Polyurethane is proberly one of the most used finishes in woodworking. I’m sure we all love it for its rich look and glass like finish, but do we know how to apply it properly. Nothing brings out the natural beauty of the grain like an oil based finish.
First of all before I bring you from start to finish there are some precautions. We using polyurethane varnishes , make sure you are in a well ventilated area. If this is not possible open a nearby window for sufficient air flow. If you are not near any windows wear a good quality dust mask with organic cartridge.
The room that you will be varnishing in MUST BE as dust free as possible. Try to have a separate room for finishing (garage/shed. Finishing in a room full of dust is bound to unsettle the dust and it will settle all over your piece while you let it dry as most polyurethanes take 12 hours to fully dry.
You can get a glass like poly finish by following these 3 stages:
Stage one: ‘Sealing the surface with polyurethane’ to do this we dilute the oil based polyurethane to the following mixture
1part mineral spirit / 2 parts poly
Gently stir these contents to advoid bubbles in your finish. With a good quality brush, lint free cloth or sponge applicator spread in long even strokes.
If you want to stain the piece sand the piece with 220grit sand paper and clean using mineral spirits and a rag (Do this before you apply the dilute the grain).
Step two: after leaving the diluted coat to dry for 12hrs or so. Then apply an undiluted coat in even layers and let to dry for 24hrs.
Before the final coat sand down bubbles or dust specks, etc. Remove these by using a 400grit sand paper and then clean surface with mineral spirits.
Step three: ‘final coat’ Brush on the final coat within 48hrs of the second coat. Use the same care with this coat as you did with the rest. Now sit back relax and enjoy the mirror finish.
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Remember you can add as many coats of poly as you want this article is just the basic 3 coats