Under floor paste on vermiculite?

[phippsj]

I just finished pouring my vermiculute insulation layer on top of the hearth. I certainly see how the compression strength will be there, but I am having a hard time understanding how to spread the under floor paste on top of the vermiculite, especially with a notched trowel. Should I put a super thin coat of cement or fire mortar on top of the vermiculite to have a solid surface to spread the floor paste? That part was not clear to be from the instructions, and I guess my search skills are not up to par because I can't seem to figure it out from the other posts here (although I am sure the answer is here!)

Thanks!

[phippsj]

Re: Under floor paste on vermiculite?

OK, so it looks like everything but the top 1/4" is solid. Perhaps that top portion dried too quickly? I think I am just going to try to make a slury and see if I can't get that layer to 're-attach' to the overall insulating layer. It seems that when dried, it would be OK to get a layer of the fireclay mixture down...

[dmun]

Re: Under floor paste on vermiculite?

It's sometimes easier to lay your floor on a dry mixture of sand and fireclay, and when you get the floor the way you want it, wet it to solidify it.

[phippsj]

Re: Under floor paste on vermiculite?

It's sometimes easier to lay your floor on a dry mixture of sand and fireclay, and when you get the floor the way you want it, wet it to solidify it.

What is your opinion of using Heat Stop 50 fire mortar instead of fireclay? I am having a hard time finding fireclay for whatever reason.

[dmun]

Re: Under floor paste on vermiculite?

It's generally considered not a good idea to mortar your floor down. Some people look at this giant pile of masonry and don't realize that it is an object in motion, forever expanding and contracting with every firing. You want to sit as lightly as you can on the insulation layer.

There's also the issue that fireclay is about ten cents per pound, as opposed to about a buck a pound for heat-stop.

BTW I didn't use the leveling mixture. I just plunked my bricks down on the board. If you've gone with the vermiculite insulation, you can also level the floor with the sludge from cutting your dome bricks in half.

[asclepius]

Re: Under floor paste on vermiculite?

I put my vermiculite concrete down, and it is level so I am about to put my fire bricks down. Should I put a layer of fire clay down on top of my vermiculite concrete and let that dry before putting down my bricks? And if so, what combination fire clay, lime, etc should I use? (I am not using a ceramic board, just vermiculite concrete)