breathing

[LazyJack]

People speak regularly on this forum about the necessity for wood to 'breathe'. What does this really mean? Isn't wood dead?
If, in the context of wood and boats, 'breathing' refers to the flux of moisture in and out of the wood driven by moisture gradients (and not by the wood because the wood is dead), most of us endevour to minimize this process as much as possible either by a stable external environments or coatings to minimize the changes in moisture content. What is the role of 'breathing'?

[Bob Smalser]

The ability to lose moisture content as the air loses moisture content.

Gaining moisture ain't usually the problem...the problem is losing it. Polyester goos, for example, absorb water and help the wood gain moisture. Problem is they also seal the wood up so tight is never loses it....and eventually rots if the goo is applied too thick.

[LazyJack]

Why would you want the wood to change moisture content when the air does? Don't you want it to remain stable? Isn't that the point of coatings, to slow the flux of moisture and dampen (no pun, honestly)any changes the environment undergoes? It would seem that the ultimate would be that unobtainable coating that never gets dinged and is impervious to any moisture whatsoever. The wood stays where ever it was when you coated it (no breathing). At the other extreme is NO coating so that the wood changes moisture content freely and easily, gets wet quickly, but dries out quickly too (breathe free and easy but shrinks and swells, checks, weathers and eventually falls apart). Seems like most finishes fall somewhere in between.
I use oil based alkyd enamel, captains z-spar, and/or West epoxy for all my marine finishes...tested, tried, and true...but I never apply it with the intention of allowing the wood to 'breathe', in fact I apply up to six coats in order to slow, as much as possible, the frequency and amplitude of moisture flux in and out of the wood. Am I thinking about this all wrong?

[ 06-12-2005, 05:36 PM: Message edited by: LazyJack ]

[Bruce Hooke]

Duck :eek: :eek: :eek: :D

[Puka]

A quite reasonable hypothesis. But will the audience be?
Maybe, a more evolved wooden boat person can succinctly put us straight here. ;)

[Donn]

"..a more evolved wooden boat person.." Is there such a thing?

[Puka]

Somehow, I dont think so. Unless you speaking of a "plastic boat person" convert? There now.

[Stiletto]

Bob has answered your question regarding what breathing means. In my view the difference between your point of view and his answer is that in traditional forms of boat building in the past there were not the range of sealants and epoxies available that are nowadays commonplace.

Epoxies and other means of sealing out moisture do work well until some failure of the envelope happens. Unless that failure is addressed quickly, that envelope can become a bag which holds water and the rot that comes with it.

Having said that, my personal experience with repairing my trimaran has led me to favour thorough encapsulation of all parts with epoxy.

When I was repairing stringers etc in poorly ventilated spaces, it was the epoxied areas that were still good and the redleaded ones that werent.

Were you looking for a more evolved person or a more evolved wooden boat? ;)

Good luck with the search whichever it was.

[George Roberts]

I agree with Stiletto.

I will add that if you fail to seal all of the wood tight (assuming that is your goal), you will have problems.

[LazyJack]

So Bob, just curious... did you seal your dory tight or are you going to let it breathe with the ambient environment? I took the seal it tight route so I need to jump right on the few dings I accumulated in the varnish last season.

[ 06-12-2005, 10:05 PM: Message edited by: LazyJack ]

[Bob Smalser]

OK....I'll bite.

"Why would you want the wood to change moisture content when the air does? "

Cause it's gonna anyway...you are just slowing it down. Stop it at your peril.

"Don't you want it to remain stable? Isn't that the point of coatings, to slow the flux of moisture and dampen (no pun, honestly)any changes the environment undergoes? "

Yes.

"It would seem that the ultimate would be that unobtainable coating that never gets dinged and is impervious to any moisture whatsoever. The wood stays where ever it was when you coated it (no breathing)."

Impossible....and there's no shortage of fireplace kindling from those who try.

"At the other extreme is NO coating so that the wood changes moisture content freely and easily, gets wet quickly, but dries out quickly too (breathe free and easy but shrinks and swells, checks, weathers and eventually falls apart)."

Keep UV and soil bacteria away from it, and raw cedar and other durable woods can last forever. Wanna see some century-old fence rails?


"I use oil based alkyd enamel, captains z-spar, and/or West epoxy for all my marine finishes...tested, tried, and true...but I never apply it with the intention of allowing the wood to 'breathe', in fact I apply up to six coats in order to slow, as much as possible, the frequency and amplitude of moisture flux in and out of the wood. Am I thinking about this all wrong?"

None of those are impervious to water vapor, whether in one coat or 6 coats. All additional coats get you is slower UV degradation of your finish.

"So Bob, just curious... did you seal your dory tight or are you going to let it breathe with the ambient environment? I took the seal it tight route so I need to jump right on the few dings I accumulated in the varnish last season."

That dory was filleted in Bondo and covered with gelcoat I spent many unprofitable hours taking off and repairing the extensive rot damage resulting from. Frankly, now that I know what to look for, I'll never touch a gelcoated wooden boat again. I replaced the damaged wood and used either red lead primer and alkyd oil paint or Daly's Teak Oil and and Epiphanes-McClosky varnish mix.

