Floor buckled

[dublintom]

I decided to seal the dome before any curing and slapped a load of concrete over the 3" of ceramic blanket. I made a lot of small fires and really took my time curing the oven. I have built fires and reached temperatures of over 700F at this stage. I wasn't pushed about cleaning out the oven after each fire and when i did so today i see that the floor has buckled quite badly, 3 bricks have risen by 1/2". I built the dome on top of the floor and allowed the ceramic insulation to cover the floor bricks so i would have thought there would be expansion space there.
There are two things i may have done wrong: 1. I mortared between the first course and the floor. 2. the bricks for the floor originally had a 1/2" taper from 3" to 2 1/2" which i took out by applying home made mortar and letting it set. I laid the bricks on a sand and fireclay mixture as recommended and they were perfectly level and tight.
On the positive side the dome has held together quite well.
I am thinking of cutting away the concrete at the bottom of the oven and trying to tap down the bricks but my feeling is that the floor is too bad to ever get right.
I could try and lift the floor but given that i have built on it i won't be able to lift it all or i could put a new 1" floor on top.
Any advice appreciated while i lick my wounds!

[trapper]

Re: Floor buckled

Is it possible for you to get a mini grinder inside the oven and grind the bricks down?

[fxpose]

Re: Floor buckled

Are you able to easily lift out those offending bricks or are they underneath the dome wall?

[dublintom]

Re: Floor buckled

The worst offending bricks are not under the dome wall although there has been some movement with those. I've been thinking that i am going to have to lift most of the bricks and relay them and between that and a small grinder I might get it somewhat right. I suppose I'm still worried that this could happen again as i don't know what caused the buckle.

[dmun]

Re: Floor buckled

This is quite unprecedented. Your floor bricks should expand at the same rate as the dome, so I don't know what's going on here. I don't quite understand what you did with the tapered bricks and the mortar, so I can't comment on that. Is there a lot of exposed mortar between bricks?

What insulation are you using under your leveling mixture? Board? Vermicrete?

[dublintom]

Re: Floor buckled

I used 4" vermiculite under the floor. The bricks for the floor were 9 X 4 1/2 . They were 3" thick at one end and 2" at the other. I simply leveled them with a skim of mortar and let it harden before laying them. There is no mortar used between the bricks as they were just laid tight together. I will see if i can upload an image.

[dublintom]

Re: Floor buckled

Pictures of the floor and front of the oven which has big cracks on the outside concrete. There is only small cracks in the dome probably from all the movement in the floor. I just measured the highest brick and its 3/4" raised.

[dublintom]

Re: Floor buckled

Decided to tap down the bricks with a wooden mallet. They slipped down easily but not surprisingly they cracked. That floor is not salvageable so I am thinking of going for a castable floor, pity because i really liked the herringbone design of the bricks but in the tight confines of a finished oven i don't think i could lay a new floor too level.
I had thought of putting 1" of castable on top of the existing floor, but i don't know if it is going to keep moving and 4" of mass seems a lot in the floor.
The other option is to take up as much of the floor as possible and lay fire clay and castable over that. What thickness should i have the castable section if i go down that route?

[Tscarborough]

Re: Floor buckled

Something is not right. You say the bricks were tapered, did you lay the large side up so that the visible joints were tight? If you did that, I might could see where you could get some heaving. I would not have used them at all, or would have done a 45 degree running bond and alternated the orientation so that the joint was tight.

As for repair, I do not think you are going to find a long term solution, no matter what the cause is.

[fxpose]

Re: Floor buckled

I used 4" vermiculite under the floor.

Something is definitely wrong here.

When you said 4" of vermiculite, I'm hoping you meant vermicrete (mixture of vermiculite and portland cement).

[dublintom]

Re: Floor buckled

Yea 4" vermiculite concrete which was left for 4 weeks before i did anything else. It was very firm.

[texassourdough]

Re: Floor buckled

You might consider pulling the floor and relaying a looser fit floor - and if it isn't smooth enough - use a sander to even it up. The bricks don't need a super tight fit to be a good, functional floor.

[Les]

Re: Floor buckled

I have been on this forum a little over 5 years and I have NEVER seen anything like this. It has always been deemed safe to place the dome on top of the floor, but this obviously makes a strong argument against doing that. Has your hearth slab been compromised in any way? If thats not the case, I would remove all the floor brick that you can and grind down the rest. Place a thin ceramic board down to get an even surface and replace the floor. It's a butt load of work but it will get your oven back to working.

Good luck!

Les...

[Tscarborough]

Re: Floor buckled

I disagree Les. Placing the dome on the floor has nothing to do with this, nor does mortaring it down.

I hate to do forensic masonry diagnosis (although I do forensic masonry diagnosis often) from a few pictures, but my best guess is that the wedge of refractory cement underneath the chamfered bricks has failed in some places forcing one end of the brick up. Thermo-tumescence is the correct term, but I have not seen it with these materials. If it were a compressive failure, it would be more or less uniform around the perimeter, and the upthrust ends would have an equivalent downthrust end, which they do not appear to have.

[Stray Catalyst]

Re: Floor buckled

I'm still in the planning stage. If I don't want to place the dome on the floor, should the FB insulation be sized to the outside of the dome, or the inside?

Stray