pizza oven falling cement

[peterpane]

i bake bread for a restaurant using a rosito-bisani modular pizza oven. to achieve certain qualities in the breads, i spray water into the oven at the beginning of baking using a garden mister. i have begun to notice that the spray seems to be causing chunks of the cement, which is plastered between the modular slabs which make up the dome, to crumble and fall. how concerned should i be about this? should i stop spraying? (the steam from the spray allows for a nice bloom in the loaf and a nice thick crust). can i put new cement between the dome slabs? what should i do?

[dmun]

The refractory mortar between the elements of your oven shouldn't react to the steam from misting: This is a pretty standard baker's technique. If it's the right kind of mortar, it should have plenty of resistance to temperature shock to remain intact. I suspect that someone used cheaper mortar to build your oven.

You can point the oven from the inside: When it's cold, crawl in with the kind of carbide hook tool that they use for re-pointing tile in bathrooms, and scrape out any loose or crumbly mortar. Then mix a refractory mortar mix like "heat-stop 50" with water to a peanut butter consistancy, and squeeze it into the cracks. After a couple of hours, go in and sponge off any excess, and your ready to cure. A week to set, then small fires, and cool, progressively hotter, until you are back to baking temperatures.

I know that the down time might be a problem for a commercial oven that's fired consistantly. In all likelyhood, you don't need to do any more than scrape out the pieces that are in danger of falling into your food. Those things are pretty self-supporting.

[james]

I like David's advice. Get the mortar outta there, and repoint new mortar in. I have done some experimenting with cracked pieces and Refrax to see what would happen, and the results are good. In fact, we completely assembled a Forno Bravo oven that had been dropped by the shipper and destroyed. We put it together with a lot Refrax (inside and out) and it cooks great and is lasting well. Don't do this at home, but it was a good thing to know.

Is it only the mortar that is calling in? Are the oven dome pieces themselves holding up and not cracking or starting to spall (flake)? If the dome is in good shape and it is just the mortar, I think it will work well.

I would highly recommend Refrax over the U.S. made mortar. I know that it will stand up to the heat and thermal cycling.

James

[peterpane]

the oven dome seems to be in pretty good shape, although it is pitted a bit. it is more the mortar filling the cracks that seems to be falling out, although it's stopped or slowed down in the last couple of weeks.

yeah, the oven is being used constantly. is it okay to patch the cracks without an extended curing time?