Oven support wall cracking Modular Refractory Oven Installation Discuss Oven support wall cracking in the Pizza Oven Design and Installation forums; My concrete block oven support wall cracked on both sides all the way down to the bottom. The cracks are ...

[nyknicks]

My concrete block oven support wall cracked on both sides all the way down to the bottom. The cracks are hairline cracks. Has anyone else experienced this with their support wall?

[Unofornaio]

Is the oven on it already?
Which wall sides or back?
Was there a footing or just a slab?
Is there a crack on the slab? (wet down the slab and watch the water it will find even the smallest crack, you will see bubbles.

A crack through block indicates serious movement.

If there are no other visible cracks clean a 1' square section of the crack with soap and water rinse well after dry paint the area with white paint or a light paint. Put register marks (black lines) on the paint on either side of the crack parallel to the crack and a couple running right across the crack horizontally. measure the parallel lines and note the measurement (exactly) the horizontal lines can me measured after they have moved. this will tell you what direction it is moving if you cannot figure it out visually.

At first guess Id say the slab on grade is cracked also, look closely
Check it and get back...don't panic it can be fixed.

[RTflorida]

Slab movement was my guess. Several possible causes - base not compacted before the slab pour, lack of reinforcement within the slab (rebar or mesh), or slab is too thin.

I will concede judgement to Uno - he is probably one of the forums best authorities on masonry.

I'm very curious to the cause and solution if we are only talking about the block on slab.....without the hearth slab and dome. Just the block by itself really is not that much weight when considering the overall project.

[nyknicks]

The oven is already built. These cracks accured after the oven was used. I believe the problem is that the mason did not stagger the concrete blocks. The cracks fun all the way down the mortared seem. I believe the oven floor support moved when the oven got hot and caused the hairline cracks in the mortared seem. The oven floor itself did not crack but I can tell it sure does exspand when hot. Does this make sense? I also found a hairline crack in the front of my oven floor support. This is the part above my wood storage opening.

[Unofornaio]

Wow...
Why in the world did he not stager the joints?
Are the block fully grouted (all cells)?
Is there steel? where?
How thick is the hearth slab?
How wide is the span?
How big was the steel to carry the block over the opening?
You say oven floor did not crack is this a FB oven?
A crack in the hearth (support slab) is/could be a big concern.

CAUTION: Comments form a full blooded Italian to follow
If this guy laid the block with the joints lined up he was not a mason and if he did this there is probably more that was not done right. The hearth slab (support slab) for this oven design even with the hottest longest fire should not rise to a heat level that would create cracks such as these if built correctly so it may not be the heat. If he was your friend I'm sorry but I call it as I see it, don't take it personally.
On a positive note hairline cracks are not necessiarily an indication of structural issues. There are a lot of variables here so get back to me.
Pictures would help a lot if you have em..

[Archena]

Is there any rebar running up through the block? I've seen (and laughed hysterically at) something done that way - it was reinforced with rebar and concrete was used to fill the holes (not unlike some mortarless systems - although those usually stagger as well).

[nyknicks]

The foundation is about 5' by 5' and 4 inches thick with 3/8" rebar. The blocks are mortared and 3/8" rebar was used from the foundation up through the block and bent to tie in the support floor. This was done on every corner and in the middle of each wall. He also added rebar all around and across. Two 3/8'' rebar was also used from the slab up the block on each side of my wood storage opening under the oven support floor this rebar was bent to help support the opening, its about two feet wide. The oven support floor runs across this opening. First he layed about a 3" slab and then a 3" vermiculite plastic cement mixture over the concret slab. This is what the oven sits on. The person who built this structure is recommended by FORNO BRAVO. His name is JIM HEMSTALK. He is on your web site as a recommended mason in Northern California. I got the oven from my cousin who had them brought over from Italy The company is Trinchini Caminetti. I'm not sure if I spelled that correctly. The cracks are very small and you cant even see them unless you look closely. I'm going to assume this is a small problem. It makes me feel better.

[Unofornaio]

Originally Posted by nyknicks

I'm going to assume this is a small problem. It makes me feel better.

You should have said that sooner.... In that case I will not spend anymore time figuring out whats going on.

Good luck..

[nyknicks]

I would still like your opinion on what you think. Does the constrution of the oven sound like it's going to hold up?

[DrakeRemoray]

Sounds like a small problem to me. Can you post some pictures?