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pcazeles
06-05-2008, 10:41 AM
When I bought my 1961 32ft 8 months ago, I found out that all the caulking below the waterline had been done with Sikaflex.

Does someone has experience with such method:
. roughly how long does it last (so far basically no seawater in the bilge)
. how difficult is it to remove the old Sikaflex when re-caulking becomes necessary
. is this a trade-off with the cotton method which seems to be pretty difficult to apply

Many thanks in advance.

SchoonerRat
06-05-2008, 10:52 AM
The Sikaflex is not the caulking. I'd be willing to bet that under the Sikaflex you'll find cotton or okum. That is the caulking. It's necessary for the two to work together. I've never worked with Sikaflex, but many people swear by it. If your seems were properly caulked and payed, your bilges should stay reasonably dry for years before they need any touchup. You will likely sell her before she needs a complete recaulk.

pcford
06-05-2008, 11:09 AM
When I bought my 1961 32ft 8 months ago, I found out that all the caulking below the waterline had been done with Sikaflex.

Does someone has experience with such method:
. roughly how long does it last (so far basically no seawater in the bilge)
. how difficult is it to remove the old Sikaflex when re-caulking becomes necessary
. is this a trade-off with the cotton method which seems to be pretty difficult to apply

Many thanks in advance.

I infer that you are saying that a previous owner has used Sikaflex in lieu of proper caulking on your boat. Polyurethanes are too hard/stiff to be used as seam compound. (there is probably a proper mechanical engineering term.) Using the stuff can warp planks and strain fasteners. With that said, and just between the two of us, I have used it on a sloppy plank replacement on a boat which had be done by a previous owner. I just used it on the single plank.

If the hull seems ok, I would not mess with it. It is a nightmare to remove.

Some have said there is a problem with it in underwater use. I typically use it for bedding down the lower margin and sides of a runabout 's lowest transom plank. I do this because it is a common place for rot to start. If the plank needs to be removed, it can be fairly easily remove with a router. Never had any problems.

Lew Barrett
06-05-2008, 11:28 AM
To amplify on PC's comments. There are various types of Sikaflex, and with some good luck yours will be the less aggressive of them, but reefing long Sikaflex filled seams doesn't sound like a fun job to me. Better would it have been had the prior owner used an oil based compound.
However I do use Sikaflex for bedding relatively permanent items; pads under electronics or permanent deck fittings where I find it far outlasts today's oil based compounds. For deck fittings I will be removing for routine work, oil based compounds are preferable. I am unfamiliar with any caulker here who would use Sikaflex for the bottom, though. If the boat is otherwise tight and sound, I'd just let it be until another day. If not, be careful when you remove it not to damage your caulking bevels.

Bob Cleek
06-05-2008, 11:37 AM
If it ain't broke (or leaking), don't fix it! Ditto to what the last two guys said. Sikaflex is a BRAND name. There are several Sika products, each for a particular use and each offering particular advantages and disadvantages. Like "Jello," there's raspberry and there's lime, and so on. I can attest that Sikaflex is NOT what you want to put on deck seams. It dries out and breaks down in sunlight. In underwater seams it may fare better, but as for me, I wouldn't use anything other than Interlux seam compound for plank seams anyhow.

SchoonerRat
06-05-2008, 12:10 PM
I infer that you are saying that a previous owner has used Sikaflex in lieu of proper caulking on your boat.
If that is the case, you will probably need to recaulk sooner rather than later. The only way to know for sure is to pull out some Sikaflex and look under it. Best to leave the question unanswered till she actually starts leaking

felthamscruiser
06-05-2008, 02:30 PM
hi ihave to add there is a number version of sikaflex which is used as a compound come sealer and there is also boatlife caulk which is the same but requires water to help with the cure i know of a bloke who used this stuff few years ago who had seeping seams and never leaked again is flexable sticks to wet surfaces and i think its a great product i have used on couple of seams were i had a seeping and next tide gone ///

there is a class teaching boat building on clinker design and they only use sikaflex and boat life caulk no cotton at all

Smacksman
06-05-2008, 05:25 PM
Well they wouldn't use cotton on clinker anyway. Oakam is better on carvel seams but a bugger to work. Cotton is easier as it is pre-worked into strands ans supplied in a ball. It will rot less if soaked for a bit in linseed before use (not too much as it needs t absorb moisture to swell and seal)

Seams are traditionally stopped with red lead putty which eventually goes rock hard and can crack especially if there is regular change in moisture content of the planks. Rake out and re-stop.

Forget brand names for mastics in a tube - look on the tube and go by their type.

