Hearth extension

[Cedrusdeodara]

G-rott,

Yeah, that's what I figured. I found and ordered a 6' by 2' by 1/2" MC300 Micore board online for like $37 with free s/h. That'll do the job for me. One 1/2" Micore layer, one 1/2" Hardibacker layer, and then thinset and slate tile.


Brian

 

[edthedawg]

OK still a lot going on here. OHNODOC - question for ya: how many of these finish tiles do you have? possibly enough to do an entire new surface? are they new/available at a local store?

Right now i'm thinking you may do best to break it all out, lay in your Micore, set 1/4" Durock/Wonderboard over that, and then your tile on that - all new surface, no breaks, nowhere for it to fail (it MAY fail at the joint, and i'd think it likely, so better safe than sorry). You can use layer(s) of 1/4" Durock in the front or the back to level it out as needed.

You do want Durock under your tile - you can't bond it right to Micore.

Mastic is NOT acceptable for a hearth - you need to use a thinset MORTAR.

You can use a mortar called Flexbond for the entire project to help w/ the dissimilar substrates, their motion, etc. it's an enhanced polymer-infused mortar w/ excellent flexibility.

Hope this helps - keep the questions coming!

 

[ohnodoc]

G-rott wrote:
Micore will have enough durability in the center or field of your hearth after you tile over it. Adding a layer of dura rock will help. Any problems you encounter will be at the edge, there I would cut back the size of the micore and build up with dura rock a few inches wide. The thin set mortar can be used to even out the edge where the materials meet.

The edge of something stronger sounds like a good idea, except for the fact that I would have to buy an entire sheet of Durak for a 10 foot strip 2-3 inches wide. I have some leftover GP DensShield tile backer that I would prefer to use to avoid buying the Durrock. TheGP DensShield tile backer seems dense enough to walk on, and it is made to hold tiles. But it says on it "not for flooring". Would that still apply given that it would only be a 3 inch border around the Micore?

 

[ohnodoc]

Regarding the 1/4 inch asbestos equivalent default r-factor that the UL uses, I checked my notes from the phone call with the inspector that told me this, and it is 0.89, not 0.86 as I wrote earlier. My apologies.

 

[edthedawg]

G-rott,

Yeah, that's what I figured. I found and ordered a 6' by 2' by 1/2" MC300 Micore board online for like $37 with free s/h. That'll do the job for me. One 1/2" Micore layer, one 1/2" Hardibacker layer, and then thinset and slate tile.


Brian

NO Hardibacker = nonono. Use Durock. Hardibacker may be "cementitious" but it is NOT non-combustible. It's ok to use on the far side of your minimum R-value if needed (I did this) but it cannot lay between your Micore and tiles.

 

[edthedawg]

G-rott wrote:
Micore will have enough durability in the center or field of your hearth after you tile over it. Adding a layer of dura rock will help. Any problems you encounter will be at the edge, there I would cut back the size of the micore and build up with dura rock a few inches wide. The thin set mortar can be used to even out the edge where the materials meet.

The edge of something stronger sounds like a good idea, except for the fact that I would have to buy an entire sheet of Durak for a 10 foot strip 2-3 inches wide. I have some leftover GP DensShield tile backer that I would prefer to use to avoid buying the Durrock. TheGP DensShield tile backer seems dense enough to walk on, and it is made to hold tiles. But it says on it "not for flooring". Would that still apply given that it would only be a 3 inch border around the Micore?

1 - You can not tile right over the Micore. I guess you could try, but it'd break the first time you stepped on it. You need at least the protection of a 1/4" thick sheet of Durock / Wonderboard to provide the necessary stability under the tiles.

2 - Just buy the Durock / Wonderboard for the whole surface - don't skimp and try to just protect the edges. you really need it all over. And it's cheap stuff.

3 - GP/DensShield is NOT rated for continuous exposure over 120*F. While it's arguable how hot it would actually get, it's probably not an approved material for hearth duty. Have you discussed using this specific product, in this specific application, with the inspector and/or someone from GP?

 

[atvdave]

I also have the Lopi freedom bay insert. My hearth is a bit different from yours but all I had to do is get a non-combustible material to put in front of the hearth. I just went to Lowe's and purchased a hearth rug for around $15.

