[George Blanz]

I’m hoping you folks can help me with some information. I am an owner/builder, but I am at “arm’s length” to the Corian installers on this job.

I am in the process of getting a Corian top for a remodel job. The cabinet refacer suppposedly works in coordination with the Corian installer. The cabinet refacer’s version of preparing the tops of the cabinets to receive Corian consists of placing 3″ wide strips of 3/4″ plywood only around the perimeter of where the Corian will go. This just doesn’t seem right to me! That will produce an 18″ span of unsupported Corian in the depth dimension, and even greater spans in the width dimension. It seems to me that the cabinets should be topped with a solid sheet of 3/4″ plywood that goes completely underneath the Corian. Is there any reason (apart from the cost of the plywood) why this would NOT be a good idea?

I noticed elsewhere on this site that there is a nice collection of “Fabrication Manuals”, but notably missing a manual on Corian fabrication/installation. Does anyone have such a manual available, or am I missing something here (like DuPont doesn’t like to “share”??)

Lastly, it’s my understanding that the adhesive that will be used to attach the Corian to the plywood will be simply good ole 100% silicone. It seems to me that this is probably adequate; just the weight of the Corian would probably pretty much hold it in place! But I’m just wondering: is there a better choice for an adhesive?

Many thanks,

George

P.S. Love the site!!

[Norm Walters]

geebee, the fabricator may have a strip of plywood running the length of the countertop already attached to the Corian when they install it, but you are correct, it must be supported every twelve inches, this is accomplished by running a narrow piece of plywood down the center. As far as putting a full sheet of plywood as an underlayment, this is not allowed for many reasons, solid surface expands and contracts and a full underlayment wouln’t allow for that, also you would get heat buildup that couldn’t dissipate. Silicone is the correct adhesive to install a solid surface countertop, and used sparingly I might add. If you have any more questions ask away. One more note: if the fabricator is not certified by Dupont, you will have no warranty.

[George Blanz]

Hi, Norm,

Thanks very much for your reply! This is probably going to sound argumentative, but I certainly don’t mean to get into an argument with you. So I’ll preface my comments with a “with all due respect…”

Your response is almost VERBATIM what the cabinet refacer said to me! So I’m assuming that this is information that has been widely circulated. I just wonder:

(1) If I set a truly hot pot directly on the Corian, I have already voided the warranty anyway! Corian, being largely made of plastics, does not conduct heat very well in and of itself (compared to, let’s say, granite.) So most of the heat loss from the Corian is going to be by radiation and convection from the upper surface, before it has time to conduct through to the bottom (or even to the surrounding Corian.) It’s hard to imagine that the potential loss of radiation caused by solid plywood underneath would be significant in the overall survival of the Corian. Worst case would be that perhaps the plywood should have a pattern of holes drilled in it, to facilitate heat radiation and air contact – say, maybe, 2″ holes on 6″ centers or something.

(2) As you confirmed, the Corian is properly held in place with silicone adhesive. The flexibility of the silicone should allow for considerable expansion and contraction (+ & – 1/4″ or so) without breaking the glue bond. If the Corian expands or contracts more than this, there are going to be bigger issues with the slab even fitting!

(3) None of these restrictions apparently apply to the (overhanging) bar top, which has a 100% solid plywood underlayment. Is it inconceivable that someone might set a hot dish on the bar top? (A passthrough to the living room.)

To me, these issues seem less important than providing the superior strength that a “membrane” of plywood (even with holes drilled in it) would offer. Have there been case studies done on this, or has anyone witnessed a disastrous install over a solid plywood surface?

Respectfully,

George (GB)

[Andy Graves]

Howdy George,

I have been fabricating and installing counters for over 20 years and this is our method. All tops should have 100% support +/- 3/32″. On all the partitions it needs to have support in the middle of a 24″ span. Overhand support can be accomplished by full underlayment or corbels.

When you talk about strength, the plywood add no additional usable strength. How “strong” does it need to be? It is a countertop.

As for heat dissappation, Norm is referring to the air temperature. Heat get trapped between two solid substrates and the lack of air circulation causes problems.

If this is a commercial job, there is absolutely no warranty anyway so the installer can pretty much do whatever he wants and get away with it. But is sounds like he is doing it right to me.

Over engineering the project will not make it better. In fact sometimes it causes more probelms.

Keep asking questions. We are here to help.

[George Blanz]

Hi, Andy,

Clearly, I’m not familiar with the breaking strength of Corian. I have never tried to break it!! The biggest piece I’ve really had access to is the little 6″ x 6″ samples they have; it seemed pretty stiff, but there wasn’t really enough there to flex. And I figured the countertop store where I saw a full-sized display countertop probably wouldn’t take too kindly to me jumping up and down on it! (I am 6′ 8″ and 270 pounds…!)