Oil Based. - Cheapest. Ok for use out of the weather. Brittle when old. No elasticity. Do not use as stopping and shouldn't be on a boat.

Silicone. - Difficult to paint over. The most elastic mastic. Degrades in sunlight. Impossible to sand down. Do not use as stopping.

Polyeurethane. - Fairly elastic but goes hard after a few years. Very quick drying (get that masking tape off quick!). Expensive. Very good adhesion (almost a glue!). Cures with moisture. Easy to sand down. Ok for stopping on very stable carvel hulls. Good deck stopping.

Polysulphide. - Slow to cure but can eventually be sanded down. Elastic and stays elastic for years. Mid price range. Good adhesion. My choice for stopping and bedding jobs if you have time for a full cure.

My 2c.

Ian McColgin
06-05-2008, 06:57 PM
Having seen a wonderful old boat almost ruined by SeankyFlux &

Loving the stuff myself in its righteous place:

First you must understand the role of caulking in carvel planking. When wet, the planking - skin - is in compressive tension. This mean a firm contact plank to plank be either slightly distressed plank edged or firm cauling. SneaklyFlux and ALL OTHER things that come out of a tube are too soft for this function. Even if they hold for a season in motor boats (they'll not last a serious beat on a sail boat) they will not hold another season. Too much wiggle of the planks on the metal fastenings.

Second: Over proper caulking and red lead or something I like proper underwater seam compound mixed, if the planks are a bit dry, with roofing tar to make something that will ooze out easily with the splanks' expansion. SneakyFlux and DeathCork are brilliant products in their places - I use both - but not here.

G'luck

pcazeles
06-06-2008, 11:34 AM
Thank you all for your feedback.

As I bought the boat after the previous owner passed away, I don't know what was done on the seams (any cotton caulking beneath, which Sikaflex has been used,...).

Anyway I'll follow the old advice "if it ain't broken don't fix it".

Mr Novice
01-25-2009, 05:38 PM
Hi pcazeles. Great thread! I have been reefing the seems of a 17 ft cedar lapstrake, and have come across brittle red led caulk, seemed over with putty, in some places silicone calk, and large areas under the keelson where sikaflex was used for stopping. After I get this all out, I intend okum and cotton.
For Ian McColgan: in your thread above, what do you consider "proper underwater seem compound?"

Lew Barrett
01-25-2009, 09:31 PM
I'll answer with brand names from my point of view, not that you asked me directly. Pettit underwater seam compound is the bee's knees, but I doubt it's available in the UK. Interlux underwater seam compound is quite similar, lasts about as well, but is a bit harder to trowel in. I could be mistaken, but I could have sworn they are both oil based.

dhic001
01-25-2009, 09:55 PM
Having a boat caulked with Sikaflex, i'll chime in here. Zeltic is almost completely caulked with Sikaflex below the waterline. There is no oakum or any other traditional materials in the seams, purely marine underwayer sikaflex. For the original 8 years after the job was initially done, no seams ever leaked. Unfortunately she dried out badly bweing left out of the water for about 6 years, and some seams broke the sikaflex joint. These have had a small amount of sika added to the gap, and a fairing over the top, it appears to have been reasonably successful.

Swan was done completely with Sikaflex in every seam, and to my knowledge has not been redone at yet (over 12 years after relaunch). Swan was done with a softer form of Sikaflex, which allowed about 30% compression and expansion. The only Sika joint that failed was where oil had contiminated the plank.

Alan decided when he did Swan that although the Sikaflex initially cost a lot, it was no more expensive than all the items that go into traditional caulking, and was easier to do. Remember that traditional caulking is an art, and if its done incorrectly, can do great damage to your planking.

While your boat doesn't leak, stick with the Sikaflex, but don't let it dry out excessively. Thats my two pennies worth.

Daniel

Lew Barrett
01-25-2009, 10:15 PM
Caulking, or re-caulking a traditional plank on frame boat is no small matter, and as you say, there are tricks that earn the guy behind the mallet his daily bread. I can't imagine that the initial cost of the material (Sikaflex in your case) would exceed the cost of a proper full on caulking job. Twelve years is a long time to retain tight seams, 20 years is an eternity for a caulked boat. The only question I have based on your experience is what it might be like getting the old stuff out when the time comes. If that's no harder, I'd say you've done very well indeed.

dhic001
01-25-2009, 10:23 PM
Caulking, or re-caulking a traditional plank on frame boat is no small matter, and as you say, there are tricks that earn the guy behind the mallet his daily bread. I can't imagine that the initial cost of the material (Sikaflex in your case) would exceed the cost of a proper full on caulking job. Twelve years is a long time to retain tight seams, 20 years is an eternity for a caulked boat. The only question I have based on your experience is what it might be like getting the old stuff out when the time comes. If that's no harder, I'd say you've done very well indeed.

