Re-using Soaking wet FB Board?

[Fclark]

OK am building a 42" Pompei style oven, I have a beautiful slab poured on my base, and laid down the 2" FB Board as directed. Unfortunately - rookie mistake on my part - we had several heavy rains in the days after and I did not cover it well enough and the FB board has absorbed enough water to float a canoe and issoft as a sponge. I have pulled it off and set it under cover with a fan. I'm concerned about long term performance and stability of this stuff now, and reconsidering options. One option I'm considering is crumbling the FB board (it falls apart pretty easily when it's wet!) and mixing it into cement to create an insulating concrete and then pour the insulting slab. Any thoughts? Will the FB Board recover? Should I just scrap it and mix the vemicultite concrete instead?

[UtahBeehiver]

It will dry out and firm up. As long as you dry it out the thermal characteristics will be good. One consideration, 2" is minimum floor insulation, if your budget can stand it install more or install a v-crete base with your CaSi board on top. Never heard on any one breaking up the Ca Si and putting in v-crete. I would stick with more conventional insulating methods.

[Larry P]

I wouldn't assume you can make an insulating concrete using broken down ceramic fiber as an aggregate. Typically with insulation, it's the gaps between the material that give it its insulating properties.

[Gulf]

Like Russell said "let it dry". Crumbled and mixed with portland it would take twice the thickness, at best, to achieve it's factory insulation factor.

[Fclark]

Ok - thanks for the replies - I won't tempt fate by crumbling expensive FB board. What I'm unsure of is how long this stuff will take to dry after being saturated? 36 hours later it's still very heavy and soggy feeling. If I lay my hearth over semi-wet FB board will I risk trapped moisture damaging the hearth or slab - or would you just expect it to dissipate with a patient slow fire curing? Or should I be patient and just park the stuff for two weeks??

[UtahBeehiver]

IMHO, I would wait for the board to dry out. Once you trap the moisture under the hearth it will take substantially longer to drive the water out and it will affect the floor temp. acting like a heat sink.Are you going to pour a v-crete sub base or stay with 2" of CaSI or add more Ca Si?

[JRPizza]

If I lay my hearth over semi-wet FB board will I risk trapped moisture damaging the hearth or slab - or would you just expect it to dissipate with a patient slow fire curing? Or should I be patient and just park the stuff for two weeks??

I had 5" of Insblok board that was way more saturated than I realized when my in-process build got a pretty good soaking last fall. The completed dome sat covered for the winter, and some of the water left the exposed edges and migrated into the adjacent bricks but there was quite a bit of it still trapped. The first few fires the underside of the hearth got hot, and later bigger fires started some water migration (seeping) out from under the oven (you can see pictures on my build thread). If you cure following the schedule and keep your fires going for hours at a time you should be able to dry 2". What might be more of a problem is handling and working around wet board. Mine got pretty soft when wet and fortunately I had the floor and first course laid before the soaking. Hopefully you can get it to the point where at least the edges firm up enough to avoid damage while you are working with it. Were you lucky enough to get it cut/shaped before it got wet?