Salvaging damaged oven (and measures to prevent it)

[Christoffer.Ceutz]

Hello, I'm new here and and looking for help.

I have been asked (because I'm the internet research person) if there is anything to be done to restore the oven in the pictures. We are somewhat experienced in DIY, but when it comes to the requirements of a high temperature oven, we aren't as confident. All of the repair questions I've found so far have been much smaller cracks than this, so I'm not sure what approach to take.

I'm imagining that we would need to chisel off the damaged mortar and replace it, but I'd really appreciate any advice!

The Danish weather is probably to blame for this, so we know it will need to be covered to prevent it, but input on preservation would also be greatly appreciated.

Hope you all are well
Cheers
Christoffer

[SableSprings]

Hi Christoffer! Would you please post some pictures of the inside of the oven? If these cracks are just in the outer render coat of a brick oven, then the repairs will be basically simple. If this is a cast oven, it would be good to also know the approximate thickness of the casting material. You are correct in assuming the best move for this oven is to provide a cover from the elements. In Denmark, I'd assume a covered structure around the oven and a table or two would extend "pizza season" quite a bit!

The pictures of the inside and any additional info you have would be very helpful in getting some repair options. Also, if you can determine (or find out) what the insulation is under the cooking floor, it would be very important.

Get back to us & I'm sure the forum members can come up with some direction for you on either repairs or rebuild.

[Christoffer.Ceutz]

Hi Mike!

Thank you very much for your reply! I'll see if I can get some more pictures tomorrow morning of the inside. I don't know much about its construction, except what I can see. It's bricks on the inside, and there appears to be no cracks in there, which is good, I assume . And regarding insulation material, I sadly don't have any idea. I have been told that it is from Portugal, but I don't suppose that says very much...

And a covered structure would unfortunately be a bit troublesome with its placement at the moment. Are there any good removable cloth/tarp covers that can protect it well?

[Christoffer.Ceutz]

I was wrong... The oven does have some cracks inside, I just managed to miss them.

[SableSprings]

Christoffer, could you tell if there was any insulation underneath the cooking tiles or between the dome bricks and the outer masonry? It looks from the photos that it has no insulation...just bricks on the hearth and cement/masonry layer on the outside of the dome. Even though the cracks look bad, the dome itself should be stable. I would worry more about bits of joint mortar dropping out from the upper dome onto food. I'm also a bit concerned that the bricks don't appear to be firebricks and will be subject to spalling (surface flaking off).

Do you know what the owners intend to cook in the oven? Just an occasional pizza or longer term baking like breads & meats? If the oven doesn't have some type of insulation board/layer underneath the cooking floor they may never be able to get the oven up to proper temps and would also face issues with retained heat baking. I used an oven in Italy (built into a hillside) that I was unable to heat enough to bake a couple of loaves of bread...the surrounding dirt was a very effective heat sink that "stole" my fire. Pizza was difficult to do as well since I had to move coals off a spot, cook one pizza on that spot and then repeat the process. No insulation on the base just made it nearly impossible to bake or cook anything...I went through a LOT of wood determining that the oven was really more an historical art piece than a functional oven...certainly might be an issue in Denmark with the cost/availability of hardwood.

You could add insulation on top & re-coat the oven outer shell (wouldn't need to remove the old cracked layer) after a long, slow curing process--but putting insulation underneath the cooking floor would require some major work. In all honesty, you could make this oven prettier but if they wanted to actually use the oven frequently, tearing down the dome and doing a proper build might be a better investment (IMHO). Having a base insulation layer would improve the justification for repair instead of replacement, so that's an important piece of information we need to know.

[Christoffer.Ceutz]

Again, thank your for taking the time to answer, Mike.

I can't say for sure if its insulated or not. I haven't used any other oven than this one, so I have no reference :-/. A couple of times, I've put my hand on the underside of the oven, and while it was warm, it was not like hundreds of degrees C (I didn't burn myself). So maybe it's insulated on the bottom?

Functionally, it has been fine for our skills (it's my in-laws'). As far as I recall, we've only ever used it for pizza. So I think the primary objective for my father-in-law is to restore the appearance (and hopefully preserve it better in the future). But if functional improvement isn't too large of a task, that might be something we want to do as well.

What would be the practical steps to restoring the appearance? Should we knock off the loose parts of the outer layer and apply a new one? If so, we might find out if it's insulated along the way.

[SableSprings]

Because the hearth was warm underneath, my guess is that it is NOT insulated or very minimally at best. For an insulated oven you should not feel warmth underneath. What "warm" means is that your pizza oven fire is not only heating the cooking floor, but the concrete slab. The slab is acting as a giant heat sink...no problems if you only use it occasionally and aren't concerned about needing a bit more wood to heat up the cooking floor bricks. Since you've been using it and are happy with how you use it, then going to a lot of expense to tear down & rebuild is probably not worth it (IMHO)

Putting insulation underneath would probably be next to impossible, so I'd leave that alone. I really would like to see you find some ceramic insulation batting, perlite, or vermiculite for the outer dome. The batting is expensive, but the best. Mixing 10:1 either perlite or vermiculite with Portland cement would give you some decent insulation over the dome when applied to at least 3-4" (7-10 cm) thickness. I'd strip off the broken, cracked exterior render...no reason to keep extra mass there and then apply the insulation over the dome. Since your oven is probably pretty damp, you'll want to do a very slow curing process to drive out that moisture and not cause any more cracks. Once the oven and outer insulation are dry, you can apply a couple coats of stucco or some other masonry product. There are several that offer water proofing additives. You can test the dryness of the dome by putting a piece of clear plastic over it...if moisture is still present, you'll get condensation on the plastic indicating a need to continue slowwww firing.

It is important to understand that your oven will need to be protected more from the elements than it is currently. There is NO product on the market that will give you 100% waterproofing for very long. If the oven is out in the elements, water will find its way in and break down whatever you do now to fix the existing problem. Building a little enclosure would be well worth your time. One additional advantage of an enclosure is that you would insulate the outer dome, but then build your enclosure to protect & hide the "rough" look of the insulation on the dome...no need to do the outer render/coating...

Lots of examples on the forum of these relatively small protective enclosures. Hope that helps.

[SableSprings]

Just a few other thoughts...If removing the outside mortar/cement coat proves difficult, it wouldn't be a problem to leave it on. Adding insulation over the dome would help speed up the heating process even with the added mass. In fact, leaving it on if it's been applied directly to the dome bricks might keep some of the cracked dome pieces more in line (so they don't become a pizza topping...). In noting the broken floor tile, I wondered if you had thought about replacing it or had a source for those cooking floor tiles/bricks. Depending on how much space (height) you have from the floor to the dome, you might even think about adding a layer of insulation on the existing floor and placing a new cooking floor on top. It would certainly make your working area smaller, but adding even 2-4 cm layer of a 5:1 (perlite or vermiculite to cement) insulation would make a big difference and improve the functionality and performance of the oven.