Alan worked out the cost of Sikaflex versus caulking cotton, putty and white lead. the labour cost didn't come into it, as he did it himself. Sikaflex worked out to be the better option. I removed very little of the older sikaflex on Zeltic, what I did remove was hard to get out, but probably not much harder than the odd bits of traditional caulking that I removed in upper seams. If the job takes a bit longer to do, but has to be done less often it would seem worthwhile.

Daniel

Ian McColgin
01-27-2009, 11:36 PM
To those reporting good luck with Sitka Flex for caulking - details please, most especially is it a sail boat or motor boat???

dhic001
01-28-2009, 12:04 AM
Both vessels I've mentioned are powered vessels, either steam or motor. Swan is definitely the weaker and more flexible of the two, but is also the one thats had to put up with some pretty foul coastal weather. Both vessels lived for a long time in drying berths, which puts various stresses on the vessels. Based on the experiences with Swan, I see no reason for it not to be used on a well built sailing vessel.
Daniel

Ian McColgin
01-28-2009, 12:51 AM
Thank you dhic001. The stresses on sailing versus motor hulls are profoundly different and things that can work on motor boats do not always work on sail boats. The skin tension bit I mentioned above is not nearly so important in a hull that's not under the wracking strains of rigging.

I've seen the effects of elastic materials as caulking on sailboats. A sure way to ruin the boat. Just give a little thought to rigging stress. The stresses on a motor hull are different enough that it's not impossible for a substance like Sitka Flex to actually be at least slightly better than conventional caulking in that application.

Side note on seam compounds and application. I do find it nice to mix underwater seam compound with roofing cement - a common practice here to make it easier to work. But even straight out of the can, it's best not straight out of the can. Pack the seam compount into a really tough grease gun (a new gun, never had grease) and you'll have a nice bead to squeeze into the crack - less work in application and less waste after pushing around with the putty knife.

G'luck

floatingkiwi
01-28-2009, 01:10 AM
Ian, what material(s) should I use, in exactly which seams,(or not), on the folkboat?
Kerry

dhic001
01-28-2009, 01:11 AM
Thank you dhic001. The stresses on sailing versus motor hulls are profoundly different and things that can work on motor boats do not always work on sail boats. The skin tension bit I mentioned above is not nearly so important in a hull that's not under the wracking strains of rigging.

I've seen the effects of elastic materials as caulking on sailboats. A sure way to ruin the boat. Just give a little thought to rigging stress. The stresses on a motor hull are different enough that it's not impossible for a substance like Sitka Flex to actually be at least slightly better than conventional caulking in that application.



All very well to say that Ian when you don't know the boat concerned. Swan has endured some attrocious conditions, considerable wracking and strains that many boats never endure (try falling on its side on the mud at low tide). The Sikaflex has stayed intact throughout, and no seam damage was ever evident. I'm speaking from my experience with a very old, and considerably weakened launch that does move considerably.

Anyway, thats my views on the matter, each person has to make their own decision based on the vessel they have.

Daniel

Ian McColgin
01-28-2009, 01:50 AM
Thank you Daniel. I am glad Sitka Flex works for your motor boats. It is a wonderful product.

I doubt that you will find a sailboat navel architect who would specify Sitka Flex for a sail boat as the wracking strains of the rigging above and the keel below even in moderate weather are several orders of magnitude more severe than the wringing out a motor boat might take in rough weather. Motor boats take other strains and more severely - engin thrust, pounding and such - which is why they are engineered a bit differently.

Give a simple example that I hope is well known. The "file bottom" - a sort of diagonal cross planking used below the waterline in some semi-planing hulls - is ever so much more suitable for the beating that a power boat's bow can take than regular longitudinal planking forced to that shape. But you'd never use that bow on a sail boat and even on bows that come close and have such hollow that they are hard to plank, you'll not find file planking on a sail boat because such planking can't share the strain of the foretriange or, if a catboat, the incredible wracking of that big fat mast up in the eyes.

Assuming smaller size boats - under 20 tons - the stresses on power boats are so overwhelmingly fore and aft that elastic seams can be made to work at least for a decade or two.

All real cruisers ground out. I'd not call a motorboat tipping with a dropping tide wracking - more a thud - any more than I'd call Granuaile plopping her bilge 6' verticle drop when some idiot let go some dock lines as she lay against a warf dried out at low tide. That's just bump, not wrack, and elastic versus conventional caulking is not the issue.

