Saturday, September 15, 2012

An Interesting Observation About Paint

For those of us who are obsessed with small boats it is almost impossible to avoid becoming aware of the complexities of painting. Unfortunately, I have the sort of personality which over-complicates everything, and the subject of painting and varnishing was a vicious trap just waiting for me to come blundering along.

It was all a lot easier when I didn't know what I was doing. As a child, and as a young man, all I had to worry about was opening the can, stirring until the lumps disappeared, tipping in a little turps until the brush stopped dragging and everything was sweet. I assumed that bristles came out of brushes, so therefore I didn't try to pull them out of the applied paint, and I didn't get angry or stressed.

I also assumed that paint stuck to everything, so I didn't get stressed about chemical bonding windows, sanding of shiny surfaces to get 'tooth', and matching primers, undercoats, and topcoats. In addition, nobody told me that I would be struck down by lightning if I painted directly from the can rather than decanting into a separate pot. Oh, life was much more simple in those days.

Unfortunately, experience, common-sense, an inquiring mind, and a genetic predisposition to over-complicate everything has thown me headlong into the paint and varnish trap. Trust me whan I say that I have a true love/hate relationship with paint, and to a lesser extent, varnish.

A nice job of painting and varnishing. The Phil Bolger-designed Harbinger we built back in 2003/2004. She was built strip-diagonal, with an inner layer of 7mm Western Red Cedar strip, followed by two diagonal layers of 3mm Hoop Pine.
I think I'll write a few more articles about the various paint systems that I think are appropriate to small craft which live on trailers, but at the moment I want to bust a specific myth.

Two days ago, my wife, dog Brandy, and I went away on a 24 hour holiday. Hitching on our little caravan and having loaded my old sailing-canoe on the roof-racks, we set off for a nearby lake and spent 24 hours reading, sailing, paddling, and walking. We tend to regard visits to nearby destinations as not being "proper" trips, but the fact is it makes sense to maximise the stay time and minimise the travelling time. In this case we had no option - nearby destination, or no trip.

Not bad for a holiday destination less than 15 miles from our house!
 The boat on the car is an Iain Oughterd-designed MacGregor Sailing Canoe which I built in 1991. She has been on a number of interesting and long journeys, but in recent years she has sat around gathering dust due to my workload.

Because of the simplicity of this short trip, I just spent my time fiddling around, and I took the opportunity to wash the canoe and remove many years of built-up storage dust and mildew.

Scrubbing the old boat in pleasant surroundings
The outside of the hull and the gunwales were showing significant deterioration in the paint film. This boat had originally been painted with a single-pack, oil-based enamel, but the outside of the hull and the gunwales had suffered physical damage during a period of heavy use. As a result of this damage, a few years ago I decided to sand back and repair the hull and gunwale surfaces, and after very careful surface preparation, paint them with an exceptionally high-quality single-pack oil-based polyurethane-modified enamel from a very well-known international paint company based in Europe. The inside of the canoe was OK, so I left the original paint in place.

I was very pleased with the high standard of the new paint job, but when loading the canoe for an outing less than a year after completing the re-painting, I was horrified to note the appearance of some very fine cracks in the paint film, presumably caused by checking of the plywood veneers beneath. The planking of the boat is 5mm Hoop Pine Marine Plywood made to AS/NZ2272, which is one of the most stringent plywood standards in the world, so I knew that there was no problem with the quality of the plywood. As the surface preparation was good and the paint was one of the best available, I just shrugged my shoulders and decided that single-pack oil-based enamels are not suitable over Hoop Pine and (from what I have heard from American and Canadian writers) Douglas Fir plywoods. The fine surface checking of these plywoods has no effect on them structurally, but it obviously cracks through oil-based enamel paint - something I have encountered many times before, I have to say.

Back to cleaning the sailing canoe. After finishing the outer surfaces of the hull and gunwale, and noting how badly the paint cracking had progressed, I rolled her over to continue cleaning on the inside.

Contemplating the interior of the sailing-canoe.
Suddenly, like a bolt out of the blue, I realised that my old sailing-canoe was being a teacher, but that I, as a student, was somewhat slow. As I scrubbed away at the inside of the hull using my big sponge and a couple of gallons of lake water, the cleaned paint showed not a single crack. The surface showed some signs of wear due to abrasion in places, but was essentially in perfect condition after twenty-one years of intermittent use. At the time I built the boat I didn't have enough spare money for a fancy marine paint, so I said nothing to anybody and went ahead using plain old oil-based house paint (Dulux Super Enamel from memory) over pink primer and oil-based house undercoat.

