Author Topic: flattening a cupped laminated countertop  (Read 788 times)

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Offline mrFinpgh

  • Posts: 235
flattening a cupped laminated countertop
« on: December 04, 2017, 06:06 PM »
I made some laminated countertops with walnut edging on them.   Unfortunately, one has a bit of a cup in it - 1/8" over 26".   

From what I've read, this is common enough and typically flattens out when screwed to the cabinet.  So far, though, it isn't flattenin much.  It looks like it actually is bending the bracket upwards.

Anyone have some clever ideas for how to get this thing to flatten out?

-Adam


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Offline Bob D.

  • Posts: 706
Re: flattening a cupped laminated countertop
« Reply #1 on: December 04, 2017, 11:22 PM »
You could run some relief cuts with a track saw on the
underside along the length of the countertop. As far as
spacing and depth of cut I don't know.

Just don't go too deep.  [crying]
-----
It's a table saw, do you know where your fingers are?

Offline bnaboatbuilder

  • Posts: 128
Re: flattening a cupped laminated countertop
« Reply #2 on: December 04, 2017, 11:35 PM »
How thick is the top? How is the counter finished? Assuming the top has a finish and the underside doesn't. Easy enough that the two sides react differently to moisture in the air.

I built a 28"x78" walnut bar top for a restaurant/bar several years back. The walnut strips were 1"x1" and varying lengths. I epoxied the whole top to a 3/4" ply substrate to keep it flat longterm.
- John

Offline Oldwood

  • Posts: 298
  • Alberta, Canada
Re: flattening a cupped laminated countertop
« Reply #3 on: December 05, 2017, 07:53 AM »
Did you make an allowance for the wood to move? The counter will shrink and expand as it takes on and loses moisture . I fasten tight on the front then hold down the back with a splash board or a slotted screw hole.

It sounds like the top is expanding but is held tight front and back.

Gerry
Real knowledge is to know the extent of one's ignorance.
Confucius

Offline Peter Halle

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Re: flattening a cupped laminated countertop
« Reply #4 on: December 05, 2017, 08:14 AM »
I think that a better description of the countertops would be helpful.  I suspect that many are reading "laminated" to mean different things.  I read it as a countertop with a plastic laminate top and walnut edging and based on responses from others it looks like they are reading it as a solid wood top made up of laminated pieces of wood like a butcher block.

I think you might get some ideas that will help with some clarification.

Peter
Disclaimer:  I have been involved with the development of some TSO Products.  I have offered thoughts and ideas freely.  I am not paid but I may receive products during the development process or afterwards.

Offline Arvid

  • Posts: 82
Re: flattening a cupped laminated countertop
« Reply #5 on: December 05, 2017, 04:38 PM »
if it is a formica laminated counter top what you have happening is laminate pulling. happens almost instantly when contact adhesive cures on the top side and moisture enters the underside from humidity. has to be a good amount of moisture for it to happen in your case across the 26 inches. usually it happens the long way and screwing it in place straightens it.  only way to make sure it does not happen is by installing it very soon after fabrication and mount it. or by laminating the underside of the top as well. making table tops years ago we had to always laminate the bottoms as well or they always warped.

Offline mrFinpgh

  • Posts: 235
Re: flattening a cupped laminated countertop
« Reply #6 on: December 06, 2017, 11:13 PM »
Thanks for the responses.  To clarify, it's an MDF substrate with walnut edging and white formica laminated on top.

Strangely, the other top, which is about the same size, stayed entirely flat.

Right now I've got it clamped to my workbench with a couple drywall shims underneath it in the middle.   Hoping that I can flex it back the opposite direction enough to get it close to flat.  Otherwise, I guess I'll break out the tracksaw and put some kerfs in it.

Thanks,
Adam

Offline Bob D.

  • Posts: 706
Re: flattening a cupped laminated countertop
« Reply #7 on: December 07, 2017, 08:43 AM »
if it is a formica laminated counter top what you have happening is laminate pulling. happens almost instantly when contact adhesive cures on the top side and moisture enters the underside from humidity. has to be a good amount of moisture for it to happen in your case across the 26 inches. usually it happens the long way and screwing it in place straightens it.  only way to make sure it does not happen is by installing it very soon after fabrication and mount it. or by laminating the underside of the top as well. making table tops years ago we had to always laminate the bottoms as well or they always warped.

So if the underside is directly exposed to humidity, and the topside is covered with laminate and for the most part shielded from humidity. Is there any advantage to put a coating on the underside to seal it from moisture (in place of laminating both sides) so that the underside, while not as well protected as the laminated side, will not absorb as much moisture and reduce the chance of warping. Would be less expensive than laminating both sides.
-----
It's a table saw, do you know where your fingers are?

Offline SRSemenza

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Re: flattening a cupped laminated countertop
« Reply #8 on: December 07, 2017, 10:23 AM »
I don't think clamping it down over the shims will yield a permanent result. When unclamped it will probably return to the warped state.

Can you also do something to dry  the bottom side? If the bottom has moisture to give up that should help flatten it. Then seal the bottom with several coats of poly or laminate the bottom.  Reattach with stronger brackets that won't bend.

Seth