Here's the important point: I'd still rather have proper caulking (or tight seam construction) with a proper seam compound over because if you don't then all the movement and stresses eventually go to the fastenings. Over time movement opens the holes, especially in the frames where the threads are, weakening the structure as a whole.

Some Folkboats are carvel and some are lapstrake. I have not worked on lapstrake boats any bigger than double paddle canoes and light dinks, where there is no caulking. (Traditional lapstrake is profoundly different than modern plywood lapstrake that's a wonderful epoxy glued joint.) If the seams need tightening you go along with the buck and pean tightening rivet by rivet. I've done a similar job on a tight seam yawl of 45' but there the rivets were all to the frames, not other planks. What little I know is that adding goop into such seams is a disaster.

In carvel planking it's easier - red lead to seal the plank edges, cotton put in by tapping on an iron, more red lead and then underwater seam compound below and topsides seam compound above.

G'luck

Jon Agne
01-28-2009, 11:20 AM
Ian, it's good to hear from you on this. I'm glad that this thread has been resurrected as I'll be refastening SURPRISE (25' Crosby) this spring as well as reefing and re-caulking below the waterline. Last spring I noticed a few proud butt ends, and on checking the screws (bronze) at random points, Alex Hadden and I decided it was time.

Interestingly, the screws at the butts were in much worse shape than the plank to frame screws, so we refastened 5 butts using bronze bolts and scheduled some time this winter spring to tackle the rest. Then around the middle of August, SURPRISE developed at leak at the stem just forward of the mast step. It only leaked while under way (sail or power). As I was already committed to re-fastening, I thought I may as well completely reef out the seam compound, and if necessary, re-caulk. I am hoping to get by without removing the garboards, as they approach 10" at their widest point, and it may be rather difficult to get them back on properly.

I agree with everything that's been said about underwater seam compound (the red lead stuff). It's fantastic for boats that live most of the year in the water, but for those of us here in Maine it is rather problematic. It dries out terribly during the winter while on the hard and proceeds to simply fall out of the seams while preping the bottom for paint.

I've had all sorts of conversations about the best seam compound to use, and as is noted here on this thread, opinions differ widely as to what works best. I am going to try regular white seam compound (above the waterline type). This idea came from a retired wooden builder here in Maine (anon by request), and he swears that it doesn't dry out like the brown compound. He has been using it for the past 15 years with no ill effects to any of the boats he has worked on.

I'd love to hear what others think.

Jon

Ian McColgin
01-28-2009, 11:44 AM
It's true that besides being so stiff it's hard to apply, underwater seam compound can have a hard time drying out in the winter.

I don't trust the white below water as it's really designed to dry more.

Try mixing the brown 50-50 with roofing "tar" (now more a plastic) and stuff that in a good grease gun for application. The tar/seam compound mix will survive multiple seasons before needing a do-over.

G'luck.

David Conard
01-28-2009, 12:06 PM
I had a 40 year-old H-23 sailboat (mahogany on oak frames) on which the seams were properly caulked with cotton and payed with Sika. I hauled her each winter and stored her in a Vermont barn. Before I bought her she was in Maine, and was hauled each winter and stored outdoors under a canvas cover. Despite many years of extreme drying cycles, the seam compund held up beautifully.

David

Bill Mercer
01-28-2009, 02:56 PM
Give a simple example that I hope is well known. The "file bottom" - a sort of diagonal cross planking used below the waterline in some semi-planing hulls - is ever so much more suitable for the beating that a power boat's bow can take than regular longitudinal planking forced to that shape. But you'd never use that bow on a sail boat and even on bows that come close and have such hollow that they are hard to plank, you'll not find file planking on a sail boat because such planking can't share the strain of the foretriange or, if a catboat, the incredible wracking of that big fat mast up in the eyes.



Actually skipjacks have file bottoms and they last a good long while, though the bottoms being a bit easier to replace than fore and aft planking may help. Cross-planked sharpies had the unstayed mast stepped onto the keelson, with the planking no doubt taking a lot of strain. Of course both types were pretty heavily built, by guys who knew their business. Probably this is a case where tight caulking between heavy planks resists wracking strains. . .

Andy B
01-28-2009, 10:30 PM
As one other reply said, the sikaflex is not, or shouldn't be, the caulking. This should be cotten, oakum, or jute, which stiffens the boat's structure, and then the seams have been payed with sikaflex. This is apparently a common procedure with the fishing trawlers that work out of the Clarence River, NSW, Australia. I believe however that Sikaflex do not actually recommend their product for underwater application. I have used it on some underwater seams in my gaff cutter and found it easy to remove and renew on a later slipping, but I only used grey primer under it, not the special primer Sika recommend in deck seams.

