36" WF Pompeii Oven in Maryland

[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 ..

[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.

[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]

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]

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?

[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:

[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.

[JRPizza]

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

[UtahBeehiver]

The cracks could of been caused by the joints lining up. But as long as the shell is good then all is well. I build mine in 2012 and I still have a few things to do on my oven, so the work is really never over....lol

[bentedesco]

Almost done!! We've been able to do quite a bit of cooking in the oven and I've used acid to clean up some of the stained glass. The crack in the back of the oven is frustrating (pictures 1 & 6) , but it looks like this is just due to thermal expansion (https://community.fornobravo.com/for...ne-crack/page2). Hopefully today, I can get the chimney laid and tomorrow cap it ...I can't believe that after almost a year this project is almost finished!

[bentedesco]

Busy day, completed all the stained glass mosaic- pretty much worked from 7am - 7pm only stopping for lunch. Overall, I think it went well, I need to figure out how to polish/buff the glass as there are some mortar streaks on some of the pieces. Only thing left is to quikwall the base, buff/polish the dome, and install the chimney! Looks like we are on track for a Memorial Day Pizza Picnic!

[bentedesco]

Just wanted to post a progress report. Yesterday, I was able to run a coat of quikwall over the dome and test various stains.

Today, I was able to run another coat of quikwall on my dome and began to decorate with the stained glass. Even though we are only partially done, I am VERY pleased with the results. I think I'm still going to skimcoat over some of the rough edges and come back with a polishing brush, to give it that finished look (an added bonus of the stained glass is that it hides any imperfections of the dome form geometry)

[david s]

Well I guess people have their own ideas and I personally prefer to seal the vent during the winter and open it up for spring when I light the first few fires.
Once I am satisfied the oven is dry and working efficiently, I re plug the vent .
Perhaps if I lived in a warm dry winter climate I would leave in open all year.
I did in fact install a 4” vent on the first few ovens I built, this allowed a screw down dome top to be fitted so it could be closed off with a twist.
However that sort of vent spoils the oven appearance so I use a 3/4” piece of copper pipe, I just use a wine bottle cork to seal it off.
Some customers like to have the dome coated with GRP in that case I would still install a 4” vent.
I don’t have a picture to hand of the twist down vent but I have one showing the vent hole.

Yes, that’s good. When you said “seal it over” my understanding was that you rendered over the hole permanently. Dry ovens still get wet again if exposed to the weather. In our case extreme humidity (we live in the tropics) for a couple of weeks, even if there’s no rain, is enough to wet oven and insulation enough to impair performance, the oven requiring at least one long slow fire to restore normal functioning.

[mburham]

I found the same bronze/copper 2" vent as inspired by your previous post! I am going to put one on either side of the entry on the outside, assumption is most moisture will enter there from rain etc.

[fox]

Well I guess people have their own ideas and I personally prefer to seal the vent during the winter and open it up for spring when I light the first few fires.
Once I am satisfied the oven is dry and working efficiently, I re plug the vent .
Perhaps if I lived in a warm dry winter climate I would leave in open all year.
I did in fact install a 4” vent on the first few ovens I built, this allowed a screw down dome top to be fitted so it could be closed off with a twist.
However that sort of vent spoils the oven appearance so I use a 3/4” piece of copper pipe, I just use a wine bottle cork to seal it off.
Some customers like to have the dome coated with GRP in that case I would still install a 4” vent.
I don’t have a picture to hand of the twist down vent but I have one showing the vent hole.