Moisture-Related Wall Panel Movement

Troubleshooting shrinkage in a recently applied wall-panel installation.

I installed a panel job a month ago. The panels were 4 x 8 x 3/4. They were installed on metal studs. I used construction adhesive and screwed the panels from the back. Each panel was splined together and glued. Now there are 1/4" gaps at every panel joint. The panels were sealed and lacquered and only sealed on the back. They were done with a particleboard core.

Forum Responses
(Architectural Woodworking Forum)
From contributor J:
I assume you're asking why it happened. Particleboard is more dimensionally stable than solid wood, but it's not absolutely stable. It does shrink when humidity is low and expand when humidity is high (though 1/4" of movement over 48" is a lot). Splining and gluing is a bad move because it doesn't accommodate that movement.

Since the problem is so severe, I'm guessing the panels were stored somewhere unheated/high humidity before installation, and the building where they're installed is heated and has no humidifier. Any chance of this?

From contributor C:
What kind of core was used? PB is best. MDF core is not quite as stable and ply core is the panel equivalent of Satan.

If you pressed these panels, cold pressing will leave a lot of moisture in the panel. Also, any earth friendly core is made with PVA glue and has more moisture in it when manufactured. Finally, FR treated core may have added liquids in it that increase the MC.

Contributor J is correct in pointing out that the MC is the culprit and you need to get a MC meter on panels in these situations. In addition, many buildings are super dry with desert-like air. Things may look good in an unheated (or air conditioned) building but when the place opens things shrink.

Also, as all things in the universe are subject to expansion and contraction, you need to build in a reveal and a float method for installation. Tell us what you plan on doing at this point.

From the original questioner:
I'm hoping the panels will go back into place. My shop is 30000 sqft heated at 68-70 in the winter. I'm thinking about filling the joints with putty but I think that's a bad idea in case they move back, as the putty won't let them.

From Professor Gene Wengert, Sawing and Drying Forum technical advisor:
It is probably impossible to get the gaps to close and the panels have been restrained as they shrink the first time. As stated, shrinkage results from loss of moisture. Putting panels in a humid location (a heated shop is often very dry) will cause them to expand. In this case, 1/4" out of 48" is 1/2% size change (or 1/4 out of 24 is 1%). For particleboard this is certainly a large number indicating that the core was fairly high in MC when you installed it (unusual event for sure, but outside storage could cause such an increase). As a side note, wood veneer or lumber will expand or contract about 1% (in width or thickness) for a 4% MC change which is about a 20% RH change.