Pine knots can leak sap and ruin the look of finished projects if the knots are not properly sealed before finishing. If you are going to paint the wood after sealing, use a latex wood sealer that is tinted white. This will give better coverage of the knots and you will not have to put on as many coats of paint when finishing the project. For projects that will be stained, use a clear wood sealer such as shellac.
Sand the piece of pine with the knot holes with 150 grit sandpaper. If there is sap oozing from the knot hole, scrape the sap off with a razor blade. Run your hand a long the surface of the wood to be sure the piece is sanded evenly. If you find any rough spots re-sand the area until smooth.
Wipe the piece of pine clean with a tack cloth, to remove the dust.
Pour a large puddle of the wood sealer onto a foam paper plate.
Dip a dry sponge brush into the wood sealer and pounce the brush up and down on the paper plate to work the sealer into the brush.
Paint the wood sealer onto the wood by using long even strokes. Do not paint over an area already sealed, or you will create brush marks that will have to be sanded later.
Allow the wood sealer to dry thoroughly.
Sand the pine again with 150 grit sandpaper and then wipe clean with a tack cloth to remove dust.
Apply a second coat of wood sealer and allow the pine project to dry thoroughly.
Always use a dry sponge brush to apply wood sealer, never wet. Sand with the direction of the wood grain.
Seal wood projects in rooms with plenty of ventilation. Wear a dust mask to avoid inhaling fumes. Safety glasses should be used when sanding wood.