You can stain and varnish MDF. There are a few things to consider along the way, however. MDF, or medium-density fiberboard, is a construction material that mimics the use of plywood and is common for use in kitchen cabinets. Although it may look like plywood at first glance, the differences are immediately apparent upon closer inspection. Plywood maintains the wood's natural grain, while MDF, made of wood fibers and resin, doesn't have a grain pattern. For that reason, though you can stain MDF, its appearance will be much different from that of less-processed wood materials.
Prepare MDF for Staining
As with any other wood product, staining MDF requires that the surface be smooth, clean, and free of old paints, stains, or other finishes.
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Fortunately, the factory surface of MDF is mostly smooth. Its grip on old paint is easy to break with a chemical paint stripper. Stain and varnish are almost as easy to remove with a power sander and 100- to 120-grit sandpaper. Remove any old paint and stain from your work surface using the appropriate method and be sure to work in a well-ventilated area.
Once you have a bare MDF surface, continue sanding through to 180-grit paper to ensure a smooth finish. Pay particular attention to edges, which are often rougher than large, flat areas of fiberboard. Finish sanding by using a damp rag followed by a tack cloth to remove all traces of dust.
Stain and Varnish Materials
Medium-density fiberboard is denser than natural wood and accepts finishes differently. Due to its higher density, applying wood conditioner is generally unnecessary before staining MDF. You have numerous stain options for finishing the material. Any solvent-based stain will work best, as oil-based products penetrate better into MDF than water-based products. To mimic wood-grain texture, consider choosing contrasting colors of stain to apply in layers.
Shellac, real varnish, or oil-based polyurethanes are excellent choices for finishing. To highlight the smooth nature of MDF, semi- and high-gloss sheens are popular finishes.
How to Stain MDF
Staining MDF differs from staining natural wood. Use a synthetic-bristle paintbrush to apply the stain of your choice in long strokes to mimic a wood-grain appearance. For more detail, allow the first stain to dry and lightly apply a coat of lighter or darker stain over the first with a stiff-bristle paintbrush. The technique may require practice, so learning on a scrap piece of material is a good idea.
Allow the stain to fully dry before applying polyurethane, shellac, or another finish with a paintbrush using the same long strokes as with the stain or simply apply a spray version of polyurethane, shellac, or another finish product. Allow ample drying time for your project before handling or reinstalling it.