Osmosis, varnish & wood

[J. Dillon]

With over thirty coats of varnish on my bright work I would think it would be dam near waterproof. Well guess again. :rolleyes: On horizontal surfaces where moisture can collect and sit from rain, due etc., my thwarts have definite signs of expansion and contraction. :eek: I can see where the wood has swollen and now returned to former dimensions now that it has had time to dry out in my basement.

Consequently some splined glue joints have let go. :( After cleaning them all out I'm presently reglueing and putting in "butterflies" as well as splines on insecting joints at right or near angles. I hope this works but only next season will tell.

Anybody else have osmosis tales ? :confused:

JD

[thechemist]

What sort of glue did you use to glue those splined glue joints together?

[J. Dillon]

Chemist,

Resorcinol on white oak. I'm now using epoxy on the reglue job.

Maybe 40 coats this time and a trained seagull to wipe up the rain and due puddles, and sometimes in the fall duck s..t. :eek:

JD

[Scott Rosen]

Did you apply CPES as a sealer under the varnish?

Have you considered that heat/cooling cycles will also cause these problems?

[J. Dillon]

Scott,

When I built this boat back in 95, I never heard of CPES . The WB Forumn wasn't even around.

Heat cooling cycles....MMMM something to think about. :confused:

JD

[Scott Rosen]

JD,

I've seen separation in varnished joints that were exposed to the sun.

[NormMessinger]

Whew, with all that varnish I'd put my money on heat expansion.

And anyway it would be diffusion not Osmosis, yes?

--Norm

[ 12-23-2002, 07:21 PM: Message edited by: NormMessinger ]

[Mr. Know It All]

JD.....How big is your boat? Might be a good time to strip, reclinch and refinish. I'm working on a restoration job (16ft. plywood lapstrake) I hope will be completed by spring(April-May). What kind of boat do you have?
Peace---> Kevin in Ohio

[J. Dillon]

Mr Know it all,

"Carrianne" is 18'2" V bottom sprit rig skiff of my own design.

http://www.imagestation.com/picture/sraid20/p7a2d9a07e502d0966900e849e0e9c13d/fdbb5932.jpg

At the dock

http://www.imagestation.com/picture/sraid10/p9f8889e9ed3fef496f9d6ebd54111f39/fe029891.jpg

Under sail. She now has a jib as well but I haven't a decent picture.

As you can see she has a fair amount of bright work but 90% of it is in good shape. Just one or two joint failures at the mast thwart.

JD

[Mr. Know It All]

Wow :eek: .Beautiful. :cool:

[Mr. Know It All]

Originally posted by Mr. Know It All:
Wow :eek: .Beautiful boat JD. :cool: The 1961 Lyman I'm woking on will hopefully look like this 1962 model in the picture when I'm done.

http://lymanboat.com/bull.jpg

Peace---> Kevin in Ohio

[Carlsboats]

Varnish and paint may make wood waterproof but they won't make it moisture proof. Moisture vapor will work its way through almost anything, including multiple cots of varnish on a bot seat.
Several years ago Michael Dresdner, a well known
expert on wood finishing matters, reported to a symposium of guitar makers about experiments done
on instruments, some with interiors left raw and others with coatings of various kinds on the inside. This was in response instrument makers who have decided to coat the insides of their products to "keep them from taking up moisture."
In the experiment, one side of the wood samples was exposed to high humidity and the other side was left bone dry. Within hours to a few days at the most, the relative humidity on both sides was the same. Tht was true for both finished and unfinished samples. Dresdner reported that the moisture simply went right through the finish. Yes, the presence of a finish did slow the
process of equalization, but not for long.
Many types of coatings were tried --paints, epoxies, etc., but the only finish that actually prevented the passage of moisture vapor was gold leaf.
Dresdner likened the commonplace finishes to a bowl of dried-out noodles. The surface looks and feels dry to the touch, but if you put water on it and wait a while, the water will permeate the pasta.
Thus, according to this experiment, the idea that by painting or varnishing a guitar, or a boat, you can keep the wood from taking up moisture, is just plain wrong.

