Varnishing over Caulk

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Jan 25, 2010
Vessel Name
Vessel Make
PT Europa Sedan 41
Hello all, I am in the process of refinishing my teak caprails on my 41' PT Europa trawler. I have removed the old varnish and ready to start the process of recoating. After much research on varnishes, my choice thus far is Epifanes. My question is:* Where the upper fiberglass deck supports ( Europa trawler) are attached to the caprails, there was a bead of BLACK caulk to seal the seam. This caulk was varnished over. I removed all the BLACK caulk along with the varnish. My intention is to replace the caulk with BOATLIFE Life-Calk ( polysulfide base ) in the color of TEAK. This stuff is paintable, so I think the process would be to apply caulk first, then varnish over. I think the TEAK color will look better than BLACK under varnish, or at least not stand out as much. Does this make sense? or should the caulk be applied after the varnish? The photo shows the caprail prior to removal of old caulk. This has been alot of work so far, so I want it done right. Any help is appreciated.



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An alternative to recaulking, although the polysulfide is the right stuff to use, would be to epoxy the joint.* Others may, and might be right to disagree, but I would mix epoxy with sanding dust to the consistency of runny peanut butter, place same in a plastic baggie, nip a small bit off the baggie in one of the corners, then squirt a bead of epoxy into just the joint like you were icing a cake.* You can then use a plastic epoxy stirring stick or other plastic sharp edge to remove all the epoxy except that in the joint.* Let it kick for a couple of hours, then wipe it down with a rag soaked in MEK.* This will remove any other excess and glaze the tiny bead.* Next day, lightly sand the joint.*

I would also then put a couple to three coats of epoxy thinned with MEK to the consistency of paint thinner onto the wood before varnishing.* This will give a better substrate for the varnish, especially over teak.* These penetrating epoxy coats should be lightly sanded with 100 grit to remove any fuzz.*

You might consider Flagship.* I like Epifanes, but not so much the exterior product although others swear by it.* The Flagship will hold for a very long time over an epoxy base applied as described.* I did the oak rudder apron on my Cape George and it lasted 5 years without breaking down, including being half underwater for 6 weeks on a sail to Hawaii and back.* The spruce mast was done the same way and it lasted 6 years before it needed a couple of maintenance coats here in the NW.

I haven't used Bristol, although others swear by it....

Yup***'s one to strongly disagree w the epoxy seam. Actually I can't believe my eyes/ears. Of course whatever one puts in the seams of wood boards or planks must be able to maintain adhesion to both pieces of wood, seal the gap (seam) from water and all the while doing this as the wood expands and contracts in various weather conditions. Epoxy itself being rigid (compared to flexible caulking) would not allow the wood to contract in dry conditions and it would seem obvious that one side of the epoxy seam would split the wood or break away from the wood at the seam. Carl, how on earth would the epoxy deal w the forces of the expanding and contracting wood?
Ditto on Eric's comment. Highly recommend against using epoxy in the joint. While wood dust mixed in with epoxy does create a bond that has more elasticity than straight epoxy, the wood WILL move far more than the epoxy putty will allow. Another thing to think about is the fact that all caulks seal well in two directions not three. This is why a bond breaker (seam tape) is used in wooden decks that have a square groove and not a V-joint. Consider how wide the seam is and if the bottom of the seam can also be pulled because of shrinkage, consider a small seam tape, or cotton twine before the caulk is applied.
Done it in exactly the same type of environment on my boat between the bow sprit and the deck, and didn't have any problems over 10 years of observation.* Perhaps it has to do with the fact that the mixture of epoxy and sanding dust is about 30% wood at that consistency.* As an example, I had some significant rot on Marvin windows on the south side of my house.* The estimate to replace them didn't bear thinking about.* I gouged out a great deal of punky wood, framed up a dam and poured layers of epoxy/wood dust mixture to replace the lost wood.* If differential expansion rates was to be a problem, I would see it by now, and I see nothing.

Since I've done it, I don't have trouble describing it, although am certainly not offended if maintaining a caulk joint seems the safer route.

Follow up edit:* I found the coefficients of expansion for mahogany, which has precisely the same coefficent of expansion as epoxy, or 3 in/in/°F x 10<sup><sup>-5* </sup></sup>.* I doubt teak is much different than mahogany, as one of the main reasons teak is so valued for cabinetry is precisely because it doesn't expand in humid environments, causing drawers or doors to stick.

-- Edited by Delfin on Sunday 3rd of April 2011 08:28:48 PM
nomadwilly wrote:Carl, how on earth would the epoxy deal w the forces of the expanding and contracting wood?
Teak doesn't expand and contract.* That's why it's used in exterior boatbuilding.

Cantina wrote:
Hello all, I am in the process of refinishing my teak caprails .... This caulk was varnished over..This stuff is paintable, so I think the process would be to apply caulk first, then varnish over. .....
******* I did the same thing about 4 years ago & caulked first and varnished over it. I also used Epiphane varnish. Now a very light sanding once/year and it looks great,



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All wood expands and contracts but teak, cedar and others have high degrees of dimensional stability compared to most species of wood. Metal and most all other materials aren't stable either but if you have a wood planked surface narrow planks will minimize the dimensional stability issues and wide planks will be much more troublesome. That's why teak decks have very narrow planks. Cap rails suffer a small amount from dim. stab. issues that result from expansion and contraction end wise but all wood has much much less DS issues lengthwise along the grain but there is usually some distance between the joints on a cap rail so some issues will be present. Whatever the amount of expansion and contraction between seams the material there must be flexible enough to accommodate the movement.
All,** Thanks all for quick reply. If every time I had a question in everyday life that was answered so thoroughly as this, life wood be a breeze! I will consider both epoxy and caulk, but I'm leaning toward caulk. Epoxy is great stuff, however possibly too permanent for this application. I might want to remove these supports for repair someday and the caulking will will be more willing.

SeaHorse....Beautiful wood!

What was the question?* Varnishing over Caulk?* LOL

Fiberglass deck supports riding on top of teak will move.**Fiberglass has a much higher thermal expansion coefficient then teak. *This is why caulk is*used in this application.* It allows*for the different materials to move at slightly*rates while still maintaining a*seal (as long as the caulk is in good condition).

As far as the varnish first or caulk first I'd lean toward caulk first however varnish first may be more difficult and the UV properties of the varnish won't be protecting the caulk. Also varnish in the seams will mean the adhesion of the seam compound to the teak will then dependant on the varnish instead of the seam compound. The varnish will become brittle w age and the film will fail (crack) over the seam/caulk probably right on the caulk/wood line. But if you have a good seam compound it may adhere to the teak and that is a good case for caulk first. Some seam compound/caulk is especially formulated to adhere to teak and I believe Boat Life has such products. Practically nothing will properly adhere to teak and for that reason I've ditched varnish altogether both outside and inside.
Quick question can you in fact spar varnish black polysulfide life calk? I cannot get answer from company as yet as their tech is out of town!
Quick question can you in fact spar varnish black polysulfide life calk? I cannot get answer from company as yet as their tech is out of town!

Yes you can. It will crack as the caulk flexes, but I varnished sections of a teak deck (accents, like the king plank) for years with no issue.
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