Thinest Hearth Pad Possible for R=1.2?

[Hoopdancer]

I'm close but not there yet. I'm in the process of adding and refinishing hardwood flooring near the end of it seems a never ending renovation. I would like the tile or final finish of the hearth pad for a new Heritage Hearthstone (r=1.2) to be flush to the top of the 3/4" red oak flooring but have not found anything that will satisfy this. Is it possible to thinset tile to the surface of Fiberfrax? I've read in posts that doing this with Micor is not suggested because it is too soft but have not seen anything describing the strengths of Fiberfrax. Is it possible to bond sheet-metal of sufficient gauge to the surface of Micor and then tile? I'm guessing that I will need to add a tapered piece of oak trim around the tile and end up with something around 1-3/8" total height using micor or fiberfax, concrete board and tile. I would prefer to be flush or to be just slightly above the existing floor as the stove will be placed close to center of a small home between the kitchen and living room.

The only other question would be "Should I get Blueblack enamel or Matte Black finish on my new Heritage?"

Thanks for any help or advice.

 

[sksmass]

...I would like the tile or final finish of the hearth pad for a new Heritage Hearthstone (r=1.2) to be flush to the top of the 3/4" red oak flooring but have not found anything that will satisfy this. ...I'm guessing that I will need to add a tapered piece of oak trim around the tile and end up with something around 1-3/8" total height using micor or fiberfax, concrete board and tile. I would prefer to be flush or to be just slightly above the existing floor as the stove will be placed close to center of a small home between the kitchen and living room..

You are on the right track. I think the answer is going to involve Micore.
If you use 1/2" micore 300 (r value 1.03) then
1/2" Durock (r value ~.26) then
1/4" tile (r value ~ negligible)
you end up with a ~1.25" rise plus a bit for thinset.
Edge that with a tapered oak threshold down to your finished floor grade.

 

[Hoopdancer]

I talked to some guys in the industry today and one recommended using "1/4" hardie board" (with an r value of 0.13) on top of 1/2" micore 160 (r value of 1.27) which would give me an r value of 1.4 in only 3/4" that would be ready for tile. I've tapered the oak trim around my hearth from 3/4" thick to 1-1/8" over 3" and expect that this will cover most of the exposed tile edge. Thanks for your input "sksmas". Lots of experience and wisdom on this site. Anyone have any input on matte finish vs enamel and if you could buy again would you get enamel finish this time?

 

[begreen]

For an underlayment on top of soft micore, I'd feel much better with at least 1/2" cement board for stiffness. A stove is heavy and 1/4" board is going to flex. Also, Hardie board is not cement board. It appears that Wonderboard is the last true cement board available unless you can find someone that still has some original Durock in inventory.

 

[CountryBoy19]

For an underlayment on top of soft micore, I'd feel much better with at least 1/2" cement board for stiffness. A stove is heavy and 1/4" board is going to flex. Also, Hardie board is not cement board. It appears that Wonderboard is the last true cement board available unless you can find someone that still has some original Durock in inventory.

Actually, after reading recent information posted here on Durock NextGen, I would not be afraid to use it. The only thing they changed when going to the NextGen stuff was adding pearlite (non-combustible) to the board to make it lighter. They just didn't pursue the UL listing for hearth use. So while it appears that the Durock NextGen won't work for a hearth; it is actually almost identical to the old Durock, they just didn't have it tested for hearth use so it doesn't have the little sticker. Knowing this, I would say that Durock is still "OK" for a hearth. When I say "ok" I mean, it may not be to code or 100% acceptable in the eyes of the inspector, but the product itself will work just fine.

 

[sksmass]

Like BeGreen said, 1/4" backer seems a little flimsy. Also, you could call around local lumberyards asking if they have any original Durock in stock. You may be surprised that they will have it. Most contractors don't want the stuff, preferring the new Nextgen Durock for its lightness. So, the yard might have some "old gen" just gathering dust and will be eager to sell it to you. I found some that way.

 

[begreen]

For an underlayment on top of soft micore, I'd feel much better with at least 1/2" cement board for stiffness. A stove is heavy and 1/4" board is going to flex. Also, Hardie board is not cement board. It appears that Wonderboard is the last true cement board available unless you can find someone that still has some original Durock in inventory.

Actually, after reading recent information posted here on Durock NextGen, I would not be afraid to use it. The only thing they changed when going to the NextGen stuff was adding pearlite (non-combustible) to the board to make it lighter. They just didn't pursue the UL listing for hearth use. So while it appears that the Durock NextGen won't work for a hearth; it is actually almost identical to the old Durock, they just didn't have it tested for hearth use so it doesn't have the little sticker. Knowing this, I would say that Durock is still "OK" for a hearth. When I say "ok" I mean, it may not be to code or 100% acceptable in the eyes of the inspector, but the product itself will work just fine.

