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Dave Carnell's Boatbuilding Page:
Articles from Boatbuilder and Other Magazines 

Introduction:

I am a retired chemical engineer who has been messing about in boats for well over 50 years. e-mail me

 

Contents:

Latex Paint For Boats

Waterproofing WoodWATERPROOFING WOOD

Page A3

A4

Page A5

A6


 


Latex Paint for Boats

WARNING:  Warning this article contains material that may be offensive if  you think painting is more fun than boating. 

When I bought my first yacht (27’ auxiliary sloop) for $300 in 1951 I quickly learned that if its for a boat, the same material costs several times as much as if it is for your house.  Oakum was $1/lb. at the marine supply store; five pounds for a dollar at the plumbing supply store.  Marine paint cost several times as much as house paint of similar composition.  I worked for a major chemical company that also made paint and knew that their paint that made the most money and on which they spent the most on research was house paint.  Houses are out in the weather all year-no winter cover or inside storage.  Their owners expect to repaint them infrequently, such as every ten years or so.  They also expect a good paint job will require little preparation before repainting.   Back then the only house paints were oil paints, so my yacht was painted with top quality oil-based house paint.

All paints consist of binders or resins, pigments, solvents, and additives.  The binder forms the film that sticks to the boat and holds the pigment there.  The pigments color the paint, make it opaque and have a good deal to do with UV resistance.  Solvents keep the binder dispersed or dissolved and the pigments dispersed in an easy to apply state.  They allow the paint to be applied in the correct thickness and then evaporate from the paint film as it
dries.  Mineral spirits, a petroleum distillate fraction, is the most common solvent in oil-based paints.  In latex paints, water is the major fluid.  It does not dissolve the latex particles, but disperses them in suspension.  Small amounts of special solvents are present to control the coalescence of the latex particles into a tough, tenacious film and to slow down the drying of the latex paint.

Through the years latex paints have developed to the point where 100% acrylic latex paints are better than oil paints on all counts.  They are more durable and tougher.  They resist chalking and fading, retaining their color especially well when exposed to bright sun.  They are easier to apply, going on more smoothly and with less brush drag.  They have less tendency to grow mildew.  They have almost no odor and no fire hazard.  Cleanup is with water.  They can be recoated in as little as one hour.

The 100% acrylic latex is the key to the outstanding latex primers and paints now available.  The weather resistance of these polymers parallels that of the acrylic molding powders that make red automobile taillight and stoplight lenses that last forever without fading.  I checked out all the top quality exterior primers, paints, and porch and deck paints at both Lowe’s and Home Depot-they are all 100% acrylic latex products (the Glidden latex exterior primer at Home Depot used an organic nomenclature I hadn’t worked with for 50 years, but my Handbook of Chemistry and Physics translated it to 100% acrylic copolymer latex).  All of the products are available as custom colors mixed to your desire.

Your new boat went together pretty fast-instant boat or tack and tape construction.  What kind of a paint schedule can you use to get it in the water next weekend.  Let’s say the inside will be all one color and the outside all one color, not necessarily the same as the inside.  You can do the outside in one day, the inside the next, and give it a couple of days before you launch it.

Here is the schedule.  Sand it all over with 60 grit and clean up the dust.  Put on a coat of latex primer.  That will raise some hairy fuzz, so after drying a couple of hours give it a once over with 60 grit to defuzz it.  Put on a coat of your exterior latex paint.  Gloss is the toughest and most durable, but also shows surface imperfections best.  Semigloss is almost as tough, durable, and easy to clean as gloss while not showing surface imperfections.  For me, it is the usual pick.  I have stayed away from flat paint.

You won’t have to sand after the first coat of finish paint and you can easily recoat in the afternoon.  That finishes half of the boat.  The next morning turn it over and repeat the schedule for the other half of the boat. 

If you use two colors on the outside of the boat, you will add another day to the painting.  If you use different colors for the bottom and the side on the inside and have a steady enough hand to cut it in at the chine you can do it in one day.

While it is best to wait a week for the paint to dry hard, don’t let it keep you from getting in the water before next weekend.

A posting on the rec.boats.building newsgroup on the Internet asked if latex paint was good below the waterline, as if it was going to wash off.  Look around your neighborhood.  All those houses painted with latex paint sit out in the weather all the time.   My boats live in the water with their latex paint jobs.  Platt Monfort recommends for waterproofing the Dacron® skins of his Geodesic Airolite boats “...the simplest method being a good quality
exterior latex house paint.”

How long is the latex paint job going to last?  My sailing skiff that lives in the water was three years old this spring.  The inside, especially the bottom, was scroungy from bilge water and having been through two hurricanes, so I gave it a one coat repaint job this spring.  It looked great until Hurricane Bonnie messed it up this year.

The 16-year old Uncle Gabe’s Flattie Skiff (Sam Rabl) built of ¼” fir plywood was painted when new and then about 9 years ago.  It looks pretty scroungy, but the interesting thing is that while the paint on the wood has been scoured off by hurricane winds and general wear the paint on the epoxy-fiberglass joints in the sides is perfectly intact and looks great.

A fellow who was donating a boat to our local museum told me he had the real secret to boat painting.  He had painted a production plywood boat with latex primer and latex paint.  He was sanding the paint off and found it was almost impossible to remove the last traces of the latex primer because it had penetrated the wood to some degree.  Well, nothing soaks into wood like water and some of the pigment particles are bound to be carried along with the water vehicle of the latex paint.