I was seeking a material to pay the seams with that would retain flexability, unlike putty, but Sikaflex would have been too expensive to do the entire boat. So I used bitumous "Hydroseal" or "Duraseal" mixed with red lead and talcum powder. The talcum powder increased the viscosity of the mix so it wouldn't creep out. I have found this this to be satisfactory after 15 years.

JormaS
01-30-2009, 07:20 AM
What goop to use in the underwater seams? I always thought the the right thing would be to use what was used when the vessel was built --- or at least some surrogate close to that original stuff.

I assume we´re talking about carvel built hulls, with seams caulked with cotton or oakum in order to make the hull rigid and the seams tight. What ever comes on top of that caulk is there to protect the caulk but not to ensure water-tightness. Am I right so far? I´m not a boat builder so please correct me if I´m wrong.

I´ve used bitumen compounds (that´s roofing tar) as long as I can remember. Nowadays they often contain a rubber-like ingredient which makes them stay elastic for some years. Andy B interestingly suggests adding talcum powder. I think I have to try that.

If the boat was built with Sikaflex on top of the cotton or oakum, that’s fine. But I doubt that it was. I haven´t checked it lately, but to my knowledge the Sika company never recommended it for underwater use. I believe it is not because polyurethane would not cope with water. Rather it is because it is hard to maintain a proper glue line in immersed wood.

Sikaflex is a polyurethane compound just like 3M 5200, Tremflex, Soudal, and tens, or maybe hundreds of other similar products. Some of them are intended as glues, the more elastic versions are sealing compounds. They were, and still are, mostly intended for use in the construction business (curtain walls, etc.), but during the twenty or so last years have found their way into boats where they have become, I think, the most widely misused stuff, right after alcohol!

In order to successfully use a polyurethane sealant as a seam compound one has to match the joint´s dimensions with the modulus of elongation of the compound, usually expressed as “hardness” on the Shore A scale. The most elastic Sikaflex is Shore 15, and the stiffest I think is Shore 40. The 3M 5200 is Shore 60 or 70 as I recall (this can easily be checked, it´s all to be found in the product data sheets).

If a boat builder prescribed a polyurethane sealant on top of the cotton caulk in the seams of a carvel built hull, I´d be truly amazed. Which doesn´t mean it couldn´t happen, of course. I just don´t understand the logic. I suspect that the whole issue has risen from the fact that we nowadays have the opportunity to see our underwater seams more often than our fathers did. We tend to pamper the boats more than is necessary, and we may put emphasis on rather trivial things in stead of doing what is urgent. Because we haul the boats for the winter, the hulls dry out and the seams tend to leak when the boat is launched, and we think that is because the goop again has failed, when in fact it needn´t have anything to do with the seam compound. To make the hull tight we think that what is good for the deck seam is good for the bottom as well, forgetting that it is an infinitely more difficult task to make a proper polyurethaned seam stay tight between the bottom planks - - especially if the boat is hauled each autumn. Which, again, doesn´t mean it couldn´t happen…but that would be exceptional in my view. If the bottom planks dry out even a little, that will put an enormous stress on the seam´s glue line, and it will let go at one edge of the seam, especially when a typically “normal” Shore 40 compound is used. When the planks take up again, things will be OK of course. The big headache comes only when that expensive stuff has to be reefed out and replaced one day.

Quite simply I believe we have been misled to believe that if a modern adhesive-type sealant is good for one application, it is good for mostly everything.

On the other hand, maybe I should stop whining….because.…truth be told, we love doing the seams and all that stuff. As we age, it almost beats sailing!!!!:eek:

techclub
12-03-2010, 04:05 PM
WARNING USING SIKAFLEX 291 FAST CURE.......

... on a Aprox 1930, 40 ft kauri displacement launch

Having removed the fiberglass from the hull (was done early 1980's) coating from the wood and picking out the epoxy from all the seams and scraping them back to clean wood and removing and replacing the old cotton with new and red lead coating the seams and cotton as it went in and all the bare sanded wood in red lead I wanted to use the best thing (claimed) I could get to go and seal this puppy to last my lifetime (well maybe another 30 years ).

A Bugger to get in and if it was warm it would drip everywhere but with a few side seams done I got the flow of it and slowly carefull not to get air pockets or gaps by using a putty blade to scrape and pressure it in all looked good.

Now note this boat was out of the water for AROUND 5 YEARS and had a coat of fiberglass on it so real dry and all bare wood was covered with tarps when rain was around (all upper decks are glassed)

So...I went away for 6 weeks to sort out a few things and returned to put on undercoat/primer and antifoul BUT MOST of the seams have cracks on both sides of the plank, above waterline (used the white) below water line (used the black) at the few plank end joins and basicly everywhere!!!

