I know this has been discussed before but I'm still confused on building my own hearth pad. I don't know what is best to use as far as cement board. It looks like there is Hardibacker, Wonderboard, Durock, and another product called Micore. I'm installing a Jotul 500 Oslo. I know there are hearth pads out there you can buy for $500-$600 but I don't want to spend that much. My friend tells me that a lot of these cement boards should not be used for hearth pads. He bought his hearth pad for $200-$300. I still would prefer to build my own. Sorry if this has already been discussed many time but I'm getting confuse. Any advice would be appreciated. Thanks
hearth material questions
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Micore is an insulation material and should only be used as a substrate to increase R value. Cement board has some insulation value and also is an excellent substrate. You want this on top of the Micore (if needed) and as an underlayment for the tile or stone used on the hearth. The bond between tile and Micore would be crappy because of the fibrous nature of Micore. The bond between tile and cement board (with a latex thinset) is excellent.
Because the hearth for your Oslo only requires a noncombustible surface to sit on, you have many options and don't have to worry about achieving an "R" value. This was the same situation with my stove and I simply got some Durock and grouted tile to it for looks.
The manual for your Oslo states that the hearth dimensions must be at least 54.25" wide by 50.5" deep.
The manual for your Oslo states that the hearth dimensions must be at least 54.25" wide by 50.5" deep.
It all depends upon what your stove manufacturer calls for in terms of the insulative requirement of the hearth beneath the stove...usually expressed as what's called an R-value. Start from that, and determine what you need to build. Some materials (as Be Green said in the case of Micore) have good insulative properties, but not so good structural properties. Others, like Durock, are the opposite. In any case, whatever "sandwich" of materials you come up with must meet or exceed the manufacturer's requirement for the specific stove. Rick
cdirks said:
As Nic mentioned with the Oslo (unless they've changed the requirement) you only need to have ember protection . . . which could technically be met by putting down any non-combustible material. That said . . . I'm a big believer in not just meeting requirements, but exceeding requirements and would suggest using a piece or two of Durock or similar cement board -- if you could get your hands on some original 1/2 inch Durock and not the NextGen Durock it would be even better since this is listed for use as hearth material -- and then over the Durock lay down tile, stone, etc. In my own case with my Oslo I went with two sheets of 1/2 inch plywood (for rigidity as a base), a sheet or two of 1/2 inch Durock (I forget how many) and then put down 1/4 inch thick slate tile on top using latex modified thinset. I then sealed the grout lines and stone (well after grouting) with a stone sealant.
Don't bother buying the pre-made products . . . they look nice, but as you have discovered they can be pricey. If you have just a little bit of DIY skill (and I'm talking really basic stuff like being able to cut lumber/plywood, use a trowel, etc.) you can build a custom hearth for a lot less money that can look as good as the expensive stuff. As for your friend . . . he may or may not be wrong . . . as mentioned it all depends on the stove manufacturer and what they require for the R (insulation) value.
Just curious Jake....why is it that my Jotul Castine hearth requirement is (as I recall) R2, but the Oslo, if I'm understanding you, has none? To my understanding, they both have the same basic design, only the Oslo is larger. What gives, if you know?
That said, I'm not convinced that my Castine hearth needs any R value at all. I've never felt the hearth get even warm to the touch directly beneath it, even after a whole night of 600 degree plus firing and the ash pan empty. In fact, I had the bottom heat shield on it for the first week, and then realized that it was performing no good function at all, and took it off completely. My sense is that the bottom ash pan compartment gives adequate insulation on the bottom. Was Jotul just going overboard with this design requirement? If so, I'm a sucker, because I layered up three thicknesses of crete board, micore, metal roof flashing topped by a seven 1/4" limestone slab. Really, most nights after prolonged burning, it is almost cool to the touch!
That said, I'm not convinced that my Castine hearth needs any R value at all. I've never felt the hearth get even warm to the touch directly beneath it, even after a whole night of 600 degree plus firing and the ash pan empty. In fact, I had the bottom heat shield on it for the first week, and then realized that it was performing no good function at all, and took it off completely. My sense is that the bottom ash pan compartment gives adequate insulation on the bottom. Was Jotul just going overboard with this design requirement? If so, I'm a sucker, because I layered up three thicknesses of crete board, micore, metal roof flashing topped by a seven 1/4" limestone slab. Really, most nights after prolonged burning, it is almost cool to the touch!
ploughboy said:
Not really sure . . . I could give some guesses about the Oslo having a deep ash box and bottom shield which may reduce the temps significantly , but it would just be a guess . . . perhaps JotulGuy will stumble across this thread and give a better opinion.
My own feeling . . . I would always follow the manufacturer's recommendations . . . or even exceed them . . . and sleep well at night.
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