Opening Laminate Joints Mystery

in a long MDF and laminate countertop? March 14, 2005

I have an install where the substrate/laminate is shrinking. The countertops and backsplashes are opening up at the seams. There are long runs -12 foot sections. 2 inch thick substrate. Has anyone had this problem? I think it is moisture. Possibly the board was green or not allowed to sit around the install area for 2-3 days. I need some help!

Forum Responses
(Laminating and Solid Surfacing Forum)
From contributor R:
Is the splash separating from the counter? If this is the case, it's usually caused by shrinkage in the home itself. If the splash is attached to the wall, not the counter, when the floor joists shrink, a gap forms between them. This is more likely in new construction.

From contributor G:
How old is the countertop? If within 1 year or less, it probably is not a settling problem. Most likely it's a moisture problem with the core, long shot laminate. Laminates are very stable materials unless exposed to extreme environmental conditions. You probably had a core material with a moisture problem. The best core for laminate is MDF or particle board, industrial grade. I think you could ask your laminate supplier to check out the job and give you some advice. Most laminate manufacturers have a tech support hotline for you to call.

From contributor R:
My apologies - I read the post wrong. When I've had a bad joint, it's usually the laminate. Some of the wholesalers store their laminate in unheated warehouses. Try drying out the laminate in a warm, dry rack for a few days before install. Wouldn't hurt to do it for the substrate as well.

From the original questioner:
The counter install is about 3 months. The substrate is 2 inch MDF in 12 foot runs. I don't know the manufacturer. How do I tell that? Will it be marked on the exposed surface? Is anyone aware of a recall on a run of 2 inch material? Will the manufacturer be honest with me regarding a problem? What moisture content should I be looking for in MDF?

This is a big problem. I believe the countertop subcontractor charged the GC about $30,000 for the completed tops and backsplashes. Now the finger pointing is starting.

From contributor R:
Please go into as much detail as possible about scheduling, jobsite heat, drywall, painting, shop heat, conditions of warehouse materials, etc.

From the original questioner:
Conditions as I know them to have been:
- Laminate counter install 12 foot sections butt jointed on a u shaped perimeter install. 2 inch thick substrate MDF
- Renovation project - interior space
- HVAC changed out but space never colder than 65 F, because it was an interior space -no exterior walls. Temp now 70-74 F.
- Floor - existing slab, 30 years old, very little disturbed, several cuts for conduit
- Framing - new steel studs
- Ceiling - new install, suspended 2x4 tile
- Walls - drywall, painted with latex paint
- Counter install very soon after new walls, paint, etc. (1-2 days)
- Countertops unloaded from truck and installed - no wait period
- Mounted to walls on fire treated 2x2 cleat with metal angle brackets for support every 48 inches
- Metal strapping used as blocking
- 4 inch backsplash glued to walls
- Unsure of fabricator's shop conditions, but am told they have a controlled environment. Laminate work is their primary function.
- Open joint conditions have gotten progressively worse as time has passed. Install now about 3-4 months. Some joints open as much as 3/16 inch. Counter butt joints open more in rear than front edge. Laminate remains firmly attached to substrate... no lifting at this point
- MDF moisture content unknown then and now
- Laminate storage unknown
- Glue storage, brand unknown

That's about it as I know it. I feel it is a moisture problem but how do I prove or disprove my theory?

From contributor R:
Am I to assume the counters came pre-laminated in 12' lengths and were bolted together? Also, I've never heard of 2" MDF. Was it laid up in a shop? If it was, what was the procedure for it?

From contributor S:
Plastic laminate is a forest product - layers of paper made from wood. It has a grain just like wood that follows the scratch pattern on the back, although the grain is not related to the scratch pattern, but to the grain of the paper. MDF is the ideal substrate because it expands and contracts most like p-lam. The laminate will shrink faster at this time of year because of the dryness of winter air, and because it is on the surface. It will also pull away from the ends of the core because of the flexibility of contact cement. There is a solution to prevent this from happening, but I do not have an answer for fixing the problem.

When we fabricate large tops we spray contact as usual, and just before sticking them, we drizzle white glue in a zig-zag pattern at the ends near the seam. Hold the bottle about 12-18" from the surface, and zig-zag a fine line back and forth, about a pencil lead wide. The contact will hold, and the white glue will provide a rigid bond, right where you need it. Note that this may not help if you spray with 100%+ coverage. The white glue needs some of the core clean to grab onto.

From the original questioner:
Yes, it came to the site in 12 foot lengths made up at the contractor's shop. The MDF is 2 inch material from the manufacturer… not two 1 inch pieces glued up. I was surprised to see 2 inch material. Yes, the sections were bolted together. I think two bolts per section, but it could be three. The counters are 32 inches deep. Any ideas as to why the problem? Any solutions besides massive amounts of caulk or a tear out? Thanks for the help.