When they said a 6″ overhang is the maximum unsupported length they allow, I figured the stuff wasn’t as strong as 3/4″ plywood. As far as potential loads go, let me offer a humorous example I used when writing to the installers:

“Supposing Aunt Gertie decides to hop up onto the countertop, and sits right in the middle of the surface. The countertop is 24″ deep, minus the 3″ strips at each edge, leaving an 18″ span of Corian that isn’t supported by anything. I would think that a crack was imminent, and I don’t mean Aunt Gertie’s backside! “

So when you say “how strong does it need to be?” – I really dunno. My motto has become: “Overkill is just barely enough!” I would certainly feel better about another 3″ strip down the center of the 24″ span (which is not currently there); but that kinda begs the question: why stop there? However, I do get your point about over-engineering.

Anyway, the bar top is about a 12″ overhang as I recall, and it is supported by both solid plywood AND corbels; so that at least should be “Aunt Gertie” resistant.

A question: you said…

“All tops should have 100% support +/- 3/32″ …”

Could you explain a bit more what you mean by that? “100% support” sounds like a solid sheet of plywood to me.

I truly appreciate your openness to questions, and your invitation to me to keep asking! A good discussion is usually helpful to everyone involved. This is a great site, and I think it will become a tremendous resource for lots of people interested in the technology of countertop fabrication.

Thanks,

George

P.S. This installer IS “Corian-certified”, so theoretically there would be a warranty; but nobody wants to go THERE unless they have to. I am hoping this place (and this countertop) will be stable and reliable for the next ten years or so, and I am doing everything I can to make sure that happens.

[Andy Graves]

I have and Aunt Gertie [EMO]bigsmile.gif[/EMO] Just Kidding.

100% support to meet warranty standard would be better said. That means that full perimetier support and support a minimum of 3″ at any opening or sink. Material will be warrantied by the manufacturer if the counter does not overhang no more than 6″ without support.

As for a full sheet of material, that will not be warrantied for any manufacturer so don’t bother with that. I guess you could cut holes in a full sheet and then put the top on, but that is just overkill.

Aunt Gertie will not be able to break a piece of material with an 18″ span front to rear. The stuff is very stong.

+/- 3/32″ means that the cabinets should be level to within those tolerances to meet warranty standards. Silicone is acceptable to make up the difference and should be place with a thumbnail size dolup every 8″.

[Todd w]

George,

A hot pan is more likely to scorch the surface, the heat dissipation
issue has more to do with crock pots and other heat generating
appliances which will impart heat over a long periond of time.

Your Corian guy should include an additional support in the middle of
the cabinets, but otherwise his technique seems sound. A properly
installed top should support 300# at mid-span with 1/8″ deflection or
less.

Andy,

Corian does warrant their material in commercial applications, but not fab or install.

“This warranty applies to all Corian®
product used in commercial projects or commercial applications on or
after November 1st, 2004.

DuPont warrants to the owner of the
original installation of Corian® solid surface that Corian®
products shall be free from materials defects arising from the
manufacture of Corian® sheet or shape products for a period of ten
(10) years from the date of purchase of your Corian® solid surface.
This is a product only warranty, not a fabrication
and/or installation warranty.”

Similar to residential warranties from other manufacturers.

Todd

[Andy Graves]

Todd,

I stand corrected, thank you.

[Gordon Shell]

As a former Certified Instructor for Dupont Corian, I am confident to say that it sounds as though the installer is following the proper procedure for installing the tops without voiding the warranty.

The fabricators are required to abide by Technical Bulletin CTDC-117. In this document Section 1. paragraph 2 states “Provide only perimeter support (top edges of cabinets with or without build-up strips).

Paragraph 10 states ” Do not install Corian over underlayment or over old countertops”.

Please refer to chapter 9 in your Corian fabrication manuals for rules of supporting Corian.

Andy is correct, a normal person sitting on an unsupported 18″ span of Corian most likely will not cause a failure.

If your looking for hard numbers the actual strength of the product is below;

Tinsile strength=6000 psi

Flexure strenth=10,000 psi

[George Blanz]

gshell wrote

The fabricators are required to abide by Technical Bulletin CTDC-117. In this document Section 1. paragraph 2 states “Provide only perimeter support (top edges of cabinets with or without build-up strips).

Paragraph 10 states ” Do not install Corian over underlayment or over old countertops”.

Please refer to chapter 9 in your Corian fabrication manuals for rules of supporting Corian.

Gshell,

YEAH, BABY!! Now THAT’S what I’M talkin’ about!!! SOURCE DOCUMENTS!!!

