insulating hearth pour

[waynebergman]

Its been about ten days since I poured the structural hearth. Now finally my vermiculite has arrived. My question is with this 10 days inbetween the pours do I need to do anything to prep the set concrete of the strucural hearth. Also is it ok if I do half of insulating hearth pour today and the other half tomorrow. Any need to keep it damp after the insulating hearth pour is complete?
thanks wayne

[maver]

You shouldn't need any prep for the structural hearth. It's ok to split the vermiculite concrete poor but harder to achieve a truly level surface if you split it. It will help the insulating layer harden if you keep it damp several days.

[dmun]

When you mix your vermiculite concrete you will find that it will absorb a lot more water than other aggragates. I mixed mine by hand in a mortar tub, and just kept adding water until there was some dampness visible at the bottom of the tub. The wet portland will tend to sink to the bottom, being heavier, and this will provide good adhesion to your slab.

Everyone, me included, thinks the stuff is wierd to work with. It won't achieve any kind of a finish. I just ended up patting it down with the trowel to get some sort of flatness on the surface, then keep it damp for a couple of days, but otherwise ignore it for a week. It does get rigid, if not rock-hard.

The good news is that the tub of insulating concrete is light to lift unlike the rock-and-sand stuff.