Cracking veneer

      Why are cracks appearing in a veneered mantelpiece a year after construction? March 21, 2002

A mantelpiece I built almost a year ago is now showing cracks along the grain. The job consists of five large boxes of MDF with a birdseye maple veneer. This is mounted to a wood frame over a brick face on an exterior wall. I used a water-based contact adhesive and feel comfortable with the amount of coverage I got and the bond. I may have applied too much lacquer too quickly when finishing. It seems the only solution is to scrap the project and re-veneer. I haven't checked the moisture content yet. Any ideas?

Forum Responses
Are these boxes 3-sided or 4-sided? Are the splits on all sides or all in one area? Did you veneer all sides, including the side that was attached to the wall? Is the problem area splitting or checking? Are the splits coming through the finish? Do you see any blisters? What type of pressure was used?

Locke Wilde, forum technical advisor

From the original questioner:
The boxes are three-sided with either a top or bottom. They are 3-5" deep and there is no veneer facing the wall. The splits or checks are oriented with the grain and are on all surfaces. The customer did not describe any blistering or delamination and I haven't seen the problem yet, but he is knowledgeable enough to report accurately. He described the checks as hard to see except in a certain light, but he can feel them under his fingers. Before, there was a mirror finish, so these must be coming through the finish. I used a veneer scrapper to achieve the bond.

Maple is the worst species for movement and splitting. Did you seal the backside of the MDF board (did you seal the inside of the box?)? You got moisture from somewhere. In the home, after the heat was turned on and off a few times, the material began to dry out, the adhesive lost its bond and splits appeared in the face.

You might have luck with the following. With a mixture of denatured alcohol (70%) and water (30%), wipe down the face with a clean, lint-free rag. You should be able to see the splits start to close up. If this does occur, the next step is to get a better bond. Take an iron set at 190 degrees or between cotton and wool and heat the face. Apply pressure with a scrapper and wipe again with the alcohol solution to remove heat. Let stand 24 hours, sand with scotch-brite (grey) and spray a light topcoat. This will work if the splits are not real bad.

Locke Wilde, forum technical advisor

From the original questioner:
I do not recall if I sealed the backside of the MDF. I do know I sealed all raw edges. Do you think there is condensation between the brick and MDF? Is wiping down with alcohol and water supposed to remove all the finish or just some? Will this affect the stain color? Will this keep the checks from reappearing?

The purpose of adding the water and alcohol is to make the veneer face swell and close up the splits. It will not remove the finish. If the splits do swell up and go away, that will indicate that you did not have a proper glue bond. You did not apply enough pressure or you did not apply enough adhesive or both.

Locke Wilde, forum technical advisor

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