2cm 1 piece granite fireplace surround Cracking. HELP

[granitenazi]

i installed a 2cm granite fireplace surround over a gas fireplace. i set it with a bonstone epoxy over drywall and steel studs. this is a commercial 35 floor building. i did not adhere to the firebox itself. there is a 3/16" gap between the firebox and the back of stone.

when they fired up the gas fireplace about an hour into it the granite cracked along a faint vein, and continued to spread apart. but only on the top section. the flame was shut off and crack did not continue. 3 days later fireplace was started and ran for 2.5 hours and stone spread some more. a total of 1/32" . still no cracks at bottom half.

i cannot figure out what would cause this. the stone is not even hot to the touch.

is there anybody with some experience with this. or is there a certain way i should have installed this i am not aware of.

HELP please.

Mike Baum
262-391-1058
waukesha,wi.

[Dan R.]

The heat will cause the stone to want to expand, regardless of the substrate. With square corners, the inside cut is the weak point. Cracks will generally emanate from this area.

Heat rises, so that is why the top will crack and not the bottom.

It is thermal expansion. It is easy to set in one piece but problematic when introduced to extreme heat.

[flav]

We had a similar problem with a customer. The first time we left 3/16 or 1/4" all around but it cracked. I assumed that the steel fire pit which was inside polished cutout expanded more than 1/2" or so to force the granite to crack.
We remade the piece for the customer but suggested that they top mount the fire pit, ideally not touching the granite. That is, to support it from underneath so that the steel lip was above the granite (hot air rises) so that the granite will not be super heated. If I recall correctly, we didn't hear back from the customer so I assumed that fixed it.

[flav]

Just re-read original post and see that you are dealing with traditional face fireplace. Our issue was with an open concept fire pit style.

[Steve A]

Using a more flexible bond from the stone to the sub-strate would be recommended as well. The heat will affect all the materials differently, the stone, the steel studs and the dry wall.

[Mark Meriaux]

Using a more flexible bond from the stone to the sub-strate would be recommended as well. The heat will affect all the materials differently, the stone, the steel studs and the dry wall.

x2

[Rick George]

I have done this type of install and haven't had this issue but now it scares me. I think Steve and Mark are onto something with a more flexible adhesive. We have always used TEC Superflex for fireplace installs.

[Stone Dude]

. there is a 3/16" gap between the firebox and the back of stone. .

that is your problem. The heat is concentrating in that area. We've had it happen to us. you can't leave any gaps where the smoke or heat can collect.

[Mark Gamble]

So would it be as simple as caulking to create a good seal? Or is it the gap itself causing the issue?

[Stone Dude]

I don't think caulking it would do it. I think the surround needs to be taken out and re-done to make the gaps as tight as possible, then sealed with a urethane. Sika Flex would probably work, or Last Patch from Bonstone.

I have seen this issue a few times, and it's always been the same reason.

Heat distribution needs to be as equal as possible. If one part of the stone gets hot, it needs to be able to travel and dissipate slowly. The problem is edges. Heat will escape from edges, corners, etc. edges where the stone turns from left to right, or vertical to horizontal should be tight and smooth as possible. This will allow the heat to spread through the stone and kind of dissipate slowly , as opposed to having one piece with a gap, where the heat will leave from that edge, but also build up behind the surface.

I'm not explaining it very well.

[granitenazi]

thanks guys. but after further contemplation and many different discussions. i found that the basic problem with this is that the installation should have been done with a mechanical anchor. and not a solid adhesive of any kind. meaning even silicon would not have worked if any were applied to the area around the top of the fire box. the crack has not grown since the first start up but it does open up every time the fireplace is used. which would lead me to believe that the structure behind does move slightly. Also to the idea of caulking there is 2000 deg fire caulk in the joint. so i believe tight or not this would still happen if a stiff adhesive was used.

long story short use mechanical anchors, of course that was the way i was going to do it initially but of course i went against my gut because i was running out of time. but also even if this is done i think the thickness of stone is also very important. the thicker the stone the better. 2 cm is not a good idea in this case.

some of this info i did get from the nice people at Marble Institute of America. very helpful.

i hate being humbled by something im supposed to be good at !!


thanks everyone.

Mike

[Dan R.]

IMO, mechanical anchors would yield similar results (cracking). The thermal expansion of the granite itself appears to be the main issue. The crack never got any bigger after the initial break, because the granite never got any hotter, therefore never expanded any further.

The solution would be to install in pieces, rather than a one piece surround. If the legs and header are separate, then the pieces can move without causing stress at the corners.

[Stone Dude]

Mechanical anchors are not going to eliminate the cracking. if anything, when installed identically to the way it is now, mechanical anchors will make it worse. The fact that it is expanding and contracting with use is allowing a little cushion. Make it super rigid and what do you think will happen? The problem is heat distribution, not the mounting system.

[Kowboy]

Mike:

The cut and unfinished edge of the stone has microscopic stress risers. When heated, the stone begins to cleave at one then spreads. This happens in solid surface, stone, and metal.

Solid surface fabricators are required by manufacturers to radius all cut-out edges to 1/16" and abrade until all tool marks are removed to eliminate stress risers.

I would pull the piece and refabricate with all cut edges radiused, all tool marks removed, and even polish the unexposed edges just to make sure. Reinstall with dime-sized dabs of silicone every 12" or so; no mechanical fasteners.

I'm providing a link to substantiate my theory,http://www.badgermetal.com/ml-vs-polish-stresses.htm, but last Wednesday at Steve's Polishing Pro Systems class at Braxton Bragg in Knoxville, TN, I put a 3" crack in a 1/2" thick Absolute Black practice tile from the heat of polishing alone. Of course, it started from the raw edge and went in. In all fairness, I shattered my pane of glass too.

