Why varnish hull before painting

[Larks]

Probably a naive question but I'm wondering if there is a reason or any commonality in first varnishing a hull prior to painting as I've noticed on the terrific "Wild Swan" restauration web site http://homepage.mac.com/wildswan/PhotoAlbum10.html
(ie is this a regular practice and what does it achieve?).

Here's Wild Swan with varnished hull then final bottom paint (I hope there's no issue in copying these from their web site??):

http://homepage.mac.com/wildswan/.cv/wildswan/Sites/.Pictures/Wild%20Swan/Varnish%20on%20the%20Hull%20before%20bottom%20pain t.jpg-thumb_269_202.jpg (javascript:openSlideShow2(86,'en'))

http://homepage.mac.com/wildswan/.cv/wildswan/Sites/.Pictures/Wild%20Swan/IM000770.jpg-thumb_269_202.jpg (javascript:openSlideShow2(90,'en'))

thanks
Greg

[Lew Barrett]

I suspect they did it as a sealer, used much like shellac, and because varnish builds quickly and fills the wood better than a base coat of primer. A couple of coats of varnish will fill the wood well, and paint adheres very well to varnish. I don't see it used as a strategy around here, but if you have the time, it couldn't hurt. Just speculating.

[ron ll]

I'm sure it goes without saying, but just for the record the, "paint adheres very well to varnish" statement has a couple of obvious caveats. Oil base enamel adheres very well to fresh or sanded varnish. Acrylic paint does NOT adhere to old unsanded varnish. Don't ask me why I know that. :D

[Bankdorys]

the varnish sets off the bronze hardware... maybe just for the "studio shot"?

[Thorne]

In some instances it allows you to later take that part of the boat to bright finish -- whereas if you'd primered and painted, you'd never get the paint out of the grain later.

Other than that, dunno.

[Gary E]

How come those who look at their varnish boat parts and think...that's to dingy looking, think I'll paint it.. it's easier...
Then not long after that the paint peels off... so much for paint sticking to varnish...

Another thing...
If enamel paint was suposed to be used over a primer... and from my memory. it is...
Why is primer not varnish?? ....

From Dictionary.......
varnish, homogeneous solution of gum or of natural or synthetic resins in oil (oil varnish) or in a volatile solvent (spirit varnish), which dries on exposure to air, forming a thin, hard, usually glossy film. It is used for the protection or decoration of surfaces and may be transparent, translucent, or tinted. For oil varnishes a hard gum or resin, often a fossilized plant exudation such as kauri or copal, is dissolved in oil (commonly linseed oil or tung oil) and is diluted with a volatile solvent such as turpentine. Spirit varnishes are commonly made of soft resins or gums, such as shellac (http://www.reference.com/browse/columbia/shellac), dammer, mastic, or sandarac, dissolved in a volatile solvent, e.g., alcohol, benzene, acetone, or turpentine. Enamel is varnish with added pigments.

[Canoeyawl]

The reason is, as Lew said, to act as a sealer.
If you paint directly on bare wood there is a risk that the oils and solvents in the paint will leach into the wood before drying leaving mostly pigment on the surface. This is an undesirable condition for the next coat to adhere to.

[Eric Hvalsoe]

Evidently this company uses a bottom paint that they feel adheres well to whatevery clear sealer they first coat with. Could be an oil based clear, could even be a penetrating epoxy sealer. Some bottom paints are in fact recommended over bare wood. On topside work I typically start with a clear sealer such as Old Salem, then pigmented primer, if building over with urethane or alkld topcoats. Of course penetrating epoxy if topcoating with epoxy products. If super concerned about durability I might even seal with penetrating epoxy topcoated with any marine finish.
In the livery of the Center For Wooden Boats we (they) occasionally paint over perfectly good varnished surfaces - the boats serve under significant duress and it is asking a lot for the staff to maintain a varnished surface. For whatever reason, these surfaces could later be brought back to their former varnished glory.

[pcford]

In the livery of the Center For Wooden Boats we (they) occasionally paint over perfectly good varnished surfaces - the boats serve under significant duress and it is asking a lot for the staff to maintain a varnished surface. For whatever reason, these surfaces could later be brought back to their former varnished glory.

In the tropics I understand that varnish is often painted over....later to be stripped and returned to bright finish.

[Jay Greer]

Quite frankly, this is the first time I have ever heard of anyone varnishing a hull prior to applying bottom paint. The primary purpose of bottom paint on a wooden hull is to first prevent the intrusion of marine borers such as gribbles and teredo worms. And, it goes without saying that surface adhering growth should be prevented from forming as well. That being said, it makes no sense to me that one would not want bottom paint to soak into the grain in order to infuse the wood with critter toxins. It also will bond better as subsequent coats are applied. My favorite bottom primer is creosote. It soaks in, prevents the critters from taking up residence and bonds well to bottom paint. I also thin the first coat with creosote. While this may be contrary to those who are thinking "Green", it is far better to preserve the wood rather than to replace planking that has been damaged by worms.
Jay

[Eric D]

My favorite bottom primer is creosote. It soaks in, prevents the critters from taking up residence and bonds well to bottom paint. I also thin the first coat with creosote.
Jay


Ok, to ask the dumb obvious question, where do you personally get creosote from? I don't usually see it on the shelves next to other primers ;)

[Jay Greer]

Actually I have a stash that I put away for future use years ago.
It can still be purchased through some chemical supply houses.
Jay