Need a new hearth pad

[TimG]

Good morning!

I have been using my Harman Mark II stove for about 15 years. We have a new insurance company and they will be coming to inspect stove. I have not had any problems with it in all these years but I need a new hearth of a greater size. According to my calculations, I need a pad of about 4'x5'. However, I don't want to spend between $300.00 or more on a new one. My current pad is only 3'x3' and is not big enough for my insurance company.

Question, can I use red brick or something else to make my own that would be cheaper? This stove is on the first floor of our home in our family room. It is on carpeting.

Thanks much for any suggestions.

Tim

 

[begreen]

Welcome Tim. A brick hearth with cement board and a sheet of metal under it may be permissible. It depends on what Harman has tested for protection. What are the hearth pad requirements for min. thickness and insulation listed in the manual?

 

[TimG]

Welcome Tim. A brick hearth with cement board and a sheet of metal under it may be permissible. It depends on what Harman has tested for protection. What are the hearth pad requirements for min. thickness and insulation listed in the manual?

Thickness is 3/8" but doesn't indicate insulation just says "non-combustible material".

 

[Warm_in_NH]

They sell some hearth "mats" too. Usually not the prettiest things but I think they're under 50 bucks and available at most local hardware stores.

 

[Michael6268]

What material do you have now?
The current manual doesnt even state what thickness. It just states "approved non combustible material".
What is approved? Who knows.
I take it as ember protection only. Otherwise they would list an insulation value.
I wouldn't use loose bricks. I would put down 3 layers of Durock topped with slate or ceramic tiles. 3 layers is a little over kill but it would give it some height.
Thats what I did with my Hitzer.
Its rated for 100k +btus. Yours is 72k.
You can always call AHS (current owners of Harman coal line) just to be sure.

 

[begreen]

3/8" mineral board was an old standard. Two layers of 1/2" Durock NexGen will get close to that level. Top it with whatever is non-combustible and visually pleasing.

 

[TimG]

What material do you have now?
The current manual doesnt even state what thickness. It just states "approved non combustible material".
What is approved? Who knows.
I take it as ember protection only. Otherwise they would list an insulation value.
I wouldn't use loose bricks. I would put down 3 layers of Durock topped with slate or ceramic tiles. 3 layers is a little over kill but it would give it some height.
Thats what I did with my Hitzer.
Its rated for 100k +btus. Yours is 72k.
You can always call AHS (current owners of Harman coal line) just to be sure.

Thanks for the idea. I don't really need any height so I don't think I'd go with 3 layers.

 

[Typ0]

What material do you have now?
The current manual doesnt even state what thickness. It just states "approved non combustible material".
What is approved? Who knows.
I take it as ember protection only. Otherwise they would list an insulation value.
I wouldn't use loose bricks. I would put down 3 layers of Durock topped with slate or ceramic tiles. 3 layers is a little over kill but it would give it some height.
Thats what I did with my Hitzer.
Its rated for 100k +btus. Yours is 72k.
You can always call AHS (current owners of Harman coal line) just to be sure.

3 layers of durock and you gotta put thinset between each layer to prevent shifting and tiles cracking....that's a lot of $$$$ in overkill if you ask me.

Build a raised hearth with 2x4s and one layer of 3/4" subflooring...then one layer of durock and your tile on top. That's what I would do....well I probably would cut out the floor where the hearth is right down to the joists...and then start with the subflooring so it was all level with my floor but that sounds like more than you want to get into.

 

[Michael6268]

I believe I said 3 was overkill.

I only put 3 cause I like a little height to it. To me if its not flush might as well raise it a bit.

Took me about 30 mins to complete. Lot quicker and easier than framing a base.

 

[begreen]

3 layers of durock and you gotta put thinset between each layer to prevent shifting and tiles cracking....that's a lot of $$$$ in overkill if you ask me.

You don't need to thinset between layers if you screw through all the layers to the base wood, once every 8" per directions. The sheets will be held completely flat and captive.

 

[TimG]

I believe I said 3 was overkill.

I only put 3 cause I like a little height to it. To me if its not flush might as well raise it a bit.

Took me about 30 mins to complete. Lot quicker and easier than framing a base.

Thanks much for the information. I don't want to go to what I consider "major construction". This is all just sitting on top of the very thin nap carpet. I don't need height with 4" legs on stove. As a matter of fact, I am going with one layer of Durock and slate or tile on top of that.

