[67shelby]

Originally Posted by Scratch

So now that it's been a little while since people on here started using the hardi-backer for oven interiors and exteriors... What's your thoughts on using it.

Have you baked with it yet?

Any regrets?



I'm planning on a 3X3X6 oven with this stuff inside and out.

I'll post results of some tests I'm doing this week. Right now, with about 5200 watts, it takes me about an hour to reach 400 degrees in an oven that is about 6 ft x 3ft x 3ft (actually about 4 inches short on all dimensions).

It is MY opinion, that the backer board is acting as a heat sink and because it doesn't have the reflective properties of a piece of sheet metal, it is keeping the heat and releasing upwards. I am in the process of covering the top of my oven (inside) with sheet metal, after having run some expirements with different configurations. By the end of the week, I should have a semi-scientific opinion on the use of backer board vs. sheet metal on the inside top of the oven.

I am also using the backer board on the doors, and I have sheet metal ordered to replace it as well. I will replace them and then do another set of tests to determine how much they sink as well.

I have already put sheet metal (offset 2 1/2 inches) on the bottom between the backer board and the elements (based on my first attempt to do this, I put the elements on the top thinking it wouldn't make that much difference). When I put the elements next to the backer board, mounted just like they would be on an oven using the same hardware, it baked the backerboard and charred the insulation. Then put a piece of porcelin covered metal from the oven between the elements and the backer board thinking that it reflect the heat back down, but that really didn't work either, I baked the backer board even more. When I say I baked it, I baked it. It was dry and crumbly. I do not think that having them on the top vs. the bottom would make much difference in that aspect. If you read the original post, the manufacturer said if it was exposed to a 500 F temp, it would be ok, but when you have elements, they much hotter than 500 degrees. The lesson here being I would not have the elements close to the backer board, even separated by a piece of porcelin covered metal was not enough.

So, in my opinion, the backer board has become my enemy and for the most part, I'm covering it all in sheet metal and thus, it has made my project more costly. Others can chime in, but when I posted my question, only one person answered who was using backer board in a finished oven and he was using kerosene heat, which is not as hot as using elements. NOTE that this is a novice opinion as this is the first oven I've ever built.