Sealing wood? (followup on Mongo's post)

I've always had the question, never understood the answer...?

What do you do with wood before you paint it?
Why do you do anything with it?

So here's a 17 yr old piece of wood in the rear seat of my skiff. It's spent most of its life in the Salt air. Now its inland and still spends most of its life out doors.

The Paint from the past is shreded and split away from the wood.
So I'm getting ready to paint it. I want it smooth.
I dont want splinters and I dont want the seat tearing up my cushion.
I sanded all the loose stuff off the seat.

So would some Porch n' Deck paint be good?
How about just plain old Log Oil?
Do I have to seal it first?
What does sealer do?
Can I just seal it and forget it?

Somebody spend some time talking about the reasons for paint and the prep for the different reasons.

Yes, I've owned wood boats since '49' and calked with Cotton, sealed with different kinds of putty, painted with different kinds of paint.
The one thing that's constant is that everything changes.
Every time I got ready to paint, something was different.
In all that time, I dont think I ever really understood all I knew about paint!

 

sealing your wood is just extra protection ( i think,, i love wood boats,,, wont work on them tho,,hehe) in case water gets past your paint.but without the "sealing" i would sand,, blow off REAL good,,then paint her with deck & porch paint,,,,unless your skiff is worth $180 a gallon for awl-grip,,hehe
but i will say wait for the "woodies" to chime in about the sealing,,,,but,, if paint is on thick and right,,,thats your sealer too.

 

Once before (in the old days) I was painting a Cedar boat.
I took a quart of the paint and thinned it. I put two coats of that thinned paint on to use as a sealer and as a 'lure' to pull in the thick paint.
I figured the thinned paint would sink in further than the thick stuff, which would give the Thick stuff something to stick to.

I guess it worked, the thing was still painted and looked good when we took the chain saw to it 7 or 8 years later.

From where the sun stands right now, I shall paint no more forever! (except for this little boat seat)

 

ya thinning will help with sealing IF it isnt ply.and either way,,i think it'll be alright,,,maybe this will be the LAST paint you spread on her.

 

You can bet on that!
Thanks

 

Sealing wood for paint, I've often already epoxied the surface. My rudder is an example. It's plywood with glass cloth and epoxy. After two seasons, I see no paint letting go.
My seats are fir ply, and those will soon be replaced. No epoxy was used to seal the wood. After one season, paint is letting go.
Somewhere in between would be jobs properly prepped, primed, and painted. Those do pretty well, but never as well as epoxy-primed areas.
You might hear that paint will let go from parts that are only partially epoxied.
Well, no, I wouldn't agree with that. The WOOD may move enough to crack the epoxy layer because it's expanding and contracting more than the epoxy can stretch and THEN the water can get into the part from the epoxied side, but this is rare unless the part is wide (like a seat or a coaming).
More likely, incomplete epoxying will cause problems in the bilge. In the open air, especially inside a cabin, a simple coat of varnish or paint without epoxy is fine. Even putting nothing on the wood inside while epoxying the outside above water (just to prove a point) won't necessarily cause a disaster.
Any covering on the surface slows moisture transfer a lot. This allows the wood to take up evenly (moisture change from inside to outside are nearly identical because the transfer is so gradual).
Too much moisture under paint will cause lifting however. Not on the epoxied side, but the painted side. It's doubtful this will happen, however, unless moisture in the form of constant ongoing humidity, rain, or immersion is taking place. Otherwise, the half-paint/ half epoxied piece will expel moisture as often as it takes it on, never reaching the more saturated level that liofts paint.
Bottom line is to follow general good practices. Keep the surfaces sealed well by regular maintainence. Epoxy-seal for a longer lasting paint job or if you might not be able to maintain a good painted surface. Epoxy will forgive poor maintainence.
You can mix sealing mediums (epoxy and paint or epoxy and varnish, etc.) if the non-epoxied surfaces are well covered and maintained, and if the part being sealed is not wide solid wood like a seat or a coaming. I'd see no problem with an inside to outside bulkhead where the material is plywood and the interior is only painted. The outside paint certainly won't peel.
When I put anything together, I think about the kinds of moisture trasfers in the piece that could happen so fast that one area might be a lot more damp inside than another, and then I make sure to prevent such unequal moisture distribution. A bare area, even submerged for a few seconds will cause havoc, causing not only extreme unequal moisture content, but excess moisture that could lift paint, or expand/warp wood.

Alan

 

Alan hit the point most have missed here. Moisture vapor transmission and it's control.

Traditional build methods permit substantial amounts of moisture gain and lose from it's wooden structural elements. As a rule most modern methods do not.

This is why traditional building methods employed Dutch oil and paint coatings. These permit a fairly high percentage of moisture transfer, though the coating. Since the structure is designed for this movement, it's okay.

Natural oil finishes are highest on the list of moisture vapor transmission around 76%.

Flat acrylic (unmodified latex) paint is second highest around 57%.

Gloss acrylic and flat enamel paint is around 47%.

Good quality marine varnish about 28%, gloss marine oil paint a few precent better.

Good quality spar urethane around 24%

Old fashioned 3 pound shellac about 22%, which compares equally to cheap quality polyester resin.

Good polyester resin (iso) 19%.

Vinylester resin 12%.

Cheap, unrefined epoxy 9%.

Good quality marine, laminating epoxy 3%.

The epoxies have a clear and distinct advantage over all comers, though vinyester is quite good, if the movement can be controlled through engineering.

Interestingly, 3 pound shellac is better then clear spar polyurethane, varnish and lower grades of paint. I guess these old timers had a clue about what was going on in their wooden boat creations.

In the end, you have many choices of materials. You also have nearly an equal number of choices in application. None better suited then others, unless a specific task is desired on a specific problem.

To directly answer the original poster's question about what to do with raw wood - well it depends on the application. In some situations, you'll want a very hard paint system like a two part polyurethane, but other applications may require an oil finish. As for your skiff's seat, any good quality paint will keep splinters out of your butt. With any coating, prep is 90% of the game. If it's prepped properly (for the tasks asked of the coating and/or required by the wood), it will last quite a while, much more with good care.

 

see ,, i knew the wood dudes ( Alan,Par) would show up,,, they probably saw the words "wood" and "the1much" ,, and screamed that it might be too late,,,,haha
Thanks guys

 

Well, I may not have been able to absorb all that good technical information.

I found some Automotive primer and saturated the seat with it.
After a day or two, I put the Acrylic Latex Floor paint for outside and inside on the seat. Two coats.
It sure feels good. Smooth n' slick. I just wonder what it'l be like after a year out in the sun? Good I hope.
Thanks to all. I was impressed with all the knowlege.

 

good for you man!! ,, now,, you HAVE to come back next year and let us know how it stood up.
Happy boating