Difficult to see here, but the outside is in poor condition but the interior is nearly perfect
The point of this overly-long story is that books, magazines, internet forums, and group conversations frequently contain debates about the difference between "marine" paint and "house" paint. I hasten to add, that by "house" paint I am refering to oil-based single-pack house paint which I guess is based on an alkyd resin. 100% acrylic water-based house paints are another thing again, but aren't what I'm talking about here.

Some people say that the only difference between "marine" and "house" paint is the printing on the can. I disagree, as most of the marine single-packs that we have available to us in Australia are polyurethane-modified enamels, and they do have a very hard and shiny surface. Regardless of the chemistry, the arguements have continued for as long as I can remember with the conspiracy theorists saying all the paint is the same. By the same token, there are many people who throw their hands up in horror at the thought of using "house" paint on a boat, despite the fact that some towering authorities have said it is OK - the late John Gardner being one of them - surely a weighty recommendation.

Sailing after the wash. The sail is not as per the plans, being a sprit-boomed leg-o'-mutton from a Bolger Nymph set on a yard and boom as a boomed lateen - I just can't stop rig experimentation. The mast is the one for the proper rig, which explains why it looks to be too long in this photo.

I've been up, down and around the painting tree many times, but for twenty-one years an experiment had been conducting itself in my own back shed. My Macgregor sailing-canoe has delivered a verdict to me which says that house paint is fine to use on a small sailing, rowing, or paddling boat made from wood. In fact, in this application it had performed better than the marine paint. Now don't get me wrong - the marine paints are extremely good as long as they are used in an appropriate fashion. In fact my favourite single-pack polyurethane enamel is Norglass Weatherfast which is a marine paint, and my favourite non-polyurethane-modified paint is Hempel Multicoat which is also very much a specialist marine paint (which is self-priming and self-undercoating as well!)

A pleasant evening sail
I've got plenty more to say about paint, including a discussion about the use of 100% acrylic water-based house paint (known as "latex paint" in the U.S. which is interesting because there is NO LATEX in water-based acrylic paint ). I'm also about to start a series of experimental applications of WR-LPU (water-reducible linear polyurethane), which I first used back in the year 2000. From my past experience, this stuff is tricky to apply properly, but if done well over the correctly prepared surface, it is exceptionally tough, UV-resistant, and durable.

In the meantime, if you feel like using a house paint such as Dulux Super Enamel for example, go ahead without thinking you are committing a nautical sin. As long as you follow the instructions and carry out the correct surface preparation, you will get a good result.

Back to the 24-hour holiday - it was wonderful, providing benefits which will last much longer than the trip away.

The view from my bed in the van...........
.......and from my camp-chair at night.


  1. Unfortunately, here in the UK we seem to have left off the requirement to tell the customer what type of paint is in the tin. The Health and Safety Gestapo have effectively removed all of the old oil based enamel paints from the choices on offer, and the only way to tell if it is actually not an acrylic is to read the brush washing instructions.
    I too have used old Dulux oil based paint on my boat, as well as an oil based custom mixed car enamel, on top of the original "Marine" single pack enamel. I'm now touching up with "Marine" single pack of unknown constitution, International "Toplac", and having the same checking problems as you, for the first time in twenty seven years. I would happily go back to old Dulux if I knew where to get some.

  2. I am just speculating here but I wonder if the house paint has been formulated with the expectation that the moisture content of the underlying wood will vary and hence the paint will be designed to be slightly flexible (especially if it will not be subject to much abrasion). Marine paint, on the other hand, is perhaps formulated with the expectation that underlying surface is stable and that abrasion resistance and hardness is more important. Hence its greater vulnerability to small wood movements.

  3. less painting; more sailing, rowing and camping I say.

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  5. Thank you for sharing this interesting and informative article, painting with airless spray gun will be faster and more interesting!

  6. Ross, I'd be really interested in your comments on 100% acrylic house paints. There are some new 'enamels' which are actually chip resistant acrylics.