9 Tips for Spraying Varnish on Wood
Get flawless results with aerosol spray polyurethane cans.
Set Up for Spraying
Spraying paint or finish provides a smooth look while saving time. But it also creates a fine mist of solvent and finish that’s dangerous to breathe and drifts and settles on everything in sight.
To avoid problems, work outdoors if possible. If you spray indoors, cover everything with plastic sheeting or drop cloths and wear a respirator fitted with organic vapor filters, especially if you’re spraying lacquer. Also, put an exhaust fan in the window. Read the label on the can for additional safety precautions.
Don’t Dent Your Finger
If you’ve ever used spray cans to finish a large project, you know how sore your fingertip can get from pressing down on the tip. A trigger handle saves your finger and gives you better control of the spray.
Don’t Swing the Spray Can in an Arc
It’s natural to swing the spray can in an arc, but this results in uneven coverage. The finish will build up in the center and be light on the edges, especially with a product like polyurethane spray.
Overlap the Polyurethane Spray Swipes
To get even coverage, overlap the spray about halfway onto the previously sprayed section. If you just overlap the edges, you’ll get a narrow band of thicker finish where the two strips meet. Overlapping at least 50 percent solves this problem — you’ll apply about the same amount of finish everywhere.
Keep the Spray Tip Parallel to the Surface
Focus on keeping the spray tip an equal distance from the surface as you move it along. At the same time, keep the can moving at a steady pace for an even coat. The goal is to apply just enough polyurethane finish to wet the surface without creating runs.
You can also prevent runs by applying several thin coats rather than one or two thick ones. The finish may look blotchy after the first coat, but additional coats will produce a uniform finish.
Start the Polyurethane Spray Paint off the Edge
It’s hard to get even coverage if you start or stop spraying on the surface you’re coating. The spatters that happen when you first push the button can blemish your work, and products like polyurethane spray build up in one spot if you don’t move fast enough.
Here’s an easy and foolproof way to avoid these problems: Start spraying before you reach the edge of the project, move across at an even pace, and stop after you’ve gone past the far edge. This technique guarantees an even, spatter- free coat of finish across the entire surface.
Seal Dark Stains and Exotic Wood With a Mist Coat
Spraying a heavy coat of finish over dark wood stains or some oily exotic woods can ruin your project’s appearance. The solvent in the finish can dissolve the stain or the color in the wood, causing it to bleed or turn muddy. To avoid this, prime these types of projects with several thin mist coats before applying a thicker coat of finish.
Apply a mist coat by raising the can higher than normal and moving it faster than usual. This will reduce the amount of spray hitting the surface. Mist coats dry quicker than a full coat, so you can typically apply several mist coats with less-than-normal waiting time. Wait for the previous coat to dry to the touch before re-coating.
Brush, Then Spray
At $4-plus per aerosol can, it gets pretty spendy to build up a smooth polyurethane finish on a large project. But you can still take advantage of the flawless finish provided by aerosol cans.
Start by applying two coats of finish with a brush. Then carefully sand with 220-grit sandpaper and remove all dust before using spray cans for the final coat. If you don’t know much about finishes, just make sure your liquid and spray polyurethane finishes are the same type.
Build a Turntable
When you have a small project with many sides to apply polyurethane to, placing it on a turntable will speed up your job and make it easier to achieve good results. Instead of trying to move around the project as you spray, just give the turntable a little spin.
You can build a turntable like this by mounting lazy Susan hardware to a scrap of particleboard or plywood, then mounting a plywood or particleboard disc to the hardware. Check the instructions before leaving the store so you can pick up any screws you’ll need.