Brush Apply Oil Based Paint to Wood and Fiberglass

Preparation of any surface to be painted is up to 75 percent of the painting task – here’s my way to complete the last 25 percent using oil based polyurethane paint, on a first project, and for many to follow. Alas, I cannot and do not guarantee results. I will tell you how to get started. I will urge you to be consistent – do as much as you can the same way you did it to start with, limit the changes at first; same materials, tools, and techniques; in short order, you will see for yourself the benefits; over time, your work will approach and then may attain professional quality. The pain of self-discipline is less than the pain of regret.

Almost all projects using oil based paints require multiple painting sessions. There are many reasons why this is true; most are described in the following paragraphs. Take some on faith now, your experiences as you work will likely convince you of the rest.

Once the cleanup from the surface preparation is complete, it is time to study the shape of the surface to be painted, determine the area of that surface to be painted in each session, and to allow for the weather. Next, you must tape or otherwise protect adjacent surfaces. For this first and every following session, you must manage the paint, apply it to the surface, care for the brushes, and cleanup. Other conditions, such as weather changes and dust and dirt from adjacent work will happen. Wait for conditions to improve.

By way of example, a typical session might be: apply one coat of Interlux Brightsides marine polyurethane paint (paint number 4359 white) to a 2′ x 5′ horizontal section of fiberglass gel coat, typically 20 or more years old. The surface is smooth (no spider cracks), dry, and free of wax. Surface was washed clean and wet roughened with an abrasive pad to remove most chalked gel coat. For this project, no primer is required before the first coat.

Manage the paint – first steps: Start with a new 1 quart can of Brightsides (or other marine polyurethane paint), you also need 1 or 2 empty 1 quart paint cans with lids, 1 pint of Interlux 333 reducer, a paint can key, cone paint filters, 1 ounce measuring cups, quality bristle paint brushes suitable for oil based paints, paint stir sticks, neoprene gloves, newspapers, rags or towels, a small hammer, and a few 4 d finishing nails. I strongly recommend an inexpensive digital food scale so quantities can be measured by weight (see following post). Set the can of paint on a clean firm level surface and open it. Use the hammer and a 4 d finishing nail to punch 8 holes in the trough where the lid was, spaced around the perimeter of the can.This is so that the paint that gets in the trough mostly drains back into the can. Solids have settled to the bottom of the new can of paint. Stir the paint until you are sure all solids are mixed; then stir until there is no drag between the bottom of the stir stick and the bottom of the can. If you don’t mix completely, success/consistency in future steps cannot be assured. Pour half (16 ounces) of the 32 ounce/quart stirred/thick paint into one empty paint can (see next post for hints). Use a brush to clear the can trough of the paint that did not drain and replace the lid. You will have to clean this brush.

Manage the paint – ongoing: We are working with the 16 ounces of paint in the formerly empty can; thin this paint 10% by adding 1.6 ounces of Interlux 333 reducer, mix well. It is not possible to obtain consistent good results using polurethane (or other oil based) paint without thinning. All else being equal, if the paint is applied too thin, the result is that more coats will be needed, but a good outcome is assured. If applied too thick, a smooth finished texture is unlikely, runs will appear in vertical surfaces, drying/hardening takes much longer – you will waste much more time (and expensive material) if you have to do it over.

For my typical project (first session described above) I would figure two or possibly three coats to cover, with 24 hours minimum between coats. You can push this wait to overnight as you become more experienced.

A few word here on taping and cleanup. If you are working outside, you must use a high quality rain resistant (marked 2 weeks) 1″ wide blue masking tape to protect adjacent surfaces. I do not usually re-tape between coats – sometimes, after the last coat, run a utility knife blade point gently along the tape/paint edge to reduce the possibility of lifting.

Application to the surface: The two elements of painting needing close coordination are managing the paint at the time of application and applying it to the surface. Insure the temperature of the paint and the temperature of the surface are the same. Target 75 degrees (F), never work colder than 65 degrees or warmer than 80 degrees or in direct sunlight until you build more skill.

The last thing to do before you pick up the brush is to correctly adjust the consistency of the paint in the can you are about to use. Though it is not wide, there is a range of consistency between too thick and too thin that will work fine for the session. First indication is how the paint flows and drips off the bottom of the stick you just used to stir the paint….

There is not much mystery about how things are going while painting. There are many tell-tales – here are four. Drag on the brush …. Wet edge …. Layout flat …. Runs ….

Limit length of session to prevent paint from drying in the heel of the brush ….

In summary, get consistency correct before application begins, verify that it is correct at the start of application and correct if required, or curse under your breath at the runs or other defects you will observe after the session is complete.

Paint has both protecting and sealing properties in addition to improving appearance ….

Oil Paint Brush Cleaning Best Practices: See following post

Project and Session Cleanup: Remove tape protecting adjacent surfaces ….

Finally: I hope I have convinced you that the results you can obtain are worth the effort. On smooth wood or fiberglass, these polyurethane paints look great for years. A maintenance coat after a few years easily restores the gloss to original. Please read the directions on the can. Much work has gone into making these paints provide great results and ease of use. But there is work involved. No quick fixes here. Just like in woodworking, knowing where your thumb is while using the band saw, know that in painting, the major waster of time and money is having to do work over.

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