Laminate and Substrate Movement

      A question about what might cause melamine laminate to pull loose from a countertop leads to an in-depth look at the materials involved. April 18, 2006

What causes laminate seams to open up after installation or being stored? After searching this site, I found a variety of opinions, mainly about temperatures. I think it could be something more. I believe it's all caused by bad glue (contact (conbond)) application. My boss leans more toward the rolling of the laminate.

Forum Responses
From Gene Wengert, forum technical advisor:
I vote for the substrate (if wood) expanding due to moisture gain.

From contributor D:
Both laminate and substrate react to changes in EMC; they are both wood of some sort. If the materials are stored in different environments, then assembled, or they are shipped to or stored - finished - in an unstable environment, there can be problems. So it is not so much which is shrinking or expanding as it is the difference. Contact glue is a flexible bond by definition, and will allow the two pieces to creep relative to each other. If a rigid bond is used, and the pieces want to acclimate to each other or a new environment, then the part may bow or cup. Keep substrates and laminates in the same and similar environment to normal interior temps and humidity to eliminate problems. Let materials acclimate to your shop before using. Don't ship unless the receiver knows to have the site under control.

From contributor J:
It is the laminate. Ideally, laminate should be stored flat and have a chance to acclimate before use. This isn't always possible, but will greatly reduce the shrinkage.

From contributor M:

I vote for the laminate shrinking. You see it all the time on particleboard. I do some work for a door company that applies HPL to hollow metal doors, and they first move it into a dehumidification room to dry it out or it will crack in the field after it dries and shrinks. If they pre-dry it, no problems.

From the original questioner:
Let me rephrase: In my case, I believe temperature is not the problem. For example…
Two tops, same room, same day, same color, same, same, same. One guy did one top, different guy does the other top; one perfect top, one not so perfect top. Oh, also one top has windows behind it (the good top), the other one has a wall behind it (bad seam top). I think it has to be in the rolling of the laminate or the glue application. To the laminate shrinking believers, does it shrink equally along the length and width?

From contributor B:
What about a sagging substrate? Wouldn't that pull the seam open?

From the original questioner:
Yes, I believe laminate shrinks too, but seams shouldn't open up. I think if it's glued and rolled properly and later the laminate shrinks, it should bow the countertop before releasing at the seams, producing a concave cupping effect.

From the original questioner:
The laminate on top also has pulled away from the laminate edge along the front.

From contributor T:
I recently asked this question to my Formica laminate representative and he advised me that laminate does not shrink, only the particleboard substrate does. This expansion and contraction of the substrate is the culprit. I always wood glue both sides of my seams, clamp them, and they will be fine.

From Gene Wengert, forum technical advisor:
Many laminates do not shrink or swell with moisture. In fact, non-wood laminates are stable with moisture changes, as they do not absorb moisture. They can change size with temperature (but homes seldom have a significant temperature variation), but wood does not. Note that if you have a composite wood substrate, the first time it gets wet it will swell quite a bit more than predicted. This is called springback. When it dries, it will not return to its original size. This is one reason why using a water-based adhesive on composites may not be a good idea.

From contributor U:
Plastic laminate does change size with the changes in relative humidity and the MC of the material. From oven dry to 100% saturation, it can change .4% in length and .5% in width. Laminate is made of paper and resin and does have a grain. The rates are not the same between the length and width. This change can amount to 1/2" in the length of a 12' sheet and about 3/8" in the width of a 5' sheet. These values are extreme and would not be encountered in normal use.

That said, the rules are 48 hours acclimation at the job site before cutting and bonding. Acclimation would be un-rolled in the room it is going to be installed in, not in the garage. The substrate also changes and for this reason, it is recommended that PB and MDF be used as a substrate, not plywood. Plastic laminate, particleboard and MDF change at similar rates as the laminate. Because of the cross laminations and glue line, plywood does not change at the same rate as the laminate. The glue line can sheer if the substrate and laminate do not change at similar rates. Seams in laminate can, will and do open or close - it is a problem that can be minimized by following the rules. I do my best to minimize my exposure by following the rules and informing the customer that their layout has a seam and if it changes, it is not considered a defect, just a property of the material chosen. Formica has some good information in their Craftsman Program.

