Seam Seal

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.

 

Unfortunately, the industry (like many others) is full of these types of "wives tails" or "magic formulas" etc., most don't work or don't work as well as the more traditional repair or maintenance procedures.

The way a carvel hull works is, the caulking string gets pounded (literally) into the seams, which forces each plank against the one above and below it. This makes the planking a homogonous whole, solid as a rock, if done correctly (it's an art, a skilled craft). This (the caulked seam) is then covered with a compound that will protect the string, from abrasion or being washed out and other nasty things, that can happen to it. A properly caulked carvel is dry and tight inside, assuming the planking and seams were in good shape and no other structural issues needed attention.

There are a few other methods to do carvel seams, but are less effective then the tried and true pounded caulk. One is wedge seaming the boat. Wedges of the same type of wood are glued and pounded into custom ground seam gaps. On moored or docked boats this can work very well under the waterline, though is of questionable usefulness above the LWL or on trailered craft. If these wedges remain at a reasonably constant moisture content, they work well. If they cycle through wet and dry periods often (like trailer boats do), the glue lines fail and the seams leak. The same is true if the boat will spend long times ashore as well as afloat, it'll just take a little longer for trouble to show up.

The short of it is, you have to reef out those seams, get them clean of the tar and grit, then prime, caulk and compound them properly. This is a job for a pro, not a backyard, shade tree kind of jig. The seams have to be clean, not mostly clean or sort of clean. The caulk needs to be pounded with a skill that takes a while to master and the tools aren't usually available, most being made by the boat carpenter or from specialty shops that sell two or three a year to a select few, who's numbers are rapidly diminishing.

In your area there will be one or two that really knows their stuff. Find them and see how many lessons a case of beer can earn.

 

Thanks for the reply Par. This isn't some wive's tail that I'm trying to track down, it was the way and still is the way many boatyards recaulk working vessels, it was also navy spec. Any article mentioning caulking a working boat, the seam seal is either straight concrete (which isn't very forgiving and often gets knocked out), or cement mixed with roof patch sealant. The guy I talked to about it said to use number 2 portland cement. Type II portland cement generates less heat at a slower rate and has a moderate resistance to sulfate attack, unfortunately I can't seem to find any.

The boat is already corked it just needs the seams sealed. The Oakum caulking does very little in keeping the water out, it basically just stiffens the hull. The Antifoul paint is usually gooped in the seams to keep the caulking in place. The seam sealant, whether it be sikaflex, slick seam, or tar/cement is what ensures the craft is water tight. Unfortunately the tar cement mix that I've tried turns out to be a runny roofing tar substance and only develops a really thin skin. I'm not sure if that's the way its supposed to work but it never really sets, which surprised me. I'm wonding if it was cause I was using type 10 or I portland cement and it is missing an ingrediant that the roofing tar reactes to. I haven't used it on the boat until I get some further guidance but the only people that seem to know anything about it are the guys in the shipyards 2,000km from where I am right now.

 

I don't suppose this is anything you don't know but the paint companies like Petit and Interlux have their seam compounds and they seem to be very good.
I have used linseed oil putty for seams above the waterline; my Dad told me it should have a fair amount of pine tar mixed in thoroughly with it to keep it from getting so hard and brittle as it would eventually get without it. I've often used portland cement mixed with linseed oil for seams below the waterline; it never hardens.

 

If you could only see the boat yards here in Thailand. they can pull out a trawler -rip the entire side of it out and put it back in the sea within a week. They saw ribs out of slices of tree by hand with big 24 inch power saws or chain saws. They never seam to measure anything. At a normal yard there will be say 50 women caulkers, Yep women, covered from head to toe and boy they are good, using cotton waste and some bright yellow paint like antifoul or red lead to caulk in the seams.

After caulking they mix up some stuff that does look like cement with oil ( sorry dont know).

After watching them for hours ( some are attractive actually) I saw that if theres a bit of wood damage that does not need serious attention they will caulk in different sizes of polypropelene rope to get a base so that the cotton doesnt dissapear inside the boat. Then followed by the cotton waste untill the sound of the hammer and chisell changes to a solid thump. Fantastic.

The labour cost of any worker in these yards is 300 baht per day,-- Are you ready for this,-- that is about 7 us dollar per day and no they are not being taken advantage of it just does'nt cost that much to live there.