Joe

[Dan R.]

How can removing surface tool marks effectively address the inner structure of stone? Plastic, metal and stone all have very differemnt properties and lumping them into a generalization is wreckless and irresponsible, IMO.

[tim farr]

It wouldn't be the first time he's been reckless and irresponsible

[Stone Dude]

Mike:

The cut and unfinished edge of the stone has microscopic stress risers. When heated, the stone begins to cleave at one then spreads. This happens in solid surface, stone, and metal.

Solid surface fabricators are required by manufacturers to radius all cut-out edges to 1/16" and abrade until all tool marks are removed to eliminate stress risers.

I would pull the piece and refabricate with all cut edges radiused, all tool marks removed, and even polish the unexposed edges just to make sure. Reinstall with dime-sized dabs of silicone every 12" or so; no mechanical fasteners.

I'm providing a link to substantiate my theory,http://www.badgermetal.com/ml-vs-polish-stresses.htm, but last Wednesday at Steve's Polishing Pro Systems class at Braxton Bragg in Knoxville, TN, I put a 3" crack in a 1/2" thick Absolute Black practice tile from the heat of polishing alone. Of course, it started from the raw edge and went in. In all fairness, I shattered my pane of glass too.

Joe

I'm sorry, but this doesn't apply to stone and saw cut edges like metal. metal is a far more efficient conductor of heat than stone and it applies in that sense. it has no affect here. Webbing, casting lines and burs can affect heat distribution on metal, but it would take a lot more than that in a piece of stone to cause it to crack like what is being discussed in this thread.

you breaking the piece of black absolute is exactly what I am talking about here. Concentration of heat in one area, in this case friction from a diamond pad (most likely) is not able to travel through the stone evenly. the outside areas of where you are working stay cold, the difference in temperatures reach a certain point and the piece snaps in half. I watched Scott McGourley do it at Stone Expo several years ago.

Same thing happens if you don't cap fire pits properly. Heat can build on the inside edge, or get underneath in certain spots, the outside edge stays cold, and pop.

The grooves left from a diamond blade saw are not significant enough to have any bearing on this issue, in stone. In metal, possibly.

[Kowboy]

How can removing surface tool marks effectively address the inner structure of stone? Plastic, metal and stone all have very differemnt properties and lumping them into a generalization is wreckless and irresponsible, IMO.

Dan:

It isn't the "inner structure of stone" that's the problem. It's the micro fractures from tool marks on the outside that's contributing to the problem here. Of course plastic, metal, and stone have very different properties, but they all share micro fracturing.

It's "reckless", not "wreckless" by the way.

Joe

[Kowboy]

This is from page 4 of the Trendstone Fab Manual:

11) Avoid “Stress Risers”, (i.e. gap, sharp angled inside corner etc). Stress risers weaken the overall performance and eventually can cause a crack in the quartz countertop.


http://www.projectstone.com.au/ws-conte ... _Guide.pdf

Joe

[Dan R.]

Kow,
That is completely different from tool marks.
Thanks for the grammar lesson.
Your tooling supposition is still incorrect.

FYI: Kowboy was booted from the member's area of this website a while ago. He raises his little troll head from time to time, but is a harmless for the most part.

[Jeff H.]

[Curtis R. Marburger]

FYI: Kowboy was booted from the member's area of this website a while ago. He raises his little troll head from time to time, but is a harmless for the most part.

[Stone Dude]

This is from page 4 of the Trendstone Fab Manual:

11) Avoid “Stress Risers”, (i.e. gap, sharp angled inside corner etc). Stress risers weaken the overall performance and eventually can cause a crack in the quartz countertop.


http://www.projectstone.com.au/ws-conte ... _Guide.pdf

Joe

Joe, you are citing a Quartz manufacturer's recommendations, yet you are making up your own stuff. What you pointed out that was contributing to the failure is not mentioned in the article you cited. Not only that, stress risers do not always translated to heat distribution issues.

If there were sharp edges significant enough to have any impact on the heat distribution, they would actually help. Read my prior posts. This is how heat sinks work. Heat will leave from the sharpest or thinnest point. Vents in disc brakes, head sink and vented differential covers on trucks, those finned covers inside computer components? They are there to ensure there is no overheating, not the other way around.

You also cited a manual from a product that is manufactured under stress. Granite can take a lot more than ES.

[szw21]

those finned covers inside computer components?

Cam a comment on this - my understanding is that the fins serve to increase cooling efficiency by increasing the contact area with the surrounding air - if you take the fins and imagine them flattened you can see that if you add the vertical area sections they are a lot more than the flat area of the chip on which the heat sinks are sitting and that increases heat transfer. So for the chip example at least that is the purpose of the fins - not that all the heat transfers better out of the ends of the fins.

Same concept with other finned components such as radiators, ac condensers and evaporators etc.

[Stone Dude]

those finned covers inside computer components?

Cam a comment on this - my understanding is that the fins serve to increase cooling efficiency by increasing the contact area with the surrounding air - if you take the fins and imagine them flattened you can see that if you add the vertical area sections they are a lot more than the flat area of the chip on which the heat sinks are sitting and that increases heat transfer. So for the chip example at least that is the purpose of the fins - not that all the heat transfers better out of the ends of the fins.

Same concept with other finned components such as radiators, ac condensers and evaporators etc.

you're right, but with metals like aluminum that conduct heat extremely well, the heat will leave the thinner areas faster because it can move through it quicker. That's what I remember at least. But you're right on the surface area, I forgot about that entirely.