Granite Countertop Underlayment

[Beachboy]

PArticule board, MDF, plywood, or marine plywood.

which material would you want as your underlayment to support your granite counter tops in both kitchen & bathrooms? I need to know why you'd use one material over the other too.

I was under the impression the marine plywwod would be the best avenue to take with regard to moisture in the islands.

Do any of you have MDF stories, good or bad with regard to using it as an underlayment?

[craigwatanabe]

Re: Granite Countertop Underlayment

PArticule board, MDF, plywood, or marine plywood.

which material would you want as your underlayment to support your granite counter tops in both kitchen & bathrooms? I need to know why you'd use one material over the other too.

I was under the impression the marine plywwod would be the best avenue to take with regard to moisture in the islands.

Do any of you have MDF stories, good or bad with regard to using it as an underlayment?

No way with particule or MDF. At the least use treated plywood. You can go with marine ply but I've seen people use the green hardiboard as an underlayment simply because it's the best suited for that application. Hardiboard is basically cement board with a lot of fiber. Green Hardiboard is used as a backing behind tiles in showers and behind backsplashes in kitchens. It will stand up to water or moisture better than plywood.

You can find green hardiboard in the flooring department at Home Depot.

[salmoned]

Re: Granite Countertop Underlayment

Underlayment! What a novel idea, but why? I've always just used a framework as a spacer for the countertop (to achieve the desired height above the cabinets). Are you laying granite tiles?

[craigwatanabe]

Re: Granite Countertop Underlayment

Underlayment! What a novel idea, but why? I've always just used a framework as a spacer for the countertop (to achieve the desired height above the cabinets). Are you laying granite tiles?

It's always recommended to use an underlayment for kitchen counters especially something friable as granite for added strength so you don't accidently crack that expensive countertop.

[alohatim]

Re: Granite Countertop Underlayment

I agree: Treated plywood. Even though hardiback is waterproof, I don't think it would support weight horizontally like plywood. It is my understanding that the glues used in most plywood these days don't breakdown in water so marine plywood is unnecessary.

[Beachboy]

Re: Granite Countertop Underlayment

Underlayment! What a novel idea, but why? I've always just used a framework as a spacer for the countertop (to achieve the desired height above the cabinets). Are you laying granite tiles?

no, granite slabs! What is happening is I'm pissed off with the work at my home. After agent convinces me to upgrade both bathrooms & kitchen with granite slab counters. I find out her builder used MDF for the underlayment!! This just look like another form of pressboard/particule board to me. I'm worried sick about what moisture is gonna do to it in due time!
Seems to me that having granite counters supported by particule board is defeating the purpose of having quility work.

[Composite 2992]

Re: Granite Countertop Underlayment

MDF is pretty dense but is about as water resistant as cardboard.

Plywood is a lot better option. The main difference between conventional plywood and marine grade is that there's no voids in marine grade. Of course the glue used between the plys has better water resistance, too.

However, notice that marine grade ply is never treated. It's to help ensure that polyester fiberglass resin will adhere well. Apparently fiberglass resin generally doesn't adhere well to treated lumber. So while marine grade plywood is definitely more solid, it's also more vulnerable to termites.

So I'd recommend treated plywood. To support the load, plywood works best when oriented edgewise.

Also, whenever carrying stone countertops, always carry them edgewise. I heard of one instance where a slab broke when a supervisor insisted that his worker carry it flat.

[cezanne]

Re: Granite Countertop Underlayment

Underlayment! What a novel idea, but why? I've always just used a framework as a spacer for the countertop (to achieve the desired height above the cabinets). Are you laying granite tiles?

I've seen that done with 1x4 frames nailed onto the cabinet tops and I think that's suffice. Sheet underlayment is overkill if you're going with the regular 3/4" granite. Granite is some hard stuff. I'm told that even an overhang of 10 to 12 inches wouldn't need support.

I wouldn't worry about the MDF. If it really bothers you... just paint some varnish underneath.

All of that said... I went with baltic birch-ply for my install. Talk about overkill.

[craigwatanabe]

Re: Granite Countertop Underlayment

No no no!!! Do not use 1x4's they're too weak for the weight of granite. Even 2x4's can be too weak if laid down flat. You always lay load bearing framework on edge to support heavy loads.

