Building hearth

[kevinmoelk]

Howdy folks. I started building my hearth pad last night. Constructed a 2x4 frame with studs 13" on center for added support. This lays right on the hardwood floor and is secured by some screws.

I then plan to lay some plywood down... I think I have a 5/8 or 3/4 sheet around here somewhere. On top of that will be 2 layers of 1/2 thick cement "wonderboard".

Now here is my question: Tile or Slate? Advantages, disagvantages?

Also, thinset morter to glue them down of course, but what about the grout? I assume grout is not combustible? Or should I grout with the thinset too? Is there a special grout I need to be using?

I'll post pictures a little later tonight, want to get some work in today.

-Kevin

 

[Gooserider]

Howdy folks. I started building my hearth pad last night. Constructed a 2x4 frame with studs 13" on center for added support. This lays right on the hardwood floor and is secured by some screws.

I then plan to lay some plywood down... I think I have a 5/8 or 3/4 sheet around here somewhere. On top of that will be 2 layers of 1/2 thick cement "wonderboard".

Now here is my question: Tile or Slate? Advantages, disagvantages?

Also, thinset morter to glue them down of course, but what about the grout? I assume grout is not combustible? Or should I grout with the thinset too? Is there a special grout I need to be using?

I'll post pictures a little later tonight, want to get some work in today.

-Kevin

What is the R-value you are trying to reach? According to(broken link removed to http://www.chimneysweeponline.com/horvalue.htm) 1/2" Cement Board (Wonderboard) is only good for 0.200, and I think most stoves want 0.800 MINIMUM between the stove and combustibles (like your framing and plywood!) - I think you'd be better off with at least one layer of a ceramic board like Micore that has 1.100 per 1/2"...

Any code guru's care to confirm?

Gooserider

 

[masterswimmer]

I'll be tagging along. I'm in the middle of building mine also. Using it for pellet though.

swimmer

 

[kevinmoelk]

Howdy Gooserider. I checked the manual again, and it does not specify a certain fire resistance rating beyond stating that a minimum 3/8" non combustible surface must be used underneath the stove. Beyond that I'm using two layers of wonderboard, so .400 plus a layer of 1/4" porcelin tile on top of that. I do not see any specification on the box of tile either as to its fire resistance. The tile guy at Hoe Cheapo said that the porcelin tile was the preferred tile for hearth construction, but he could have just made that up too. I tend not to place too much faith in those guys.

The stove does sit on legs and does have a bottom heat shield, so perhaps that is why there is only a 3/8 minimum? Does anyone else think my hearth design will be unsafe? I could not find Micore. Only found wonderboard and hardibacker.

-Kevin

 

[kevinmoelk]

I see on the chart that gypsum wall board has a resistance of .450. Does that mean I can place plywood, then gypsum, then the 2 layers of wonderboard to achieve the r.o.t. .800? Or should I not worry about it since my manual states only a 3/8" non combustible surface is needed?

 

[kevinmoelk]

Here's a copy of the information in the owners manual.

-Kevin


CLEARANCES TO COMBUSTIBLES
WARNING: BE ABSOLUTELY SURE THE DISTANCE BETWEEN THE HEATER AND THE
SURFACE OF ANY COMBUSTIBLE CONSTRUCTION IS NOT LESS THAN SHOWN ON THE
DIAGRAM BELOW.
Floor Protection: The floor in front and under the heater must be protected with a minimum of 3/8” thick noncombustible
material. The covering must extend 16” in front of the door opening of the heater and 8” to either side of
the door opening and 8” to the rear or to the wall, whichever is smaller. In all installations a 16” minimum
hearth extension (in front of the stove) is required as measured from the door opening of the unit.
Reduced Clearances: Clearances to combustible surfaces can be reduced with the use of listed double wall
connector pipe. See the clearances with double wall pipe on the following page.
Diagram A: Top View-Parallel Installation Diagram B: Side View-Alcove Installation

 

[nshif]

Drywall is considered a combustible surface so you gain nothing there. I think you are fine with 2 layers of wonderboard and tile.

