Granite Countertop Underlayment

[craigwatanabe]

Re: Granite Countertop Underlayment

Huh? The countertop only provides support for what's on top of it. The cabinets are self supporting, as well as supporting the countertop. The countertop lies dead on the spacer frame, which lies dead on the cabinets. That is to say, the only forces on the countertop and frame (or underlayment) are from gravity and both are supported by the cabinets alone. There are no sheer forces in this situation [unless you're imagining a countertop with a large, unsupported overhang (which is NOT recommended)].

I will tell you point blank: Granite countertops need to be laid down on a continuosly flat underlayment and 3/4" ply or solid wood is an absolute must. Sheer forces include cabinets mounted to the walls and floors that shift due to floor or wall movement. The word sheer in this case implies lateral forces which has nothing to do with gravity.

Granite has veins that are their inherent weakness and if laid on an uneven surface varying in as little as a 1/16th", even a 40lb load will crack that 1" thick granite slab. Heck even the weight of itself can cause cracking if not laid correctly.

Sheer strength support is for lateral movement. But because of granite's high tensile strength, any lateral movement up to the limits of it's flexpoint (which is virtually 0&#37 will cause it to shatter at it's weakest point which could be any one of a number of veins running in any given direction of that slab.

If you want to (and it seems you have already in several instances) go ahead and don't use an underlayment but for the reasons stated above, that will be a sad mistake. I've spoken to many installers and ALL of them indicate the imperative use of a 3/4" underlayment when laying down Granite slabs.

Also it has been recommended to use treated plywood when laying down separate slabs or tile due to grouting. Grouting is water-based and is also porous (just like marble). Because of that water will seep thru the grouting and ultimately pool on the underlayment. Non-treated wood will retain moisture and rot. Once wood is wet or rotten it attracts nesting ants and roaches.

Regarding the issues of gassing, your wooden home is constructed almost entirely of Hi-bor treated wood (not too many places allow the use of Walmanized green wood), from the sub-flooring (if on post and pier), to the exterior walls, headers and studs to the trusses and pearlings.

Building codes here in Hawaii demand the use of treated lumber in all new home construction not only because of it's insect and rot resistance but because treated lumber takes longer to burn than non-treated lumber.

If you have desks, entertainment centers and other furniture made of pressboard (as in most cases) MDF underlayment is a moot point. BUT any underlayment is better than none at all.

Roger check your PM

[kani-lehua]

Re: Granite Countertop Underlayment

okay. so i took a look at some cabinetry at home depot, iwilei, yesterday. it didn't look like it was solid wood?

[escondido100]

Re: Granite Countertop Underlayment

i have intalled all the brands of cabinets at Home Depot and Lowes...... the term solid wood is misleading.....usually the face frames and doors are "solid " wood. the boxes are made from a variety of materials...... the least expensive ones are mainly particle board....you have to pay extra for all plywood construction.....and even then they sneak in some masonite and PB.
the secret to getting good cabinets is in the installation... there are many shortcuts that may lead to poor quality.... an experienced carpenter will know what details are important......in the year that i have been an installer for HD i have seen many nightmares of homeowner installs as well as carpenter installed cabs..... a good framer does not a finish carpenter make....however a furniture maker will probably never finish the job.... there is some middle ground.....
I have torn out PB cabs that have been installed less than 5 years.....they usually just fall apart once a few key components have been removed (thats my trade secret)good kitchen cabs should last about 15 years...... and they will if they are installed properly.....and yes the top of the cab provide alot of shear strength to the box. you should always have some type of structural top. there are ways to get that strength without it but again why give all the trade secrets away......
one thing i will put out there is based on my experience.(30yrs).... the best ready made cab available at HD or Lowes is "kraftmaid" with the upgrade to all plywood and NO melamine. there are still some cheesy factors with kraftmaid but from an installers point of view they are he best.the best route is custom local built but you will pay and wait for that option.

[craigwatanabe]

Re: Granite Countertop Underlayment

...the best ready made cab available at HD or Lowes is "kraftmaid" with the upgrade to all plywood and NO melamine. there are still some cheesy factors with kraftmaid but from an installers point of view they are he best.the best route is custom local built but you will pay and wait for that option.

To me custom is the only way to go if you want quality and longevity in your cabinets, that way you know what's going into the construction and how it's being built. I leave the pre-fabbed units for garage storage. Kitchen upgrades cost a lot but will reward you with a huge return on investment come assessment time, why go cheap on cabinets or installations.