 

Caulking carvel with Portland cement

Sounds like the same source which advises using a narwhal tusk as an aphrodisiac....

As Par wisely says, oakam (in pitch) pounded home is the traditional - tried and true - method. For cosmetic purposes a final layer of putty will give a smooth surface to the hull.
Wooden splines (hard to shape) dipped in glue, well hammered home are a less trustworthy - but still a traditional method.

It is a time consuming job, and as Par says the seams must be thoroughly clean before re-caulking. A triangular paint-scraper or similar angled blade (filed to a quarter inch point) acts as seam cleaner. A slate chisel (at least eight inch broad X quarter inch wide blade with corners rounded off) and wooden mallet serve to hammer home the oakam.

As a final coat - and here Par may disagree - I'd apply a mix of one third white spirit; one third boiled linseed oil; one third timber preservative. Allow first coat to be absorbed, then add a second; third; fourth etc until timber takes on a dry matt glow. Paint to desired colour.

 

Thanks for the info guys,

Oakum/cotton does very little to make a seam water tight, it simply makes the hull solid by tightening everything up. The seam seal that is put on over oakum/cotton is not for cosmetic purposes it is for making the seam water tight.

I should have gone to Thailand, coulda cost only 21 dollars to have the job done. Jack Frost, the mix with oil is probably the cement with roof patching sealant mix. I'm trying to find someone who's used this to figure out if what I've concocted is in fact the proper mix before I use it on the boat.

Gilbert, thanks for the input, I'll have to start looking more seriously at those products if I don't get anywhere with this.

 

Actually the bedded caulk, once pounded in a properly prepared seam, provides the sealant. The caulk hardens the area of plank edges it contacts, with the pressure of the pounding. This hardened area can become a problem in older planking, but in healthy planks, swells nicely. The seam compound just protects the caulk and pretties up the hull. The planks are put into compression with the caulk, which swell when wet. The swollen planks mash the caulk which also serves as a gasket, keeping water out.

I have a similar mixture, Bergalia, for those insisting on something other then the standard, modern materials like sikaflex, slick seam, one and two part polysulfide, polyether or an oil based compound. Mine is only different from yours by the addition of a little tar and Japan drier.

I've seen cement based compounds used on hulls, but the results have never been satisfactory, mostly falling out or making reefing out difficult. It's common for working craft to stuff just about anything into seams to get a craft through a few more seasons, but pleasure boats shouldn't have to suffer this same fate.

For what it's worth, there are two general roof patching compounds, one petroleum based and the other acrylic.

 

When I was a kid (late 1940s) my stepfather was a commercial fisherman (purseine) and we lived just a few blocks from the fisherman's terminal in Everett, Washington USA. I used to frequently walk down to the yard and watch the work being done to commerical fishing boats on the ways. These were mostly 50ish foot long purseiners with heavy planking. In recaulking, the seams would be cleaned out with a reefing iron. Then linseed oil was brushed (slathered) into the open seams. Oakum was next pounded in (THE OAKUM WAS USED TO TIGHTEN THE PLANKS AND SEAL THEM!) until it was slightly below the surface of the planks. A day or so BEFORE launching a mix of Portland cement (different people used different formulas and all seemed to work) was applied as a seaming compound over the oakum. The bottom was then painted with antifouling pain and AS SOON AS POSSIBLE thereafter she was put back in the water. You don't want the seaming compound (cement) to have dried completely before launching - it is very important that it simply hold in the seam!

I have, over the years since then, recaulked many wooden, carvel planked boats. If the planking is sound (well fastened) and the seams in good condition, the caulking (oakum for heavy planked work boats, cotton for light planked small pleasure craft) should keep the water out. If it doesn't then there's work to do on the planks, not the caulking. Most people (including many who say they know how to caulk) try to take planking which should be replaced/repaired and make it watertight by depending on the seaming compound.

If there's a boat yard near you which does work on commercial wooden hulls or barges and has a couple of "old timers" (at least 70+ yeaars old) go there ask them "how to". That's how I learned and I have had 50 footers on land for 3 months in the summer in Port Townsend, Washington - completely refastened every plank below the water line. Recaulked and plunked 'em back in the water. After a week or so to swell up, the only moisture in the bilges was a damp line between the keel and garboard.

