Inside Dome Repair

[Xabia Jim]

I've got a modular oven basically made from a number of precast firebrick pieces. (Call it a Spanish Econo model, not the high quality Forno Bravo ovens available from James )

Anyway, I've noticed that some of the inside mortar is flaking where the formed blocks were put together (probably cracked during transport and/or placement) and I'm wondering about whether to smear some high heat mortar (Refrax?) over them or just not worry about it.

I'm particularly wondering if you would get good enough adhesion after the oven has already been in use? Maybe after a pizza night when all the soot has been burned off?

Anyone done something like this?

XJ

[Frances]

Re: Inside Dome Repair

Interesting question, I have some shrunk joints on the inside of my oven and was wondering whether to fill them in sometime or not.

I was thinking you'd maybe have to re-cure the oven afterwards, to a greater or lesser degree.

[Dutchoven]

Re: Inside Dome Repair

XJ
Is it affecting the food at all?...sounds like spalling...result of the heating and cooling cycles on brick...maybe a little bigger brick in your case...I don't know that the refmix would help the situation though

Frances
If you have joints that have shrunk I might suggest filling them or pointing them...you can mix some mortar very stiff and using a shortened pointing trowel(it is very thin about 1/4" wide and 12-16" long) squeeze the mortar into the joint. You should cut off part of the end of the trowel to make it easier to use in the oven. Another option is...I don't know if they have them in Switzerland but here in the US it is called a grout bag...basically a piping bag like one would use to decorate a cake...except you will use it to squeeze mortar into the joint...just the opposite here on the mortar consistency...quite loose...in both cases finish the joint(by rubbing it with a finishing tool or wooden dowel) until it shines.

And you probably would have to recure slightly depending on what type of mortar and method you use.

Hope this helps
Dutch

[Xabia Jim]

Re: Inside Dome Repair

Dutch

It really looks like an inferior mortar mix was used. It has some pretty large grains of sand in it. It's not the bricks that are spalling (yet ) but I can flake off fairly large chunks of the mortar.

Not really affecting the food but obviously would not be fun to have as a pizza ingredient. I'll probably just keep ahead of it removing any loose pieces for now.

Thanks

[Frances]

Re: Inside Dome Repair

Thanks Dutch, sounds like good advice! I'll wait for some warmer weather before I crawl in there again though.

Just out of curiosity, why does one finish the joint like that?

[james]

Re: Inside Dome Repair

Great advice Dutch, I agree.

I have done repairs on ovens from the inside, and it works. My thinking is to buy the best quality Refrattario you can find locally -- buy the most expensive, because you don't need a lot. Also, you should make sure your oven dome is wet when you apply the mortar. You want it to cure slowly and you don't want the dome material sucking the moisture out of your mortar.

But don't do anything until you have to. Keep cooking Jim.
James

[Dutchoven]

Re: Inside Dome Repair

XJ
You very well could be right on the mortar...probably too cementitious( is that a word...sounded good)also...stay ahead of the process so you don't get any in the food. As James says wet the joint and do use the best mortar you can get your hands on...you will have to force the new stuff to bond with the old...in lower temp applications I have heard of painting the joint with elmer's glue as a bonding adhesive but...don't think that would work in the oven

Frances
You finish brick joints in that fashion to insure adhesion of the mortar to the edges of both bricks touching that joint. In cases of exposure to the elements it makes the joint more waterproof...in the oven case it will ensure a smoother surface on the inside of the dome. I forgot to mention in that post that...you finish the joint when the mortar is thumbprint firm...there are tools you can buy to finish mortar joints but most would be too big for joints like those on the inside of the dome...If I remember correctly didn't you use a fireclay and sand mix for your oven...if so you might be able to use your fingers as opposed to the trowel...could be fun...you could even ask Hansel und Gretel to get in your oven to do it for you!!!!
I know I'm bad
Best
Dutch

[james]

Re: Inside Dome Repair

Make sure you get a high temperature mortar. They don't have any Portland Cement in them, which is the weak spot for high heat application, and lots of heat up/cool down expansion and contraction.
James

[Xabia Jim]

Re: Inside Dome Repair

Mortar bag....sounds like a zip-loc with the corner cut out would work....

Thanks, now to find a high heat mortar here....

[Dutchoven]

Re: Inside Dome Repair

XJ
Are you in Spain right now? If so maybe I send you a grout bag? It will stand greater stress than will the ziploc...sometimes you have to give quite a squeeze.
Let me know what you think!
Dutch

[james]

Re: Inside Dome Repair

Mortar bag; light. Mortar; heavy.

Jim, you are in the land of brick fireplaces -- I hope you can find a good local firebrick mortar.

While you are at it, can you send me some concrete balusters. They are incredibly expensive here.

James

[Xabia Jim]

Re: Inside Dome Repair

Yeah Dutch you're right....no don't send me one, I'll find a way. I'm not in a hurry yet...

James, .....I could send you pallets of those....and so many designs to choose from! Now come to think of it....you're already shipping heavy stuff from Italy....what's a couple more pallets?

[CanuckJim]

Re: Inside Dome Repair

XJ, Frances,

Using a grout bag is certainly faster, but the mortar must be pretty goopy to get it to flow, and you must use the finest grain brick sand you can find, unless you're using Refmix or similar. Can be a sloppy operation, so put cardboard on the hearth. I have some bags kicking around as well, XJ, if you're in need and Dutch can't find his. Frances, the joints are tooled using a pointing trowel for two reasons: 1. by pushing in with the trowel, you will find any areas that have air pockets (you want the joints to be completely full), 2. the pressure and repeated swiping across the mortar from the steel trowel draws remaining water to the surface of the joint and makes it shine. This shiny bit is much stronger when cured than it would be otherwise (just left rough, ie.).

Jim

[gjbingham]

Re: Inside Dome Repair

CJim,
As I look inside my oven, I see a few joints between bricks that don't have mortar showing in the joint. Do you consider it worthwhile to get inside there and work mortar into those areas?
Thanks!

[CanuckJim]

Re: Inside Dome Repair

George,

Yes, I do, and here's why: You don't want the sharp corners and edges of the brick directly exposed to flame. They will get very hot indeed, and that will lead to spalling over time. It's a hassle, but I'd fill them.

Jim