In an open house, prospective buyers will instinctively look at the Kitchen then the Master bedroom as their first impressions of a place to buy. And when in the kitchen they look at the countertops and faucet hardware then appliances.

When I check the integrity of a granite counter top (especially an island) I'll fill a glass of water and set it on it's top. Then I'll go to the side and give the side of the countertop a good tap with the open palm of my hand. If I see any ripple in the glass of water, I know no underlayment was used and I tend to shy away from these homes.

If you can spot a poorly crafted countertop installation with this simple test, I guarantee you will find many more surprises in the general fit and finish of the home build.

Working at Home Depot's Hardware department, I work with hundreds of general and sub contractors. A lot of them are honest but occasionally I will find those fly-by-night contractors who come in from out of state, buy inappropriate tools, fasteners and construction material for their builds.

Because "Bright" or non-galvanized nails are about half the price as the standard "Galvanized" 16-penny framer nails, some will opt on the cheaper nails. Hawaii's codes demand the use of Galvanized 16-penny nails for rough-in work framing because of the use of treated lumber.

On T-111 exterior trim the standard is the 8-penny boxed galvanized nail. I cannot believe how many carpenters don't know that and use inferior fasteners on home construction here. Come inspection time, these builds will fail and won't pass the "Final" inspection by the county Building Department.

I've heard of homeowners who've paid contractors and have since left only to find out the construction was below code. The homeowner is then faced with the reality of having to pull out all nails (despite the interior walls and exterior facades laid in place) and having to rebuild the rough-in (hence make sure you have a box of Manapua just in case)

Oh the horror stories I hear on a daily basis! Beachboy I'm sure you can relate to some of these.

If you feel your contractor is using sub-grade construction techniques, there are "Code-Check" flip books we sell at Home Depot near the Pro Desk that can help builders identify what meets code and what won't.

YOU WILL BE SHOCKED AT WHAT IS CODE AND WHAT ISN'T. I had an owner-builder buy a 32-inch wide stand up fiberglass shower stall from us because it's the only stall that would fit thru his bathroom door opening (walls and trim up already). He was told by the county building inspector that his shower stall was too narrow and he needed a 36-inch wide stall instead. Had he told the associate this was for a new build instead of a smaller remodel we wouldn't have sold him the narrower stall, but as an associate we cannot quote building codes to our customers. It is then up to the customer to make sure of what they need to pass code. I will generally hint at codework but will not state it to our customers or else I'll get disciplined.

He ended up having put in a more expensive custom built stall because it had to be fabricated within the bathroom to facilitate building code.

Another customer had to rip out and reframe his casement windows because the window sills were 1/2" too high from the interior floor.

Then there was the guy who ran 14-gauge Romex wire throughout his home for ALL electrical circuits because 14-gauge was cheaper than 12-gauge. Upon inspection he had to rewire all 20-amp and higher circuits.

Outside and shower "canned" electrical lighting demand the use of sealed enclosures.

Codes codes codes, and many times people won't pass inspection because of their lack of understanding of what they are and why they're put in there.

You need a fireproof backsplash for stoves against walls, GFCI for all electrical outlets exposed to water (such as in kitchens, bathrooms and all exterior plugs around the home).

You need self closing doors on all entryways from enclosed garages to the interior of a home.

On all new builds wired in with battery back up smoke detectors are required.

And that's just for standard builds. If you're building for ADA (Americans with Disabilities Act) compliancy, there's a ton more codes to adhere to such as countertop height, lever style door hardware, grab bars, hand railings and ADA compliant wheelchair ramps.

There's so much code out there it's almost mind-boggling. What seems like a safe build could actually be out of compliance with county building codes.

[i-hungry]

Re: Granite Countertop Underlayment

Good thread on home improvement. I knew some of the information discussed but learned lots of details.

Just would like to add to the recommendation for the plywood underlayment. Yeah I realize I'm beating an already dead horse. But also consider the sink moreso for the vanity sink. The underlayment has to be cut to fit the sink through so the support is less than maximum. Of course the weight of the sink add to the total weight of the countertop. With that said, I wouldn't consider plywood underlayment as overkill. Its just enough.

On the topic of MDF, I thought the formaldehyde problem was more related to the modification of the material. It would be way more hazardous for the person who has to cut or sand the MDF boards.

I think its weird that they put MDF as an underlayment. I don't think I would change it. Just try to make sure the water doesn't leak into it.