Micore + Durock Strategies?

[BillGriggs]

I'm doing a hearth in front of a manufactured fireplace. I'm following manufacturer's ancient instructions (although it sounds like they are overkill). Planning on putting down 1/2" of micore 300, and then 1/4" of durock with 1 5/8" Durock screws to hold the whole thing down to the subfloor. This will get a layer of thinset and 3/8" tiles.

1. Will 1/4" durock be fine? I've seen 1/2" recommended elsewhere, but I'm trying to keep tile as low as possible? Original hearth was simply tiles glued to millboard and almost all tiles survived 30+ years.
2. Durock (and other backerboard) instruction lists need for a layer of thinset below. I've not used micore before, but this doesn't seem necessary in this instance. Should I use thinset, or will a ton of Durock screws be fine?
3. Is Flexbond an ok mortar to use for a hearth application, or should I try to use unmodified thinset?

 

[WoodyIsGoody]

I'm doing a hearth in front of a manufactured fireplace. I'm following manufacturer's ancient instructions (although it sounds like they are overkill). Planning on putting down 1/2" of micore 300, and then 1/4" of durock with 1 5/8" Durock screws to hold the whole thing down to the subfloor. This will get a layer of thinset and 3/8" tiles.

Will 1/4" durock be fine? I've seen 1/2" recommended elsewhere, but I'm trying to keep tile as low as possible? Original hearth was simply tiles glued to millboard and almost all tiles survived 30+ years.

I don't see a problem but I've never used it on top of Micore so I'm not positive.

Durock (and other backerboard) instruction lists need for a layer of thinset below. I've not used micore before, but this doesn't seem necessary in this instance. Should I use thinset, or will a ton of Durock screws be fine?

I would bed it in thinset before using lots of screws. In this case your not concerned about the bond, it's about the bedding. A thin coat is fine.

Is Flexbond an ok mortar to use for a hearth application, or should I try to use unmodified thinset?

I would always use a well modified thinset unless there was a specific reason not to (like tiling on Ditra or Kerdi). It's hard to find thinset that isn't good these days, Flexbond is a good choice as long as your tile isn't clear or translucent. For bedding the backerboard, any old thinset, modified or unmodified, will be fine, it can even be an open bag that's been sitting around a year or two.

 

[BillGriggs]

I would bed it in thinset before using lots of screws. In this case your not concerned about the bond, it's about the bedding. A thin coat is fine.

Thanks Woody! I've not used micore before, have you used this technique on some? Will it take to the thinset ok? I couldn't tell if it was more on the end of fiber/millboard or softer.'

I saw that with durock you're supposed to join panels together with mortar and mesh tape. Will this be ok for hearth application? I'll need to join two pieces together because of the shape of my hearth.

 

[begreen]

You'll want to use 1/2" Durock for rigidity. Micore is soft. There is no need for thinset between the cement board and the micore. It won't bond well. Just be sure that your substrate below the micore is flat and level. Screw the cement board down per directions. I think it asks for one screw every 8". Any good latex-modified thinset should work.

 

[WoodyIsGoody]

Thanks Woody! I've not used micore before, have you used this technique on some? Will it take to the thinset ok? I couldn't tell if it was more on the end of fiber/millboard or softer.'

I've not used thinset on micore but Durock is not approved for tiling unless the Durock is bedded in either mastic or thinset. Mastic is flammable so you need to use thinset. Because you are fastening the Durock to the subfloor, the bond is of zero importance. However, there will be some bond and the entire assembly will be more stiff because of it. The hearth you removed had tiles bonded directly to asbestos board! To help the thinset spread on the micore you can mist the micore and wipe it down with a damp sponge before trowelling the thinset. And, no, the thinset will not harm the micore. Micore has minimal swelling.

I saw that with durock you're supposed to join panels together with mortar and mesh tape. Will this be ok for hearth application? I'll need to join two pieces together because of the shape of my hearth.

Yes, thinset and mesh tape will be fine. And it's especially important since it's on top of Micore.

