Calcium silicate board, to cut or not?

[Filthymutt]

Ok, I found Calcium Silicate board. Could only buy 3/8" thickness and it only came in 1220 x 2440cm (4' x 8') sheets. So I bought 5 sheets and will stack them to get about a 2" thickness.
Now, having seen a lot of photos of people cutting their FB Boards to be roughly the shape of the oven, is there a reason for this? Or can I just basically cut them in squares to approximately fit the entire top of the hearth?

Thanks,
Bob

[Bec1208]

Re: Calcium silicate board, to cut or not?

Ok, I found Calcium Silicate board. Could only buy 3/8" thickness and it only came in 1220 x 2440cm (4' x 8') sheets. So I bought 5 sheets and will stack them to get about a 2" thickness.
Now, having seen a lot of photos of people cutting their FB Boards to be roughly the shape of the oven, is there a reason for this? Or can I just basically cut them in squares to approximately fit the entire top of the hearth?

Thanks,
Bob

A newbie to building, but I will toss in my 2 cents. I cut the board too tight and wasn't careful laying out the first course. Ended up having to cut some additional board and push in under the unsupported edge of the brick (see pic). I covered the board with some very thin refractory mortar that was applied with a brush. So first advice is if you cut it, leave yourself and extra inch or so around the perimeter.
The advantages I see in cutting the board are primarily that there is less opportunity for water to be wicked in under the hearth, the outer blanket can fully envelop the hearth and dome, and the cut off pieces can be used to insulate the door and for the thermal break. The advantage of not cutting is just that, not having to cut the board (not a pleasant job). Bruce

[Filthymutt]

Re: Calcium silicate board, to cut or not?

A newbie to building, but I will toss in my 2 cents. I cut the board too tight and wasn't careful laying out the first course. Ended up having to cut some additional board and push in under the unsupported edge of the brick (see pic). I covered the board with some very thin refractory mortar that was applied with a brush. So first advice is if you cut it, leave yourself and extra inch or so around the perimeter.
The advantages I see in cutting the board are primarily that there is less opportunity for water to be wicked in under the hearth, the outer blanket can fully envelop the hearth and dome, and the cut off pieces can be used to insulate the door and for the thermal break. The advantage of not cutting is just that, not having to cut the board (not a pleasant job). Bruce

Thanks for that. I really prefer not to cut if I don't have to. After all, since my board is so thin I'd have to do a lot more cuts and with every cut it will get harder and hard to stay uniform.
If I can just cut a simple square to fit the hearth, maybe a little short of the edges then insulate the edges with vermiculite I should be ok.

Thanks much for the input.

Bob