[Mike Field]

So what about gold-leafing those thwarts, Jack? smile.gif

[J. Dillon]

Mr Know it all or Kevin,

Looks good. :D Hope you restore it to the way she should look. ;) Are the bottom two images your boat ? She seems to be beautifuly done now. :D How did you strip of the old varnish, chemicaly or with a scraper ? I bet it was tough working between the frames or ribs. ;)

Carlsboats,

That is an interesting concept about moisture penetrating but not water. I do think the plane presentation has something to do with it. All vertical surfaces are OK, the varnish holding up perferctly as the water or moisture drains off. But where it can "puddle" and collects is where the trouble starts.

Chemist, Is that osmosis working to allow moisture to penetrate varnished or painted surfaces ? :confused:

Mike,

I guess gold leaf is the answer? ;) With the price of gold going down and varnish up, they might in the future cost about the same.
:rolleyes: But will it look as good as varnish ? ;)

JD

[Mr. Know It All]

JD......Unfortunately those pic's are not of MY boat but I'm using them for inspiration since it's almost an exact match of the model I have. :D I started out with chemical stripper and hated the mess and toxic fumes. I soon switched to heatgun and scraper after getting some great advise here on the forum. I still have a long way to go but hope to have her in the water sometime in 2003.

Peace----> Kevin in Ohio

[Paul Scheuer]

JD: To me the true genius of traditional boat design is knowing how the parts will move relative to each other, and treating the intersections appropriately, to minimize the effects of the inevitable intrusions. The parts will move. If you really want a monocoque (sp?), you need a whole different approach. Very nice boat, by the way. Got any more pics ? Maybe some close-ups of the problem areas, sail plan.

[thechemist]

Quote:
Carlsboats:
Varnish and paint may make wood waterproof but they won't make it moisture proof. Moisture vapor will work its way through almost anything, including multiple cots [coats] of varnish on a bot [boat] seat.
<snip> the idea that by painting or varnishing a guitar, or a boat, you can keep the wood from taking up moisture, is just plain wrong.

J. Dillon:

Carlsboats,

That is an interesting concept about moisture penetrating but not water. I do think the plane presentation has something to do with it. All vertical surfaces are OK, the varnish holding up perferctly as the water or moisture drains off. But where it can "puddle" and collects is where the trouble starts.

Chemist, Is that osmosis working to allow moisture to penetrate varnished or painted surfaces ?

Unquote:

Well, let me say this about that.

Where liquid water sits on a surface, the water vapor concentration [under the water-puddle, against the varnish] is much higher that where moist air sits on a surface. Thus, your observation that the varnish fails where water puddles is logical. Varnish may be a relative barier to water vapor, and better to the liquid form, but evidently the bond of the varnish to the wood is the weak link in the adhesion-chain.

Various products or techniques have reputations for improving varnish life. That is one thing that will help.

The surface design that allows water to drain is another thing that can help, but in this case you are stuck with what you have. Consider weep holes to allow puddles of water to drain. Naturally, the inside of these holes in the wood should be treated to make them water-resistant, or lined with stainless tubing.......

There are no absolute water-barriers. Water in the vapor state is individual molecules, about three angstroms in size, and they go through anything that has spaces between its atoms or molecules of about that much, or more. Even gold leaf is permeable, just not very fast.

The key to making wood stable is to make it stable in the long-term, which means long compared to the time of water-exposure. The moisture content of the wood thus tends towards the average seasonal or annual humidity of the air where you are, and varies little, due to the effectiveness of the moisture-diffusion-barrier surrounding the wood.

This is the theory of the WEST-System "epoxy encapsulation", but it only works on doors and other structures that are not exposed to liquid water for long periods.

I personally immersed WEST-coated cedar in water, and weighed it at intervals. It showed little weight gain for about fifteen weeks, as I recall, and then a very abrupt weight gain of over twenty percent. What happened there is that water VAPOR slowly diffused through the epoxy film, and the wood expanded as it does when it absorbs water. Eventually the epoxy could not stretch enough to accomodate the wood expansion, and the expanding woood fractured the epoxy coating, and then liquid water soaked in through the cracks.

That's osmosis, the migration of something from a region of greater concentration to a region of lesser concentration with the intention of bringing into being an equality of concentration in both regions. Usually the regions are separated by a semipermeable membrane, and one speaks of osmotic pressure as a driving force or pressure developed across the membrane.