From contributor R:
Rule number one in laminate is that the substrate and the laminate should never be joined at the same spot. Unfortunately, this rule is often broken. If the decks had been assembled on site using standard millwork practices, overlapping layers, staggered construction, glue, splines, etc. and then laminated, the joints would be practically invisible and stay that way. If you need to use white glue to hold the laminate, it means the substrate or laminate is either not dry or is not acclimatized. My guess is you have a bunch of things happening on the job and probably the 2" MDF is the culprit, due to its unusual thickness. It might be having a delayed reaction to humidity/temperature changes.

From contributor D:
It sounds like there may be some movement going on that is pulling the joints apart. When the tops were installed, did the installer glue the joints together? We do a tremendous amount of postform tops. All joints assembled in the plant are bolted, glued and a spline glued and stapled over the bottom of the seam. In a 25" deep top, there are 4 bolts. In the 17 years I've been with this company, I've never seen a top separate at the joint for anything other than water damage.

If your tops were not glued together at the joints and no spline was put over the bottom of the seam joint, I would think that you should be able to remove the tops, reassemble the joints properly and reinstall without too much trouble other than time.

From contributor R:
That's not going to work. He's mentioned that the joints are open more at the front than the back. You'd have to recut all the miters. Have you checked the humidity in the building? Are they washing the counters a lot? My take on this is that the counters need replacing and it's the counter guy's responsibility. When it's reinstalled, don't use 2" MDF, and preferably have the laminate laid on site. It only takes a day and there will never be any problems.

From the original questioner:
Thanks to all for your ideas. The joints are butt joints, not mitred. I don't know why they are more open in the back than front. Plus the backsplashes are butt jointed and shrinking. The area we are talking about is five school classrooms, about 25' x 25'. This is a perimeter install. A lot of lineal feet. We have a meeting Monday with the GC, p-lam fab guy and the architect.

From contributor C:
The 2 inch MDF sounds very heavy. I am guessing that this was used to span the 48 inches between supports. With 48 inches between supports, the counter may still deflect just slightly and this may be just enough to pull the joints apart (as the material deflects, it shortens the straight line overall length). The joints being open more in the back than the front could be due to the bolt pattern. On the post form tops we build, there are 3 bolts on a straight joint in a 25 inch top. If we were to cut bolt slots into 2 inch material with our saw station mounted routers, the cuts would only be 1/2 inch deep. This would leave 1 1/2 inches of material above the bolts. If the bolts are at the bottom of the 2 inch material, then the top may still pull apart slightly. If only a couple of bolts were used, the back may open more if the bolts are closer to the front. Also, did the joints line up completely tight when first installed? Just a few wild guesses.

From the original questioner:
As it turns out, the MDF is 1 1/2 inch thick material. All the rest of the previous facts are true. Don't know if this changes anything. I still think it is shrinking lengthwise as evidenced by the backsplashes opening up that were glued to the wall… not attached to the counters.

From contributor E:
Did anyone check for level? The weight of 2" MDF sagging could play a part in movement, along with humidity.

The comments below were added after this Forum discussion was archived as a Knowledge Base article (add your comment).

Comment from contributor A:
Another thing to consider is shrinkage in the 2x2 cleat. If it runs continuously and is glued to countertop, it can grow or shrink at a different rate than the substrate, causing a bow in or out against the wall. This could cause all the symptoms listed. The weight of the tops could also transfer a lateral force through the supports. Check for straightness at the wall and at front of countertops and check level from back to front to determine how much the top has sagged.

Comment from contributor B:
It appears to me that the gapping at the joints was caused by sagging as was previously mentioned but not elaborated. The front edge of these especially heavy and deep tops were not supported. The back edge was supported both by brackets and a continuous cleat. As the unsupported front edge of the top sags in the center, the straight line distance between the two ends at the front gets shorter than the flat rear of the top.

This would explain why the gap is wider at the front than the rear. A few full depth supports under the top may be the only solution to keep tops this deep and this heavy from sagging.

Comment from contributor C:
As I read through all the other comments, I was surprised no one said anything about movement due to changes in temperatures. I have never seen a joint open up more than 1/16” though.

I had a shop in the Washington DC area that was subjected to some pretty good swings in temps. Most of the problems I had occurred in the summer months. Fabrication often took place in 95 degree temps and then we installed in 70 degree environments. I saw a lot of contraction due to this. Humidity can be a factor as well, but I believe most of the problems I had were due to temperature changes. There’s not much anyone could do about this issue other than installing AC in your shop. This would probably lead to higher overhead, higher prices and less work as the end result though.

Some of the comments from the OP seemed to indicate this was installed in cooler or at least moderate weather. My joints were tightest going from a cool environment into a warm environment. Someone else commented that P-lam and MDF move about the same; not true. Do an experiment and you’ll see. Lay up a small piece of p-lam over MDF or flake, cut with a saw and then put it into a refrigerator for an hour or so. You’ll see the edge has pulled back from the substrate.