 

[kevinmoelk]

Nshif, that's what I thought too, but it's listed on the chart Gooserider put up and is in the list of "common hearth materials" unless gypsum and plasterboard is something other than drywall, which to my knowledge they are the same.

-Kevin

Please help guys, I just got home and I'm just about to build this whole thing today. Thanks.

 

[nshif]

Here's a copy of the information in the owners manual.

-Kevin


CLEARANCES TO COMBUSTIBLES
WARNING: BE ABSOLUTELY SURE THE DISTANCE BETWEEN THE HEATER AND THE
SURFACE OF ANY COMBUSTIBLE CONSTRUCTION IS NOT LESS THAN SHOWN ON THE
DIAGRAM BELOW.
Floor Protection: The floor in front and under the heater must be protected with a minimum of 3/8” thick noncombustible
material. The covering must extend 16” in front of the door opening of the heater and 8” to either side of
the door opening and 8” to the rear or to the wall, whichever is smaller. In all installations a 16” minimum
hearth extension (in front of the stove) is required as measured from the door opening of the unit.
Reduced Clearances: Clearances to combustible surfaces can be reduced with the use of listed double wall
connector pipe. See the clearances with double wall pipe on the following page.
Diagram A: Top View-Parallel Installation Diagram B: Side View-Alcove Installation

Well if thats what your manual says you should be fine with 2 layers of wonderboard and the tile.

 

[Gooserider]

Here's a copy of the information in the owners manual.

-Kevin


CLEARANCES TO COMBUSTIBLES
WARNING: BE ABSOLUTELY SURE THE DISTANCE BETWEEN THE HEATER AND THE
SURFACE OF ANY COMBUSTIBLE CONSTRUCTION IS NOT LESS THAN SHOWN ON THE
DIAGRAM BELOW.
Floor Protection: The floor in front and under the heater must be protected with a minimum of 3/8” thick noncombustible
material. The covering must extend 16” in front of the door opening of the heater and 8” to either side of
the door opening and 8” to the rear or to the wall, whichever is smaller. In all installations a 16” minimum
hearth extension (in front of the stove) is required as measured from the door opening of the unit.
Reduced Clearances: Clearances to combustible surfaces can be reduced with the use of listed double wall
connector pipe. See the clearances with double wall pipe on the following page.
Diagram A: Top View-Parallel Installation Diagram B: Side View-Alcove Installation

Agreed, if that's what the manual says, you are probably OK. I've just noticed that the VC manuals I've been looking at go into more depth of specifying an R-value, and showing how to calculate it (and they also have legs and a heat shield on the bottom...)
Have you checked with your stove supplier to see if they say it is OK?

Gooserider

 

[kevinmoelk]

Thanks guys. Spoke with some other folks via PM and the consensus seems to be that my set up would be okay. The main consideration would deal with upgrade of the stove. But since I don't plan on upgrading anytime soon it's not so much of a concern for me. Off to hearth building I go! Already got the OA done for the most part, holes cut and pipe ran, but waiting until the stove is in place before I button it all up. I decided to run straight to the outside with the OA. I'll post some pictures probably tomorrow or the next day of my progess.

Thanks again.

-Kevin

 

[elkimmeg]

KEV: IT would take considerable typing to post two pages concerning the relationship of the stove height, to what is required by the NFPA 211
In almost all cases, what is acceptable is following the manufacture's specs. Specs to which have been tested and certified

 

[begreen]

Agreed, if that's what the manual says, you are probably OK. I've just noticed that the VC manuals I've been looking at go into more depth of specifying an R-value, and showing how to calculate it (and they also have legs and a heat shield on the bottom...)
Have you checked with your stove supplier to see if they say it is OK?

Gooserider

Lots of variations from stove to stove due to leg height, ashpan, lower heat shields, firebrick floor, etc. The Castine manual basically says the hearth has to be non-combustible. I am comfortable with that, it's barely warm under there. But other stoves could bake a cake under them and in that case one wants a good insulated, non-combustible barrier between the stove bottom and the floor.

 

[kevinmoelk]

Thanks Elk and BeGreen. Well I fell okay about my build then. I cannot find anything to refute what the manual states. It's too bad Country doesn't list a specific R-value, but oh well. An inch of wonderboard, some thinset mortar, and tiles should be sufficient. Thanks guys. Just trying to be safe.

