The Rot Doctor


Subject: Caulking
Date: Thu, 26 Dec 2002

Once again I need your expert advice.

I am preparing to start recaulking etc. this spring. In the past I cleaned the bottom and caulked my seams with 5200 and then bottom painted. We spent 2 years living on our boat here in Michigan. When we had her pulled this fall I noticed the vast majority of the caulk (5200) had fallen out of the seams. I have never replaced or replenished any of the cotton etc. On reason I feel this might have happened is I was told to apply a coat of thinned bottom paint on before caulking. But I think the 5200 did not adhere well to the bottom paint that was in the seams.

Correct. In years past the thinned bottom paint was used as a primer prior to filling the seams with the standard seam compound, which was an oil based compound, and so compatible with the bottom paint. 5200 however is a polyurethane compound and will not bond with the paint. It was bad advice.

The modern seam compounds (which include the polyurethane's, as well as the thiacol-based and the polysulfides) require a clean wood surface for good bonding. The seams can be primed with our CPES, which will increase the bonding ability of the compounds, especially if they can be applied between about 4-24 hours after the CPES has been applied.

I am now thinking that I should remove all the 5200

Yes, pull it out.

and pound new oakum in the seams and seal them with Slick Seam and then bottom paint. What do you think??

If pulling out the 5200 also pulls out the caulking cotton, then yes you will have to recaulk. However, often the compound comes out and the cotton remains. In this case it is usually only necessary to gently re-tamp the cotton and apply new compound. I would guess that this will be the case with your Trojan.

Pounding in new caulking is not something we recommend generally for the amateur. There is a real "feel" and technique involved, and the inexperienced person rarely has it. I have done some in my time when in foreign ports and there was no one else to do it, but at all other times I have depended on the professionals.

Unless you are prepared to absolutely clean each seam down the bare wood, I would suggest that you do a simple cotton re-tamp, and then fill the seams with one of the traditional bottom seam compounds. We do not like Slick Seam. It is basically a wax and tends to contaminate wood. Look for the simple underwater seam compound sold in boat stores.

The boat is a 1971 Trojan 42 SeaVoyager. We did a lot of replanking above the water line. As usual the wood below water is like new.

Also the entire boat was built with silicone bronze screws, should in you opinion, I look at refastening? Everything seems very solid.

If things seem solid, then there is no need to consider refastening. You can inspect you interior hull framing/joints and see if you see any serious signs of things coming apart, or any soft wood. And, of course, the soft wood can be repaired with our products.

Thanks Guy G.


You're welcome and feel free to come back anytime you have questions.