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The effects of UV, the hammering heat and humidity on Epoxy and Wood joints.

Back in the UK the greatest threat to a varnish finish was moisture ingression, lifting your finish and the green house effect which promoted the growth of the dreaded black spore fungus.

But living in the tropics is something else! I cannot believe the damage UV, Heat and Humidity inflict on epoxy and wood joints. even those that are coated with paint.

Both masts were built out of what's locally known as Igem (Podocarpus Imbricatus) better known to the rest of us as Yellow Pine. They were built as per plans, long scarfed lats, rebated to form a dodecagon and then rounded. The first mast was built in my absence using Ampreg (GL approved) and looked great! But when I got back, though it was stored indoors, I noticed some of the seams started to open up. I put this down to poor preparation of the wood or a poor resin mix ratio. The building of  the second mast I supervised myself, the preparation was good, moisture levels checked and the resin , Epolam, this time (Lloyd's approved), was weigh accurately using a digital scale.

The work was done and it all looked great. The masts were primed and varnished, same as "Gaia" prior to being moved outside to the assembly point. Since the masts were to be the last things fitted to the ship. they were covered with a light polyester cloth, laid on trestles and set to one side while my apprentices and I got on with the rest of the work.

Within 9 months I cannot get over the amount of cracking, splitting. shrinking and movement in the wood, varnished surfaces especially seem to come out worse but painted surfaces are not safe either as the constant expansion and contraction soon results in hairline fractures on the joints which are then vulnerable to moisture ingression .

I built a Wharram Catamaran to sail to, and to sail in warmer climates, I guess I just have to resolve myself to the fact that owning a wooden boat, especially in the tropics is going to take a hell of a lot more vigilance and maintenance than owning one in more northern climates.

Again like Gaia, it looks like I'll have to now paint the masts if I want to get any longevity out of them, I'll also have to order a long pair of socks from the sail maker that can be stowed at the mast bases and raised using the halyards when the boat is moored up just to give them some further protection from the hammering sun.  

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I used SICOMIN Surf Clear Epoxy with Varnish on my mast. This epoxy is as UV resistant as epoxy can be... No problems yet 

Hi Edward, no the masts were not covered in glass, just epoxy primer and varnish, though the quality of the varnish you can get around here leaves a lot to be admired. If you're going to varnish a quality varnish is required I just thought a local varnish would get me through the interim prior to finishing, I thought wrong. I'm currently sanding them back, running a router with a 10mm straight bit up the areas that have been split and gluing in a spline, after that, I think a layer of cloth is in order. The tops of the masts that were painted white have received no damage whatsoever.

I spoke to a few of those that work on high end yachts like Lurrsen and Feadship about the problem and they simply said it's all about maintenance, they have quality covers for everything, When the yacht is in use and the covers are off even a drop of water on the varnish work is enough to magnify the suns rays and do damage so they have crew that just wipe down everything constantly until the covers can be put back on.

On hindsight I think I was far too optimistic as to how much varnish work I could have on my boat, looks like now it has to be all paint. Fortunately I know wood graining and rocking techniques to make the paint look like wood. Not the real thing, but close.

Hi Jacques, I'm finding that even the surfaces covered with glass, fairing compound and paint is coming under fire. I'm beginning to see some hairline cracks on the fairing compound. This will lead to problems later if it's not addressed now.

Thanks Michael, I'll look out for that! I wouldn't mind running a few tests.

When building a composite wood boat, it is important that all wood surfaces are completely coated with epoxy in order to encapsulate the entire part, which keeps the moisture content from changing. The epoxy must then be coated with a UV resistant coating (paint being one of the best solutions,) anywhere sunlight may contact the epoxy coated surface.

It sounds like your masts were not adequately coated with epoxy on the interior surfaces. This would allow moisture/dryness to attack one side of the wood causing expansion/contraction within the individual pieces. It also may be the case that the interior of the mast pieces were coated, but interior lines or electrical wiring chaffed the epoxy exposing bare wood.

Another solution is to only apply epoxy to the glue joints, then coat the mast with a high quality latex paint which will allow the wood to breath naturally, yet prevent most forms of checking.

Regardless of the methods used, wood (solid lumber) needs maintenance and restoration from time to time, especially when used for mast construction, due in part to the amount of movement imparted on the structure over time.

Yes, I agree that the only way to build a composite boat for the tropics is to fully encapsulate the wood in epoxy, plus fiberglass cloth (biaxial  below the waterline) on the exposed surfaces, and then finish with a light tint paint. What my experience in South Florida as a boat carpenter for over 35 yrs has shown me is, however, that coating ..."with a high quality latex paint which will allow the wood to breathe" is no solution, as the paint-to-wood bond will crack and fracture within a few years...That said, anyone who has a chance to see the Ariki's quality craftsmanship (now at Crackerboys' Boatyard in Riviera Beach) of Budget Boater would do well to try to come even close...I calculate that a 46 ft Wharram needs around 80-100 gals of epoxy, plus 250 yds of 6 to 11 oz cloth...

With high quality latex paint (and a properly prepared surface), the bond will not break any faster than any other high end paint or varnish. Latex paint manufacturers live and die by being durable, easy to apply, and having a firm and long-lasting bond. The market in latex paint is so fierce that they spend many millions of dollars in advertising to sell paint at $30 per gallon, yet yacht/automotive paint manufacturers spend a fraction in advertising to sell $700 per gallon paints. If latex paint didn't work, the paint companies would go out of business spending millions on advertising. Some of the most well known names in wooden boat design and craftsmanship promote and use latex paints.

Latex is not for everyone. But I have seen it used on wooden boats for decades with little complaint, lasting far longer than a few years.

dennis schneider said:

What my experience in South Florida as a boat carpenter for over 35 yrs has shown me is, however, that coating ..."with a high quality latex paint which will allow the wood to breathe" is no solution, as the paint-to-wood bond will crack and fracture within a few years...

As for this particular statement below, the credit goes to Boatsmith, not myself. With boat building, I do not rise to this high level of fit and finish in a boat. Custom cars and motorcycles, yes. Boats, no.

dennis schneider said:

That said, anyone who has a chance to see the Ariki's quality craftsmanship (now at Crackerboys' Boatyard in Riviera Beach) of Budget Boater would do well to try to come even close...

I used polyurethane 1component coat on the epoxy coated beams of my Pahi 31, this is now lasting for 12 years and looks nearly like new, the maintenance has been pretty marginal, the coating is called Coelan, quite difficult to apply, but when done properly it lasts forever and can copy with quite some abuse.

However, if you trap some moisture or do not apply it in the right way it can go horribly wrong.

I built a 30 foot  hollow wooden tapered mast and have had it in the tropics for 5 years now and have had no problems with checking or delimitation still has original paint. I built to the following specs.

- wood was Australian red cedar, Mast laminated and scarfed from 12" 2" sec
- epoxy coated inside and out no cloth
Jotun vinyl primer between epoxy resin and white Jotun epoxy topc coat
I suspect yellow pine may not have been the best choice for spar material. The Jotun vinyl primer between epoxyresins and epoxy paint seams to be a great combination. I used it on the hull and have not painted in 5 years and it may last another 5. This paint schedule was recommended by the technicians at Jotun Thailand.

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