Granite Benchtops Information Required

[stemail23]

The background:

We're in the process of installing a new kitchen. The cabinets are standard water resistant particle board. The flooring will be ceramic tiles layed on James Hardie ceramic tile underlay on top of yellowtongue over timber joists. The kitchen is a U shape, approximately 3m across the back by 2.5m on each side. There will be two cutouts for the sink and cooktop in the benchtop, each in the 800-900mm width range. The benchtop that we are considering is "Uba Tuba" granite.

A few questions about the granite benchtops we want to install:

1) How are the cutouts in the benchtop normally managed? It occurs to me that the two approaches would be to either cut a single hole in the center of a single large slab, or to simply cut a slab in half, as it were, and then match appropriately sized granite spacers front and back of the newly formed hole. The second method would obviously result in visible seams at the corners of the cutout, but the reason I bring it up is:

2) One of the stonecutters I've spoken to about the job refuses to give me a quote for 20mm benchtops. His claim is that 20mm granite is dangerously prone to cracking at the corners of cutouts (especially on a kitchen layed on a timber flooring substrate, as opposed to a concrete slab) and that he will only quote on 30mm or 40mm stone. Nobody else has given me this warning. The reason I'm particularly suspicious of the advice is that the suggestion that 40mm top might alleviate the problem, given that a 40mm top is simply a 20mm surface with an extra 20mm edging strip across the front, I can't see how this would help. The question is then, Is this a genuine warning, or is this guy simply trying to charge me extra by pushing me to get thicker stone than I actually want?

The two questions are related, because it strikes me that if a cutout is manufactured such that there are cut joins at the corners of the cutout, then it is these that might potentially fail, a much simpler fix down the line than having to replace a slab that has a genuine crack which has propagated from the weak point at the corner of a cutout hole.

3) In addition, we want a raised granite servery on one side of the kitchen that will be approximately 300mm wide atop a 1150mm high, 110mm wide stud wall. The overhang will be mainly on one side, with only about 20mm overhang on the other side. Is 20mm granite sufficiently robust to handle this design alone, or should the design include some extra surface beneath the proposed granite top? If so, what sort of design should I be looking at?

All suggestions, observations and advice appreciated.

Cheers,
Steven.

[HappyHammer]

1) How are the cutouts in the benchtop normally managed? It occurs to me that the two approaches would be to either cut a single hole in the center of a single large slab, or to simply cut a slab in half, as it were, and then match appropriately sized granite spacers front and back of the newly formed hole. The second method would obviously result in visible seams at the corners of the cutout, but the reason I bring it up is:

Normally they'd be cut on-site by the installer as a single hole not two halves. Lots of dust:eek:

2) One of the stonecutters I've spoken to about the job refuses to give me a quote for 20mm benchtops. His claim is that 20mm granite is dangerously prone to cracking at the corners of cutouts (especially on a kitchen layed on a timber flooring substrate, as opposed to a concrete slab) and that he will only quote on 30mm or 40mm stone. Nobody else has given me this warning. The reason I'm particularly suspicious of the advice is that the suggestion that 40mm top might alleviate the problem, given that a 40mm top is simply a 20mm surface with an extra 20mm edging strip across the front, I can't see how this would help. The question is then, Is this a genuine warning, or is this guy simply trying to charge me extra by pushing me to get thicker stone than I actually want?

I had 40mm (20mm strip around the edge on my counter tops and I they were still ####ting themselves when they lifted them into place, they only have to twist slightly as they're lowered and you have a nasty crack or it breaks and they drop the lot on the floor. The 40mm edge looks much better than the 20mm IMHO. This was on a timber substrate floor, although they didn't recommend the 40mm we chose it.

3) In addition, we want a raised granite servery on one side of the kitchen that will be approximately 300mm wide atop a 1150mm high, 110mm wide stud wall. The overhang will be mainly on one side, with only about 20mm overhang on the other side. Is 20mm granite sufficiently robust to handle this design alone, or should the design include some extra surface beneath the proposed granite top? If so, what sort of design should I be looking at?

I don't think the granite would break it would be more about the strength of the adhesive and your stud wall.

HH.

[HappyHammer]

Welcome to the forum BTW Steve.

HH.

[b1ueshift]

I had granite benchtops installed recently, having built the carcasses myself first. The granite seems quite strong, but supporting it is an in-exact science.

The supplier persuaded me to install a melamine base over the entire area over the top of all the carcasses to support the granite - the maximum overhang of unsupported granite is less than 50mm. The sink cut-out occurs at a join where two slabs of granite form a corner. Only one of the slabs has a cut-out on it's end which was easier for the supplier to cut than a hole in the middle of a slab. I reinforced the fingers of granite in front of and behind the sink with 90 x 35mm pine beams under them fastened to the carcasses. The supplier advised that the front finger of stone was most critical because people lean on it sometimes.

None of the suppliers I talked to advised against 20mm granite and I have seen it in another kitchen as well. Having said that, a double width bullnose definately looks better and would be stronger, but it's more expensive.

[HappyHammer]

- the maximum overhang of unsupported granite is less than 50mm.

