Seam Seal

[justplanecrazy]

I'm recaulking a cedar carvel planked troller and have heard the best seam seal is number 2 portland cement mixed with roofing tar. I didn't have access to number 2 so I tried the general number 10 mixing it 1 to 1. It turned out like a slightly thicker tar that wouldn't set. Is this what is supposed to happen? Is it supposed to turn into a more solid solution similair to polyuerethane caulking or is it supposed to be runny tar and only develop a very thin skin? Anyone have any experience with this? I've only used it on test pieces of wood and haven't committed to the real deal yet.

What other seam seals are commonly used? Anyone know how long a boat can sit out with Davis Slick Seam before being launched? Any beta is appreciated.

[Daddles]

You're not having a lot of luck with this are you. I'd have thought that by now, someone on the forum would have been able to give you some guidance, but it appears no-one knows about this mix.

I guess my first question would be, what's the difference between number 10 and number 2 Porland cement? Would using the different cement make the mix behave differently? If not, then I'd suggest playing with the ratios to see what comes out and make a best guess from there. As for what you're looking for, mate I'm more of a novice than you are with this stuff.

Richard

[bitingmidge]

...and I'm a bit gun-shy! :D :D :D

(but don't have an experience with that old-fashioned stuff that I can share!)

P
;)

[Daddles]

...and I'm a bit gun-shy! :D :D :D


BOOM
Must be pirate's day :D

[boatchippy]

We usually use linseed oil putty with a mixture of white lead or paint for paying seams after caulking hulls. Seems to be the easiest and best.

[Daddles]

We usually use linseed oil putty with a mixture of white lead or paint for paying seams after caulking hulls. Seems to be the easiest and best.

That's what I've seen fishermen using on their carvel boats here, blokes who've been using the same boats all their lives.

Richard

[bloggs1968]

Boatchippy has given good avice - linseed putty is the way to go.

In saying that, I was talking with the skipper of the Alma Doepel a while back and he told me that she had always leaked a bit and when they recaulked her, they used cement as a seam compound. He said he had heard that a lot of commercial fishing boats in Brittish Columbia had used it for years with great success. I must admit, I'd never heard of it til then and have never tried it but he reckoned it was the first time the boat was dry in years.

FWIW

AD

[bitingmidge]

OK I just can't sit here!

The logic behind using plaster or cement is completely lost on me too. I've heard of it, and shudder at the thought, but there may be something in it:.

Cement is a rigid material, so filling a seam with it shouldn't work, as the timber will move and the cement won't, leaving a crack at the junction of the two materials.

I'm thinking it's purpose would be to "bulk out" ie make less fluid, the seamng compound?

As I've said, I've heard of it, but it just goes against all the experience and training I've had! Can someone please explain?

P

[justplanecrazy]

midge, I don't think the cement mix that they use is typical cement. I've heard that they mix it with very little water. I guess it probably produces the same results as the boats being caulked with a strip of wood being glued into place between the seams (wedge sealing?). I can't remember what that method is called. I think the cement makes a rigid seam and doesn't provide the movement that the regular compounds do. The lead putties don't make much logic either as they don't rebound to original form. After being compressed it stays compressed, leaving gaps where it once was. Hence the crack lines on a boat using lead putty. The working ships using cement do have problems with it falling out and need to be reworked fairly often. That's why they came up with the roofing tar/cement compound. It's used a lot in the PNW and never drys out.

As far as type II cement, it contains no more than 8% tricalcium aluminate (C3A) for moderate sulfate resistance. I'm not sure if this would affect the reaction between the two products or not.

[Boatmik]

I thought I did a reply to this.

Hmmmmm.

As far as I know the portland cement is not a common approach in Australia - I've only ever seen the linseed oil and white lead (or a bit of antifoul as Viking suggested in another thread).

Before doing a google search I thought someone was yanking our chain. After all cement is hard and brittle.

But did a google search and it appears to be quite a common approach in the USA and fulfils some Naval specification.

Anyway do a seach on google - there is heaps of info out there.

boat caulking portland cement tar

should get you a few pages of info.

As far as what is "BEST" I wouldn't hazard a guess. In fact I think everyone follows their own prejudices in these sort of matters and it really depends on whose prejudices you line up with best. A caution though. Sometimes certain methods are restricted to certain geographical areas for a reason.

For example I've seen roofing tar oozing out of the deck seams of a boat on a hot OZ summer's day and people's feet were sticking in it and transferring it all over the boat. Wouldn't that muck up your topsides if it started oozing out the seams on a hot day. But MAYBE it isn't a problem with the particular mix they use.

It's a bit like all the smart types that decide to paint a boat in Australia with a dark colour like they do in the USA or England. EEEEK. Very hard on a boat. Doesn't absolutely mean you shouldn't do it, but be aware that our environment is different.

MIK