[NormMessinger]

Okay, so I was having a senior moment. Varnish is a simi permeable membrane and water is moving (diffusing tongue.gif ) from a greater concentration to a lesser. But when does osmosis occur when there is not a membrane?

--Norm

[thechemist]

Originally posted by NormMessinger:
Okay, so I was having a senior moment. Varnish is a simi permeable membrane and water is moving (diffusing tongue.gif ) from a greater concentration to a lesser. But when does osmosis occur when there is not a membrane?

--NormI give up.

When?

[NormMessinger]

I didn't think ever but you said usually.

--Norm

[J. Dillon]

Kevin,

Did you use the heat gun & scraper on the bright work ? Was it difficult to prevent the wood from being scorched.

Chemist ,

Thanks for the explanation as to what is going on.

For now the reglue job and the additon of a "butterfly" with it's locking together of ajacent wood members and the additional glueing surfaces should do the job. Of course 30 additionl coats of varnish attended by trained moisture clearing sea gulls will guarantee success. ;)

I will post finished pix of this project.

JD

[paul oman]

Hello:

seal the wood first with a coat or two of epoxy (thinned or unthinned) and then protect the epoxy with a few coats of varnish. It is a combination that is much better than either one alone.

PS. - pleased to see a boatbuilder in Hamden CT - spent a lot of time hiking all over Sleeping Giant State Park there!

cheers

paul oman
progressive epoxy polymers
www.epoxyproducts.com/marine.html (http://www.epoxyproducts.com/marine.html)

[thechemist]

Originally posted by NormMessinger:
I didn't think ever but you said usually.

--NormOh.

That.

I was hedging as other phenomena involve molecular passage through a membrane but might not be considered osmosis, such as water on one side of a water-permeable membrane and vacuum or dry air on the other side, carrying away such water molecules as make it through.

For a discussion of osmosis, see http://urila.tripod.com/ and http://urila.tripod.com/osmosis.htm, for example.

If we have dry wood on one side of the varnish membrane and liquid water on the other side, and the water diffuses through and raises the average moisture content of the wood on the wood side of the membrane, that would seem to be osmosis even though we are not dealing with a salt dissolved in the water.

[NormMessinger]

Right, and if I had known what I was talking about when I first stuck my nose into this conversation it would have saved us all some key strokes. redface.gif

--No rm

[Mr. Know It All]

JD.......I only used the heatgun on the outside of the hull. The few scorch marks sanded out pretty easy and will be painted over anyway. I used chemical stripper for the inside above the waterline which will be finished bright and yes it was a pain in the arse. Removing about 20 coats of varnish between the planking and the ribs takes some patience.

[thechemist]

Originally posted by NormMessinger:
Right, and if I had known what I was talking about when I first stuck my nose into this conversation it would have saved us all some key strokes. <snip>

--No rmNot necessarily. I misspoke earlier. Having considered those osmosis references and varnish films and so forth, I have to say that the movement of water through a varnish film is NOT osmosis because it is not a thermodynamically reversible process.

It is diffusion.

For there to be osmosis, there needs to be a membrane, and a solvent, and something dissolved in that solvent. That is the only way I know of to construct a thermodynamically revesible process involving a membrane. The membrane is called a semipermeable membrane because it is permeable to one thing but not another.

Diffusion takes place across a permeable membrane. There is no semi- because there is only one thing permeating the membrane.

Diffusion is not a thermodynamically reversible process because no recoverable work is done in the process of diffusion.

Things diffuse from regions of greater concentration to regions of lesser concentration. The net energy of the system always drops, and disorder [entropy] always increases, as a result of a diffusion process.

Getting back to the failure of a varnish film on wood, water diffusing in great concentration through a varnish film will of course swell those cellulose fibers directly under the varnish film, and the wood fibers right there will expand more than those further into the wood. This puts mechanical stress on the varnish-cellulose bond, which I assume is weaker than the varnish-lignin [winter growth rings] bond. It also stretches the varnish film, which is weaker due to being excessively hydrated.

It further seems to me that the cured varnish resin itself, being a polyether triglyceride, has many oxygen sites to which water molecules may attach themselves. I would therefore expect cured varnish to hold some considerable amount of water by weight, probably five and perhaps even ten percent by weight. As with similar substances, I expect that a hydrated varnish film will mechanically swell, both in thickness, length and width. Its bond to the wood is all that keeps it from lifting off.

