# laying hearth stone



## smmm (Aug 13, 2010)

I have a platform that is approximately 52"x90". I want to put down a hearth stone that has dimensions 0f 19 1/2" x 19 1/2". Looking for advice on how to lay the stone. 
1- What type of backer board and mortar should I use? 
2- Also any sugeestions on how to keep it all level?
3- ANy ideas on the layout. I know I will have to cut some of the stones. Should I put a row of cut stone in the middleand keep full slabs on the ends?

Any help and suggestions would be GREAT!


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## begreen (Aug 13, 2010)

Is this for a wood stove? If yes, what stove?


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## smmm (Aug 13, 2010)

Yes it is a wood stove. It is a Buck Model 81.


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## ansehnlich1 (Aug 13, 2010)

First, I am not a stone mason. If I were you, I would contact a mason and 1. ask him/her for advice, and/or 2. have him/her do the job.

That being said, a rock solid floor is the first prerequisite. You should be aware of any 'r' value insulation requirements for your wood stove. This may dictate the use of durock or some other insulating material on top of which you would install the stone. 

The most important requirement is a non-moving subfloor. I did a tile job in an old house of mine, and laid that tile out on a concrete basement floor. Then I sat a baker coal stove on top. Some time later one of the tiles cracked, right under the stove's rear leg. Who would have thought that eh? I concluded I went just a wee bit thick with the mortar bed. 

If you use durock, make sure you screw it fast to the floor so it doesn't move on ya.


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## Yagminas Masonry and Wood-heat (Aug 13, 2010)

Hi there, if the stone is going to be laid on other masonry I generally use regular type "n" mortar.  If I am laying a stone on plywood or metal I like to use construction adhesive in a caulking gun. Lepage Bulldog Grip is what I normally use.

To level- if laying the stone in a bed of mortar, use little wedges to tilt and tip the stone to where you need it then cram mortar into the joint and let it set up. Now level all other stones to this first one. If laying on a plywood box, just make sure the box is level and set the stone down to the adhesive. Bang it down with a rubber mallet- should end up very close to level.

Stone cuts- alas, that is where the artistry comes in. Try laying it out different ways before you mix the first batch. Pick the look you like.

Cheers,
Kev


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## begreen (Aug 13, 2010)

I'm no mason, but plywood + construction adhesive on a hearth seems a bit risky. I've felt hearth stonework get far too hot too touch. In the very least I would screw down a cement board substrate first, then use the bedding mortar. You never know how this fireplace will be used a few years from now. It might have an insert installed or a hearth stove placed on it. Using a plywood built base seems to be a bit of a time-bomb. Is this common practice?

Edit: My error, should have gone back over all the responses first. If this is a free-standing stove requiring only ember protection, then the plywood base is fine, though I would still use a cement board substrate.


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## firefighterjake (Aug 13, 2010)

smmm said:
			
		

> I have a platform that is approximately 52"x90". I want to put down a hearth stone that has dimensions 0f 19 1/2" x 19 1/2". Looking for advice on how to lay the stone.
> 1- What type of backer board and mortar should I use?
> 2- Also any sugeestions on how to keep it all level?
> 3- ANy ideas on the layout. I know I will have to cut some of the stones. Should I put a row of cut stone in the middleand keep full slabs on the ends?
> ...



Well I'm no expert . . . but I did read a lot of threads here at hearth.com on how to make a safe, long-lasting hearth and this is what I did . . .

I used Durock . . . over two layers of 1/2 inch plywood . . . the plywood was to keep things rigid and avoid flexing . . . the Durock was (at the time) listed by UL for floor protection as a hearth . . . and over this I put down slate using Flexbond Mortar which apparently contains some material to allow a bit of natural flexing over time. That said . . . this was even a bit of an overkill since my Jotul Oslo only required ember-protection . . . learning what your stove needs for floor protection (some require high insulation requirements) is important.

As for keeping it level . . . I lucked out . . . the floor was pretty level from the get-go . . . and I just kept an eye (and level) on the slate as I went . . . I think when I put the stove on the hearth I did use a penny or small flat washer to level out the stove a bit . . . but it wasn't by much . . . heck I can't even remember if the penny/washer is still there or not since it's under the leg.

Layout . . . it's up to you . . . I went with a random pattern suggested on the box since I had random pieces . . . but honestly it's whatever looks good to you . . . or your significant other.