When it was put in it had a 1-3 mm swell above the plank but after 2-3 days this receeded back into the seam by around 1mm.

The data specs claimed 5% shrinkage and 45 elasticity....check wiht the reps on application etc.

Hey in a I.T tech and read the manufacturers data and do a lot of resurch before shopping....

Im unsure what to do now and are awaiting inspection by sika next week so cant start to remove and the cracks range from 1 mm to 3-4mm - cant place it in the water to tighten as it will leak BAD - not good with a fresh interior.

To me it looks like the 291 has shrunk and torn away from the primer (* but not all the way so you cant just pull it out and its stuck to the new cotton)
So it might be a long hot summer - under the boat again caulking it again the right way.

Best to stick with what has worked for centuries EH. putty, lead and linseed.

I will report back with the sika response.
-

Peter Malcolm Jardine
12-03-2010, 04:15 PM
First, most of the modern caulking compounds work just fine in lieu of old fashioned seam compounds. Second, while there are stress differences on sailboats that are different from powerboats, the most common reason that caulking compounds don't stay in on wooden boats is because the god damned boat is rotten or has fastener loose and is moving around way too much. Third, there are lots of boats that don't use cottom or oakum at all in the seams, just compound. That depends on construction.

These threads often turn out like the best varnish and paint threads. Everyone has a favourite. If your system is working, stick with it.

starlightventure
03-15-2011, 05:51 AM
Well said

lagspiller
03-16-2011, 09:53 AM
I've used sikaflex in the underwater seams on my 22 square meter for about 20 years. Usually go over the bottom and 'top up' any spots I find needing a little attention before painting the bottom as part of the spring ritual. Usually very little needs attention. It works fine and has given no trouble over all the years. Store the boat indoors in winter.

kavw
03-19-2011, 06:01 AM
i've found seams caulked with ALL sorts on my 60ft sailing ketch, cotton, oakum, sikiflex, what looks like cordage (might be rolled up oakum), when I hauled to start drying there was almost no seepage.
In other words, most things seem to work some how or another.
Some one mentioned cracks of 1 mm to 4 mm, why not just fill that with seam compound? Davis slick seam, or interlux and let it squeeze out when the wood swells?

Ian McColgin
03-19-2011, 06:16 AM
I've mentioned earlier - caulking is the fiber stuff. Seam seal goes on top. A carvel hull is designed to be a structure under skin tension - the planks need to press against each other. If they don't, then they are forced to stay put entirely on the fastenings, which consequently wiggle about damaging the wood. Because the swelling and shrinking of the wood is a little hard to get exactly right, some way of allowing the planks to come firmly to each other but not so tight as to blow apart is necessary. Caulking. Instead of caulking you sometimes see a crushed wood seam where the edges of the planks are distressed a bit with a hammer. These can swell as the boat takes up and tighten down just like caulking. Really thin rivited nearly strip planking - such as in the fameous Argentinian yawl Cimmeron and in some production boats like the Kings Cruisers - might be tight seamed - no caulking at all but planking laid down to utilized reduced swelling.

However you do it, the planks need to come to some firm tension. If you eliminate the caulking and go with a substitute seam sealer all the way down, like all SikaFlex, you get a hull that can't swell to firm and the planks will wring about until the fastenings loose their grip all together.

It does happen that when a person in a hurry or operating under some strange theory about a miracle goop happens not to have seam compound at hand, he or she might use most anything, including SikaFles, Life Caulk, even epoxy or concrete. Anything works a little, but everything except seam compound introduces different problems down the line.

Caulking does not come out of a tube and is not a goop. It's fiber.

Seam compound can come from a tube if you want to spend beaucoupbucks. Many of us mix the underwater seam compound with roofing compound to make a more workable material that can move with the swelling more easily. This can be loaded into a grease gun and applied fast and neat.

G'luck

Paul G.
03-20-2011, 01:39 PM
I did my underwater seams recently with sika 221, what a tough job! scrape all the paint, break the old hard putty inch by inch, reef it all out, harden up the caulking and re caulk in a few places...... prime and then finish with the 221. The sika simply replaces the putty and does a superb job. When we had to pull her again after a month to replace another stopwater an inspection of the garboard seam revealed bone dry cotton!

Ian McColgin
03-20-2011, 02:07 PM
I'd love to hear from real boat builders - I only have 62 years of involvement with wooden boats and there is so much I don't know - about bone dry cotton. It does not sound good to me, but perhaps if you like the planks to hang entirely on their fastenings and you only want a couple years out of the boat it's fine. And then, maybe the wood's swelled enough and pushed the cotton that it only feels bone dry. After all, a properly caulked, seamsealed and swelled seam should leave a dry bilge on the inside.