In those circumstances where both the varnish film and the underlying wood have absorbed water, such as from a puddle of water sitting on a varnished wood surface, what will happen as the wood/varnish film dries out? I think the first thing is that the moist wood will allow water transport to less moist regions [in a time frame of minutes to hundreds of minutes], and some time after that [hours to tens of hours] the varnish film itself will dehydrate.

During the time where the wood has equilibrated some of its excess water but the varnish film has not yet dehydrated, we have a swollen varnish film trying to lift off of a hydrated cellulose fiber, and I think it succeeds.

[J. Dillon]

Kevin, Good luck with your restoration and hope you post some finished images soon.

Paul Oman,

Glad you enjoyed the "Sleeping Giant". It was once called "Dead Indian". I live right across the sreet and work on the trails crew maintaining them. Did you know there is a cave in the park? We clean it out once a year and do not make know its location and leave it off the map. It seems to be a cult activity entering it to perform some college rituals.

Chemist,

Thanks again for your thoughtfull input.
But what is the bottom line? does water get through the varnish and eventually get to the wood to expand it, work on glue joints and start the deterioration process ? Is there hope ??

JD

[Art Read]

"Thirty coats"? Is that all at once, or built up over a course of seasons? From a purely UNscientific viewpoint, I've always found that varnish is a lot like a woman's make-up. And I don't mean just the obvious, "cosmetic" comparison. After a suffucient build-up, (3 or 4 coats for quick and dirty, get back out on the water work, perhaps 6 or 8 coats if your feeling "fussy") adding more layers is almost COUNTER-productive. Obviously, the number of "coats" is going to add up as the seasons go by. Indeed, you'll usually get the longest lasting finish after a previous season or two's "build-up" to work with. But eventually, your film of varnish gets so thick that it starts acting more like an orange peal than a coating. It "wants" to peel off. Sanding thoroughly helps delay this, but not completely. Usually, in the real world, about this time you'd have to take it back to bare wood anyway because of dings, scratches and discolored wood. But if the boat is particularly well loved, I suppose the finish could get pretty darn thick before it "looked" bad. But that's not going to stop the early layers breaking down or keep too much "bulk" from building up. Perhaps you're just using "too much" varnish?

(Ever notice how much easier it is to scape a piece of wood that's had countless "coats" of paint slapped on than it is to get just a coat or two off? At some point, I think the "old" paint wants to stick to the new coats more than it wants to stay on the wood.)

[ 12-28-2002, 01:33 PM: Message edited by: Art Read ]

[Carlsboats]

Don't agree with Art Reed's view about varnish
buildup. Yes, you can make something paint sick by laying on too many coats, but I don't think that applies to varnish in the same way. With varnish,you want a thick buildup to keep UV from
attacking the bond to the wood. Maybe 30 coats is too much, but three or four are definitely not enough. My experience is with boats in New England: After wooding down, putting on four to six coats buys you but one season of protection.
We have now gone to 10 coats over bare wood, and find that it is holding up really well.

[thechemist]

It depends on the particular varnish. Some have MUCH more and better UV absorbers in the formulation. I forget what is in the archives. Search Building /Repair as well as Products/Resouces, in the entire text, for "Absorber". That should pull up any thread where the subject came up.

[Art Read]

Oh, I agree. Three or four coats is hardly enough to last. I look at it as a good start. ;)
In my experience with freshly wooded brightwork, I usually wind up putting down at least a couple of mid-season "refresher" coats anyway, and like I said, it's usually only after a season or two's build-up that I start getting a really durable finish. In a perfect world, I'd always have at LEAST six coats down before launching every spring, but in the real world I've gone sailing with as few as three. (Hense all the mid-season "refreshers") The most important thing is to not let it get away from you. I'm sure ten or twelve coats gives a beautiful, long lasting finish, (not that I've ever done it yet) but it will still probably need to be maintained every season. I've never actually "seen" 30 fresh coats of varnish on anything. (Not that I was aware of anyway...) But I have seen too much varnish put on top of countless, previous coats when what was really needed was a good stripping and a fresh start.

[ 01-01-2003, 03:35 PM: Message edited by: Art Read ]