Thickness of fireclay & sand mortar under hearth

[Chaslie]

Hi all. Am building an Alan Scott oven. The floating slab is not level - it is 1/2" to high in the front left hand corner over the equivalent area of around 1-2 square foot. So have increased the depth of the 50% fireclay & 50% sand mortar to compensate for this. The hearth is now level but am concerned I have done the wrong thing with most of the hearth sitting on 1/2" mortar. Do I take off the hearth and start again - perhaps see if I can grind down the slap a bit? Or will the mortar stay in place and do its job long term? All thoughts appreciated.

[dakzaag]

Re: Thickness of fireclay & sand mortar under hearth

Mortar has very high compression strength so you should be fine. It is pretty important to have a level floor so if you have a few floor brick that are lipping up, you want to address this sooner rather than later.

Fire clay and sand mixture is not really a mortar as the fire clay is not a great binder until it gets up over 2000 degrees and undergoes a chemical conversion. It is possible that as the oven dries out and the sand and fire clay dries out it might allow the floor to settle some. For future reference, lime and portland would have given this leveling compound more body to stay intact even after it dries out.

I guess it will be up to you to decide how big a deal this will be if you have a failure. I have an oven that the floor is a little more uneven that i would like. Normally it does not bother me, but if I get a sticky pie, or more precisely an over loaded pie, the little lips on the floor always seem to be in the worst location.

I would take a look at the floor now and see what it looks like a month after you tried to level it and see how it is holding up. If the area of concern is where the fire is going to be then you have nothing to worry about.

[Chaslie]

Re: Thickness of fireclay & sand mortar under hearth

Thank you so much for your reply dakzaag.

[Greenman]

Re: Thickness of fireclay & sand mortar under hearth

Like most things, the foundation, the base is a good thing to have right. You don't mention what you are using as insulation under your oven but if you are using vermicrete then you would be able to get the base level and right at that stage.

I am not familiar with Allan Scott ovens but I do recall them being mentioned in posts on here where the opinions of them were not glowing.

Good luck with your build, I am sure that you will get some advice from the forum. For my own opinion, after building 3 x 36" Pompeii ovens I would thoroughly recommend them (and so would the owners of the other 2) and the basic plans and experience of builders on the forum can be of great benefit at every step in the process.

[Chaslie]

Re: Thickness of fireclay & sand mortar under hearth

Thanks Greenman. Yes I have to have those foundations correct. The slab is insulated with a couple of inches thickness of a cement and vermiculate mix which is most likely called 'vermicrete' as you said. The next oven will be a Pompeii.