What insurance company is telling you this? If you meet the manufactures requirement's I can't see how they can tell you different.

 

[ohnodoc]

1 - You can not tile right over the Micore. I guess you could try, but it'd break the first time you stepped on it. You need at least the protection of a 1/4" thick sheet of Durock / Wonderboard to provide the necessary stability under the tiles.

3 - GP/DensShield is NOT rated for continuous exposure over 120*F. While it's arguable how hot it would actually get, it's probably not an approved material for hearth duty. Have you discussed using this specific product, in this specific application, with the inspector and/or someone from GP?[/quote]


OK, so I cannot tile directly over the Micore. This will now cause me to be very close to or higher than flush with the existing hearth.

!) How thinly can I put the thinset without losing strength?

2) Will 1/4 inch of Durock over the Micore be sufficient to give the strength needed to avoid crushing or cracking of the overlying tile when walked on?

3) Hardibacker is not equivalent to Durock. But is Wonderboard the same as Durock?

Bob

 

[Cedrusdeodara]

Edthedog,

Hardibackers no good?? Didnt say that on hearth.com's wiki R-factor table.... Where's the information saying that is no good???

 

[edthedawg]

OK, so I cannot tile directly over the Micore. This will now cause me to be very close to or higher than flush with the existing hearth.

!) How thinly can I put the thinset without losing strength?

2) Will 1/4 inch of Durock over the Micore be sufficient to give the strength needed to avoid crushing or cracking of the overlying tile when walked on?

3) Hardibacker is not equivalent to Durock. But is Wonderboard the same as Durock?

Bob

The thinset can wind up pretty thin and still hold tight. I'd reckon you can go down to 1/16" with it if troweled thin. worst case there is if it winds up too thin, you have the tiles pop loose, and you just re-mortar and re-grout them a second time...

I still haven't seen, if you're only going to make an extension that butts up to the existing hearth, how you're going to mitigate cracking? or just going to suck it up that it will happen on that seam and deal with it?

1/4" Durock / Wonderboard should be fine over the Micore. You should make sure the Micore is reasonably flat/secure to the subfloor, and probably should try to slather some thinset onto the top of it to 'bed' the Durock/wonderboard, which SHOULD then be screwed down. with your heating tubes in the floor, I don't know how you plan on doing that... unless you can determine where the tubes are and put screws where they ain't?

Wonderboard = Durock in every setting I have ever seen. Neither of these = Hardibacker.

 

[Cedrusdeodara]

From what I see, Hardibacker and Durock have the same R-value. Here's the link:

https://www.hearth.com/econtent/index.php/wiki/Hearth_Design


Once again, where is a link to suggest that Hardibacker is not suitable as a hearth material... other than just saying it and repeating it.

Brian

 

[edthedawg]

Edthedog,

Hardibackers no good?? Didnt say that on hearth.com's wiki R-factor table.... Where's the information saying that is no good???

I don't actually see Hardibacker mentioned anywhere on the R-factor table, assuming we're looking at the same page:
https://www.hearth.com/econtent/index.php/articles/k_values_what_does_it_all_mean


Just one example (there are many) of people discussing Hardibacker's inadequacies as a hearth material:
https://www.hearth.com/talk/threads/1183/

It has combustible materials infused within the non-combustible matrix. So no, it won't easily burn. and they can rate it as a "noncombustible". but we have some fairly intelligent people (note: i'm NOT one of them) saying not to use it, so I'm inclined to follow suit... And yeah, it probably would be a good idea to get the wiki revised to specifically state not to use Hardibacker - it gets brought up a lot...

 

[ohnodoc]

I still haven’t seen, if you’re only going to make an extension that butts up to the existing hearth, how you’re going to mitigate cracking? or just going to suck it up that it will happen on that seam and deal with it?

When I spoke to the inspector, he said that my plan to butt up to the existing hearth would be code, but he had the concern of the telescoping crack. I stated that I could just fill it with thinset or grout or put one of the store bought hearth pads if that ever occurs. He said that his conern was for the long term since most people live in a house for an average of 7 years. I expleaned that I have been here 16 years so far and plan to die here. Regarding avoiding the telescoping crack, he said that it would not matter what I did on top of it, the crack could still come. Thus, the idea of ripping up my current hearth and doing the whole thing over would still have the same concern. His suggestion was to put Micore on top of the current hearth and out as far as I needed, then buy a slab ov stone or marble 2'x6' (the size of my future hearth). I have given this serious thought. But it was leave me with a raised hearth in a narrow room.