ARW123
03-21-2011, 03:11 AM
... (Traditional lapstrake is profoundly different than modern plywood lapstrake that's a wonderful epoxy glued joint.) If the seams need tightening you go along with the buck and pean tightening rivet by rivet. I've done a similar job on a tight seam yawl of 45' but there the rivets were all to the frames, not other planks. What little I know is that adding goop into such seams is a disaster.

Something that has concerned me awhile on my boat - each and every seam (above & below the waterline) has had this cr*p stuffed into it and smeared into a 1/2 inch "radius". It is clear that above the waterline all this has done is trap moisture between the lands and allowed rot to progress unhindererd - where otherwise (to my understanding) it would have dried out and been fine. Below the waterline it seems a bodger's solution or a demonstration of abject laziness in trying to cure loose seams.

When my old girl finally wets her petticoats, I am more than a little worried she won't take up after all this muck has been removed.

Paul G.
03-25-2011, 05:52 AM
I'd love to hear from real boat builders - I only have 62 years of involvement with wooden boats and there is so much I don't know - about bone dry cotton. It does not sound good to me, but perhaps if you like the planks to hang entirely on their fastenings and you only want a couple years out of the boat it's fine. And then, maybe the wood's swelled enough and pushed the cotton that it only feels bone dry. After all, a properly caulked, seamsealed and swelled seam should leave a dry bilge on the inside.

This was done under the auspices of a "real boatbuilder" not a patch up job by some ignorant amateur bent on a short term fix. The seams were recaulked hardened up, inch by inch and those seams were sealed with 221. Water WILL get in albeit much more slowly than putty will allow and the sika is a dream to reef out if needed compared to old hard putty. Sika is just a modern replacement that works exceptionally well provided you understand the materials and construction.

Stevest
12-09-2016, 07:00 PM
I'm not sure if I am in the correct section ,I am new to these forums, if someone can direct me to the proper place I would be grateful.
i have a 32'wooden boat. It was built on the Clyde and designed by Mylne in 1907.
every plank is full length with no but joints..is this a sign of good boat building?
i have had the boat in my shed for over a year and is fully dried out . The seams are cotton and payed with some kind of sikaflex or polysulphide. Most of the seams have stayed in tact and have gone concave. I wonder if these could be left alone?? Some seams however have opened up much wider and the corking has become separated from the planking .
i am thinking that I will have to rake out these wider seams, check the cotton, prime the seams and re cork with some kind of polysulphide/ sikoflex. I am a boat builder but not a shipwright so I would appreciate any advise on this process.

Steve. (stevest10@aol.com)

Stevest
12-09-2016, 08:12 PM
???

nedL
12-09-2016, 08:55 PM
There can be much more discussion on this, But ...If the caulking is not actually falling out of the seams I think I would try to get some moisture back in the wood and see what things look like before doing anything.

Ian McColgin
12-09-2016, 08:57 PM
Firstly, full length planking is at the very least a sign of nice materials.

After a year out, things may well have shrunk a bit. Assuming the caulking (cotton) is not falling out. reef out the glop on top and regoober with something soft and flexible that can squeeze out as the boat swells. I use underwater seam compound (usually brown) mixed about half and half with roofing tar. As the boat swells, this will squeeze out without hurting the boat. Next haul, flatten it out before you repaint the bottom.

G'luck

deepwoodsd
12-11-2016, 12:59 PM
While this thread is active, I have a question. I am building a lapstrake dinghy using VG Douglas fir on white oak frames. I want to seal along the lands, especially the garboards. One problem is that the temperature in my northern Ontario shop is low and I want a soft product. Sikaflex 291 LOT is my choice so far. Any comments would be appreciated.

Paul G.
12-11-2016, 02:06 PM
To those reporting good luck with Sitka Flex for caulking - details please, most especially is it a sail boat or motor boat???

I recaulked with cotton then payed the seams with sika on the advice of a very practical and experienced 75year old wooden boatbuilder, we painted the seams with grey primer first and used sika 291 from memory. Heres a tip, used a compressed air gun to apply it! No leaks and minimal squeeze out but the seams were about 3-4 mm wide max.

Paul G.
12-11-2016, 02:40 PM
https://c1.staticflickr.com/1/532/31433611952_7792cde6cb_b.jpg

Had to refasten the garboard seam for another reason but you can see the sika seams

Stevest
12-13-2016, 07:59 PM
Firstly, full length planking is at the very least a sign of nice materials.

