Constructing a hearth for our Woodstock Progress Hybrid

[NectarNook]

This is an excerpt from my personal blog. I thought I would post it here in case anyone has any advice or constructive criticism to offer. This is my first time ever building a hearth, so I am really trying to cross all my t's and dot all my i's!

Thanks!

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The first order of business was using a tape measure, pen, and straight edge to figure out clearances and where the legs would stand for the wood stove. Once we had that all marked out, we measured out a wooden frame made of 2×6′s.





We doubled up the supports underneath where the legs will stand on the hearth, then added cross bracing for a bit more stability. Where the cross bracing and doubled 2×6′s meet are where the legs will be. It was pouring outside, so the wood was a bit wet to work with, but I think we did a good job. That thing is SOLID.

Once the frame was built, we got to cutting 5/8″ thick fire-resistant drywall to go around it. At an R rating of 0.49, we needed two layers to get the 0.8 R rating needed beneath the stove. The layer of tile will just be gravy now, since we’ve already exceeded the minimum R value.





I think that is the very first time I have put a close-up of my face on this blog without blocking it out. It feels strange. My dad was getting a bit carried away with taking pictures today, so I’d feel bad if I didn’t use some of them. Fun fact, I was actually talking to him when he snapped this one. That’s not a smile. That’s me saying “cow chit” because that’s what the air smelled like today. Good old rain, stirring up the fields all around us. Hehe.



So that’s the hearth pad built and ready for the next stage: tiling. You can see three sample tiles in the top corner there. I got 12×12′s and 6×6′s. Not really sure what pattern to use, or if I should do straight or diagonal. Guess that’s what the conversation will be about tonight when I Skype with my hubby. He always has great ideas. Pretty sure he’ll come up with something, crack his whip, and tell me what to do. I don’t mind because his ideas are usually better than mine anyway.

I should have this thing all tiled before next weekend since the installers are coming on Monday the 21st to get the wood stove into place. I’d like to have everything set at least 48 hours before they arrive so it has time to harden up. Wish me luck and lots of elbow grease!

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Any suggestions on how I should tile the base? I'm thinking I need to make sure the legs are coming down in the centers of the tiles instead of on the edges where the 1/8" grout will be. Or does that even matter?

I have 6x6 tiles and 12x12 tiles. The top of the hearth is 53x47, so I'll be doing some cuts no matter how I lay it out.

What about the walls? When I asked someone about it, they said the minimum clearance is only measured from the nearest combustible surface, and that it didn't matter if there was significant R rating material between the stove and the combustible surface as long as that distance was satisfied. I would like to run the tile all the way up behind and to the right of the stove. Is it okay to tile right on the OSB, or should I be tiling over fire-resistant dry wall on the walls as well?

Thanks!

 

[Sprinter]

Have you confirmed that fire resistant drywall is approved for a hearth application? I don't know the answer myself, but some materials are not, and selecting proper insulating hearth material is a common issue here.

 

[Holiday]

Good question, it is generally cement board being used underneath the stove as I don't think drywall is hearth rated.

 

[Holiday]

As far as the walls go I believe that as long as the proper clearances are met that is the only criteria.

 

[NectarNook]

(broken link removed to http://chimneysweeponline.com/horvalue.htm)

When I was looking at the cement board offered, the tags all said "not rated for hearth application." The tags on the fire-resistant drywall, however, specifically listed their fire rating at 0 in all categories. The website above seems to confirm its use in a hearth application.

Thanks for the input. I'll post here as this project progresses.

 

[begreen]

Drywall is not suitable for the top surface of the hearth. Fire resistant drywall is not listed on the chimneysweep site. This is because it has paper backing and lacks sufficient strength. It also is not meant for use as a tile backer. One heavy step on the side of that hearth would punch right through that sheetrock.

To do this correctly you need a layer of at least 3/4" thick plywood, then sufficient cement board to meet or exceed the minimum hearth insulation (r-value) requirement for the stove. Durock NexGen or Permabase are two acceptable cement boards. The cement board will also provide a proper surface for good tiling bond. Screw it down using the correct screws every 8". Use latex-modified thinset to set the tile.

Woodstock has instructions on their website for proper hearth design. Read the Planning Your Hearth article (lower right of the page installation documents) on their site:
http://www.woodstove.com/

 

[r_towle]

Agree with the above post.

Sorry to say, but I would suggest you remove the drywall, put down plywood to support the top of the hearth, then use cement board, hardy board, dura rock, or whatever you can find for the next layer, then tile on to that layer.

The drywall will certainly hold the tile, the issue is that over a short period of time, the drywall will compress under the load of the stove.
Drywall is for walls and ceilings, never for floors or a compressed load.

 

[Sprinter]

Durock NexGen or Permabase are two acceptable cement boards.

Is NexGen Durock approved for hearth applications now? I thought I read that it wasn't, but that original Durock was.

Also, is original Durock available again? I was under the impression that it was discontinued, but another poster recently said that they found it at Lowes.