 

[Hogwildz]

I used 1/2" micore & 1/4 Durok and has no issues. Make sure you use the screws required for cement board, and be be generous with them. I think I used them every 6" to 8" apart. And 6' along the edges. I have had no issues with the microre compressing or such. I put 1/2" x 18" square natural slate on mine.

 

[BillGriggs]

I used 1/2" micore & 1/4 Durok and has no issues. Make sure you use the screws required for cement board, and be be generous with them. I think I used them every 6" to 8" apart. And 6' along the edges. I have had no issues with the microre compressing or such. I put 1/2" x 18" square natural slate on mine.

Thanks Hogwildz! I finally secured a piece of micore and it seems pretty stout. I've got a whole box of rock-on screws, and plan to be very generous with them. I suppose time will tell!

 

[BillGriggs]

I've not used thinset on micore but Durock is not approved for tiling unless the Durock is bedded in either mastic or thinset. Mastic is flammable so you need to use thinset. Because you are fastening the Durock to the subfloor, the bond is of zero importance. However, there will be some bond and the entire assembly will be more stiff because of it. The hearth you removed had tiles bonded directly to asbestos board! To help the thinset spread on the micore you can mist the micore and wipe it down with a damp sponge before trowelling the thinset. And, no, the thinset will not harm the micore. Micore has minimal swelling.

Yes the micore 300 seems sturdier than I anticipated. I was thinking it would be something like compressed fiberglass insulation, but it seems almost on par with a particleboard. I think the extra stiffness will help since I'm only using the 1/4" durock. Thanks for the advice!

Do you have any input on how exactly to structure this as I put it in? I'm assuming the micore and durock should be butted up against the bottom of the fireplace, but I should leave a gap for tile grout?

 

[kennyp2339]

Firm / rigid is your friend here when it comes to tiling, before laying anything down zip a few extra screws in the sun floor 1st then work your way up.

 

[Hogwildz]

Yes the micore 300 seems sturdier than I anticipated. I was thinking it would be something like compressed fiberglass insulation, but it seems almost on par with a particleboard. I think the extra stiffness will help since I'm only using the 1/4" durock. Thanks for the advice!

Do you have any input on how exactly to structure this as I put it in? I'm assuming the micore and durock should be butted up against the bottom of the fireplace, but I should leave a gap for tile grout?

I have a raised hearth, only a course of brick high, with blue tone on top. The extension was done at floor level, so I butted the extension tight under the ledge.
You could leave a gap and either grout it, or put a bead of silicone in there, level it out or indent it a little, and try and sprinkle grout powder on top the of silicone to give it a uniform look with the rest. Grouting alone may be fine. But if there is any movement at that gap, it will crack, and eventually come out.

 

[BillGriggs]

You could leave a gap and either grout it, or put a bead of silicone in there, level it out or indent it a little, and try and sprinkle grout powder on top the of silicone to give it a uniform look with the rest. Grouting alone may be fine. But if there is any movement at that gap, it will crack, and eventually come out.

Thanks! That sounds like a good plan. Should I plan on running my modified thinset all the way up to the front too, or should my gap for caulking extend down to the durock?

 

[Hogwildz]

Run the micore,durok and thinset & all the way to seal that area as tight as you can(ember protection), then set you caulk in the gap between the tile & old hearth edge. Sprinkle generous grout power on top of the caulk(after you flat/level out the caulk. I would take a flat edge, cardboard, spackle knife, anything flat, and lightly press the grout powder into the caulk.Let it set for a day or so. vacuum up the loose grout powder. Done.

A little trick, is to run painters tape along the finished edges where you will caulk, then after caulking remove the tape, and you should have a nice clean edge that you can never get just using your finger.

On the face & side edges of the extension, you can either set your perimeter trim in place with say a 1/8" to 3/16" gap between the boards and where the sides & front of the tiles end, and either gout it in, or caulk and powder.
Or, if you set the tiles good and straight & square on the edges, you can run the trim right to the edges of the tile..

If you are going to butt the trim to the tile edges, it doesn't hurt to temp some scrap 1 x 4 boards along the perimeter when setting the tiles, that will give you a temp straight edge to work with to set the tiles to. Then remove the temp boards, set your trim and grout the tiles.

