March 7, 2004 Meeting Presentation

Peter Matthews Presentation

Peter Matthews, a product and technical representative for Interlux paint who also builds and restores canoes, gave a painting and varnishing tutorial stressing the best practices necessary for quality results.

He stated that surface preparation is 95% of the job and that means a lot of sanding. He stressed that those who don't enjoy sanding or can't develop the patience for it will not be able to produce a quality job.

Prep Work and Sealing

“Paint”, he said, “has no glue in it." It does not stick to a substrate as an
adhesive. Rather it attaches itself by filling the microscopic voids and fissures of the surface. Therefore good surface preparation is an essential starting point. On raw wood, he recommended finish sanding up to 120 – 150 grit to prep the surface. Some builders might follow this step by wetting the wood to raise the grain and then finish sand a second time.

The first finishing step is to seal the wood cells. He recommended 2 coats of Interlux 1026 Wood Sealer or varnish thinned 25% - 50% with Interlux 333 Brushing Liquid to get deep penetration into the wood. An older can of varnish that might have skinned over or might not be appropriate for finish coats is fine for this purpose.

Varnishing

Follow the sealing step by applying 2 to 3 coats of varnish with no sanding between coats. The idea is to create a film buildup on the wood. Then lightly block sand the finish with 220 grit paper.

Block sanding (sandpaper wrapped around a block of wood) is crucial because it levels the finish. If we were to look at a magnified cross section of the film coat built up at this point, it might appear as a wavy film atop the wood. Block sanding knocks off the high projections of the coat and starts to level it for the following coat.

Peter recommended a minimum of 6 –8 coats of varnish and wet block sanding between each coat with 320 grit to produce a very satisfactory finish. He also stated that if the wood is light sanded and recoated every year, the finish that should last for five years. Recoating is necessary because varnish contains ultra-violet light absorbing molecules that are sacrificial in nature. Over time, ultra-violet light eventually breaks down these molecules leaving the varnish without protection. By recoating, you are rebuilding a fresh layer of ultra-violet inhibitors that help to preserve the finish.

Painting

On painted surfaces, Peter recommended following the sealing step with one or two coats of Interlux primer 4279. The function of primer is to act as a filler. It fills imperfections in the surface and creates a base film for the finish coats. Interlux makes primer in white to be used under light colors and in gray to be used under darker colors. If the finish coat is scratched and the primer exposed, the darker primer better disguises itself against a dark color top coat.

The primer coat should be lightly sanded with 220 grit and then wiped down with a painting solvent to clean the surface. Dress the surface with a tack rag to pick up any remaining dust. Apply the surface coats by following the paint can directions and using good judgment to determine if the weather temperature and moisture level in the air are appropriate for painting. He always thins enamel paints at a ratio of 3 ounces thinner to a quart of paint. He recommended 3- 4 finish coats when using enamel paint.

Brushes

For varnish work, Peter recommended using a badger hair brush with a chisel tip. The bristles of a chisel tip taper to form a “v” when looking down the narrow side of the brush. Clean the brush with low odor mineral spirits and keep cleaning until the solvent runs clear. The final cleaning should be with Interlux 333 brushing liquid or kerosene. He recommends using a brush spinner to rid the brush of any remaining solvent.

Some builders might store brushes by suspending them in a solvent. He only recommends this technique if the brush is used nearly daily. Over time, the solvent can attack the epoxy holding the bristles together and lead to bristles coming loose during painting.

Peter also recommended precleaning a brush before using it. This involves running it through mineral spirits and drying with a brush spinner.

Epoxy

The question was raised whether it is good practice to seal raw wood with epoxy. Peter suggested that epoxy sealing works well on plywood since plywood does little expansion or contraction. He stressed that epoxy is flexible, it can follow the reasonable flexing of a hull. However it is not elastic, it will not follow the expansion or contraction of wood. Epoxy sealing should never be used on a restoration. The epoxy encapsulation will trap the wood moisture and could lead to rot if the initial moisture content was high.

Peter firmly recommended that any holes drilled through a hull's wood or fiberglass surfaces should be coated with epoxy to seal the length of the hole's interior surfaces to prevent any moisture penetration into core layers.

Conclusion

Peter's presentation was an excellent tutorial for the CABBS membership because he dwelled more on the process of obtaining a quality finish rather than the products one uses. Peter's best practices have been gained from helping boatbuilders and restorers solve their finishing problems and from his own experiences building canoes.

So get comfortable with sanding. Look at it as a time to unwind from the cares of the day, a time to listen to your favorite music. Remember, the quality of your finish is the first impression your boat will make. Make it an excellent one.

Interlux Boat Painting Guide (PDF, 1.9MB)

Reminders

DEC 14, 2008

Monthly Meeting

Cuyahoga County Library
Meeting Room
Berea, OH
1:30 PM

Guest Speaker:
Carrie Snowden
Marine Archaeological Survey Team





 

 



 

Plans & Notes