Houston We Have a Problem?

[digitalrules]

I have 4" under the floor....?

[Faith In Virginia]

I'm thinking your using the the product in a manor for which it was not intended. Most refractory cements don't act nicely when used as a real thin skim coat. When I built my oven I wiped my interior clean with a wet sponge and the exterior I just swiped over with the trowel and in a short time it developed the same cracking. So I think it's the nature of the product, works great for putting fire bricks together, not so great as a skim coat. If there is not a sufficient bond to the brick and any material shrinkage due to drying you will get that cracking. What is the name of the product you were using?

[digitalrules]

Harbison Walker Refractory mortar....

[dmun]

I have 4" under the floor.

That's great. Usually it's the other way around. Builders skip the under-floor insulation or put it under the slab, and then can't get their ovens up to pizza temps. Glad to hear it, since that's the hard one to re-do.

[Faith In Virginia]

Yup... NO. 36 ???

[Faith In Virginia]

Look at the front part of my oven, I had some left over so I smeared it on for what ever value it had to increase mass. I would have chucked the stuff out so I just smeared it on... you can see I had the same issue. It's the product not designed for that use.

Tufshot LI will work well for a thin coat if that is what you want to do.

[Laurentius]

Hi Faith,

Is that your permanent platform for your oven?

[Faith In Virginia]

No just temporary. I did not know where I wanted the oven so I just built it there. The temporary location is a work area that has electrical power. The platform is some leftover logs from a log home. I have slots in the base of the concrete slab for forks on a fork lift. So it will be an easy move when I'm ready.

[RTflorida]

A simple enough fix, as long as you insulated underneath as dmun mentions.
I hate to kick a man when he is down, but you mention that you started with the FB plans...did you stop reading them halfway through? You are hereby sentenced to have the FB mantra insulate, Insulate, INSULATE! tatooed into your forehead.

Good luck, I really hope there is insulation UNDER that hearth.

RT

[digitalrules]

Thanks, I am sure that is my problem.....Mike