I do believe so. Either a sheet of plywood laid across the cabinets and the edge of the counters laminated to hide the edge of the plywood or the plywood inset into the tops of the cabinets (if you like the thin counter top look).

This post was edited by gpraceman on Tue, Aug 6, 13 at 19:06

Thank you, gpraceman.

(We're doing the laminated edge - 4 cms).

You have helped me so much on this forum - thank you for your time and generosity.

2cm quartz with a mitered edge is standard in Europe and plywood subtobs are unheard of. 2cm quartz is sturdy enough itself. Fabricators put narrow strips of quartz or a polyurethane board as a filler for the countertop to sit flush over frameless cabinets. Polyurethane or quartz remnants are completely waterproof, what makes them superior to plywood for that use.

That's interesting information, barthelemy, thanks!

Here in No. Calif. quartz slabs are generally 2 cm and 5/8" plywood goes underneath.

Thanks, calumin, thanks, linelle! I live in SoCal. Will ask fabricator about plywood support.

Thanks, calumin, thanks, linelle! I live in SoCal. Will ask fabricator about plywood support.

I am a fabricator.

No, no subtop req'd for 2CM quartz.

Hi, oldryder!

The countertop guy came in this morning to measure/template... and said they 'always' do a 3/4 inch plywood subtop under the Silestone.

I just read your post ( it's been a long day).

Now I am confused, given that you are a fabricator and know what you are talking about.

Help? :-(

a subtop won't hurt but it's simply not necessary.

Thanks for your response, oldryder. Whew, I feel better!

Why, oh why do they put in subtops then, if it's not required?

The plywood subtop is for when you want it to "LOOK" thicker and allows for an edge treatment to look thicker. If you like the "thin" minimalist look, then no subtop (which is what we have and prefer).

If you are doing 4cm edges though, you'll need to raise it some to get your cabinets to open. the subtop would probably be necessary unless you have unusually tall gaps between the top of your cabinet door/drawer face and the top of the cabinet frame.

If you have a built up edge, it will hang down over the cabinet frame without a subtop. THat means if you have full overlay doors, it will overhang them and it won't open. If you have partial overlay doors, the top faceframe that is visible will look shorter than the bottom one because of the overhang, the same as inset.

Trust your fabricator. He's giving you correct information here.

I would just use 3cm......looks nicer, stronger...It costs a lil more but if cost was an issue you prob wouldn't be going with over priced quartz in the 1st place....

elphaba, kirkhall, hollysprings and TripHeath: Thank you all for your replies.

Yes, we are doing a 4 cms edge and we do prefer the thicker look.

2cms is what is usually used for quartz where we live.

Well, the plywood seemed to be a big deal for my fabricator and GC. My contract with the GC specifically said 5/8" plywood substrate, which initially I really didn't pay much attention to. My counter was selected, ordered, templated, fabricated and installed through my KD, not a GC subcontractor. When my old tile counter was removed by the GC, his guys looked at the old plywood (it was pretty funky) and said it was fine to reuse. When the fabricator came out to template, they had a fit because the old plywood was 3/4" and it HAD to be 5/8". A call to the GC and he went, oh yeah, sorry, we'll have to fix that. Lost a week in the process. Nobody acted like it was an option.

linelle: Eeeeeek!! Does this mean that my plywood should also be 5/8 instead of 3/4 which is what the fabricator is using? :-(
We had tile countertops, too.
Why did it HAVE to be 5.8 for your fabricator?
eeek again.

boone, I don't know if the same practices are used in SoCal as NorCal. I don't even know if the thickness of the plywood substrate is spelled out in some code. Does that 1/8" really make that much difference? Apparently my fabricator thought so. And my GC spelled out 5/8" specifically in our contract which was not otherwise rich in detail. Typical of him, I think he "forgot" and thought he could get away with reusing the old plywood from 1991.

It does seem to be the norm in these parts (North Bay Area) to use 2 cm slabs on plywood substrate and a built-up edge. I only know and understand this after the fact. Please check with your folks down there, because I don't mean that my experience will be yours. It was a minor big deal for me, fabricators standing around fuming about the wrong thickness plywood, saying it would never do.

linelle: As I said in another thread of mine, I am an over-thinker,lol.

I love the image of your fabricators standing around, fuming... and you, meanwhile, hanging about in the doorway, enjoying the show? ;-)

Of course, I know that you don't mean I should also have 5/8ths or any/eighths :-); my fabricator is going with the 3/4ths and that's that. ;-)

My 'eeks' were uttered ( er..typed) at an earlier moment of
what I call "renovation degradation" - a temporary mental unraveling. I'm much better now :-).

Thanks!!!

Amazing! Searched the entire internet. No consensus on if Quartz needs plywood underlayment. The quartz companies are also afraid to weigh in. One of the seven mysteries of the world? Just waisted an hour and with no legit answer.

2cm quartz does not need underlayment and can be installed directly on cabinets. If you do this, you can't have an edge build-up and you have to raise your cabinets so your appliances fit properly.

I would much rather have 1 1/2" wide 5/8" thick cabinet grade plywood strip underlayment on 2cm quartz than full 5/8" roof sheathing. The underlayment is a spacer only; estone needs no structural help over cabinets. If you're going to cantilever 2cm, use metal square tube.

If 2cm Caesarstone requires no additional support when cantilevered less than 8" (page 20) it is obviously okay to set it directly on cabinets.