 

[ohnodoc]

[/quote1/4” Durock / Wonderboard should be fine over the Micore. You should make sure the Micore is reasonably flat/secure to the subfloor, and probably should try to slather some thinset onto the top of it to ‘bed’ the Durock/wonderboard, which SHOULD then be screwed down. with your heating tubes in the floor, I don’t know how you plan on doing that… unless you can determine where the tubes are and put screws where they ain’t?

[/size]


This is a dilemma that I would like more ideas on. I called the retired radiant floor installer who remembers the house and me 20 years later, but he does not recall with certainty whether he left the usual 6' clearance from the hearth edge. Thus, the tubing could be underneath the entire extension. The tubes are under 1' of the gypsum/cement/sand mixture. I have concluded that all I can do is use the best possible adhesive to keep it from moving. My current plan is to use thinset between the subfloor and the Micore. Then thinset between the micore and the Wonderboard, And then a 3rd layer of thinset for the tile. I wondered if Gorilla glue would hold beter between the sublfloor cement and the Micore.

I have the same issue with the carpet strips at the edge: how do I adhere them to the cement subfloor. What I have peeled up reveals that the original wood carpet strips glued.

 

[edthedawg]

From what I see, Hardibacker and Durock have the same R-value. Here's the link:

https://www.hearth.com/econtent/index.php/wiki/Hearth_Design


Once again, where is a link to suggest that Hardibacker is not suitable as a hearth material... other than just saying it and repeating it.

Brian

Guess we were both posting at the same time. Thx for including your URL - I hadn't noticed HardiBacker included on that list. But please see Note #2 after it:

"2) At this time questions have been raised about the use of HardieBacker, it is not recommended until we receive further information from the manufacturer."

I'd be more than willing to do an experiment for you - I have a 1/4" sheet of both Wonderboard and Hardibacker at home. I could simply try lighting both of them up (in an outdoor firepit) and video the results, and post that on youtube.

 

[edthedawg]

When I spoke to the inspector, he said that my plan to butt up to the existing hearth would be code, but he had the concern of the telescoping crack. I stated that I could just fill it with thinset or grout or put one of the store bought hearth pads if that ever occurs. He said that his conern was for the long term since most people live in a house for an average of 7 years. I expleaned that I have been here 16 years so far and plan to die here. Regarding avoiding the telescoping crack, he said that it would not matter what I did on top of it, the crack could still come. Thus, the idea of ripping up my current hearth and doing the whole thing over would still have the same concern. His suggestion was to put Micore on top of the current hearth and out as far as I needed, then buy a slab ov stone or marble 2'x6' (the size of my future hearth). I have given this serious thought. But it was leave me with a raised hearth in a narrow room.

You could do a full stone slab, I suppose. But I thought you desired to keep the white & green tile look? If you can take out the existing tile, level out the entire 2' x 6' footprint w/ your Micore over the extension, then lay 1/2" Durock/Wonderboard over the entire 2' x 6' footprint (note you would just need to buy a single 3x5 sheet, cut it in half (3 x 2.5), and then trim 6" off each piece (qty 2 @ 3x2 ea.) to do this the best - no horizontal seams!), and then tile over the 1/2" Wonderboard.

You'd likely wind up slightly above flush, but:

a - it'd all be uniformly proud

b - if it's more than 1/4", you could easily add a small, mitered trim detail around the edge to make it gentler on passing toes or avoid tile chipping

c - no horizontal seams - the wonderboard ain't gonna crack unless you have a lot of movement in the floor system.

 

[edthedawg]

This is a dilemma that I would like more ideas on. I called the retired radiant floor installer who remembers the house and me 20 years later, but he does not recall with certainty whether he left the usual 6' clearance from the hearth edge. Thus, the tubing could be underneath the entire extension. The tubes are under 1' of the gypsum/cement/sand mixture. I have concluded that all I can do is use the best possible adhesive to keep it from moving. My current plan is to use thinset between the subfloor and the Micore. Then thinset between the micore and the Wonderboard, And then a 3rd layer of thinset for the tile. I wondered if Gorilla glue would hold beter between the sublfloor cement and the Micore.

