concrete dampness and ceramic fiberboard

[Dr.Lee]

First, some background information.I placed a cardboard template on my concrete platform so that I could configure my floor bricks for cutting. It was going to rain the next day so I fully covered the platform with a tarp which rested on the bricks on the template. The tarp was secured. After the rain was done I uncovered the tarp and the top of the platform and the template were both rather damp. It appears that the platform was sucking up the rain water that fell on the blocks below. The platform dried in about an hour under the sunny day at about 50 degrees F. With that information in mind my question is this. How much of a concern is it for the base of the platform and subsequently the ceramic fiberboard that I am about ready to put down to become damp from underneath even if I cover the platform from above?

[cbailey]

As you know the insulating fiberboard is quite hydrophilic. I laid 4 ml plastic sheet between the board and concrete to stop any wicking of water. Check out the photos.

Many recommend drilling a hole through the platform at the center of the dome to provide an exit for water. For my build I didn't drill the hole. I was very focused on keeping the build dry. I reason that if needed I could drill a hole later.

Cory

[david s]

You can paint the top of your slab with some sealer to prevent wicking from the stand, but remember that any barrier will also prevent moisture travelling in the opposite direction. That's why weep holes work a bit better. If moisture does get in the fire will eventually drive it out, but providing a pathway, (like a hole in a saucepan lid does), will get it out faster.

[Chach]

I used foamglas insulation under the board like some others did. its a glass cellular product that does not absorb water and is an insulator as well.

[Dr.Lee]

Thanks for the replies. They were helpful.