36" WF Pompeii Oven in Maryland

[david s]

If the oven wants to crack it will crack. I didn't have joints lined up so the crack in my oven just went right through a couple of bricks. I think it was david s that said you want your mortar to be weaker than your bricks - apparently not mine

I’m not trying to ruffle feathers and I know we’re not building kilns and the thermal expansion we deal with is about half that of a kiln, BUT the principles remain. This from Daniel Rhodes , Kilns, design, construction and operation, Pitman publishing, (generally regarded as “the kiln builders bible”)

”Expansion joints must be provided in the brickwork of kilns. If no expansion space is provided for, the kiln will bulge and swell on heating due to the expansion of the bricks In practice, a space of about 1/4 inch is allowed between the ends of every third or fourth brick. This space should not be filled with mortar. More space than this is sometimes allowed just to be sure that the wall will not be too tight. In kiln building it is much better to have a loose structure than a tight one. For this reason the amateur may have a slight advantage over the professional mason, because his bricklaying is apt to be somewhat loose and not tightly locked together. I have seen kilns made by professional bricklayers which in use suffered severe cracking and swelling due to the overly tight and precise workmanship and the lack of expansion joints.”

We’re talking around 1% expansion from ambient to stoneware temperature, so about 10 mm/m, or for an oven around half that from ambient to pizza temp. A 1/4” expansion pushing against a cooler outer decorative arch or base of the dome can certainly place stress on it if not a crack unless allowance is made. Although, as they say, there are two types of oven owners, those whose ovens have cracks and those who lie about their ovens having cracks. The same applies with kilns.

[bentedesco]

Thanks guys! It almost gave me a heart attack when I saw the crack in the back... after all that work!

I've now had ~5 fires that have gone over 1k degrees and the outer shell still is only around 100 degrees at the end a 5-6 hour pizza firing session (constant temps of ~850). Thankfully, the crack has not gotten any larger. I think I'm pretty much done with the build now and I wanted to sincerely thank everyone on the forum here for their expertise, especially @UtahBeehiver, @JRPizza , @Gulf , david s
mongota
mburham


I've gone ahead and written up a 3 page guide of "Instructions for Making a Neopolitan Pizza in a Woodfire Oven" for when I have Pizza Picnics that I've laminated and just have out on the table when my friends/family are over and want to make a pizza, here's what I've got so far, feel free to use/suggest further edits: https://docs.google.com/document/d/1Pg3b7ion1Xklsl4efzIksRBt9K-p1DKBtByFcFn-XL4/edit?usp=sharing


Thanks again to everyone here!

The finished build:

[bentedesco]

The crack in the back of the oven hasn't gotten any larger and I've had several more 900+ degree fires over the past weeks.

But, the crack still annoys me. I know it's due to me improperly staggering my courses, however, I'm wondering if I could use a syringe and pack in some additional mortar slurry? Would this work or do you think a new crack would further expand resulting in possible structural issues in the future? I'm glad that the crack isn't expanding, but if I can, I would like to try to clean this up if possible. Thoughts?

[david s]

Cracks in ovens and kilns are not uncommon. Repairing them is also usually not successful, but here's the recommended method. Wet the area to be filled, you have to get water into the crack which is difficult because it's vertical. Maybe try a spray bottle with the nozzle set on stream. Allow the water to penetrate, maybe do it a few times with 5 min wait between each. The area needs to be damp not wet before proceeding. Then try and get a thin slurry of cement and water into the crack. This is quite difficult maybe use a thin paint brush. The idea is not to fill the crack, but coat the sides of the crack with a cement rich mixture, that will maximise the bond. Wait for around 5 mins then force some home-brew, mixed to peanut butter consistency, into the crack, using something like a butter knife. Theoretically you should then keep the area damp for a week, but this is probably not possible. Allow a further week to dry completely before firing. Good luck and if you try this please report back on its success or otherwise. If you don't want to use home-brew you could try a refractory mortar (calcium aluminate cement) but you will have to use a fine sieve to separate the aggregate from the cement to get a little pure cement for the first operation.

[bentedesco]

Thanks david s , I was planning on using a wet brush to wet the bricks around the crack (similar to how I soaked the bricks before building the courses).

I went ahead and purchased these plastic Syringes: https://www.amazon.com/gp/product/B0...?ie=UTF8&psc=1

My plan right now is to fill 1 syringe up with water and soak inside the crack as you described.

After the water has begun to absorb into the bricks, I'll use the other syringe to try and insert some heatstop 50 into the crack (heatstop has a very smooth consistency, so hopefully the syringe will work, I'm going to do a small test first). If the Syringe is too small, I might try using a refillable caulk tube and trimming the tapered tip as necessary.

I'm firing pizza's again tomorrow, so it will probably be Sunday/Monday before the oven's cooled down and I can start on this

[david s]

Ok. Because the Heatstop is a calcium aluminate based mortar it does not require extended damp curing, two days should be sufficient. I still think it’s worthwhile trying to coat the surfaces of the crack with a concentrated slurry before filling. A fine sieve should separate out the aggregate. Be careful that you don’t use too thin a mix to fill the crack because the extra water means increased volume and when it dries it will shrink, still leaving you with a crack.

[Gulf]

I went back and looked at the crack that you are attempting to repair. That is not a very bad crack imo. Don't beat yourself up over it. These ovens are going to find a relief for the thermal expansion regardless of the staggered joints. With mortar that is stronger than the acutal brick, the cracks do tend to go straight and vertical. Otherwise, the cracks will stagger (zig zagging) along the joint lines. But, a crack is a crack. All ovens get them. Where it is, is just your oven's individual character. Your oven will perform just as well without repairing it. I doubt that you will be able to push mortar into that crack more than 1/4". But, if it makes you feel better, go for it.

I have a couple of cracks in my oven that have been there for 6 or 7 years. It bothered me for about a year.......... I got over it.......... I went in my oven right after plugging the keystone to do some touchups. I'm not going back in there again ..