I have the same issue with the carpet strips at the edge: how do I adhere them to the cement subfloor. What I have peeled up reveals that the original wood carpet strips glued.

You could think about renting an infrared (IR) camera somewhere - fire depts have them, as do some builders. you could use that to pinpoint the location of the pipes in the floor, if they are entirely encapsulated. (it's easier than my way, which is to drill holes randomly and look for leaks!

I can't say what the combination of cement-GorillaGlue-Micore-Thinset-Durock-Thinset-Tile would do in service - I know my construction friends have shied away from polycarbonate glues recently because they're just too strong - the substrates fail around the glue in undesired ways. If it were me, i'd probably be doing thinset between the cement floor and the Micore.

as for the carpet strips, if they are glued now, then you would re-lay new strips with the same kind of glue. If it's held for 20 years, it should continue to do so. I can't make a recommendation - you could likely contact a carpet installer for ideas...

 

[ohnodoc]

This is a dilemma that I would like more ideas on. I called the retired radiant floor installer who remembers the house and me 20 years later, but he does not recall with certainty whether he left the usual 6' clearance from the hearth edge. Thus, the tubing could be underneath the entire extension. The tubes are under 1' of the gypsum/cement/sand mixture. I have concluded that all I can do is use the best possible adhesive to keep it from moving. My current plan is to use thinset between the subfloor and the Micore. Then thinset between the micore and the Wonderboard, And then a 3rd layer of thinset for the tile. I wondered if Gorilla glue would hold beter between the sublfloor cement and the Micore.



You could think about renting an infrared (IR) camera somewhere - fire depts have them, as do some builders. you could use that to pinpoint the location of the pipes in the floor, if they are entirely encapsulated. (it's easier than my way, which is to drill holes randomly and look for leaks!

Why is screwing down the Wonderboard to the wood subfloor important?
Is it to prevent lateral movement? Is it to prevent crushing of the Micore under the Wonderboard? Or is there some other reason? Why won't the Thinset alone hold the MIcore etc in place?

I could fairly safely put some cement nails or screws in the edge next to the current hearth since the cement slab seems to extend an inch or two beyond the tile in the direction that I will be putting the extension. This would help if lateral movement is the concern. But, there is no way I can put anything in the area of the pipes at the far end of the extension.

 

[ohnodoc]

Why is screwing down the Wonderboard to the wood subfloor important?
Is it to prevent lateral movement? Is it to prevent crushing of the Micore under the Wonderboard? Or is there some other reason? Why won’t the Thinset alone hold the MIcore etc in place?

I could fairly safely put some cement nails or screws in the edge next to the current hearth since the cement slab seems to extend an inch or two beyond the tile in the direction that I will be putting the extension. This would help if lateral movement is the concern. But, there is no way I can put anything in the area of the pipes at the far end of the extension.

 

[edthedawg]

Why is screwing down the Wonderboard to the wood subfloor important?
Is it to prevent lateral movement? Is it to prevent crushing of the Micore under the Wonderboard? Or is there some other reason? Why won’t the Thinset alone hold the MIcore etc in place?

I could fairly safely put some cement nails or screws in the edge next to the current hearth since the cement slab seems to extend an inch or two beyond the tile in the direction that I will be putting the extension. This would help if lateral movement is the concern. But, there is no way I can put anything in the area of the pipes at the far end of the extension.

You screw down the wonderboard to restrict both lateral and vertical ("springy-ness") motion. Micore will compress to some extent (i.e. you want to "pre-crush" it ever so slightly), but even on a hard substrate (i.e. plywood subflooring), you still are heavily recommended to bed it in mortar and screw it down. I can't say for sure because, well, i'd never do it this way, but I think you will feel it, and hear it, "moving" a lot if you go without, plus you'll definitely increase the propensity for cracking at the location of the joint.

If you had a more uniform surface underneath the wonderboard, I'd say you could go for it. But if the Micore is only under the extension, and the rest of the panel will be over the existing solid masonry, then that'd be a cracking problem. If you don't touch the existing tile work, and only do a narrow "strip" of an extension, which sits over the cement/tube flooring, and you don't screw anything down, it *may* not crack itself (tho personally I think it will) and it will NOT maintain a crack-free union w/ the edge of the existing tile work. Perhaps the temps would be suitable for you to use a high-temp silicone in that crack, which could be color-matched to the grout you use.