Not sure about that b1ueshift. We had a kitchen island with approx 2.2m x 1m lump of granite. It had an offset hole cut within it for a 900mm cooktop and had a overhang of about 20mm on one side and about 200mm on the other so that we could tuck barstools under it. This was 20mm granite with a 20mm bullnose.

Also none of our carcasses had solid tops and nothing moved or broke. I think he might have been over compensating the surface area needed to glue these things down unless your carcasses were made of thinner material than he is used to.

HH.

[b1ueshift]

Not sure about that b1ueshift.

I'm not saying that's what should be done, only that's what I did. My installation probably has some overkill.

Anyway for $2000 worth of bench tops it seemed like a good idea to support it well.

[HappyHammer]

Anyway for $2000 worth of bench tops it seemed like a good idea to support it well.

True.

HH.

[stemail23]

Cheers for the comments guys. If anybody else is reading this then I'm keen to get as many opinions as possible, so please post. I'd be particularly interested to hear from anybody with experience of 20mm surfaces without the extra edging to bulk the profile out to 40mm and any problems you may have had.

I'm going to check with all the fitters I've already had quotes from and see what sort of installation they are proposing as regards extra support for the benchtop between the granite and the cabinet carcass. I suspect that the standard process is just to dump the granite down directly on top of whatever cabinet top surface happens to be there after the kitchen has been fitted, in which case I may engage in a little extra reinforcement of the cabinetry myself before the benchtops are installed to provide a more rigid surface for the granite.

[HappyHammer]

Cheers for the comments guys. If anybody else is reading this then I'm keen to get as many opinions as possible, so please post.

stemail23 thinking... "These two haven't got a clue I wish someone who knew what they were talking about would answer my post."

HH.

[stemail23]

My theory is that everything is just an opinion, there are no absolute answers. The opinion of an expert might be worth more than that of the average Joe, but it's still just that, an opinion, not an absolute truth, so I am interested in everything that anybody has to say, all comments help to illuminate the big picture.

Cheers guys.

[b1ueshift]

My theory is that everything is just an opinion, there are no absolute answers.

Very philosophical stemail. I would say that the best way to tell for sure what methods of support work well is to go into a laboratory with a test rig to simulated kitchen benches and test them by putting weights on them, dropping stuff on them, simulate couples getting passionate on them (it does happen), simulate the floor moving and see what happens then write up the results to share your findings with the world.

Since I doubt anyone has done this, the next best source of info is anecdotal information which is another way of saying find out what people recon.

[Pulse]

Interesting post this, anyway, my opinion, is that if a tradesman gives good advice then listen. Granite is usually cut in-situ, with the hole cut to size. Other option is to go with someone else then tell them they "told you so" when it cracks...

Cheers
Pulse

[arms]

sorry for this guys ,but seeing that this is in my life zone i thought that i should respond ,
granite being a natural product was subject to the forces of nature when it was cooling from molten rock to solid form and can have flaws and other defects in its body that are unseen until to late ,whether its 20 or 40 mm thick is irrelevant as any good stonemason in doubt will pack the top up with megapoxy and let it set if in the slightest doubt as to the character of the stone ,which brings me to the cabinets ,if you are using stone then it is vitally important to make sure that the cabinets are installed perfectly level ,this will help but only if the stone is flat ,the stones cutouts are done on site in situ ,i have granite on my kitchen (sorry HER kitchen) at home that i installed myself ,but before you guys think its easy remember that i have 25 years seeing others do it !

[journeyman Mick]

I've worked with a couple of different local stonemason companies. It may be just a regional thing, but four different companies do it, so maybe not. Usual practice when using 20mm tops is to glue stright onto tops of cabinets, rails etc. When using 40mm (or rather 20mm with a doubled edge) they all specify that they want sheets of 19mm ply fixed over the tops of the cabinets. This is to pack the top up so that the overhanging 20mm lip won't foul on the doors. Possibly what your tradesman meant (without articulating it) was that as the 40mm top would be fully supported it would pretty much rule out any possiblity of cracking due to floor flex. As others have said, usual practice is to do cut outs in situ (much dust )


Mick

[johnc]

This is not really adding much, but a solid flat base will go along way. It really is very hard to spot some flaws in granite until you hear the snap. 20mm leaves little strength in big sheets and the material is very dependant on what is underneath to prevent cracking down the track. Granite unlike marble will not readily sag or bend, is brittle in other words so flexing will snap the material. Timber floors or rather stumps can move and sag which simply means over time a saging floor could write off the bench top. Sticking to a solid ply top, making sure the cabinets are dead level, going for the 40mm edge all must help lower the risk of failure in the future.

Granite needs to be looked after to an extent, which I guess means no tap dancing or dropping of heavy pots or placing pots straight from the oven. However it is attractive, and holds its shine and very nice in a kitchen. We have a nice piece of green material in an ensuite with an oval hole polished on the inside and a porcelein bowl glued from underneath and it is not on ply but rests on the carcase uprights. But this is a very small piece, and not a large area such as a kitchen bench and we can get away with it.

John.