arch crack created stucco crack

[leckig]

I have 3 small cracks in the arch that open up only when the oven heats up. They did not bother me.

The arch is insulated, but I made a mistake - when applying the stucco I covered with it the whole arch up to the very edge of it. So yesterday, during a nice fire the cracks in the arch opened up and... they decided to open up the stucco as well.

I can easily fix the stucco, but I am looking for ideas how to prevent the cracks in the arch to propagate on the stucco. Obviously, I the stucco cannot touch the bricks, what can I use to fill the between the bricks and stucco?

[fxpose]

Re: arch crack created stucco crack

I had one area above the vent where the base coat stucco kept opening up only during roaring start ups but after shimming that crack while open I filled the crack with very fine stucco mix.
After several days I applied a couple of layers of SBC w/acrylic over that and I have not seen a crack there since after several firings.

[leckig]

Re: arch crack created stucco crack

This is an interesting fix George! The crack in my case is all together at least 4 feet long.

Is there a technique which allows to separate the stucco from the bricks, so if the cracks in bricks expands it will not crack the stucco? Maybe there is some kind of expanding or rather flexible compound I can use it to create a sealed gap between the edge of the arch and the stucco layer?

Greg

[david s]

Re: arch crack created stucco crack

Try a flexible acrylic render/stucco mix

[sjmeff]

Re: arch crack created stucco crack

Greg - I have a stucco dome and I left a thin space (~1/8", perhaps?) between the stucco and my Duratech chimney and between the stucco and my outer arch. I filled the space with clear, high-temp caulk. The stuff I got is supposedly resistant to weathering. After a year it's as good as new and so far my stucco has held up.

I have an extra can of the caulk that I'd be happy to send you. Send me a private message with your address if you're interested.

S

[sjmeff]

Re: arch crack created stucco crack

I also used SBC with acrylic mix for my stucco as David suggested in his comment.

[leckig]

Re: arch crack created stucco crack

high temp caulk - this sounds like what I need!

I appreciate your offer! Which product did you use, if I can buy it locally it may be cheaper and faster.

I dont think SBC with acrylic would be sufficient - I just cant imagine it would stretch to 1/8 inch.

[sjmeff]

Re: arch crack created stucco crack

This looks like what I got but I'd have to double check. The link indicates that it has an upper temperature range of 500F, which is way hotter than either my double-walled chimney or outer arch get (both do get hot to the touch, but I can put my hand on them for several seconds).

I ordered 3 cans and they sent me a few extra. So far I've used one, so I have several left over.

Regarding the SBC, I just meant that overall it's durable for the rest of your dome, but I don't think it will necessarily solve this issue.

S

[leckig]

Re: arch crack created stucco crack

Thanks! I will check Lowes today, if I cant find anything that may work, I will send you that PM.
greg

[david s]

Re: arch crack created stucco crack

On my ovens I leave a gap of 10mm between the outer arch and floor which is filled with vermicrete. This seems to be sufficient to eliminate cracks around the arch. I have also created a unique seal made of terra cotta that goes around the flue and also allows the oven to breathe. This also eliminates the cracking problem around the flue, which can be an easy access for water entry.Checkout my website to view what I'm talking about.

www.davespizzaovens.com.au

[leckig]

Re: arch crack created stucco crack

So here is what I have done with my mighty angle grinder:
damaged stucco 003 | Flickr - Photo Sharing!
damaged stucco 001 | Flickr - Photo Sharing!

I cut that little groove around the whole arch.

Now I need to fill it with something that I can later paint.

[leckig]

Re: arch crack created stucco crack

I fired up the oven last night to see if the stucco cracks open up even though they are not connected to the cracked arch.

Yes-they do. Looks like there is enough force to push the insulation against the stucco layer and lift the stucco up a little, so the cracks open up. It is not much, but I am afraid that if I only patch the cracks it will open up again.

Now I have a dilemma what to do.

[sjmeff]

Re: arch crack created stucco crack

Greg - how thick is your blanket insulation? When your oven is fired, does the stucco feel warm/hot?

Looking at your pictures, I'm guessing that you put the stucco layer on top of the blanket layer. I know many here have done just that without any issues. However, if you're seeing cracking, you might consider either adding more blanket insulation or putting vermicrete on top of the blanket and then the stucco on after that.

S

[leckig]

Re: arch crack created stucco crack

I have 1-2 inches of blanket plus about 6 inches of vermicrete. The oven remains cold, the temps goes up only about 10 degrees above ambient.

Can I apply another layer of stucco over the whole dome? I am thinking to use that surface bonding stuff, I found one home depot in columbus that sells that.
greg

[sjmeff]

Re: arch crack created stucco crack

Your insulation sounds comparable to my oven (I think I had more blanket, less vermicrete).

I will let a more experienced member respond regarding SBC over stucco. My novice inclination is that it would probably work well. The acrylic fortifier was highly recommended and so I used that with the SBC. It's expensive but worth the benefits (improved water repellency, helps prevent cracks during curing, etc.)

S