I can follow your thinking and would think it might be ok for a hearth requiring only an ember shield, though not officially. However, in this case, the Hearthstone requires more than just ember protection. USG was contacted about a month ago and said that the NextGen is approved for wall shielding, but not for hearths. Are you sure that they are using perlite and not styrofoam beads?

 

[firefighterjake]

For an underlayment on top of soft micore, I'd feel much better with at least 1/2" cement board for stiffness. A stove is heavy and 1/4" board is going to flex. Also, Hardie board is not cement board. It appears that Wonderboard is the last true cement board available unless you can find someone that still has some original Durock in inventory.

Actually, after reading recent information posted here on Durock NextGen, I would not be afraid to use it. The only thing they changed when going to the NextGen stuff was adding pearlite (non-combustible) to the board to make it lighter. They just didn't pursue the UL listing for hearth use. So while it appears that the Durock NextGen won't work for a hearth; it is actually almost identical to the old Durock, they just didn't have it tested for hearth use so it doesn't have the little sticker. Knowing this, I would say that Durock is still "OK" for a hearth. When I say "ok" I mean, it may not be to code or 100% acceptable in the eyes of the inspector, but the product itself will work just fine.

I can follow your thinking and would think it might be ok for a hearth requiring only an ember shield, though not officially. However, in this case, the Hearthstone requires more than just ember protection. USG was contacted about a month ago and said that the NextGen is approved for wall shielding, but not for hearths. Are you sure that they are using perlite and not styrofoam beads?

Guy I talked to at Durock said you could use the new stuff for hearths and that it contains perlite . . . and I asked twice just to be clear . . . I asked can I use the NextGen Durock to build a hearth and he said yes . . . he said it isn't listed . . . but provides the same protection . . . just doesn't have the UL sticker . . . although I should add he also said that both the old stuff and new stuff were designed to be "part of an assembly" when used as a hearth . . . what that means I can only guess.

My own take (barring any additional info which could cause me to change my mind yet again) is that I would not have any real concerns at this point if someone was using the NextGen Durock for use as a hearth . . . but I would prefer to see the old stuff.

 

[begreen]

Thanks for the clarification Jake. It would be soooo nice for USG to get this tested. I can't see why there would be an issue passing the UL test if perlite is used.

 

[firefighterjake]

Thanks for the clarification Jake. It would be soooo nice for USG to get this tested. I can't see why there would be an issue passing the UL test if perlite is used.

I agree . . . it would make the Fire Inspector and I feel a lot better . . . just knowing it had the UL sticker.

 

[Hoopdancer]

I finally found (been looking awhile) Micore 300 on the weekend but just in 16" x 16" pieces for $15 each and picked up 7 pieces to do what was needed. Today I lucked out and found a supplier who was selling a customer's Micore that was left over. The customer had to buy a lift of 80 - 4' x 8' sheets and only used a few. I was able to pick up a single sheet for $48. I'm guessing that a single sheet is going to give me a much better fire rating than 7 butt together. I know most of you are stating to not to go with the Hardie board but I have found that is does have a UL rating and figured that if I put a piece of 16ga or 14ga sheet metal (full coverage) between the Hardie board and the Micore that the combination would be strong enough to take the weight of the stove. I do plan on testing my theory using point loading prior to installation using some of the cut offs just to make sure. I expect that most if not all of you know what your talking about through years of experience but some times I have to see things for myself. I'm not sure what my final finished surface will be to finish off the R=1.2 rating as yet but probably 1/2" stone with a tapered edge. Any chance anyone can help with a decision on what finish to go with, the matte black or the blueblack finish on the Hearthstone Heritage? Thanks again for all your words of wisdom.

 

[Highbeam]

I have burned the heritage in matte black for three years. The paint has failed in many places and faded horribly in others. It looked really nice when new but has not held up. I don't know how durable the enamel finish is but from reading about the other owners' experiences I would recommend paying the extra couple hundered for the enamel.