 

[Backwoods Savage]

All is not lost NectarNook as you aren't that far along to make the switch. The rest will be easy.

 

[Holiday]

I believe the next gen durock is hearth approved. It's noncombustible and suitable for use in a fire rated system.

 

[NectarNook]

Well shoot. Back to the drawing board tomorrow, then. Going to give Woodstock a call first thing to straighten myself out because I think I got pretty confused by all the different sources I was going off of. Something else that was pointed out to me - the floor clearance is only 8" on the non-loading side, but then it says 24" to the nearest wall. I didn't catch that differentiation and thought it meant 8" to the wall.

Yep. Going to have to take it all apart and try this again. Big sigh. I'll be back again with some improvements.

 

[begreen]

I give you credit for all you have done so far. You are an impressive gal. Better to catch this now than when the stove arrives. Feel free to ask questions. We want you to have a safe and solid hearth and installation. All is not lost, just pull off the top sheetrock and add an extension if needed to meet or exceed clearances. Then cap it with plywood and cement board. That will give you a rigid foundation on which to tile.

I personally like to have the hearth a bit oversized. It gives you more room to adjust final placement of the stove and flue and there's no harm in a little extra margin of safety.

 

[Sprinter]

Well shoot. Back to the drawing board tomorrow, then. Going to give Woodstock a call first thing to straighten myself out because I think I got pretty confused by all the different sources I was going off of. Something else that was pointed out to me - the floor clearance is only 8" on the non-loading side, but then it says 24" to the nearest wall. I didn't catch that differentiation and thought it meant 8" to the wall.

Yep. Going to have to take it all apart and try this again. Big sigh. I'll be back again with some improvements.

Woodstock is highly regarded for their customer service and guidance. They'll want to see you do it right. Sorry for the confusion, but you caught it early.

Please keep us informed on how it goes.

 

[Todd 2]

Might consider the size of hearth for wood rack, tool set, ash container, decor of sorts, if that is your taste.
Hang in there, your fruit will be well worth your labor when complete.

 

[NectarNook]

Thanks, y'all. Turns out I had to special order some Micore 300 to use underneath. Ouch, that stuff is expensive! $113 for four 2x4' sheets. It shipped out this morning and should get here Thursday. By then I should have the frame rebuilt and ready to go.

Menard's only sells Durock Next Gen. I got the company phone number from them and gave their rep a call. Rep confirmed that Next Gen is definitely not for use in hearths because of a formula change two years ago. He confirmed that Durock no longer has any material rated for hearth application. Awesome. The staff at Menard's helped me call every local and not-so-local building supply company in Wisconsin. We couldn't locate ANY dealers for hearth-rated materials. I'm pretty stunned. I mean, we got a lot of leads and suggestions, but then when we called company reps just to make sure the materials were approved for hearth application, we were consistently told they weren't for use in hearths.

Also gave the folks who are installing my stove next week a call to see if they had any suggestions. They suggested Next Gen. Wonderful, eh? I think they missed the memo that Next Gen isn't hearth rated anymore, too.

Live and learn. I've removed my blog for the time being and will post an updated one with more pictures when I get this done right. See y'all in a few days!

 

[begreen]

This comes up a lot. We have little or no choice for hearth materials now that USG has not retested their cement board. The new material added to Durock NexGen is perlite, similar to the tufa that Permabase has added. This is a lightweight, totally non-combustible volcanic material. As I've said before, at this point I see no reason to consider this material as inappropriate for hearth use. It is a common sense decision. There products are test to ASTM E-84 with zero flame spread. If you want to get this approved for hearth use it is going to take some significant pressure from the hearth industry. That will require dealers and folks here communicating this to manufacturers (USG, National Gypsum and Custom Building Products) and HPBA officials.

Note: I just got through speaking with tech support at Custom Builidng Products. He said he saw no problem using Wonderboard Lite for wood stove hearth usage. These products are tested to:

• ASTM E84 Standard Test Method for Surface Burning Characteristics of Building Materials

• National Fire Protection Association (NFPA) NFPA 255 Standard Method of Test of Surface Burning Characteristics of Building Materials

 

[Papa-Yankee-Romeo-Oscar]

I used Nexgen for my hearth, seems to be quite a bit of conflicting info but the USG website specifically states "For use in a fire rated system".

 

[begreen]

I am going to call them when I get a chance. They didn't respond to an email inquiry. Kind of feeling like it's we don't care we don't have to at this point.

 

[Elle]

Nice to see another chick building a hearth! I built one out of the old coal chimney brick that was taken out of the house some decades ago. I only had to build to ember protection so that worked fine with a layer of durock underneath. Keep us posted!

 

[Papa-Yankee-Romeo-Oscar]

I tried to call them at about quarter to six and ironically got more conflicting info from USG. The website states their customer service hours as 7am-6pm central time but the recording I received stated that customer service was closed and that the hours are 7am-5pm.