[ 06-12-2005, 10:33 PM: Message edited by: Bob Smalser ]

[LazyJack]

Thanks for biting, Bob.

Gel-Coat and Bondo??!

Now I understand what generated that bitter 'polyester goo' reference...Holy Cow! Its lucky that boat found you.

[Bob Smalser]

Originally posted by LazyJack:
Thanks for biting, Bob.

Gel-Coat and Bondo??!

Common as mud in the '60's and '70's. You've seen more of it than you realize.

I've restored two gelcoated boats in a row now.

[Scott Rosen]

Bondo and gelcoat.

I finally (after two years of stops and starts) finished stripping and priming the plywood overhead in my cabin. It was a Bondo and gelcoat/polyester deal. Bondo absorbs water and doesn't let it go. The wood around it stays just wet enough to cause rot.

Let me say something about polyester over plywood. It is the nastiest and perhaps the stupidest thing you can do to a wooden boat. It gets very brittle over time, so it cracks when the wood moves, letting in moisture, mildew, etc., looking terrible, and making it impossible to paint. If you fill the cracks, more appear. Stripping it is a bear. It doesn't melt, chip or peel like paint with a heat gun. Instead it bakes into a nasty, dusty powder that requires great effort and a very sturdy carbide scraper to remove. It dulls sandpaper fast. It's resistant to chemical strippers. And when you're working overhead, the fatigue magnifies the problems.

As to the original post. Water in the form of liquid will get in to the wood. It comes out of the wood as vapor. One ounce of water produces many times that volume in vapor. So water gets in the wood quickly, but leaves slowly in the form of vapor. You need to find a way to let the vapor out. That's what it means to let wood breath.

Epoxy is not waterproof. But it slows the movement of water and water vapor both into the wood and out of the wood. The thicker the coating, the slower the movement of water. But remember, water gets in a lot faster than water vapor can leave.

The closest thing to a sealed wood boat that I've seen work successfully is a cold-molded hull.

[Ian McColgin]

In my observation and according to the literature, epoxy is waterproof (unless you boil your boat) but not vapor proof.

Here's an exhibit of the difference. A friend's wonderfully done over boat has two ashcroft layers of rotary cut cedar over what was originally a conventional mahogony hull - seems reefed and battened before outer layers added. The inside is all epoxy encapsulated.

The cedar is epoxy set and epoxy and vapor penitrable paint coated.

After the five or so year initial rebuild, the boat gained a couple hundred pounds a year to it's stabile weight. Now it looses about 150# - 200# each winter to regain in the course of a summer. If left out of the water for a season, it looses more.

Ok - that's vapor.

Pure water can get in when there is damage to the surface. At one time the boat was moored in the line of fire of the yacht club's Opti fleet going to and from their lessons. Eash time one of those little buggers hit and cracked the surface, the highly absorbant cedar would gather water, not just fully diffused vapor, and create a local swelling and blister.

Water in the bilges, like water against the outside, produces no such damage.

Viva la differance.

[Bob Smalser]

Originally posted by LazyJack:
Gel-Coat and Bondo??!

Now I understand what generated that bitter 'polyester goo' reference...http://i23.ebayimg.com/01/i/04/45/40/f7_12_sb.JPG

The next one I'm looking at is probably worse. A 1938 Rhodes that'll go for much less than the value of the bronze hardware.

Looks pretty good....so why is it worthless?

Not only is the trunk rotten, but some "restorer" glassed the carvel hull with epoxy and fabric a while back.....now I strongly suspect all I'll be able to do economically is scavange off the hardware and relegate that lovely old boat to the burn pile.

[ 06-13-2005, 09:37 AM: Message edited by: Bob Smalser ]

[Bob Cleek]

Of course, nobody's mentioned the most important reason to permit a wooden boat to "breathe," as if one could ever prevent it. It would be near impossible to build a wooden boat that didn't swell with moisture. That's what makes them watertight. Of course, I realize I'm talking to people who mistakenly believe that if they slather enough goop on the wood they can make the boat watertight without decently fitted joints, but anyway....

[Puka]

Were you looking for a more evolved person or a more evolved wooden boat? The former to help me with the later!
Don't take it too literally though.

Thanks to all for your insights.Esp. LazyJack for bringing this topic up.Measuring the moisture content of my hull drying had me pondering the variables.

In my instance,two of the plank faces(edges)
are already coated in epoxy and form a rigid beam
with the adjacent plank; water absorbtion should be kept to a minimum to avoid expansion; therefore
I favour well maintained complete encapsulation.
Whether this is prudent in the long term,time will tell.As for breathing,obviously it won't.
I can see the relative merits of timber being able to breathe on dry stored boats and immersed caulked hulls.

Minimally framed Cedar strip planked cored,structurally glassed, sandwich hulls have been in use for many years now. Are there any reports of failure in this type build?
Possibly, the trade-off, frames for glass, decreases the life span of the boat?
In terms of not being able to release water
vapour and the consequential rot.

[ 06-13-2005, 08:24 PM: Message edited by: Puka ]