I don't see why, if you really wanted to, you couldn't rent an IR camera for a day, map out the radiant heating tubes, make a cardboard template of their locations, and then use that template to safely pre-drill (thru the cement mixture the tubes are bedded in) to the plywood subfloor below? You only would need a half dozen screws, it seems.

 

[ohnodoc]

Why is screwing down the Wonderboard to the wood subfloor important?
Is it to prevent lateral movement? Is it to prevent crushing of the Micore under the Wonderboard? Or is there some other reason? Why won’t the Thinset alone hold the MIcore etc in place?

I could fairly safely put some cement nails or screws in the edge next to the current hearth since the cement slab seems to extend an inch or two beyond the tile in the direction that I will be putting the extension. This would help if lateral movement is the concern. But, there is no way I can put anything in the area of the pipes at the far end of the extension.

You screw down the wonderboard to restrict both lateral and vertical ("springy-ness") motion. Micore will compress to some extent (i.e. you want to "pre-crush" it ever so slightly), but even on a hard substrate (i.e. plywood subflooring), you still are heavily recommended to bed it in mortar and screw it down. I can't say for sure because, well, i'd never do it this way, but I think you will feel it, and hear it, "moving" a lot if you go without, plus you'll definitely increase the propensity for cracking at the location of the joint.

If you had a more uniform surface underneath the wonderboard, I'd say you could go for it. But if the Micore is only under the extension, and the rest of the panel will be over the existing solid masonry, then that'd be a cracking problem. If you don't touch the existing tile work, and only do a narrow "strip" of an extension, which sits over the cement/tube flooring, and you don't screw anything down, it *may* not crack itself (tho personally I think it will) and it will NOT maintain a crack-free union w/ the edge of the existing tile work. Perhaps the temps would be suitable for you to use a high-temp silicone in that crack, which could be color-matched to the grout you use.

I don't see why, if you really wanted to, you couldn't rent an IR camera for a day, map out the radiant heating tubes, make a cardboard template of their locations, and then use that template to safely pre-drill (thru the cement mixture the tubes are bedded in) to the plywood subfloor below? You only would need a half dozen screws, it seems.

Since the tubing is under a one-inch layer of gypsum/cement, I am worried that the accuracy of an Infra-red camera would not be good enough to separate out the distance from one tube to the next. My assumption (based on no conversations that I can recall) was that the tubes were very closely aligned. Thus, I do not think the infrared would be able to detect the small opening between the tubes after it diffuses up through the inch of gypsum/cement.

 

[Cedrusdeodara]

Edthedawg,
Thanks for catching the footnote to the table I was referencing, stating that Hardibacker is not recommended until further information is gathered, I didn't catch that. Guess I'll be returning the Hardibacker and I'll use sheetrock instead (ha ha, I mean Wonderboard/Durock).

BTW, the Youtube experiment would be cool to see. Maybe using a blowtorch at x distance for y time, etc. etc., that way the experiment is repeatable and consistent for whatever material you are evaluating.

Brian

Napoleon 1402
Stihl MS361
Speeco 22-ton hydraulic 3-pt hitch

 

[edthedawg]

Cedrusdeodara - you had me there for a second... Sheetrock. good one

I've got an 11 day break coming here - I'll see what I can do with the Big Fire Experiment...


OhNoDoc - re: tube spacing / inability to see the tubes - it's your house, dude. do what you feel is best. Worst case, you're only talking about a small hearth and it's out front of your insert. So long as you don't puncture the tubes, you can always take another swing at it. If you're really attached to a new tile/finish material and are concerned you might have to pull a mulligan, just buy enough to make two of 'em.

Happy holidays, guys!

 

[deedub]

straight from their site:
"HardieBacker™ cement board is recognized for use in non-combustible construction in NER-405."

 

[edthedawg]

Deedub - Just because it can be considered non-combustible does not mean it is rated for use in a hearth system. PVC and ABS plastics regularly are referred to as "non-combustible" - you still wouldn't want to use them in a hearth or anywhere else routinely exposed to such high temps. Did you look at some of the links I posted earlier in this thread?