How to Prime MDF


Have you experienced problems trying to prime MDF? This article explains the best product to use.

MDF (which stands for Medium-density Fibreboard) is made up of lots or reconstituted wood fibres that have been bound with wax and a resin binder. One of the problems with painting it is that as the first primer coat is applied, it causes the fibres of the wood to swell up (I suspect it also re-activates the binder to some extent too) and this 'raises the grain' of the panel.

This means that once the primer coat has dried, the surface becomes textured. Sanding the surface down and applying another coat of oil or acrylic based primer will help, but since sanding the surface removes some of the paint that you have just applied, the problem tends to happen all over again after the second coat has applied.

I have found that by far the best product to use to prime MDF is a shellac -based primer. I use Zinsser BIN but there are others on the market. It is shellac based which means that it is touch dry in a matter of minutes, and because it dries so quickly, it doesn't have a chance to soak in and cause the fibres to swell as much as oil or water-based primers.

The MDF will still need a light sand with some fine sandpaper after the primer has dried, but it will feel much smoother. After the primer has dried and you have given it a rub down, it can then be painted with water-based or oil based paints.


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