Brick oven faeries and leveling a sloping slab

[azatty]

When I returned last night from vacationing last night, I found a fully poured slab on my block stand. Either the Pompeii Oven Faeries did it, or one of my contractor clients poured it for me as a Christmas present. No one has fessed up to it yet.

However, true to form (no pun intended), the faerie/contractor sloped the hearth slab from the center to the sides so water will run off it. The slope isn't much, but I noticed it immediately and put my level on it. The center is perfectly level, but the slab drops about 1/4" inch over three feet from the center to the sides. I plan to stack three inches of ceramic insulating board under the cooking floor. My concern is that a quarter inch drop will cause the insulation (and consequently the cooking floor) to be uneven.

My thought is to level the slab under the insulation with a fireclay/sand mix (no water) and proceed as usual. I suppose that I could form it up again and pour an inch of Portland cement over it then set the insulation. Or I could level the cooking floor with fireclay/sand on top of the insulating boards. Any other ideas or comments on the above solutions?

[GianniFocaccia]

Re: Brick oven faeries and leveling a sloping slab

Wish I had Pompeii Oven Faeries that showed up and did work unannounced!

Really, the course of action is your call. Your idea to level the insulating board with fine sand/fireclay is sound. My only recommendation is to end up sloping the boards and oven floor from back to front to help any rain water drain out.

The other thing you could do is level your boards on 2-3" of vermicrete. This is what I did and I would do it again. Yes, this seems a little overkill, but you can't ever have too much insulation.

John

[Neil2]

Re: Brick oven faeries and leveling a sloping slab

Leave the slope in.

It is a good idea to have positive drainage built into your slab. The 1/4 inch over 3 feet will not be noticeable in your hearth bricks. There is always a slight gap (that fills with ash) in these bricks anyway.

Lay out your hearth bricks on the slab as is and see how it looks. You may have the perfect slab surface. If you do level it, I second John's suggestion of using vermicrete. Vermicrete is very porus so you will still have good positive drainage.

[fxpose]

Re: Brick oven faeries and leveling a sloping slab

I think leveling the insulation boards and/or hearth bricks is your call.
One area I made sure there was good drainage when I built my oven was in the landing beneath the vent, from the inner entry out.

[C5dad]

Re: Brick oven faeries and leveling a sloping slab

I think that leveling the area under the insulation board and bricks would be a good idea. Would only need a 1 inch pad of vermicrete. Leave the rest of the slope there and you will be golden!

[azatty]

Re: Brick oven faeries and leveling a sloping slab

I decided to lay 3.5 inches of vermicrete and cut down the fiberboard to 1.5 inches. The problem with the slope was that the slab sloped to both right and left from a peak in the slab center, so any drainage would be toward the oven walls instead of toward the oven opening. I do like the idea of sloping it slightly toward the oven opening, so I've shimmed the back of my vermicrete form. Thanks for the input.

[Mike D]

Re: Brick oven faeries and leveling a sloping slab

Good call on the vermicrete. I wouldn't want to try and build an oven on an uneven surface. Why cut down on the fiber board? You can't have too much insulation.

Mike

[GianniFocaccia]

Re: Brick oven faeries and leveling a sloping slab

How do you get 1.5" of fiber board? Don't they come in 1" or 2" thicknesses?

[azatty]

Re: Brick oven faeries and leveling a sloping slab

Nope, you can get it in 1.5" and 3" and even 4" thickness, too. You just have to look for it. I happened to find a local refractory supplier who had 1.5 inches in stock at a great price, so I went with it.

I decided to not double up the 1.5 inch board because of the number of joints I'd have. I'm getting 1'x3' sheets, so there are some pretty narrow cuts. I also realized that my structural slab will likely be hotter from the sun than it will be from the hearth based on the heat transference of the insulation, so I opted to add an extra bit of height with the vermicrete, too.

[dmun]

Re: Brick oven faeries and leveling a sloping slab

You can sometimes get odd thicknesses for cheap. I got 2.5 inch insblock19 for considerably less than H-W was charging for two inch material. Keep an eye on ebay.