After a year out, things may well have shrunk a bit. Assuming the caulking (cotton) is not falling out. reef out the glop on top and regoober with something soft and flexible that can squeeze out as the boat swells. I use underwater seam compound (usually brown) mixed about half and half with roofing tar. As the boat swells, this will squeeze out without hurting the boat. Next haul, flatten it out before you repaint the bottom.


G'luck


I have noticed some rather large gaps between one or two of the planks at the turn of the bilge towards the stern. They are about 6mm wide and I can see clear daylight right through. The doesn't seem to be any bevels on these planks. I am thinking I will have to spline some of these wider gaps but leave a bevel on the reduced gap so I can then cork with cotton and pay the seams with sika flex or polysulphide .. Do they not make some kind dissolvable tape that could be applied to wider gaps until the hull takes up???

Ian McColgin
12-13-2016, 08:04 PM
Caulking with a fiber and then using Sikaflex as a seam compound is just fine. I know two boats that were much ruined by the use of Sikaflex as the caulking, a very bad mistake.

Ian McColgin
12-13-2016, 08:08 PM
On the seams that are really opened, rope up a thicker strand of the caulking and push that in. Don't over-pound it as the planks will swell some. And on those wider ones, at least for the first year go to underwater seam compound mixed 50/50 with roofing glop. It'll squeeze out nicely as the boat takes up.

artif
12-14-2016, 03:37 AM
Not in my experience, but I was doing deck seams of a big old Danish trawler. The decks just moved too much between summer and winter for the sika to hold, re did the seams with Jeffery's no.2 and all was good.
It might be O.K under the WL where movement is much less.
TBH I've seen better longer lasting seam sealing with polysulphide sealants (Arbokol) seems to be more flexible.


Caulking with a fiber and then using Sikaflex as a seam compound is just fine. I know two boats that were much ruined by the use of Sikaflex as the caulking, a very bad mistake.

Ian McColgin
12-14-2016, 06:58 AM
artif has a point. I was thinking only of below waterline. One glorious eighty year old extreme yawl got new garboards nicely caulked with SikaFlex. Nearly sank first sail. I'd warned the owner, who mushed on "assisting" a not too confident would-be boatwright who thought they ought to use cotton under but got talked out of it. After the boat was hauled, the owner first wanted to force in more SikaFlex, then blamed his boatwright, and finally sold the boat to a man who reefed those seams and did the job right.

A lot of folk don't understand that carvel planking is an engineered tension structure and firm contact plank to plank is necessary. Without that, even if the planks don't move much at first, they are only hanging on the fastenings, which under wiggle strain will lose their grip.

keith66
12-14-2016, 07:31 AM
Sikaflex is a polyurethane as is Soudal, PU40 & others. I used one of the cheaper brands as a filler on a keel joint on a GRP boat & the antifoul basically melted it. Sikaflex was slightly better but the antifoul still softened it a bit.
I have seen Polysulphide (arbokol 1000) used with some sucess over cotton. On dinghies i use Evomastic, a cheap oil based mastic that is extremely good, never sets hard & is good over cotton in tight seams, also good on clinker as will squeeze out without damage.

Bob Adams
12-14-2016, 08:20 AM
Sikaflex is a brand, there are different formulations. Fortunately most I have seen are polysulfide not polyurethane. I have used it on occasion below the waterline with success. As noted above, it is not really caulking.

Ian McColgin
12-14-2016, 08:30 AM
Slight drift, but I miss the old WoodenBoat Show SikaFlex Challenge. Some very creative structures.

jgmarine
12-14-2016, 08:42 AM
I infer that you are saying that a previous owner has used Sikaflex in lieu of proper caulking on your boat. Polyurethanes are too hard/stiff to be used as seam compound. (there is probably a proper mechanical engineering term.) Using the stuff can warp planks and strain fasteners. With that said, and just between the two of us, I have used it on a sloppy plank replacement on a boat which had be done by a previous owner. I just used it on the single plank.

If the hull seems ok, I would not mess with it. It is a nightmare to remove.

Some have said there is a problem with it in underwater use. I typically use it for bedding down the lower margin and sides of a runabout 's lowest transom plank. I do this because it is a common place for rot to start. If the plank needs to be removed, it can be fairly easily remove with a router. Never had any problems.

I believe it's called elasticity?

jgmarine
12-14-2016, 08:42 AM
Elasticity

Bob Adams
12-14-2016, 05:44 PM
Back in the late 80s there was a European product called Seal Once. It was a polycarbonate (same stuff as Lexan) sealant. Cured to the consistency of chewed bubble gum, and even years later after underwater service if you pulled a piece apart it would still stick to itself. Loved it.