Are You Struggling with Imperfect Finishes on Your Woodworking Projects? Discover the Secret to Achieving Perfection with Oil-Based Polyurethane
In the world of woodworking, finishing is an essential step to make any project look complete and professional. However, many people find it intimidating and overwhelming, so we've created this article to make the finishing process accessible to hobbyist woodworkers.
Oil Based Polyurethane
One type of finish we want to discuss today is oil-based polyurethane. It's a durable finish that's suitable for both indoor and outdoor projects. Although it's not difficult to apply, we believe that our method will give you the best results.
The first step in applying any finish is to prepare your surface by sanding it thoroughly. We have a comprehensive sanding tutorial that explains how to properly sand and what grits to use. For oil-based polyurethane, we suggest sanding to no higher than 150-180 if you plan to apply wood stain or go to 220-240 if you plan to apply just polyurethane. Anything finer than 240 is a waste of time with this type of finish. We recommend hand-sanding your final grit, in this case, 220, and going with the grain to disguise the fine scratches that sandpaper leaves behind.
When working with oil-based poly, it's essential to wear a respirator with activated charcoal filters if you're applying it in an enclosed space. If you're working in a well-ventilated area, it's up to you whether you want to wear a respirator. Still, we always recommend protecting yourself when working around any oil-based finish for more than just a few minutes.
Oil-based poly typically comes in three sheens: gloss, semi-gloss, and satin. All of them must be mixed thoroughly, but semi-gloss and satin must be mixed well to start out and again between coats, especially if it's taking you more than half an hour to apply a single coat. Satin and semi-gloss finishes contain flattening agents to reduce their naturally glossy sheen, and you have to keep those flatteners suspended in the liquid; otherwise, you'll get an uneven finish.
Don't use straight from the can
You don't want to use poly straight from the can. To get rid of any crud or partially crystallized finish that may be in there, use disposable strainers that you can find wherever you bought your can of finish. After it's mixed, pour some through the strainer into a clean container and let it slowly run through that fine mesh. This will help with air bubbles as well. You don't have to strain the whole can, just do what you think you're going to need for the coat you're about to apply.
Brush VS Wipe
Whether to brush or wipe on poly depends on personal preference and the project. Wiping poly on is easy, and you can make your own by simply adding mineral spirits or another compatible solvent. Brushing on poly involves a bit more technique, but it's worth learning. You'll need the right brush, usually a natural bristle brush labeled for oil-based finishes. White china bristles come from hogs, and they're very absorbent, so they hold the finish well.
How to coat efficiently
When applying poly, it's better to apply three thinner coats than two thick coats. Always brush with the grain, and remember to work wet. This means you shouldn't try to brush wet poly over a spot that's already begun to dry. For wipe-on poly, you can quickly spread it in any direction, but you should finish by wiping along the grain. A thinner coat is going to dry faster, and you may be able to sand within just a few hours.
After the final coat, lightly sand with 400 grit sandpaper between coats, and then buff the surface with a brown paper bag. This will make it slick as snot and give you a finish you can be proud of.
As you can see, oil-based polyurethane is a great option for achieving a durable and long-lasting finish on your woodworking projects. With the right technique and some basic safety precautions, you can achieve excellent results.
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