Dark Patches on Granite

[ScotlandGranite]

Hey, hope you can help, apologies if this is in the wrong section, this seemed the most relevant area.

Have come up against a problem after installing 20mm thick granite sheets to surround an alcove that will contain a stove. The granite sheets are a light grey colour (not sure but can find out exact type/name), and they were installed by applying serveral patches of Gyproc Joint Filler (Gypsum based setting compound) to the back surface.

There are now very noticeable darker patches where the Gyproc was applied. They were installed almost two days ago, not sure if this is simply water being released as the compound sets, or worse that they have been stained. As far as I'm aware the sheets were not sealed.

Not sure whether the sheets should just be left to dry out, or if it's potentially a bigger problem. I can post up a photo as well if that helps.

Many thanks in advance!

 

[tpt]

if your lucky it will be moisture, dont seal it and leave it for a couple of weeks. if its staining from the back theres nothing you can do apart from replace anyway.

We would normally always push a customer to use a white tile adhesive for that kind of installation - the white part prevents staining. and it should be fitted using a notched trowel with total coverage, not dot and dabbed. Good luck!

 

[Richard C]

How close is the stove to the granite lining? Who advised to use Gyproc Joint Filler? It’s not suitable for tile/panel fixing &, like all Gypsum based products, will not withstand exposure to more than 49 degrees on a regular basis; sorry to tell you it will almost certainly fail in a relatively short time.

A quality Rapidset tile adhesive (BAL) will withstand 150 degrees & you should never dot & dab any tile/panel, let alone one exposed to high heat.

 

[ScotlandGranite]

Thanks for the responses, it's looking like advice should have been sought before this happened.

Hmm, the stove is going to be about about 200mm away from the panels, so your right the temperatures may well exceed that once the stove is going, but is hard to tell.

Got a heater inside will see if the patches dry out. Not sure if trying to remove the panels is even a sensible option, they are about a metre square, so can see them cracking into bits..?

 

[Richard C]

Thanks for the responses, it's looking like advice should have been sought before this happened.

Hindsight is such a wonderful thing but yes it always pays to research before you embark on something you may be unfamiliar with; there are all sorts of things that can catch you out with plastering & using the wrong materials around fires & tiling is another aspect altogether. Don’t be too hard on yourself, there are many “tradesmen” who seem to be completely unaware of even the basics let alone the stuff I know about, that’s why we get a constant stream of folks on this forum & in the media looking for advice after expensive failures.

Hmm, the stove is going to be about about 200mm away from the panels, so your right the temperatures may well exceed that once the stove is going, but is hard to tell.

I would say it’s a stone bonk certainty; I’ve measured temperatures into the high 90’s in the area & chimney breast around a multi-fuel stove & it was personal experience of failure that made me aware of what I now know & how I deal with them.

Got a heater inside will see if the patches dry out. Not sure if trying to remove the panels is even a sensible option, they are about a metre square, so can see them cracking into bits..?

Personally I would advise you remove them now while you easily can; being evaporative cure, the filler will still not be fully cured & it’s completely unsuitable due to the temperature restriction anyway.

The size of the granite panels can also be a problem around high heat output stoves. Hearths & surrounds for solid fuel appliances are rarely one piece, they are made up in sections (I usually use 600 x 300 x 10mm granite/stone tiles). If you have too large a tile/panel (& IMO one metre square is too large) they can crack due to different expansion rates caused by variation in temperature between the hottest & coolest parts of the panel.

If you give some details & even pics about the size the fire, details of the opening etc & what you want to achieve, I can give you detailed advice about the best way to proceed.

I would also advise you read through my standard stove blurb below, there may be further revelations awaiting you in the links;

------------------------------00000000000000000000000------------------------------

As this comes up so often, I’ve put together this generic post; read the links but not all may apply to you.

You can DIY a stove install but you need to understand the Building Regs (which changed in October 2010), submit a Building Notice & pay a fee. Your LABC will inspect &, assuming everything is OK, issue a compliance certificate; the BI may want to witness smoke & spillage tests. No compliance certificate may lead to difficulties when you come to sell your property; if cannot produce a compliance certificate in the event of a problem, your insurance company may invalidate your policy & reject any claim.

