good idea. Wet insulators do not insulate. As well, if you've ever seen the face of a house brick that's gotten wet, then frozen, you'll know that the force of the freeze-thaw cycle will kick the front of the brick right off. It's called spalling. Once the cycle begins, in a brick wall or an oven dome, it's virtually impossible to halt. I'd recommend that significant exterior cracks be ground out in a V and filled for just that reason. XJs on the right track with a flexible material of some sort.


Dutchoven 03-16-2008 06:09 AM

Re: External crack
There is a material used to caulk the joints in log brother usedit is his...supposed to stretch up to 4 inches I think he said...if it isn't hot it should work because I don't know how it holds up to heat

carioca 03-16-2008 11:18 PM

Re: External crack
Good to hear others DO have cracks in their render/stucco - I thought I was singularly inept in my cover-up :-)

I've noticed a crack about 5cm (2in) long starting in the two-coat render/stucco at the 'naked' arch near the top of the dome and pointing toward the apex.

I measured the outside temperature at that point when the oven was hot, and it registers 50-odd decrees Celsius (sorry about the missing F, I'm lousy at instant conversions). Perhaps I didn't put down the insulation properly at that point close to the masonry?

Whatever: it hasn't grown in subsequent fires but I agree that it will be best to push some more cement render into that hairline and paint over again.

BTW, the two render coats are covered with two acrylic paint undercoats and two acrylic top coats - I'd have though that stuff is elastic enough to accomodate minuscule movements?!



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