 

[fire_man]

I finally found (been looking awhile) Micore 300 on the weekend but just in 16" x 16" pieces for $15 each and picked up 7 pieces to do what was needed. Today I lucked out and found a supplier who was selling a customer's Micore that was left over. The customer had to buy a lift of 80 - 4' x 8' sheets and only used a few. I was able to pick up a single sheet for $48. I'm guessing that a single sheet is going to give me a much better fire rating than 7 butt together. I know most of you are stating to not to go with the Hardie board but I have found that is does have a UL rating and figured that if I put a piece of 16ga or 14ga sheet metal (full coverage) between the Hardie board and the Micore that the combination would be strong enough to take the weight of the stove. I do plan on testing my theory using point loading prior to installation using some of the cut offs just to make sure. I expect that most if not all of you know what your talking about through years of experience but some times I have to see things for myself. I'm not sure what my final finished surface will be to finish off the R=1.2 rating as yet but probably 1/2" stone with a tapered edge. Any chance anyone can help with a decision on what finish to go with, the matte black or the blueblack finish on the Hearthstone Heritage? Thanks again for all your words of wisdom.

Everything I read says its ok to use Hardiebacker for under the Hearth. Here is one Stove Manufacturer's viewpoint:Use a hearth extension constructed of a durable noncombustible material having an equal or better (lower k value) insulating value of k = .84 BTU IN/FT2 HR °F or a thermal resistance that equals or exceeds r=1.19 HR °F FT2/BTU IN. HardieBacker is stated on their website to be "Non Combustible".

 

[sksmass]

There is a difference between "non combustible" and "insulative." There are plenty of non-combustible things that will still allow conductive heat to pass right through them. For a hearth that has r-value requirements you need insulative materials covered with a non-combustible top layer.

 

[fire_man]

0.42" Hardibacker has the same "R" value (insulative quality) as 1/2" Durock.

 

[Hoopdancer]

Highbeam - Thanks for you input. If you had the choice would you go with Blueblack or Black Enamel? You have definitely talked me out of matte black. Fire_man - I'm only looking at using 1/4" Hardiebacker (r= 0.13) at this point which from other posts says heat goes through it pretty easily but it is definitely non combustible. Trying to keep as flush as possible to the hardwood flooring but I know flush isn't going to happen. Skamass - Do you know if there would be any adverse affects having sheet metal between Micore and Hardiebacker as it has no insulative properties whatsoever and I wonder if it might be a detriment and help transmit the heat like a heat sink?

 

[begreen]

Everything I read says its ok to use Hardiebacker for under the Hearth. Here is one Stove Manufacturer's viewpoint:Use a hearth extension constructed of a durable noncombustible material having an equal or better (lower k value) insulating value of k = .84 BTU IN/FT2 HR °F or a thermal resistance that equals or exceeds r=1.19 HR °F FT2/BTU IN. HardieBacker is stated on their website to be "Non Combustible".

Can you provide reference documentation, ideally from JamesHardie?

On their website I found the product is rated at R .52 per inch, same as other cement boards. But I could not find any testing or endorsement for use as hearth underlayment.

 

[Dakotas Dad]

I'm close but not there yet. I'm in the process of adding and refinishing hardwood flooring near the end of it seems a never ending renovation. I would like the tile or final finish of the hearth pad for a new Heritage Hearthstone (r=1.2) to be flush to the top of the 3/4" red oak flooring but have not found anything that will satisfy this. Is it possible to thinset tile to the surface of Fiberfrax? I've read in posts that doing this with Micor is not suggested because it is too soft but have not seen anything describing the strengths of Fiberfrax. Is it possible to bond sheet-metal of sufficient gauge to the surface of Micor and then tile? I'm guessing that I will need to add a tapered piece of oak trim around the tile and end up with something around 1-3/8" total height using micor or fiberfax, concrete board and tile. I would prefer to be flush or to be just slightly above the existing floor as the stove will be placed close to center of a small home between the kitchen and living room.

The only other question would be "Should I get Blueblack enamel or Matte Black finish on my new Heritage?"

Thanks for any help or advice.

What is your subfloor? You are not on a slab are you? I SERIOUSLY considered this...

remove sub floor were hearth area was going, skive floor joists down far enough to reach needed R value when rebuilt, sister floor joists for strength/integrity, build hearth pad, coming up to and equal with current subfloor, all nice and level, no place to stub toe.

But then thought it over, decided a raised hearth would be better to keep the dogs away from the stove.. The rest as they say, is history.

EDIT: the blue black is very nice.. but matte black is the upkeep winner.

 

[sksmass]

...Skamass - Do you know if there would be any adverse affects having sheet metal between Micore and Hardiebacker as it has no insulative properties whatsoever and I wonder if it might be a detriment and help transmit the heat like a heat sink?

Adding sheet metal as part of the sandwich, as I understand it, only really adds two things:

1) if you are using (stupidly IMO) an unmortared top layer, like loose sand in between bricks. Then a sheet metal layer under the bricks would serve as your "non-combustible of last resort" in the event that, for example, your wife accidentally vacuumed all the sand out from between the bricks

2) I have read, but not sure I believe, that a layer of sheet metal will "even out the hot spots" by conducting heat away from hot spots towards colder parts of the hearth. But if you build the hearth to proper R values, hot spots shouldn't be a problem. Better off to build a hearth that doesn't HAVE hot spots IMO.