 

[begreen]

The cement board should have a 3/4" plywood backing for stiffness and rigidity. Otherwise there may be slight sagging, particularly on carpet. That may cause cracking at the grout joints. It it were me I would use 2 layers of Durock NexGen if the original specs were for 3/8" millboard.

 

[TimG]

The cement board should have a 3/4" plywood backing for stiffness and rigidity. Otherwise there may be slight sagging, particularly on carpet. That may cause cracking at the grout joints. It it were me I would use 2 layers of Durock NexGen if the original specs were for 3/8" millboard.

Thanks. I was thinking the same thing.

 

[Typ0]

USG requires thinset under the durock as specifications for tile construction for good reason. Additionally, this hearth is going to be sitting on top of carpet. Neither the subflooring or durock are perfectly flat....you need that thinset to level everything off and provide a solid substrate to support the tile. Maybe it will be OK ... but why risk your labor?

 

[Michael6268]

When I said "added height" I wasnt meaning so the stove sat higher.
I should have said "added hearth thickness"
Just me but I like the hearth surface to stand up just a bit. So it doesnt look like a "mat".
Purely personal taste.
And I liked the added protection even though it wasn't necessary.

 

[begreen]

USG requires thinset under the durock as specifications for tile construction for good reason. Additionally, this hearth is going to be sitting on top of carpet. Neither the subflooring or durock are perfectly flat....you need that thinset to level everything off and provide a solid substrate to support the tile. Maybe it will be OK ... but why risk your labor?

My understanding is that the necessary leveling happens with the thinset layer under the tile, not between cement board layers.

 

[Highbeam]

I would and have used the thinset between layers of durock. Also stagger seams and tape the joints. That makes the bond continuous like a real laminate. Without the thinset you risk creating little air pockets that may flex when you push screws through both layers. Since the durock screws are threaded all the way up there is a likelihood that as your screw tip punches through the first layer it will create a pile of blown out cement board before it starts threading into the next sheet. Those little piles of durock debris will hold the sheets apart and prevent lamination.

 

[begreen]

OK, my bad, I stand corrected. Sorry for the confusion and thanks for the clarification Highbeam. I have not used thinset in between and haven't seen an issue yet, but I have only done a few pads and apparently that doesn't mean it's not possible to have a problem. When all else fails, follow directions. From now on I will refer tiling to those experts at JohnBridge.

 

[quotejso]

I used thin set between every layer. Is there a reason u say use durock next gen, I used hardy board it was recommended by the Home Depot people.

 

[begreen]

Personal preference. Durock nex gen uses pumice as a filler. Hardiboard uses cellulose. Durock has a higher insulation value because of the pumice.

 

[Warm_in_NH]

Just out of curiosity why use multiple layers of cement board and not multiple layers of plywood or OSB? Then just top layer with cement board to bond the tile to. If there's no R value needed, seems like a lot of extra work and money to mud them all together when you could screw the plywood layers together rather easily.

 

[quotejso]

Just out of curiosity why use multiple layers of cement board and not multiple layers of plywood or OSB? Then just top layer with cement board to bond the tile to. If there's no R value needed, seems like a lot of extra work and money to mud them all together when you could screw the plywood layers together rather easily.

there is most likely an R value needed or would just need protection from embers at door location.

 

[begreen]

A single sheet might suffice if the stove bottom is well shielded, but I don't know how hot the hearth really gets when this stove is burning so rather than guessing my suggestion was to double it. The Harman requirement is based on an old spec which is 3/8" millboard. It was typical in the day to require millboard, often metal clad. The problem being is that millboard varies in material composition and R value, but an average seems to be around r=.5 to .7.
http://www.mcmaster.com/#millboard-sheets/=8u1ce2.
I like the two sheets of Durock in this case basically as insurance. That gives the hearth an R=.78 protection value.

 

[TimG]

Wow. Thanks for all the interest and conversation with this thread I started.

I think with all that is said I will be using 2 layers of Durock (7/16" each). I plan to use thinset between layers and then screw to 3/4" plywood. On top of top layer of Durock, use tile of my wife's choosing.

Again. I appreciate all the conversation and help with this.

Tim G.

 

[Jazzberry]

I bought a remnant from a granite shop for 75.00. Diamond blade from Lowes was 30.00 for my skill saw. Got my son to lightly spray the blade as I cut it. (plugged into a gfi) Cuts almost as easy as plywood. The polished surface is much easier to keep clean rather than something with joints such as brick or tile. I actually covered my old brick pad with it. I am very happy with my new pad.