Cracked slate hearth after new installation of woodburner...

[Pebbles112]

Installer advised lighting wood burner 48 hours after installation completed. The day after we lit it, we noticed a crack. We have a stove thermometer and it did not go above 200 C.
The crack has run from the edge of the hearth, between the legs of the stove and stopped 20 cm short of the opposite edge. The crack has grown longer, but seems to have now stopped.
It is a honed slate hearth 850 mm square and 20 mm thick.
The installer is saying we must have stood on the hearth and caused the crack and is changed his mind from initially the whole installation is to be re-done to it being our fault.
He has advised us to have the hearth repaired at our cost.
What do people think and where do we go from here? Thank you.

 

[BrotherBart]

To give posters more information for informed advise, Tonbridge is in the UK.

 

[begreen]

If the hearth was properly built there should have been no deflection even if one stood on it. Was the floor leveled first? Do you know how they constructed the hearth? In particular what were the substrates and how often was it braced? To be proper it should be stiff enough setting the framing at 12" on center, using 3/4" plywood and 1/2" cement board, but it would be questionable if set on studs that are 16" on center, covered with 1/2" plywood and 1/4" cement board.

 

[Heatsource]

a hearth should support the weight of both the stove, and the operator of the stove.
its like any floor, made to stand on.

the guy saying you standing on it is what broke it is silly

 

[JSoko]

I would think the underlayment and or the mortar was not installed correctly

I had seen the same issue on some tile where they did no screed the mortar evenly and just gobbed the mortar on causing a gap , thus the cracking

over here it is highly recommended to install concrete backer board as an underlayment

 

[English BoB]

To give posters more information for informed advise, Tonbridge is in the UK.

To give posters more information for informed advise, Tonbridge is in the UK.

Installer advised lighting wood burner 48 hours after installation completed. The day after we lit it, we noticed a crack. We have a stove thermometer and it did not go above 200 C.
The crack has run from the edge of the hearth, between the legs of the stove and stopped 20 cm short of the opposite edge. The crack has grown longer, but seems to have now stopped.
It is a honed slate hearth 850 mm square and 20 mm thick.
The installer is saying we must have stood on the hearth and caused the crack and is changed his mind from initially the whole installation is to be re-done to it being our fault.
He has advised us to have the hearth repaired at our cost.
What do people think and where do we go from here? Thank you.

Maybe they stood on it during the install. Whatever that sounds like a load of B/S , pursue them to replace, good luck

bob

 

[Squisher]

Well if you didn't stand on it, and you can look him in the eye and tell him that then that kind of makes his argument null and void. It's at that point that problems could arise. If you can honestly tell him you did not step on it and he says he thinks you're lying, I'd have a hard time with that. I'd let him know how unpleased I was with his work and position in the matter and if I was going to have to pay to have it fixed it certainly wouldn't be him I was going to pay to do it.

I also agree that it would be strange to think that you couldn't stand on your hearth anyways?

 

[firefighterjake]

Guy messed up . . . as mentioned slate -- whether on a hearth or as a floor -- should not crack with normal use (i.e. stove placed on it, person walking on it, etc.) Either the slate had a flaw or the guy installed it incorrectly.

 

[Pebbles112]

Thank you to everybody who has replied so far. It is very reassuring that people out there care.
The weight of opinion suggests that the hearth was not installed correctly. We also thought the hearth should withstand a person's weight... it is bizarre to be told not to stand on it.

Having looked underneath the square hearth, there is a circle of mortar which runs almost to the edge. The mortar is roughly 3/4" thick laid directly on a concrete floor. There is no construction.

We really want to our argument as watertight as possible, before we go back to the installer and this has really helped. Thank you very much so far. If anyone has anything else to add, please do as it is all so helpful.
We will keep you posted with the outcome.

 

[begreen]

Just a guess but it sounds like it might not have been leveled properly. Or perhaps the mortar did not cure properly in that area? As described one should be able to park an elephant there without issue.

Standing on the hearth is common and to be expected, especially for when a chimneysweep is working on the stove.

 

[jeffesonm]

any photos?

 

[revdocjim]

Unless you have a personal weight problem of epic proportions, how can he suggest that stepping on it would crack it? The stove weighs several times what most people do!

 

[FionaD]

Hi Pebbles. As everyone here has said, it ludicrous to suggest that you were at fault for cracking your hearth by standing on it.

I'm wondering about the thickness of that slate - 20 mm is less than an inch thick - that's half the thickness of my granite hearth, and mine is, I belive, pretty standard. Have a look around yourself, I can't see any slate hearths specs online that are that thin... The thinnest I found was 30mm and most seem to be 40-50mm.

Is the installer HETAS registered? Although they will be more interested in hearing about faulty stove installations, rather than poor workmanship and service generally, it may do no harm for you to tell him that you will need to contact HETAS about this matter if he is unwilling to replace that hearth.

Good luck and let us know what happens.