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## begreen (Aug 13, 2010)

Thanks Jake, I keep thinking the 81 is going in a fireplace. If all the freestanding stove requires is ember protection (no manual here) then your method is a good plan.


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## smmm (Aug 13, 2010)

Thanks!  Here is what I found on the back of the stove and in the manual. Not sure what it means by "alternative".  Does that mean and alternative to using legs or pedastool? I found it at buckstove.com under stove manual.  I'm having a hard time figuring out if Jake's installtion will work. Can anyone interpret?

ON BACK OF STOVE:
Non combustible floor protector under stove for free standing installation. 16" beyond front of fuel door and 8" to side of fuel door with insulation R- Value of 1.1.

FROM MANUALQuote: ALTERNATE FLOOR PROTECTORS MATERIAL
Floor protector must be 3/8" minimum thickness non-combustible material or equivalent.
With the floor protector or hearth extension material specified as one layer of 2" thick brick
with a K* factor of 5.0, you may use alternate materials as long as the K* factor (s) is calculated
as follows:
FORMULA: Required thickness = (K of alternate material/K of millboard) X (thickness
of millboard)
EXAMPLE: An alternate inorganic non-combustible millboard with a K* of .9375
would require a thickness as follows:
Required thickness = (.9375/5.0) x 2 in.
= 3/8 inch
K* FACTORS OF ALTERNATE MATERIALS
Material K Required Thickness
Ceroform 126 .21 1/8"
Limestone 8.0 3.2"
Concrete 8.0 3.2"
Sandstone 13.0 5.2"
Marble 18.0 7.2"
Hearth extension or floor protector thickness above four (4) inches are generally not acceptable
due to cost, floor load capacity, and look. The alternate we recommend is using Ceroform No.
126 millboard 1/8" minimum and putting any type decorative brick or stone (any thickness) on
top of it.
* The K* factor represents the thermal conductivity of a material and is the time rate of heat
flow through a homogeneous material under steady-state conditions, through unit area, per unit
temperature gradient in the direction perpendicular to a surface.
14


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## Wood Heat Stoves (Aug 13, 2010)

ya i was just looking at that, ask your county insepector how they interpret it, or call buck


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## kubes14060 (Aug 14, 2010)

I am by far no expert...in fact this is my first attempt at a hearth pad.

I'm getting a Jotul Castine in Majolica Brown installed in a few weeks, so I built this hearth pad at my cabin.

I used 2 layers of 3/4 subflooring on top of my raised pad with a layer of cement board on top.  Then I dry fit the 1.5 inch thick hearthstones down in the following pattern.  Some are darker than others because of water from my wet saw.  I then just lain down about a 1/2 thick layer of type "s" mortar, which is the same I used on the walls.  I have about a 1/2 inch gap that I need to fill in with mortar yet.  Time will tell if it holds up?


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## begreen (Aug 14, 2010)

Looks like a nice project. I'd say it's going to hold up fine. It will look great when finished. Keep posting progress reports kubes.


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## firefighterjake (Aug 16, 2010)

smmm said:
			
		

> Thanks!  Here is what I found on the back of the stove and in the manual. Not sure what it means by "alternative".  Does that mean and alternative to using legs or pedastool? I found it at buckstove.com under stove manual.  I'm having a hard time figuring out if Jake's installtion will work. Can anyone interpret?
> 
> ON BACK OF STOVE:
> Non combustible floor protector under stove for free standing installation. 16" beyond front of fuel door and 8" to side of fuel door with insulation R- Value of 1.1.
> ...



I'm just a dumb firefighter so I won't even attempt to figure out the alternate floor protection goobly-gook . . . although maybe someone a lot smarter than me could figure this out.

I could figure out the first part though . . . it seems as though (if I'm reading this right . . . and you might want to double check with the stove manufacturer to be sure you and I are reading this right) you need to have a hearth that is a) non-combustible (the easy part) and b) has a R-value (insulative value) of 1.1 (the more challenging part.)

If you do a search for R values you'll find some info on R values of different products.

Here's one link . . . although some of the info is dated since the NextGen Durock appears to not be of any use to us now, unlike the old Durock. 

https://www.hearth.com/econtent/index.php/wiki/Hearth_Design/

Using this list you should be able to come up with a design that should work for you. Perhaps the easiest way is to find a 1/2 inch sheet of Micore 300 which it seems has a R value of 1.1 . . . put a 1/2 inch sheet of Wonderboard on this (another .26 in R value) and then top with ceramic tile (.08) or your choice of stone . . .


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