Laying Thin Refractory Bricks on Hearth

[Leao]

Hello!

I am going to lay my hearth with 22 x 11 x 4 cm refractory bricks. They are slightly different to what I have seen on this forum - they are thin compared to the fire bricks I have seen online and also they have a dip (I don't know what the technical word is) on one side of 3mm. See a commercial pic of them below:


Most people seem to lay their bricks out on the hearth with the side with greatest surface area facing down. Even though you would use more bricks, would it be better to lay them next to each other on their sides? For me this would be a difference of 4 cm thickness if I laid them on their faces to 11 cm if I laid them on their sides. Better for insulation? There will be a 4 inch insulating mix beneath the bricks anyway, but as the bricks I am using seem thinner than what I have seen online I thought I should check if they need to be better protected against cracking.

Most people dry stack their fire bricks on the hearth down? Seeing as my bricks have a dip, would it be better to fill it in with refractory cement? The air pocket might let out heat?

Many thanks again for your time,

Leao

[dmun]

Your firebricks are what we call "splits" (8 1/2 by 4 1/4 by 1 1/4") They are too thin to lay flat: you won't have enough thermal mass that way. We don't mortar down the oven floor, and they will act like loose tiles, possibly shifting (or breaking) when you throw logs into the oven. You can lay them on their edge: that would be a really cool look, but it's more thermal mass than you need.

Around here splits are the same cost as full price firebricks, making them a bit expensive to use: maybe you should shop around a little more. You might get the thicker bricks for the same price.

[Leao]

Thanks for the post. The bricks have been purchased already for better or worse. Do you not think the air gaps the dips in the bricks will cause should be filled in? I'd prefer to do it dry though.

leao

[Tscarborough]

The dip is called a "frog". If you use those, you should use 2 layers, preferably laid perpendicularly, and it would be a good idea to fill the frog.

[Leao]

Originally Posted by Tscarborough

The dip is called a "frog". If you use those, you should use 2 layers, preferably laid perpendicularly, and it would be a good idea to fill the frog.

Thanks Tscarborough, that's such an obvious suggestion (2 layers) but I never considered it!

Grateful as ever to the FB forum,

leao

[Tscarborough]

Along with filling the frog, you will want to use a full bed (but thin as as possible) of mortar between them, any air gap at all is going to be detrimental.

[Leao]

Would you suggest putting a thin layer of refractory cement on top of the, notoriously difficult to make flat, perlite mix in order to line the bricks up easier?