Suitability of Micore for a "walkable" hearth

[Catbyrd]

I've recently purchase my first stove (a Hearthstone Craftsbury) to go in a small living room. The only wall on which it will work to install it puts the hearth in the traffic flow of the room; consequently I want a flush hearth so that during the summer months, I can walk right over the hearth. I've purchased a sheet of Micore, over which my tile guy will put a half inch sheet of cement board before tiling. (I'm having hardwood flooring installed at the same time in the rest of the room.)

SO.. my question is - even with the cement board over it will the Micore be too soft a surface for a hearth that will be walked on often for six months of the year? My tile guy thought it would be fine for under the stove, but worried that a lot of traffic will make the grout, and possibly the tile, eventually crack.

One alternative I thought of is to puchase a premade hearth pad, put it directly on the subfloor, and have them run the new hardwood flooring around it. Any thoughts on that?

Thanks

 

[Poult]

No answers from me, Catbyrd. I've been looking at the Micore I bought for my pad, and I've wondered about how soft it is as well. But when push comes to shove, my best guess is the 1/2" of durock (type) board will be ok. Maybe someone else can comment on this, but what about putting a sheet of metal in between the Micore and the durock and add some additional stiffness that way. ?

Poult

 

[Hogwildz]

I have same set up and walk on it all the time, no problems. You could always have him add another 1/4" sheet of cement board to what he already plans to set down. You'll just have to plan & maybe adjust the HW flooring accordingly.

 

[begreen]

I've recently purchase my first stove (a Hearthstone Craftsbury) to go in a small living room. The only wall on which it will work to install it puts the hearth in the traffic flow of the room; consequently I want a flush hearth so that during the summer months, I can walk right over the hearth. I've purchased a sheet of Micore, over which my tile guy will put a half inch sheet of cement board before tiling. (I'm having hardwood flooring installed at the same time in the rest of the room.)

SO.. my question is - even with the cement board over it will the Micore be too soft a surface for a hearth that will be walked on often for six months of the year? My tile guy thought it would be fine for under the stove, but worried that a lot of traffic will make the grout, and possibly the tile, eventually crack.

One alternative I thought of is to puchase a premade hearth pad, put it directly on the subfloor, and have them run the new hardwood flooring around it. Any thoughts on that?

Thanks

What is sitting under that micore? In order to avoid cracks in the tiling, the underlayment needs to be inflexible. Reinforcing the sub-floor is an option.

Your second option is exactly what I ended up doing. I was way too busy with a full time job and getting our house back together after a foundation job to consider building a hearth pad. So I got a nice premade unit and put it on the subfloor, then had the oak flooring built to surround it. The end job finished out pretty nicely. Here are before and after pics showing the pad on the subflooring.

 

[humpin iron]

Check your installation manual for "K" and "R" values that the hearth requires. Micore is 3 times better than dura rock at preventing heat transfer to the sub floor. Dura rock is .24 K value, Micore is .86 K value. When we build a hearth, we put down micore, then dura rock, then the finish material. Screws every 4 sq inches to prevent flex. Good luck with your project. Consult the installers guide for your specif stove.

 

[Catbyrd]

Your second option is exactly what I ended up doing. I was way too busy with a full time job and getting our house back together after a foundation job to consider building a hearth pad. So I got a nice premade unit and put it on the subfloor, then had the oak flooring built to surround it. The end job finished out pretty nicely. Here are before and after pics showing the pad on the subflooring.

BeGreen, thanks for including the pictures of your premade hearthpad with the flooring around it. At this point, this might be our simplest option.

Check your installation manual for “K” and “R” values that the hearth requires. Micore is 3 times better than dura rock at preventing heat transfer to the sub floor. Dura rock is .24 K value, Micore is .86 K value. When we build a hearth, we put down micore, then dura rock, then the finish material. Screws every 4 sq inches to prevent flex. Good luck with your project. Consult the installers guide for your specif stove.

Hearthstone says I need .6 of an R value under the stove. This is where the Micore came into the picture, Hearthstone suggested it after pointing out that my original plan of 1/2 inch cement board under ceramic tile wouldn't be enough.

Thanks for the feedback, everybody.

 

[seaken]

USG publishes the k-factor of Durock as 1.92. Micore is at 0.43.

Remember, as the k-factor (Conductivity) number goes down the R-value (Resistance) goes up. Meaning that a lower k-factor is better.

In your case, if your stove asks for 0.6 in R-value and you have only 3/4" to play with you'll need to use a material with a k-factor of 1.25 or less.

With your 1/4" Micore at an R-value of 0.58 you are almost there. Mortar and tile will make up the rest. Adding the 1/2" Durock at an R-value of at least 0.26and you are more than good. Room for some stiffer subflooring if you ask me.

Sean

 

[pumiglk]

Hi All - reading for a while, posting little. This is a topic I may have some familiarity with from my recent install. Doesn't 1/8th inch of air give R value about 0.9? This seems to be the assumption in the Heartstone manual. I have an (equinox) where they suggest 1/2 cement board with non combustible overlay (tile, stone etc.) is sufficient to meet an R1 requirement for this stove? That is explicity stated along with the R value s of the air buffer - Is this widely accepted?

 

[begreen]

Hearthstone seems to be alone using the 1/8" value, some require a 1/2" of dead air space for R 1.0. Their value for Durock is not the same as posted by USG which lists it at R .26.

But regardless, for you Equinox pad, where is the air space? 1/2" durock @ R.26, tile @ R .01 = R .27.

 

[pumiglk]

My error for posting late at night. In my case there is air, probabaly 12 inches of block and 2 inches of concrete - it is up on a preexisting masonry fireplace hearth. I was responding to their somewhat casual statement in the manual - " An example of a non-combustible floor protector is a hearth constructed with a continous layer of a listed Backer board (such as Micore, Wonderboard, or Durarock) used for ember protection with a tile brick, slate, or another non-combustible facing". Lookingat the manual was puzzled how durorock was going to get you to R-1 value unless you included an R value of the Air between the stove and the Durarock. Obviously if you wanted to stack the cement board 2- 2.5 inches thick - but in my ignorance I read the statement as a single layer continous horizontal. Anyway...

Gooserider (moderator here) has posted on the use of Micor and cement board on the John Bridge tile site in this thread seems like it holds up OK built like a sanwhich. I would think liberal thinset (over the micor, below the board)and lots of screws will definately help with the stiffness factor
http://www.johnbridge.com/vbulletin/showthread.php?t=54128

 

[begreen]

I see your point. Boy, they really need a proof reader! Micore is not a backer board. Durock and Wonderboard are. Put the tile directly on the micore then put a big heavy stove like the Equinox (689#) on it and you will likely have a cracked tile job if the thinset even holds. No wonder so many folks are confused. I will get a letter off to Hearthstone.