 

[BillGriggs]

If you are going to butt the trim to the tile edges, it doesn't hurt to temp some scrap 1 x 4 boards along the perimeter when setting the tiles, that will give you a temp straight edge to work with to set the tiles to. Then remove the temp boards, set your trim and grout the tiles.

Thanks a ton this is all great.

One more thing I'm trying to think through. I was going to dryfit my tile and then try to join two pieces of trimmed durock to match those dimensions as exactly as I could, but I fear ending up with a lip on at least one of the sides. My new idea was to aim to take the durock in 1/4" or so on left, right, and front, and then fill any place the tile overshot with mortar.

Is that sort of what I should be aiming for? Our plan is to run laminate flooring up to the tile with a small expansion gap and then cover the gap with a transition piece.

 

[WoodyIsGoody]

Thanks! That sounds like a good plan. Should I plan on running my modified thinset all the way up to the front too, or should my gap for caulking extend down to the durock?

It looks like Hogwildz has you covered with solid advice. If I was confident the trim around the hearth pad was solid and well fastened I would likely use the same latex modified grout around the perimeter to save the caulking step. Yes, it will have a micro-crack between the trim and grout but not enough to hurt anything. If you go this route I recommend rubbing the trim with some warmed paraffin wax or candle (before installing the trim) to insure the micro- crack develops between the grout/trim, not grout/tile.

Also, the more dry your grout is mixed, the less shrinkage and more ultimate strength it will have. So avoid over-wetting it during wipe-down and/or mixing it too thin.

 

[WoodyIsGoody]

Is that sort of what I should be aiming for? Our plan is to run laminate flooring up to the tile with a small expansion gap and then cover the gap with a transition piece.

So it sounds like your tile field won't have a solid border trim around it?

Once you add in thickness for the two thinset layers, Micore, Durock and tile, how does the finished level compare to that of your finished floor?

 

[BillGriggs]

So it sounds like your tile field won't have a solid border trim around it?

Once you add in thickness for the two thinset layers, Micore, Durock and tile, how does the finished level compare to that of your finished floor?

Depending on how the thinWith all that together probably looking at about 1/4" - 3/8" difference.

 

[WoodyIsGoody]

Depending on how the thinWith all that together probably looking at about 1/4" - 3/8" difference.

If you go without solid trim around your tile field, the tile edges will be the most vulnerable part of the install. With that in mind, the Micore and Durock should extend at least a bit past the edge of your tiles for a proper support pyramid. And insure you don't weaken the edge of the micore when you cut it.

Personally, I think a solid wood border (perhaps in a contrasting color to your floor) might look really sharp. And, being flush with the top of your tile surface would protect the tiles from edge loads and assist with grouting.

 

[Hogwildz]

Dry mock up the tiles with the gap you want between them, then adjust your micore & durok to meet where you want to end. Or if you can't get that to work for whatever reason, trim the tiles to have the same width along the edges. You should always mark a center point and work from there. That should assure equal width & depth whether the tiles need to be cut or not. I would think with proper mock up and layout, you should be able to set the micore & durok to the dimensions the tile end up at.
Your transition trim will act as your perimeter trim for the extension. And they usually have a track you mount to the floor then snap the transition trim into that. The space left for the transition track will be your expansion gap, and will be covered with the transition trim.

I'm with Woody on the trim. I'm more of a hardwoood trim person myself. As that ban be milled down to the same height as the hearth, with no raised edge to trip over.
Laminate trim is merely a pc of fiber type board or MDF with a vinyl laminate cover. It may get beat up easier then solid hardwood. Wood can always be refinished, the laminate pc can't. But you can ptolly pry it up and replace, if they still stock that color years down the road.

My experience is they change laminate color choices often, which can be a problem down the road, unless you buy a couple back up pcs to have if/when needed.

Also, use a good dust mask when cutting the micore & durok, stuff is nasty and not good for the lungs.

 

[Hogwildz]

Sanded grout hold up better than non-sanded grout, especially on grout joints larger than 1/8"