by Rick Hill
1. Use finishes from the same batch.
All sealers, topcoats, and especially stains are made in batches by the finish manufacturer. To control any possible variations between gloss or tint, try to use products made in the same batch for each job. This increases the chance that everything will look the same when dry.
Obviously finding the same batch is not always easy and is more important in stains or enamels than in sealers or topcoats. One way to ensure the uniformity of color throughout the job is to blend the different batches into each other prior to application. If you are working out of large amounts of product, then you have to rely on the coatings manufacturer to provide colors that match from batch to batch. This is why rule tip #2 is so essential to your production, no matter what size of operation you have.
2. Use one source for finishes.
The biggest problems in finishing happen when one part of a finishing system is incompatible with another. Often the stain is not from the same supplier as the sealer and topcoat. Different manufacturers of finish use different blends to get better color, flow out, or "sand-ability." These blends will often not mix with the blends from another manufacturer's product. When one brand is used on top of another you may cause the finish to lift, orange peel, or dry slowly. This is a very common occurrence when finishers use a stain with long oils (linseed oil or mineral spirits) under a fast drying conversion varnish. By using one source you eliminate the possible incompatibility of coatings and get the support you need if any problems do occur. Try to find a source with a competent sales or technical person that is experienced not just with selling finishes, but also with spraying them. If in doubt of their capabilities, ask for references from other customers.
3. Know which solvents to use with each step in your finish system.
Solvents make up the major portion of most coatings. They affect dry times, flow out, and inner-coat adhesion. Using the correct solvent for each finish step is essential to the thinning, spraying and cleaning of a finish. If you are using one source for supplies, you can ask the company's technical representative which is the best solvent for each product. The wrong solvent can gum up your guns, lift your finish, or slow the drying.
4. Measure the viscosity.
Coatings are affected by temperature, humidity, and time. You can determine how a coating will hang, fill, and flow out by knowing the thickness (viscosity) of the coating. The viscosity cup has a small hole in the bottom that lets the coating drain out slowly. Determine how thick the coating is by counting the amount of seconds needed to drain the cup. Immerse the entire cup in the paint, raise it out, and start a stopwatch. When the first break appears in the stream of paint running from the hole in the cup, stop your watch. This is your viscosity. Knowing the viscosity will tell you how well your paint is going to flow out, when to add thinner, and how well the paint will hang or run on vertical applications. Most finish manufacturers suggest the proper viscosity for their coatings and the type of viscosity cup to use, so check which kind of cup to purchase by asking your coatings supplier.
5. Use virgin thinner when thinning coatings.
There are many types of thinners and blends of thinners. Some of the very inexpensive thinners are made from recycled solvents from other paint or solvent customers. These recycled thinners can be useful for cleaning out your equipment, but be very wary of using them for thinning coatings. They may contain oils or silicones from past lives that will cause fish-eyes in your finish. Spend the extra dollar to make sure your thinner is clean and has enough solvent to work well in your coating.
6. Filter your sealers and topcoats.
7. Drain the water and oil out of your compressor, filters, and lines.
Set up a regular maintenance schedule on your shop calendar to drain the lines, change the filters, and drain the compressor. Compressors condense air, therefore heating and causing the air to hold more moisture. As the air moves through the lines it starts to cool, leaving condensation behind. If the moisture is not removed from the lines or if the compressor leaks oil into the lines, it ends up in your finish--causing fish eyes and craters.
8. Inspect the wood for flaws prior to each coat.
By reflecting a bright work light at an angle on your product, you can see dried assembly glue, sanding marks, and dents before staining. Any imperfections you find prior to staining, sealing and top-coating will save the immense amount of labor involved in sanding or stripping the mistakes out later.
9. Stir constantly.
If a coating says to agitate prior to spraying, agitate during spraying. Stains have pigments that can settle out quickly, especially in dark colors. Coatings contain sanding or flatting agents that will also settle. If you don't constantly agitate the coatings, your final colors and sheen may vary.
10. Educate yourself.
Attend as many seminars on finishing as possible. Try to tap the knowledge that suppliers offer in as many ways as possible. Try new products on non-production pieces, dabble in marbleizing, faux finishes, dye stains, glazes and fillers. The finish can set apart your custom work from the mass produced market, so make the finish as much a statement of your work as the piece itself.
Rick Hill is an independent representative and consultant for industrial wood finishes. He has been involved in the woodworking industry for 12 years, and has been known to actually hold, shoot, and clean a spray gun.
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