Fixing a bowed board already in place

[Aaron Karp]

I've been working on some simple shutters by gluing strips of 1/4" poplar to both sides of 1/4" MDF, creating a raised panel effect. (see photos). Recently the weather in the Northeast US changed from warm and humid to cold and dry, and a few of my assembled-but-not-finished panels have warped. I was hoping to get them painted before this happened but nope.

In designing the project I'd also hoped the MDF core would keep everything straight. No luck there either.

Other than remaking the panels and hoping for a better result, is there anything I can try to straighten them out prior to painting? Thanks!

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[John TenEyck]

Leave them leaning against a wall or, better still, on edge on a bench, where the air can freely circulate around both sides. They should straighten out on their own when the moisture imbalance is gone. Stuff that was flat and straight but then warps is caused by moisture imbalance. The best way to prevent that is to leave your raw materials dense stacked and your in-process stuff out where air can circulate around it so moisture is absorbed/given up equally.

John

[Andrew Hughes]

I’m thinking the panels are not going to behave well.
Gluing solid wood to a dead substrate Mdf. You broke the laws of Mother Nature

[Aaron Karp]

I’m thinking the panels are not going to behave well.
Gluing solid wood to a dead substrate Mdf. You broke the laws of Mother Nature

Is that because no air can circulate behind the poplar? Or is there something else inherently wrong with this approach?

[Bruce Mack]

I’m thinking the panels are not going to behave well.
Gluing solid wood to a dead substrate Mdf. You broke the laws of Mother Nature
I disagree. The wood is balanced in thickness and species. I think this was a vendetta, not an error.

[Tom Willoughby]

I am sorry that you experienced that Aaron. As the other posters have noted, solid wood will have dimensions that fluctuate with humidity changes and if only one side is exposed to the air, only one side will move creating a bow. I bet that if you remade it the same way, the same thing would happen again when the humidity changes. There are a couple of things you could do that would help if you were to remake them:

1. Create a floating MDF piece in the center that allows the popular to expand and contract.
2. Use MDF for the edge pieces as well rather than solid wood, which won’t change dimensions with humidity.

The only suggestion I can offer to help remove the bow on the existing pieces is to add water to the “short” side (cupped side? Maybe with a wet cloth and an iron?) and/or remove water from the “long side” potentially with a hair dryer.

Good luck!

Tom

[Bradley Gray]

add water to the “short” side

This could work. An old furniture dealer trick is to lay table leaves or shelves concave side down in grass in the sun.

i would dampen the concave side and clamp to a flat surface with stickers for a few days

[Mel Fulks]

You have made a giant “weather stick”. Can’t remember how they are used . ….think it shows humidity. Most shutters now are fake, that is
….they don’t shut …or open . That means that they could be bolted to the house, THAT would straighten them.

[Cameron Wood]

If these are to be decorative, they could be fastened down, maybe to sleepers, and somewhat behave. If they are to be operating, on hinges,

they will have an abundance of 'character'. Any mdf in exterior use will have a short and disappointing life, judging from some of the stuff I've repaired or replaced.

[Aaron Karp]

These are intended as functioning (hinged) interior shutters.

I'll try the dampening/clamping trick, and then prime and paint as soon as it's flat!

[Warren Lake]

ive seen shops take MDF 1/4" then cut out same size then drop on and cut out a rectangle, then glue that so it looks like a flat panel door rail and style door They put one on each side. Seems pretty odd to me and mickey mouse but its a pocket hole world.

Most would do it with a solid rails and styles MDF panel inserted into a groove for the tongue on the rails.

Id do it as taught solid rails and styles mortise and tennon with haunch. Panels were mostly solid or baltic birch but MDF a decent consideration and reasons why

[Greg Quenneville]

Aaron I tried something similar but ended up making traditional pine rails and stiles with laminated FJ and a laminated 24mm MDF core. Being heavier I had to domino all the joints right through the ogee profile.

The first trial version like you made had no stability, especially when closed against the afternoon sun.