 

[Simonkenton]

"Laid directly on a concrete floor." Do you mean it is down in the basement and the entire floor of the basement is concrete?
Or is it on a floor in the house, which is made of wooden joists with plywood on for subfloor, and then concrete on top of that?

 

[Pebbles112]

Hi Pebbles. As everyone here has said, it ludicrous to suggest that you were at fault for cracking your hearth by standing on it.

I'm wondering about the thickness of that slate - 20 mm is less than an inch thick - that's half the thickness of my granite hearth, and mine is, I belive, pretty standard. Have a look around yourself, I can't see any slate hearths specs online that are that thin... The thinnest I found was 30mm and most seem to be 40-50mm.

Is the installer HETAS registered? Although they will be more interested in hearing about faulty stove installations, rather than poor workmanship and service generally, it may do no harm for you to tell him that you will need to contact HETAS about this matter if he is unwilling to replace that hearth.

Good luck and let us know what happens.

Thank you FionaD for your advice. I will check out the minimum thickness for a hearth. He said it was 20 mm.
Getting HETAS involved is a possibility...thank you for that.

 

[Pebbles112]

any photos?

 

[rwhite]

Is that carpet the slate is sitting on? Any pics with a larger overall view? You say you can look under the edge of the slate. If that is the case I'm guessing that the slate wasn't floated and laid properly, or the stove was installed before the mortar dried and it crushed the thinset making it uneven. This is all assuming that it isn't sitting on carpet.

 

[Pebbles112]

Is that carpet the slate is sitting on? Any pics with a larger overall view? You say you can look under the edge of the slate. If that is the case I'm guessing that the slate wasn't floated and laid properly, or the stove was installed before the mortar dried and it crushed the thinset making it uneven. This is all assuming that it isn't sitting on carpet.

 

[Pebbles112]

Hello rwhite. The installer had cut away a square of carpet to put down a mortar mix. This then was put directly onto the original concrete floor of our lounge. The slate was then laid on top with an expansion gap round the edges.
He since has said it is our fault as "someone as stood on the edge of the slate and caused it to crack."
We feel the same as all of you that this is ridiculous.

 

[Jazzberry]

Was he a licensed contractor or similar and do you have contractor laws there? Something like a Better Business Bureau? If it was in CA you could nail him. There should be some form of consumer protection against bad contractors since problems are so common.

 

[Pebbles112]

Was he a licensed contractor or similar and do you have contractor laws there? Something like a Better Business Bureau? If it was in CA you could nail him. There should be some form of consumer protection against bad contractors since problems are so common.

He is a licensed HETAS engineer in order to fit the stoves and has signed off our paperwork.
I am hoping we can resolve this amicably - otherwise yes we will need to involve trading standards.
Such a shame when it gets to that point. Love your post. Thank you.

 

[rwhite]

Makes sense now. I would almost bet that it was not floated properly (or too much thinset) and the stove was set prior to the thinset drying. That would cause the rear to go down and pull up on the front. In that case your installer is correct, his poor work created a situation that when someone stepped on it it cracked. Did the installer set the stove as well?

 

[Pebbles112]

Makes since now. I would almost bet that it was floated properly and the stove was set prior to the thinset drying. That would cause the rear to go down and pull up on the front. In that case your installer is correct, his poor work created a situation that when someone stepped on it it cracked. Did the installer set the stove as well?

Yes he installed everything.
Gosh thank you for this!

 

[rwhite]

Yes he installed everything.
Gosh thank you for this!

Makes sense now. I would almost bet that it was not floated properly (or to much thinset) and the stove was set prior to the thinset drying. That would cause the rear to go down and pull up on the front. In that case your installer is correct, his poor work created a situation that when someone stepped on it it cracked. Did the installer set the stove as well?

I meant to say "not floated properly (or too much thinset)" But you get the idea, his work likely caused it to happen. He "might" have even done everything correct up to the point of setting the stove, but if you put a 600 lb stove on a fresh float job before it dries, somethings gotta give. I would bet if you pull up that slate you'll find compressed mortar under the stove and "pulled up" separated mortar at the front.

 

[jtaves85mcss]

IMHO, rwhite and other previous posts have your answer on all counts. That crack clearly originates from the front leg of the stove, indicating problems with the install. Likely due to not leveling the floor and floating/screeding the mortar bed correctly. Or perhaps the mortar wasn't sufficiently cured and the weight of the stove caused the slab to deflect right in the middle of its length.

Just for clarity and confirmation did you observe the installer and can you describe the process used in completing the install?

For example, did your installer pull back all the carpet to one side of the room, then use some type of curbing to lay out the mortar bed with a level across the curbs first, screed the mortar bed off, then lay the slab, level it, lift it and back butter with just a portland cement mix and tamp back to level? Or did they simply cut the carpet, pour a bucket of mortar out and smear it around and then slap the slate on it? The former would likely have prevented the cracking and the later will increase the chances of a poor bed which will allow deflection and cracking. Any dips, hollows or voids under a slab that size and thickness will lead to problems.

That slab install should have sat for a minimum of one day and two would be much better before placing the stove.