You can go cheap by no underlayment, but in time as framework warps and sags you'll regret it as your granite slab edges separate. You never lay stone or manufactured stonework on anything but a continous flat surface for even weight distribution. Granite is very heavy material and simple framework will not hold up to it over time. At least an underlayment will give that framework stronger sheer strength. Let the underlayment take the stresses of the sagging frame. If you secure granite to an open wood frame and that frame buckles, the granite will crack at the stress points.

And regarding handling large flat friable material, yes always handle it vertically and do not carry it flat. It will bow and crack.

[kani-lehua]

Re: Granite Countertop Underlayment

okay. so do the same principles apply to other types of countertops? natural stone (pre-fab granite, marble, limestone, onyx, travertine), solid surfaces (corian, gibraltar, LG hi-macs, staron), quartz composite (silestone, onequartz, zodiaq), richlite, concrete, nevamar, ceramic & porcelain tile or wood?

if the underlayment is meant for support purposes, what does moisture have to do with it if the natural stone countertop is sealed?

[Beachboy]

Re: Granite Countertop Underlayment

not sure how that works, but granite counters put off their fair share of moisture from what I understand!

[Beachboy]

Re: Granite Countertop Underlayment

One other concern I have with MDF is "out gassing". Shouldn't agents or builders inform buyers when this type of building materials(health hazards) is used on one's new home being constructed? Buyer should definitely have the option when hazardous materials are gonna being used to construct part of their home, right?
I found this about MDF on internet:

"According to most cancer institutes, MDF must be sealed with paint or polyurethane to prevent formaldehyde being released into the air (a process known as out-gassing). This is necessary because formaldehyde contains known carcinogenic (cancer causing) properties."

I'm pretty worried about this!

[escondido100]

Re: Granite Countertop Underlayment

aloha.... i am a general contractor in kona..... i actively import pre fab granite counters from china and i work for both lowes and home depot as their cabinetry installer and kitchen remodeler.
Granite: some installers will use nothing as a sub base if the granite is 1 inch or more thick..... the best material when using a subtop is cabinet grade 6 ply ply wood......... the treated stuf is exterior grade and it is hard to get the warpage out of it for this application. the cabinet grade is really stable and flat.....the extra plys add a lot of strength......HD has a maple plywood for 39 to 49 a sheet which is a bargain......they get it in china......this last year i have probably done twenty kitchens with it and have had no problems.....the granite installers love it.....one time when HD was out of the 6 ply i used the 3 ply fir and it was a lot of extra work to get it flat.
NEVER use MDF or particle !!!!! also the green board that was referred to is also not to be used as it is a drywall product and is only moisture resistant and not structural...... i have torn out dozens of old kitchens and PB and MDf are both usually a terrible mess after just a short while.....you would be surprised....... as to the slats that were mentioned.....that is used in preparation of soild surface type counter tops and is usually put in by the installer. ie....corian or silestone or similar products must breath properly and the manufacturer has very specific instructions on the sub surface to be used. hardi backer or wonder board is used as a base for tile installations.....usually used over plywood...glued and screwed......when you go this route you have to think about elevation details and edge treatment.....we tear out a lot of tile over plywood only..... it is easy to demo compared to proper install with hardi backer....... i see a lot of sub standard work here in hawaii.......so many of trhe trades people have come from all over CONUS and all have different ways of doing stuff...... a contractor from arkansa building 80K homes is gonna do it different than a guy from La Jolla where home cost at least 1M or more......and the local folks that learn the trade here are lucky when they learn the right way to do things and seem resistant to change...... my 2 cents....hope it helps.

[kani-lehua]

Re: Granite Countertop Underlayment

i'll have to take this all into consideration when building my next home. i have had no problems with my corian countertops that were purchased through home depot (o'ahu) and installed by superior solid surface. after reading escondido100's post, my conclusion is that the "underlayment" is for structural/support?

[Composite 2992]

Re: Granite Countertop Underlayment

escondido:

So that means building a frame-like support out of ply without a plywood top, and having that structure support the granite or Corian top? That sounds like what I saw done by Solid Surface technologies for a remodel job a while back.

As for plywood, is that 3/4"?

Regarding cabinets, the best I've seen so far is made of 3/4" ply. Often maple or birch. The doors vary a lot but the boxes themselves are almost always ply and never composited particle or MDF.

I'm toying with the idea of making my own cabinets someday. Just learned how to make the doors with the mortise & tenon joints and floating panels. I was lucky and someone gave me the necessary router bits.

I enjoy doing things like this but don't know if I could do it as a job. Besides, which, I'm way too slow!