Things You'll Need
Yellow woodworking glue
Small clear plastic Dixie cup
Newspaper or small drop cloth
If you have ever built a cabinet, counter, bench, or table out of medium density fibreboard and then tried to paint it, you probably noticed very quickly that the edges can suck up a lot of paint. This leads to the repeated application of coats of paint or primer to the MDF, until it stops soaking all of your paint. To avoid having the MDF suck up the paint and to keep your primer and paint applications to a minimum, you can quickly and easily seal its raw edges.
Take a small, clear, plastic Dixie cup, and using a sharpie, divide it in four equal sections; draw the lines of each section on the Dixie cup.
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Divide the lower fourth into four parts and draw the lines on the cup -- the reason we are doing this is because only a small amount of the glue-water solution is needed. If you have a large project, it is always easier to make more of the glue-water solution.
Pour yellow woodworking glue into the cup so that it fills up three of the four sections you created in the lower fourth of the cup -- the glue should be equal with the third line up from the bottom, leaving you with one line left to fill in the lower fourth of the cup.
Pour in enough water to fill up the last section. You should now have a full 1/4 of your overall Dixie cup composed of three parts glue and one part water.
Take the popsicle stick and stir up the solution so that it is equally mixed.
Place your drop cloth or shop rag under the piece of MDF board that you want so seal.
Dip a small foam brush into the Dixie cup and into the water-glue solution.
Brush the glue solution onto the MDF edge face -- over ever exposed part of the edges. Wipe off any excess drips or drabs with a shop rag.
Let this dry for at least two hours in a warm shop.
Sand the edges smooth by hand with 220-grit sandpaper.
Prime your MDF board and the edges and let it dry. Paint your finish coat only once.
Store any extra solution in an air-tight glass jar for a little while, but discard after use.