 

Seam seal,

Trust me, justplanecrazy - if your caulking doesn't make the seam watertight - you're not doing it properly....

I spent 25 years fishing the Arctic Circle in a carvel-built trawler. Leak-free. The only water taken on board was from heavy seas through the hatches.

 

Bergalia, with all your experience I'm surprised to hear that you've never seen cement being put into the seams. Check out this link...

http://www.woodenboatvb.com/vbulletin/upload/showthread.php?t=6961&highlight=bear ****

From the mouths of the guys making the working boats floatable in the PNW, they say the oakum/cotton keeps the boat tight and keeps the water from rushing in but in order to keep it watertight, you have to have a good seam compound. Cement is common place in seam compound and the PNW has standardized cement with roofing tar mix. I imagine this applies more to work boats that have been recorked regularly and are starting to tire, rather then pleasure boats being reefed with tweezers and cleaned with 220 grit sandpaper.

My boat is not in perfect condition. I'm simply trying to make it usable and sellable due to a lack of interest of people willing to put the time and money into restoring it. I'm asking less than what the equipment on board is worth so if it means it floats for another 5 years with no repairs, then I'm all for it and the buyer is still getting a bargain.

If this were the case why would they be using a mixture as nasty as portland cement and tar for a seam compound. A lead putty would protect the seam and be a heck of a lot easier to reef out. My understanding is that a perfect corking job will leave you with a boat that seeps very little. An imperfect corking job with a good seam compound will leave you with a boat that doesn't seep at all. The poor corking will tire your fastenings and pop planks but if a proper seam compound is used it'll still be water tight until that happens.

 

Justplanecrazy -If you are happy wih the idea of using cement - go ahead. Personally I wouldn't trust it to 'flex' without cracking under the stress of heavy seas. As for it being 'traditional' - whose tradition - and how old a tradition. I believe mobile telephones are now considered a 'traditional' method of communication...
The point is - you've got yourself a timber boat. Now that IS traditional. Welcome aboard.

 

Hey Bergalia,

Looks like you've had a hare raising experience.

Just wanted to say "Hi." We haven't passed the banter for a while.

Here's a whiskey at cha. Or is it whisky? I can't keep it straight.

Cheers.

 

Caulking putty, stopping compound below the water line.

Hello to all from Down Under. Just read your post in regard to caulking Justplaincrazy, (jpc) hope you dont mind the abbreviation. I have a 21 foot carvel planked Sydney Harbor launch, at least thats how the old girl was advertised when i bought her!. I have hauled her out 2 times in 3 years. Each time with the intent of scraping her backside, renewing the bearing at the skeg and giving her a few fat coats of middle of the range ablative antifoul. Never has she gone back into the drink on time, in fact at the moment she sits in my driveway, blocked and chocked safely and nearly 10 months have passed! Visitors have no trouble finding my home at all, just look for the house next to the boat. I had never caulked a boat before but i watched, read, listened and learned. I am by no stretch of the imagination a wizz at this tradition but she took on three parts of no water after i first launched her and she stayed damp just along the garbord and a little water leaked through the stuffing box packing nut around the prop shaft, about a drop every 2 minutes whilst on her swing mooring on Sydney Harbor and a drop evry 10 seconds or so whilst underway at a cracking full speed of 4.3 knots care of her old faithful Bukh 20hp diesel. If i read correctly you are at the point of paying, puttying the seam which will cover the renewed caulking?. I used what we call here, glazing putty. It is a linseed oil based putty straight out of a plastic can. It is soft and easy to apply to the seam and quite inexpensive. I apply this to the below water line saems and also the above water line seams. The trick is to apply whatever paint, barrier coat or antifoul about 5-7 days after applying the putty to the seam. I found that pushing the putty into the seam about 3mm or so below the plank edges so that as she swells in the water the putty doesnt push to far out proud of the seam under the antifoul. Having this little method well mastered i came across a similar recipe that you came across just last night. Use equal parts of portland cement, (no number mentioned) and fibergum. Mix together until you get the consistency of a putty, paste and pay this mixture into the seam. Im going to give it a whirl and see how it works. sounds similar to my Linseed oil putty but probably less expensive. Maybe the fibregum gives a better consistency? Anyway let me know if you would like to hear how it goes. To all out there in wooden world, happy days.