Hearth finishing details

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John_M

Minister of Fire
Dec 10, 2008
614
Central NY
I have finished the framing construction phase of my new hearth. It will be 78" wide x 56" deep x 12" high. Space was available so I made it large to have room for tools, log cradle, ash can, and an occasional person who wants to sit near the stove after hours of snow blowing. An outside air kit (OAK) will direct air to the area directly beneath the pedestal of the new stove. That area, about 4 cubic feet, is well sealed and insulated to prevent cold air from migrating to the rest of the house.

My next step is to install the Durock and tile. I have the impression that all I need do to install the Durock is nail or screw it to the two layers of 3/4" overlapped Advantec flooring using fasteners specified by Durock. Then finish all the seams as specified by Durock.

Here are a few questions:
1) Even though not required, would it be a good idea to set the Durock in the latex modified thinset morter and then fasten it?
2) Should I run the Durock and tile snug to the back wall and edges of the hearth or should I hold it back about 1/4" to 1/2" and use caulk to fill in the back and edges?
3) If I should use caulk, what kind of caulk should I use? (Clearances to combustibles will not be an issue);

I am one of the few persons in the civilized world who does not own a digital camera so I cannot post a photo.

Best Wishes and good health to all.

John_M
 
My shot at answers, keeping in mind I'm not at all a tile person.
1) Good idea, yes; but probably not necessary. Bedding in thinset creates one big solid chunk out of the multiple laters (Advantec and Durock), and makes for a more stable foundation. That said, I don't think you'll have any probs if you don't use thinset and just screw/nail it.
2) Are you also doing the back wall for a hearth? If so, either is fine but you might want to ensure a way for air to enter the bottom and exit the top behind the wall to allow convection cooling. If no back wall is necessary/planned then I'd leave a gap and caulk it.
3) Fire-rated caulk is available in a couple colors, and not very expensive - or just use grout.

Good luck, we just finished ours a couple weeks ago.
 
We have hearths that are similarly raised and are tiled under both stoves. I finished the one out in the new studio in December. The husband framed out the hearth and put 3/4" plywood over the framing. On top of that he placed Durock, screwing down through it into the plywood. He routed out trim boards to cover the raw edges. I laid a bed of thinset mortar and tiled on top of that, grouting the tile right up to the trim boards, the masonry chimney, and the sheetrock of the wall where the hearth returned to it.

The plan was approved by the code enforcement officer with no questions (we used the basic plan in the Woodstock manual). I will note, however, that the mortar has cracked along the masonry chimney. I'm not sure if that's not due to my own inexperience with the materials, though. But it came out nicely and I'm pleased with the overall result. I don't think it's necessary to put mortar between the Advantec and the Durock at all.

(I'll be priming Advantec this very weekend and then giving it a light sanding in preparation for a couple of coats of deck paint. My sample board came out OK... last time I painted floors it was in the house and it was plywood, not Advantec.)
 
OK, I think I have the hang of this now:
1.) Conproco "Structural Skin" over masonry block:
354501730.gif

2.) Drywall compound (multiple coats) over Structural Skin:
354501737.gif

3.) Hearth framing (blocking was added for extra beef between the "joists"):
354501733.gif

4.) 3/4" plywood topped with 1/2" Durock, trim boards in place and pre-finished:
354501742.gif

5.) Tile on thinset, pre-grout:
354501732.gif

6.) In place, corner detail:
352906476.gif

7.) Long view:
352906474.gif
 
Hey Bobbin, you did an excellent job on this project. The tile pattern immediately caught my eye. I'll lay mine out the same way to see how it fits. It looks like you used 2x 10's for the framing and the same for the stringers. I did essentially the same and included the 45 deg. outside corners. I had a bear of a time with the corners because the lumber I had was twisted, warped and bent. Gosh, I fought those corners. It looks like you used 1 x 3's for the trim and I'll use the same on both the top and bottom. I'll route a 1/4" radius on all the trim. It looks like you left enough room around the perimeter of the tile for a grout seam. I wanted to do the same but didn't know if I needed a space with caulk to allow for some expansion.

Thanks again for the suggestions on the Advantec and Durock. I really wanted to avoid the extra work and mess of having to thinset the Durock to the two layers of Advantec. I would do it if necessary but am more than willing to eliminate any unnecessary work.

You mentioned painting Advantec. I recently built an office area in my very large garage. I used 5/8" sheetrock on the interior walls and 5/8" Advantec on the exterior walls. After a little sanding then priming and painting with two coats of color the Advantec has a great informal, textured look. I am happy I did it that way.

Best wishes,

John_M
 
John, I was disappointed with the cracked grout. As I said, I'd never done any masonry or tile work before and I found the directions on the grout a little vague for a rank beginner; I wasn't sure if maybe I didn't quite have the consistency of it quite right... you know, maybe too dry or something like that. I did wonder at the time if there was something more flexible I could have used along the chimney edge, but I opted for the grout. In hindsight I wish I'd done the research to come up with something more flexible for that chimney seam... I urge you to check out the options. And report back.

I also found the application of the masonry materials was rather hard on my hands and wrists. I was really tired after each step (and the clean up), lol! But again, that was probably due more to inexperience and selecting tools that were probably a tad too large and therefore quite heavy when loaded with material (duh!). It was helpful to have a good pressure sprayer with water in it, and a bucket of water to keep the tools and surfaces moist as I fumbled through each step.

I will tell you that I did a dry fit with the full tiles and fiddled around with the arrangement before I committed to cutting anything. I had never used a wet saw before, but taking my time and THINKING about the overall effect before plungeing in willy-nilly made the cutting pretty painless. The tiles that are cut out to go around the corners of the chimney were the toughest to cut as I had to turn them on the saw bed to cut into the corners and finish them off with a diamond blade on a hand saw that looks like a coping saw. I did the entire hearth with 25 sq.ft. of tile and have only a small amount of pieces left over. Make sure you seal the grout after it's had time to cure!

Good luck with your project and I'm glad to know I'm on the right track with the prep. work for the Advantec paint job. It was a fun project and thanks for the compliment.
 
Bobbin, During the last week or so I read an artile by a professional tile installer and she/he recommended using a seam of caulk at the intersection of the vertical back wall and the horizontal hearth. The type of caulk was not specified. Because of its distance from the stove, that corner caulk would not need any high temperature or fire ratings.

I do not like silicone caulk except in specific applications. It is almost impossible to remove completely from a surface and it is not paintable. My favorite caulk for all applications requiring caulking before painting is the DAP 230. It holds paint very nicely, is easily cleaned up, sticks very well and seems to expand and contract without damaging the paint on its surface. Unless I see something to change my mind in the next few days I'll use my DAP 230 for the back corner. This way, I can continue my wall paint right down to the tile.

Another comment about the painted Advantec: Friends and visitors who have seen the new office area have offered unsolicited comments about how good the painted Advantec looks. At first they think it looks like heavily textured sheetrock and they want to know how I did it. When told it is Advantec their usual reaction is that they had never seen Advantec treated that way and really like its looks. Sometimes we venture into unknown waters and discover some hidden benefits of taking risks with different designs.

Best Wishes,

John_M
 
Check at a tile store for color matching sanded(1/8" ot larger joints) or unsanded(less than 1/8" joints) caulk. In general you always want to caulk where there are two planes(wall and floor, wall and wall, etc) that intersect and between tile and another material since they will expand and contract differently. Your install looks good, I still have a bit of work to finish mine.
Good luck!
 
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