From contributor T:
Laminates are an oil byproduct.

From contributor J:
Wrong. High pressure plastic laminate is 6 to 8 layers of kraft paper bonded with phenolic resin glue, and topped by a melamine plastic facing. All this is hot pressed at many thousand PSI to a unified bond. This material is then run through a thickness sander while held on a vacuum table to standard industry thickness.

From Gene Wengert, forum technical advisor:
If the shrinkage of a laminate is 0.5%, then that is 0.025% for each 5% RH change. Wood has about 0.25% shrinkage for a 5% RH change or about 10 times more. So when the substrate is changing about 10 times more than the laminate, it is logical to me to conclude that the substrate is the issue. (Stated another way: A 1% RH change in wood will have the same size change as a 10% RH change in the laminate.) As mentioned, some laminates are indeed wood-based (more accurately, cellulose-based) and will change slightly with moisture changes. Non-wood laminates are stable with moisture, as I stated before, but not all laminates are without wood.

From contributor U:
Plastic laminate made by the major suppliers such as Wilsonart, Formica, Pionite, Nevamar use basically the same manufacturing process and materials. Kraft paper is saturated with resin, dried and cut into sheets. The color layer is printed (usually somewhere else), saturated with resin, dried and cut into sheets. There is a shelf life to these papers once saturated - that is, they need to be heated and pressed within a certain length of time (approximately several months).

All layers of paper are brought together at the time of lay-up. The number of paper layers will depend on the laminate being manufactured. The color layer may or may not have a top sheet or film - this depends on color and use. A chem-surf laminate usually will have an additional layer of opaque paper saturated with resin (also dried before lay-up). It is then pressed using heat to bond all the layers.

The chemical makeup of the resin will change slightly depending on its intended use. Flooring laminates are the same thing, but with a top layer where aluminum oxide has been added to extend the surface life, they also are made of paper. I know of no plastic laminate not made of paper.

Thermally fused melamine is about the same thing, only without the kraft paper layers under the color layer. The resin mix will be adjusted to suit this application. Of the substrate material currently available, particleboard and MDF most closely match the expansion rate of laminate and the best service can be achieved using these materials. Wilsonart does make a phenolic material not made of paper (other manufacturers may also), however this is not something typically used on counter surfaces.

From contributor T:
As stated before, the substrate is swelling, causing the laminate to pull away from its contact cement bond. More than likely, the substrate in question is pb. If you don't use a sealer on the exposed edges, the pb will continue to swell no matter what atmosphere it is in. Being that many kitchens and vanity cabs are made this way, the ones with no sealer are the ones that look like the laminate shrunk.

Also, vulcanized fiber and rubber are derived from oil.

From the original questioner:
I think if it's glued and rolled properly and later the laminate shrinks (or substarte expands), it should bow the countertop before releasing at the seams, producing a concave cupping effect. Any comments on this?

From Gene Wengert, forum technical advisor:
You are correct if the adhesive is extremely rigid. However, oftentimes the adhesive is not rigid and therefore allows creep and so the substrate expands somewhat independently of what the face is doing. If the expansion (or change in moisture) is very rapid, the adhesive does not have time to creep and then crowning (+ or -) will happen indeed.

From contributor J:
Bowing is only a problem if the panel is free to move. These applications are all held flat by their fasteners, such as the screws holding the laminate top fast to the cabinets. Other times it may be the type of construction using intersecting planes.

From contributor C:
If the adhesive wasn't allowed to cure properly before laminating, that could give you adhesion and moisture problems.

From contributor O:
Will sealing the bottom of the substrate reduce warping? Like when you only finish one side of MDF, the whole thing turns into a skate-park... I think I will try that. I got a countertop coming up in three weeks.

From contributor U:
Sure, it will help. There are phenolic backer sheets just for that purpose. Or you can use leftover laminate. Some suppliers offer re-grind sheets for that as well.

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