# Thermal Break



## katoman (Apr 26, 2009)

Ok, I've got a fireplace hearth that's built on top of the existing concrete floor. It needs to have a new top put on it. Currently there are ceramics on it.

It is wet with condensation which I'm pretty sure is being caused by it being in contact with the bsmt slab.

So when we resurface it, I want to install some sort of "thermal" break to prevent this condensation. Any ideas? Would a layer of tar paper do the trick?

We're going to be probably installing a new stone surface.


----------



## Tscarborough (Feb 25, 2006)

How much room do you have to work with?


----------



## CanCritter (Feb 9, 2010)

no on the tar paper...adhereing hearth will be ....well a lesson in futility..if your gettting alota moisture wouldnt hurt to get weeping tiles inspected or cleaned out re roots ect to help drainage..only thing that comes to mind is thinset or a mastic but you still have the moisture issue...could be a mold issue down the road re basment...enshure sump pumps workin as well


----------



## aptpupil (Jun 12, 2010)

seems to me like you'll need a couple inches to get a proper break and then have something good to adhere the tile to. rigid foam with 1/4" durock on top, for example. i'm guessing you don't have that much space though.


----------



## katoman (Apr 26, 2009)

This is in a walkout bsmt. The hearth is at ground level. Four feet of foundation below that. Exterior masonry chimney, block foundation attatched to the house under the chimney.

If I tore it out down to the concrete floor, I have about 6" to work with.

This is not a leaking issue. This is being caused by the dampness of the slab coming up into the masonry hearth and condensing on top of the existing ceramics, in that the room is warmer than the slab.


----------



## Tscarborough (Feb 25, 2006)

Ceramic board or perlcrete if you have that much room.


----------



## katoman (Apr 26, 2009)

Tscarborough said:


> Ceramic board or perlcrete if you have that much room.


TS - never heard of either. Would you have a link to a manufacturer?

Thanks.


----------



## Tscarborough (Feb 25, 2006)

http://www.industrialinsulation.com/ceramic_fiber_board.htm 

or their calcium silicate board. Perlcrete is portland cement and perlite mixed at a ratio of 1 portland to 3 to 10 parts perlite, probably 4-5 for your application.


----------



## hdavis (Feb 14, 2012)

perforated brick can help out - have the perforations line up horizontally so wicking is reduced and you can have airflow through it.


----------



## dom-mas (Nov 26, 2011)

You could look up Air bloc. Don't know anything about it really except that they produce trowel on air and weather barriers. You might find something that suits your purposes


----------



## JBM (Mar 31, 2011)

I might try some sort of tar paper or ice and water shield under durock screwed down to the concrete.


----------



## katoman (Apr 26, 2009)

JBM said:


> I might try some sort of tar paper or ice and water shield under durock screwed down to the concrete.


Now that's creative thinking. The ice and water shield would stop the transfer of dampness and the durock would give bonding to the masonry.

Thanks, good thinking :thumbsup:


----------



## hdavis (Feb 14, 2012)

Kato, are you thinking that the room moisture is condensing on the cold tiles, or thinking that moisture is coming up through the bricks and tiles?


----------



## katoman (Apr 26, 2009)

I think the room temp is condensing on top of the tiles. I'm still trying to figure out how to prevent this. 

That's the only place it's condensing. The concrete floor right beside it is fine.


----------



## CanCritter (Feb 9, 2010)

cold air leak around fireplace faceing?...cold air through fireplace meets warmer hearth area? furnace may be drawing air through fireplace////seal and see if that helps..if so figure out how to block drafts


----------



## hdavis (Feb 14, 2012)

CanCritter said:


> cold air leak around fireplace faceing?...cold air through fireplace meets warmer hearth area? furnace may be drawing air through fireplace////seal and see if that helps..if so figure out how to block drafts


I was thinking the opposite. If it's humid and warmer outside than in the basement, and there is no draft going up the chimney, you can get reverse flow. Outside air cooling and getting condensation. Same idea. Should mostly be a spring time thing, since the cellar and hearth should warm up over the summer. No matter what, a thermal break and using perforated bricks would help.


----------



## CJKarl (Nov 21, 2006)

Does that area of the house have central AC?
My 1st thought was condensation from the air. But when you said the slab next to it is dry, that confuses things. Is it possible that humid air is being drawn in, in the area of the hearth?


----------



## dom-mas (Nov 26, 2011)

CJKarl said:


> Does that area of the house have central AC?
> My 1st thought was condensation from the air. But when you said the slab next to it is dry, that confuses things. Is it possible that humid air is being drawn in, in the area of the hearth?


This has me confused as well. I thought you figured that the fireplace was wicking moisture. Remember a fireplace should have a seperate footing from the rest of the house. The floor probably has VB and insulation under it, the fireplace would not. No idea if that's the cause but that's where my thinking goes.


----------



## katoman (Apr 26, 2009)

This is a cottage. No heating or air conditioning running at this time. After reading all your guys thoughts, I tend to agree that this is just the warm air (it has been really hot) meeting the cool surface of the tile.

I'm not understanding why I'm not getting this condensation on the concrete floor though.

Friday we bricked up the opening for insurance purposes. This fireplace will be done next year. So I'll see if that had any effect on Monday.

I'm about to install the subfloor this week, so now is the ideal time to deal with this issue, although I will still be able to tear it out next year.

Interesting yet confusing thing going on here. I'll keep you posted if I observe changes, but I'm thinking to proceed with the ice and water shield idea.

Thanks guys :thumbsup:


----------



## aptpupil (Jun 12, 2010)

got a picture?


----------