Lots of archive threads on this, & other things you have to watch out for, here a few links for you to read:
http://www.stovesonline.co.uk/stove_building_regulations.html
http://www.planningportal.gov.uk/uploads/br/BR_PDF_ADJ_2010.pdf
http://www.hetas.co.uk/public/certificates.html
http://www.solidfuel.co.uk/pdfs/buidling_regs_consumer leaflet.pdf
//www.diynot.com/forums/viewtopic.php?t=183614
//www.diynot.com/forums/viewtopic.php?t=211524
//www.diynot.com/forums/viewtopic.php?t=242738
//www.diynot.com/forums/viewtopic.php?t=224751

& some more sobering just in case you think it’s all a load of old tosh:
http://www.solidfuel.co.uk/main_pages/news.htm
http://www.dailymail.co.uk/news/art...wood-burning-stove-leaks-carbon-monoxide.html
http://www.eveningnews24.co.uk/news/warning_over_heaters_after_norfolk_couple_s_death_1_811099

Also get at least 3 quotes from local independent HETAS installers:
http://www.hetas.co.uk/nearest_member

You might be pleasantly surprised & you should ask yourself if you really want all the hassle & risk getting it wrong; climbing onto the roof with an 8M stainless steel snake on your back is not for the feint hearted!

__________________


Read more: //www.diynot.com/forums/viewtopic.php?t=267604&highlight=#ixzz1I6jlicut

 

[ScotlandGranite]

Legend thanks Richard,

The project has been carried out taking into account the building code in terms of dimensions/safety etc, but as you can tell myself and the tradesmen clearly lacked knowledge of adhesives/sizing etc for the finishing!

Hopefully have inserted an image below, so have three large 20mm thick granite sheets (1 off 950x1150mm, 2 off 700x1150mm). We did split the hearth into smaller sizes in anticipation of cracking with the heat, but seems we should have gone the same way with the slabs.

So do you think trying to pry them off and cut them down to size is the best option? Not sure how good a hold the filler will have, may be a very nasty excercise..

If the patches were to fade we could mechanically fix the sheets and leave them as is, but as you say may lead to a breakage given the size..

//www.diynot.com/network/ScotlandGranite/albums/10389/39093[/img]

 

[tictic]

cant seem to look at your pics...but you will have bleeding through the granite...patches etc....


they are f e c k e d mate...sorry....

 

[Richard C]

tictic; the link doesn’t work but you can see the pic in the OP’s profile album

The blotches are moisture staining caused by water in the filler leeching through the porous granite & if you use the wrong (contrasting) colour tile adhesive, it can permanently stain the tiles as tictic suggests. As you’ve not used adhesive but Gyproc joint filler (which I assume was either white, grey or pink) you may be lucky & the staining may fade & hopefully disappear altogether.

As for what to do next; I can see why you’re reluctant to start prying the slabs off the wall & the way forward (assuming the stains disappear) may be to add some mechanical fixings to see how they hold out but, again, you must allow for expansion including around the steel fixings themselves. The problem is that the gypsum based dabs of joint filler will probably crumble & disintegrate behind the granite slabs under the effects of the heat & without any support; the slabs may start moving around. As far as the size of the slabs goes; if you decide to leave them in place, you can only hope for the best.

 

[ScotlandGranite]

Thanks again guys, is such an asset being able to speak to someone with direct experience.

Yeah I can see prying them off being a nightmare, either way it looks like the slabs are likely to break. So will probably first progress and try and get rid of the patches, then get some fixings that allow plenty movement for when the gyproc fails. Might as well leave the slabs and see if they crack, can replace with something more appropriate if that time comes.

Have been trying to educate myself on granite over the last few days, the gyproc was pure white so hoping it's simply water. Am going to attempt a poultice to remove the moisture, similar to problems with water stained granite countertops.

I'm now thinking our hearth slabs are also too large, so may put something between the feet and the hearth to isolate the heat somewhat and allow a bit of stove movement. Any idas of something appropriate?

 

[Richard C]

Granite is fine as long as you break it into small sections immediately in front of the fire. I don’t make up hearths only surrounds; I buy slab hearths ready made which are usually split into 3 equal sections, with the centre section split into further smaller sections similar to this:

View media item 39112
This one is cut away for a fire basket but they come in many different patterns & sizes & you can even have them custom made; usually from 20mm granite sections set into concrete & power polished so all you see are lines in the surface.