FWIW: I asked Ron at Woodstock about adding sheet metal into my hearth build in anticipation of my new Fireview and he said it was unnecessary.

I am going to end up with a ~1.5" height difference from my hearth to the subfloor. The sandwich will be composed of:
3/4" micore 300
1/2 Durock (old gen)
1/4" porcelien tile

Then subtract from that ~3/4" of carpet pad plus carpet on the room floor, the NET difference becomes ~3/4" which I will accommodate with a tapered oak threshold around the hearth.

 

[Hoopdancer]

Skasmass, your 2nd point makes total sense to me. The heat from the stove would be concentrated close to the stove but the sheet metal would conduct the heat away to areas of less heat. This process would dissipate the actual heat load over a larger area and would lessen the concentrated heat loading on the insulative materials by spreading it out over a larger area. Definitely has to be a plus. The reason I was adding the sheet metal was because I'm looking at using only 1/4" concrete board and wanted to spread the weight from the stove over a larger area so as not to crush the Micore 300. Seems to be a few issues with BeGreen our trusty Moderator accepting Hardiebacker without a "hearth" designation. What to do......... Not sure I want to remove the subfloor just yet and cheating is not an option. The wife in example 1 ...... has this happened? Your scaring me.

 

[sksmass]

Skasmass, your 2nd point makes total sense to me. The heat from the stove would be concentrated close to the stove but the sheet metal would conduct the heat away to areas of less heat. This process would dissipate the actual heat load over a larger area and would lessen the concentrated heat loading on the insulative materials by spreading it out over a larger area. Definitely has to be a plus. The reason I was adding the sheet metal was because I'm looking at using only 1/4" concrete board and wanted to spread the weight from the stove over a larger area so as not to crush the Micore 300. Seems to be a few issues with BeGreen our trusty Moderator accepting Hardiebacker without a "hearth" designation. What to do......... Not sure I want to remove the subfloor just yet and cheating is not an option. The wife in example 1 ...... has this happened? Your scaring me.

Add the steel layer if it appeals to you. It certainly can't hurt. 26 gage steel is only like 0.02" thick.
But if I were you I'd get a professional opinion on using 1/4" concrete board. That just seems too thin for comfort to me. You really don't want to have to do a hearth twice.

No, the wife example was a figment of my imagination but I could see it happening.

 

[firefighterjake]

Skasmass, your 2nd point makes total sense to me. The heat from the stove would be concentrated close to the stove but the sheet metal would conduct the heat away to areas of less heat. This process would dissipate the actual heat load over a larger area and would lessen the concentrated heat loading on the insulative materials by spreading it out over a larger area. Definitely has to be a plus. The reason I was adding the sheet metal was because I'm looking at using only 1/4" concrete board and wanted to spread the weight from the stove over a larger area so as not to crush the Micore 300. Seems to be a few issues with BeGreen our trusty Moderator accepting Hardiebacker without a "hearth" designation. What to do......... Not sure I want to remove the subfloor just yet and cheating is not an option. The wife in example 1 ...... has this happened? Your scaring me.

Add the steel layer if it appeals to you. It certainly can't hurt. 26 gage steel is only like 0.02" thick.
But if I were you I'd get a professional opinion on using 1/4" concrete board. That just seems too thin for comfort to me. You really don't want to have to do a hearth twice.

No, the wife example was a figment of my imagination but I could see it happening.

Agree on the 1/4 inch . . . I would want to at least go to 1/2 inch . . . I share the same philosophy of not liking to do the same job twice . . . I would want to be sure there is absolutely no flex in the backer board to which I would attach the stone or tile.

 

[begreen]

Mentioned this earlier. Use at least 1/2" cement board for tile underlayment. Micore is soft. You need something rigid on top of the micore or risk cracking grout or a tile with the weight of the stove on the tile.

 

[Highbeam]

And really, what's 1/4"? Like a layer of frosting on a cake, a pencil width. The increased height is hardly worth risking breaking up your tiles.

I agree to skip the steel sheet. It is unnecessary and any benefits are miniscule. Your stove manufacturer specified an R-value and that's all you need. No reason to go to extreme measures to make it even better.

The blue-black is closer in color to the inevitable ash/dust coating that your stove will get. The gloss black looks cleaner but like a black car it will always look dirty unless you clean it daily. I vote for blue-black. Be sure to see the colors in person as they look much different than on the hearthstone site. The seafoam green looked way different in person.