Tips and Techniques for Finishing Trim
Updated: Oct. 13, 2021
Achieving a flawless finish is all about proper prep, taking the correct steps, and applying the right product with quality tools.
Finishing Trim
We asked a 40-plus year painting veteran to show us his best practices for perfection. Here are a few of his favorite staining, sanding and finishing tips to help you create rich, silky-smooth trim.
Test Stain Colors First
Try out the stain on a sample of the same wood you plan to finish. You can create your own custom color by mixing two or three stains (of the same type) together. If you go this route, it’s important to mix up a batch big enough to finish all the wood. The odds of achieving identical results on the second batch are slim. Keep a little extra on hand for touch-ups and repairs.
Sand Wood for Even Finishes
The trim you bought may look perfect, but it likely has imperfections from the milling process that won’t show up until you stain it. Sand every contour and flat area in the direction of the grain with a combination of medium-grit sanding sponges and pads. When necessary, fold 120-grit paper to get into tight cracks and grooves.
Clean the Room First
If possible, work on your sanding and finishing in different rooms. All that sanding dust will affect the clear coats. If you have to sand and finish in the same area, do whatever you can to clean the room before applying the sanding sealer and clear coat. If you’re in a garage, open the overhead door and use a leaf blower to blow dust outside. Use a shop vacuum on the floor, and damp-mop it so your feet don’t stir up dust.
Stain One Piece at a Time
Saturate the wood with a liberal coat of stain using a natural-bristle brush. Wipe off the stain with clean cotton rags in the same order you put it on. That will enable the stain to soak into all areas of the wood for about the same amount of time. Wipe with light, even pressure. Refold the wiping rags frequently so you have a dry cloth for most of the strokes, and grab a new rag whenever one gets soaked. Work on one piece of trim at a time to keep the stain from drying before wiping.
Dry-Brush Crevices
Stain will pool in cracks. Use a dry paintbrush to remove it from each piece after it’s been completely wiped. Wipe the brush on a clean rag or brush it on newspaper to clean off the stain between strokes.
Dispose of the Rags
Rags soaked with oil-based products can spontaneously combust and burn down your house. Spread out stain-soaked rags away from other combustible items, and let them dry before disposing of them.
Apply Sanding Sealer First
Sanding sealer is the perfect foundation for the clear coat. It’s formulated to dry quickly and has more solids than conventional clear coats, making it very easy to sand. And varnish adheres better to a well-sanded, sealed surface. Pick a sealer that’s designed for the overlying finish, preferably the same brand. After the sanding sealer dries, sand it with fine-grit sandpaper and sanding sponges. Remove dust with a tack cloth.
Don’t Skimp on the Brush
Buy a 2-in. or 2-1/2-in. brush, and don’t buy the cheapest option. If you take care of it and clean it well, a top-quality brush will last a long time. A cheap brush is more likely to leave brush marks and shed bristles that could get stuck in the finish. China (natural) bristle brushes are the choice for oil-based products; synthetic for water-based.
Long Strokes Create a Smooth Finish
If you can, arrange your trim boards in such a way that after you brush on the desired amount of finish, you can make your last couple strokes in one continuous pass. That will ensure no overlap marks. If you do end up with imperfections after the finish dries, sand them out when you sand before the next coat.
Oil vs. Water-Based Topcoats
Oil-based finishes are a little more durable than water-based, but the difference isn’t nearly as great as it was 10 years ago. Oil will yellow unstained wood more than water-based products will, which can be good or bad depending on the look you’re after. Yellowing isn’t an issue with stained wood. Water-based products dry faster, which helps keep dust from settling into the finish, but fast drying may be a disadvantage for slower, meticulous workers. Cleanup is easier with water-based products, and the odor isn’t nearly as strong.
Polyurethane vs. Varnish
What’s the difference between polyurethane and varnish? The quick-and-dirty answer: Varnish contains a resin and a solvent (oil or water). Once varnish is applied to wood, the solvent evaporates and the protective resin is left behind. Varnish can contain one of a few different resins, and polyurethane is one of them. Varnish that contains polyurethane just goes by the name polyurethane. The upside to polyurethane is that it’s tougher (like a plastic coating) than the other varnishes. The downside is that it can appear cloudy when it’s applied too thick, and it’s harder to sand between coats.
