The Fresh Loaf

News & Information for Amateur Bakers and Artisan Bread Enthusiasts

8' x 6' Hearth Slab Thickness

Wilsonk6's picture
Wilsonk6

8' x 6' Hearth Slab Thickness

Hello, 

We are building our first Alan Scott oven for a small at home bakery. We're converting plans from the Bread builders book up to a 6 1/2' by 4 1/2' oven. We are doing this with very little experience and with help from a local mason. My question is, with a hearth slab size of 8' x 6', how thick does it have to be? 

We were planning on doing 5 1/2" thick hearth slab but the cost of refractory cement was higher then anticipated ($5,500). We were thinking of going down to his suggested thickness of 3 1/2" (for a smaller oven) but we're worried about structural stability especially considering the cladding would only be 2 1/2" on the sides and 3" on top. Note, we will be using firebrick for the floor, walls and dome.  

Any feedback from someone who has worked with larger size ovens would be greatly appreciated!

ps. Does the wooden form under the insulation slab really stay through life of oven? 

Thank you much + Happy baking!

Wilson & Lela 

Mountain Mills Food Co. 

Nyago's picture
Nyago

Hi Wilsonk6!

I built a standard sized Scott oven 7 years ago and it is fantastic! I used standard concrete mix for the hearth slab, not refractory cement. I used a thin layer of refractory mixed with sand to weaken it under the hearth bricks. Then used a standard mix of refractory cement in the dome. I think I spent about $300 on the refractory cement for the whole project. Even with the oven cranked up making pizzas, the outside of the firebrick doesn't get above 550 degrees, so I'm not too worried about the integrity of the standard concrete. The thickness was 3.5" plus the insulated slab at 3.5" I believe. Add in the thickness of the firebrick, and the whole slab is pretty massive already. I'm not sure you would need to go thicker.

After the hearth slab was set, I knocked out the wood frame so that the slab is completely suspended. It freaked me out, but it's been working great for year now! 

Here's a few pics I found on my phone:

 Slab

Suspended slab

Finished oven

Nyago's picture
Nyago

I misspoke in my comment. The slab was poured with Portland cement, NOT concrete mix. I think it was $7 per 90lb bag :)

 

 

Wilsonk6's picture
Wilsonk6

Thanks for the info Nyago.