When I rebuilt my 1964 Simmons Sea-Skiff 20 I used a heat gun and a wide chisel to remove about a dozen layers of old oil paint.  To repaint I used latex primer and then two coats of Lowe’s “Severe Weather” 15-year guarantee semigloss latex exterior paint custom colored to match the “Simmons blue” that was next to the wood.  It
has been three years and three hurricanes ridden out on the mooring since the boat was launched.  Except where the boat has rubbed fenders or the edge of the float and on the cockpit floorboards the paint is in first class shape.  I do need to repaint the floorboards.  In my survey I found that Lowe’s has an exterior 100% acrylic latex skid resistant paint (Skid-Not®) that can be custom colored.  I believe I will try it.

I am not alone in appreciating the outstanding performance of 100% acrylic latex paints for boats.  Thomas Firth Jones, boat designer, boatbuilder, and author of Boats To Go wrote in Boatbuilder several years ago that he preferred latex paint over oil paint for boats for all of the reasons cited above.  He did comment that he paints his tiller with oil-based paint because the latex paint stains there.

I was talking with “Dynamite” Payson one May weekend a couple of years ago and he told me he was going to repaint his skiff with latex paint that weekend.

Jim Michalak, boat designer and builder, uses latex paint on his boats.

Phil Bolger reported in Messing About in BOATS that his personal outboard boat is painted with semigloss latex house paint.

Boatbuilders are traditionalists and it has been a hard sell to get them to accept plywood, stitch-and-glue construction, epoxy adhesives, and other similar innovations.  Don’t let tradition keep you from benefitting from the ease of application and outstanding performance of 100% acrylic latex paints.
 
 


A2:

The woodworker/boatbuilder mythological belief that linseed oil waterproofs wood was proven false close to 100 years ago. The U. S. Department of Agriculture Circular No. 128, October, 1930, Effectiveness of Moisture-Excluding Coatings on Wood, described work done at Forest Products Laboratory beginning in 1914. Their conclusion then, and in all their subsequent work, was that while some treatments slowed the dimensional changes of wood as it absorbed water “...a linseed oil coating had little effect.” During World War I (1914-1918) much trouble was encountered with wood airplane propellers getting out of balance and changing shape as a result of moisture changes. FPL developed covering propellors with aluminum leaf (extremely thin aluminum foil) that performed best at preventing shape changes and was used. The 1930 Bulletin described work after World War I that included coatings of five coats of linseed oil plus two coatings of floor wax and, also, soaking wood in linseed oil. They also tested the complete range of paints, enamels, and coatings available at the time. They had their best results with aluminum paints and some varnishes. Again they concluded, “Coatings or treatments with linseed oil, floor wax, and the like were low in effectiveness.” FPL research on the subject continues today. The latest publication I have is Research Paper 462, December, 1985. Results reported include treating wood with linseed oil and linseed oil dissolved in mineral spirits. In both cases, the treated wood absorbed more water in a high humidity (90%) chamber than did untreated wood A modern myth is that epoxy resin penetrates sound wood and that epoxy coating prevents water from being absorbed by wood. Except for end grain, and especially plywood edge grain, eopoxy does not penetrate sound wood to a significant depth. This is true for epoxy thinned with large amounts of solvent, except in contrived experiments with balsa wood, a natural sponge. FPL found that three coats of epoxy resin gave the lowest water absorption of any of the coatings they tested, but after 60 days at 90%RH the epoxy-coated wood had absorbed 73% as much moisture as if it were uncoated. Boats are immersed in water, so I measured water absorption while immersed of ¾” pine coated with three heavy coats of epoxy resin. These coatings were about twice as thick as used at FPL. In fact, their total weight was a little over 30% of the weight of the uncoated wood. Immersed in water they absorbed 20% by weight of water in 200 days. That is the water content required to sustain rot organisms. There are two other requirements for rot to occur-presence of the organisms and oxygen to sustain them. The rot spores are astronomically larger than water molecules, so if the wood did not have them to begin with, epoxy coating would likely keep them out. As to oxygen, the oxygen molecules are far larger than water molecules and do not have the unique properties of water molecules that make them capable of penetrating any organic material-natural or synthetic. I learned this the hard way while supervising spending a couple of million dollars around 1960 on a DuPont research project to make building products and pipes of resins reinforced with kraft paper. Dry kraft paper is a pretty strong, stiff material; wet, it is like the proverbial dishrag. The chemists doing the experiments tried every polymerizable mix they could conceive, including epoxy resins, to make products that wouldn’t lose their stiffness in long-term contact with water. The research director held his head in his hands when I reported that we had had zero success. I also coated exterior fir plywood (three equal thickness plies) and underlayment lauan plywood (thin skins and thick core) with about 30% of their weights of epoxy resin. The fir plywood took about 1½ years of soaking to reach 20% water absorptiion, but the lauan hadn’t reached that point in two years and looked as if it never might. This resuly hints that the glue lines between skins and cores of plywood are quite effective barriers to water absorption. David W. Carnell 11 March 2004

 

Questions:

You may call Dave Carnell - 910-686-4184;
7:30AM to 9:00PM, Eastern time or e-mail me: davecarnell@ec.rr.com
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