Bowing in a Veneered MDF Panel

Troubleshooting a piece of veneered MDF that bowed after being left in the veneer press overnight. January 12, 2015

Does anyone have any idea why this would happen below? 1 3/16 MDF, veneered both sides at the same time with 20 mil paper backed walnut, plastic resin glue, using a frame press and table is flat. The panel was flat when it went in.

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Forum Responses
(Veneer Forum)
From Contributor E:
It looks to me like you first glued two pieces of MDF of different thicknesses and then sanded the face of the thinner piece to size?

From the original questioner:
Nope, a solid piece of MDF. The line you see is probably from the comp. cutter leaving a mark.

From Contributor E:
Ok, that being a large piece how did you apply the glue did you do one side then lay it on the veneer to do the other side?

From the original questioner:
Mixed the glue, rolled it on one side placed veneer, flipped panel and rolled the other side, laid the veneer and then set in frame the press. This happened in all about 15 minutes or less from the time I started rolling to the time I closed the press.

From Contributor C:
Some questions for you:

1. How long did you press this piece?

2. At what temperature was it pressed?

3. Was this a water-based plastic-resin glue?

4. When you took this piece out of the press, how did you store it?

My first guess is that it was a water-based plastic resin glue and you either A. left it in the press way, way too long, or B. when you took it out of the press you did not position it so that equal air and pressure got to both sides. I use water-based plastic resin-glue with great results. I keep it in the press for the required amount of time, then take it out. That is, I do not leave it in the press overnight, or for an extended period of time. After removing it from the press, I then store it on edge so that air gets to both sides of the piece equally. There is no effect from gravity trying to bow the panel one way or the other. When I used non-water-based glue I followed the same procedure with the same great results: no bowing.

From the original questioner:
It is water based, it was left overnight. The panel bowed as soon as I opened the press and removed it. I think I also figured out the problem and solution by the way. Since temps are cooler here overnight then the recommended 70 degrees I cover the table with a heat blanket to keep it warm. As a result I think the top of the panel dried out much more than the bottom, hence the bow. What I did this afternoon was to turn it over and apply the heat for a few hours to help speed up the drying on the other side. It has seemed to work as now the panel is almost dead nuts flat again.