[EMO]roar.gif[/EMO]

OK, I got a little overexcited there – sorry. Gshell, is there a way that a person (say, me) could get their hands on a Corian manual, or even just Chapter 9? If you have them in electronic form (e.g. PDFs), I could give you my email, or you could fax them to me if you’re willing (and I’ll send you $10 or something via Paypal to cover the long-distance call…) I’ll shoot you an email to the “info” address on your Website, and we can talk. (BTW: NICE website! I’m not a big fan of fancy Flash-type stuff, but yours is impressive!)

I got into the Commercial Corian site myself last night, and found a FEW of their technical bulletins (why not all, I wonder?) In particular, CTCD-135 (http://www.corian.com/corian/documents/pdf/coverlamn.pdf) states that you CAN install Corian over a laminate surface, apparently without having to deal with strips, etc. Another link (http://www.corian.com/corian/documents/pdf/spandesign.pdf) states that there is “no limit to number of support strips allowed.” Logically, this would seem to include “full coverage”. Again, I’m not trying to be argumentative just for the sake of it, but it seems that DuPont “speaks from both sides of mouth.” (And to reiterate: it sure would be nice if there was a Corian fabrication manual online here at FabNet… sighhhh….)

With regard to warranty: Todd, the cabinet fabricator is Sears (I think I can say that without getting anybody into any trouble), and they have a “DuPont-authorized” (or whatever the term is) Corian installer who subcontracts with them to install countertops. Sears claims that the product IS warranteed, but only if it is properly installed (i.e. we COULD insist on an installation scenario which did not abide by Corian guidelines, but we would not be entitled to any warranty protection.) You have raised a very important issue, which I will in turn raise with Sears (I’m in the middle of a snippy letter to them anyway.)

Thanks to everybody for their contributions! Keep ’em comin’.

George

[George Blanz]

A followup on the warranty issue:

I found this document on the DuPont site:

www2.dupont.com/Surfaces/en_US/assets/pdf/corian_warranty.pdf

… which seems to indicate that there IS a “Residential Warranty”. Thoughts?

George

[Norm Walters]

George, there is a Total Fabrication Class put on by ISSFA almost every month in Las Vegas. It consists of four, ten hour days, where you and another person actually fabricate a countertop, step by step, going back into the classroom to talk about each step. If you have the time, you may find this very interesting, also the instructor Bill Wolle could answer any question you may have about the fabrication, and installation of solid surface.

[George Blanz]

Hmmm… I’m going to assume that’s a “here’s a good source of information” post, rather than a “get lost, kid, you ask too many questions!” post…

[EMO]bigsmile.gif[/EMO]

Thanks, Norm. It WOULD be an interesting class — if I could just get done with this darn countertop thing so I would have time to take it!! Maybe someday…

GB

[Todd w]

George,

I didn’t mean to imply that Corian ™ doesn’t have a residential
warranty, quite the contrary, I think they have the best in the
business. As far as I know they are the only ones that warranty
the fabrication and installation. Most brands offer only a
materials warranty (someone can correct me if I’m wrong) similar to
Corian’s commercial warranty.

GShell,

“The fabricators are required to abide by Technical Bulletin CTDC-117.
In this document Section 1. paragraph 2 states “Provide only perimeter
support (top edges of cabinets with or without build-up strips).”

I took this to mean the perimeter of each cabinet, not the
countertop. It seems to be common practice to apply build-up to
the countertops before install, in this case build-up is applied around
the perimeter with a strip down the middle to hit the edges of each
cabinet, if build-up is applied to the cabinet it is applied to the
perimeter of each cabinet. It seemed the origional poster
(George) was talking about build-up around the perimeter of the tops.

Todd

[George Blanz]

Hi, Todd,

WIth respect to warranty: Oh. (!) Thanks for clearing that up. [EMO]bigsmile.gif[/EMO]

With respect to “perimeters”: excellent point! I would be a lot happier (or at least “less unhappy”) if the installers had provided strips around the perimeter of each CABINET! That, plus one down the middle, would probably hold up even Aunt Gertie! (With apologies to anyone who has or ever had an overweight Aunt Gertie…)

I’m still thinkin’: by the time you get all those strips cut out and laid down (and hopefully glued AND nailed in), wouldn’t it be just about as fast to take a sheet of 3/4″, cut it to the shape of the countertop, and cut out large holes over each cabinet area (leaving “strips” around the perimeter and a “strip” in the middle)? The ADVANTAGE of this would be that the “strips” thus formed would have a shear strength that could NEVER be achieved by nailing and gluing strips together…

Am I over-engineering yet, Andy??? [EMO]bigsmile.gif[/EMO]

George

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