-Kevin

Elk, come on and type it in! I know how much you love typing!

 

[begreen]

Wrench. I don't know about you, but after even a few hours of beating on nails, my hands feel like hams. Working at the computer is like typing with boxing gloves on. I can only imagine how Elk's feel after a long day of swinging a 22 oz. hammer.

 

[kevinmoelk]

Oh, I can empathize for sure. Swung a hammer for a couple years myself, and I was an auto tech also. Busted knuckles, tense muscles, hang nails, the whole bit. I feel especially tired when I work on the Scouts. Yes, International Harvester Scouts. You guys are old enough to remember those. I have a thing where I only use hand tools, nothing air powered when I work on them. Keeps things quiet in the shop and keeps up my hand skills. After wrenching on those beasts my hands are wrecked.

Don't take it personally Elk, I was only teasing.

-Kevin

 

[Corie]

Since heat flow through those boards is basically one dimensional, if you install the stove and get the surface temperature of the tiles, its very easy to calculate a very good estimate of the temperature of the wood framing beneath.

When the time comes if you're concerned about things, let me know and we can figure it out for you. I'm sure it will be sufficient, but I, like many here, have learned to err on the side of caution.

 

[kevinmoelk]

Well now you guys have me worried. I haven't yet set down the tile, so now is the time to add some layers if I need to. So let's take a vote. How many folks think I should add an additional 2 layers of wonderboad or some other noncombustible?

Where can I find the ceramic board people keep referring to?

Also, should I upgrade, or some other home owner upgrade, to what R-value should I build the hearth? Certainly the upgrade stove will be limited by the hearth dimensions. Which by the way are 42" wide and 44" deep to the wall (there's a small extension, but that was added for a space for tools). The stove is a Country Striker S160.

I don't want to do this twice. I don't want to tear apart my work already done. But certainly NOW is the time to make adjustments before I tile.

-Kevin

 

[tutu_sue]

Maybe you can get in touch with dealer or manufacturer and get the R-value required. Then no worries for you.

 

[babalu87]

You need to be cognisant of the K-value as well as the R-value, though they are related they are not the same.

You need to find a source for Micore 300 and put a sheet of that under the cement board.

(broken link removed)
They should be able to help you find a local dealer. It is best to look into BUILDING suppliers rather than Home Deep-oh or Lows

Read here
https://www.hearth.com/articles/64_0_1_0_M1.html

 

[Gooserider]

Well I'm sure there are probably stoves that would require more, but I would expect that if you were to add a 1/2" sheet of Micore (or equivalent) you would probably have something that would handle almost anything out there that would fit on the pad.

I would also mention that it would be very important to DOCUMENT what is under the tile so that anyone looking at upgrading in the future will know what they are dealing with.... Part of the problem I have with my current setup is that I don't really know what is underneath / behind the bricks that are visible on the hearth and backstop - And I'm not sure how to find out in a non-invasive way. (or how to do a minimally invasive procedure to find out if needed...)

Gooserider

 

[begreen]

My vote is micore would be overkill unless you plan on replacing the stove with something in the relatively near future. Predicting the future is very hard unless you're Frank Ivy. You could add the micore and still be under-rated for some stoves. Too hard to tell. Either build it to spec for the stove - essentially a non-combustible surface, or build it for whatever the future can throw at it - metal studs on 12" centers and 2 layers of durock placed at right angles over each other.

 

[Corie]

Again though, if you can get your hands on it, it adds what, 30 dollars to your installation?

I just feel like we're still talking peanuts when it comes to safety.

 

[nshif]

If it were me (and I do tend to get a little carried away ) Id cut up the hardwood flooring down to the subfloor ( just in the foot print of the hearth, lay a sheet of wonderboard, form it, and pour concrete. Then just tile over that. 1/2" wonderboard, 3 1/2" slab plus tile outta take anything you can put up there.

 

[MountainStoveGuy]

not all stoves have a listed r value for them, and the specs the manufacture lays out is enough. Jotul has some models like this, so does rais and scan. If it says 3/8" of non combustable thats all it takes.