CPES over cotton caulking?

[DanO]

Would CPES be advisable to help seal cotton caulking before paying it with traditional Interlux seam compound? I was thinking a coating of CPES might help seal the cotton and keep it seated. I had originally planned to lay red lead primer over the cotton, but thought I'd like to hear pros and cons about CPES for this part of the project. CPES first, then red lead? Maybe I'm being overcautious...?

Dan

[johngsandusky]

I wouldn't use any kind of epoxy for this unless you're sure you'll never have to recaulk, or remove a plank. I don't even believe you should paint caulking, it will just harden it. I've heard that it will rot if you don't, but I've pulled a lot of old cotton out of my boat, unpainted and intact.

[Thorne]

I'd stick to the traditional materials in this case -- CPES is great (in my biased opinion) for what it is intended for, namely penetrating wood and making a good 'binder' for paint, epoxy or varnish.

Seems like it would really mess up the cotton caulking, causing it to both stick where it shouldn't, and to not absorb what it should.

(scampers quickly away before the "CPES is Bunk" crowd arrives waving torches and pitchforks...)

;0 )

[Boatmik]

Long thread on whether CPES is useful or not
here ... http://www.woodenboat-ubb.com/vbulletin/upload/showthread.php?t=52046

[orphan314]

Do not seal with CPES . It will fully saturate the cotton and keep it from swelling properly. I seal my seams with red lead ... not so much as to keep the cotton from rotting (although it will help), but to keep the cooton from wicking the oils out of your seam compound. You want to keep the seam compound soft enough that it will squeeze out when the planking soaks up. If your seam compound hardens it can create a compression set problem (ie reduce the springiness of your planking).

[johngsandusky]

Orphan, that makes sense to me. My boat has a variety of seam compounds, most hard and crumbly, though probably decades old.

[Bob Cleek]

I've been musing over this question for some time myself. The soaking of cotton caulking with thinned paint to keep it from creeping after it is hardened up (and perhaps to prevent soaking up oil from the seam compound, although I doubt this one) is standard practice. However, I've often thought that CPES might be just the ticket for this purpose. First off, it isn't going to make the cotton stick in the seam any less than paint would. I'd expect it would work better because of its high viscosity. Paint really doesn't soak into hardened cotton much at all, unless it is thinned down to darn near nothing. Good hard cotton has the consistency of wood, practically. CPES would also have a much greater effect on preventing the cotton's rotting, again because of its ability to penetrate the hard cotton and exclude a greater amount of moisture.

As CPES remains flexible and does not turn into a plastic rock like epoxy resin adhesive, I don't see CPES soaked cotton becoming so hard that it damages the plank seam edges. Also, contrary to the comment above, I doubt there is much to be gained at all by cotton "swellling," so CPES's preventing this is a non issue. What causes the boat to remain watertight is the WOOD swelling against the hard packed cotton caulking... not the other way around.

Me, I'd say go for it. It can't be any worse for the job than thinned paint and may well be better. It sure will be easier to apply than paint as well. The only downside is that it may make the seam compound stick rather well, which could make reefing it out a bit more difficult, but I don't expect so much so that one would want to avoid it.

Let us know how it works!.... or call Steve Smith at Smith's and ask him. I'm sure somebody has tried it and reported the results to him already. He surely knows all there is to know about his products.

[Jay Greer]

What I learned from the old master boat builders I apprenticed with was that bee's wax disolved in turpintine makes the best seam primer for cotton caulked seams that are to be payed with oil based seam compound. We use it on decks and above the water line. Below the water line it is red lead and turps. It has been working for me for the past fifty years!
JG

[DanO]

Thanks for the suggestions, guys. Bob...your thinking's the same as mine on the issue. I figured the cotton might be better preserved and that the paint and/or seam compound may stick better to the cotton. I'm not sure what I'll do at this point. It's gonna take maybe take a week or so to complete the caulking, so we'll see. I'll keep you posted.

Dan