Synthetic Caulks

[Undaunted]

I am faced with replacing the bedding compound under my white oak sacrificial keel (12' lapstrake dory) and have been looking to see if anyone has a suggestion for a synthetic compound that might last longer than Dolfinite, but to no avail, anybody have any ideas?

Must be waterproof below the water line and replacable in maybe 10 years...

SWG

[Jim Ledger]

Roofing tar and tarpaper has a lot to recommend it. I've got it on my catboat's worm shoe and when it gets blocked up it still squeezes out after half a dozen years. And it's cheap.

And worms don't like it.

[Undaunted]

Jim,

Do you put the paper between layers of the roofing tar? Would it run/drip on a hot day the boat was out of the water you think?

Scott

[Jim Ledger]

Shoe...tar...paper...tar...keel.

It squeezes out like any bedding when you screw on the shoe. Clean it up with thinner. Pretty soon it skins over and that's that. Paint won't stick to the tar seam , though, but that's not really a problem.

[sdowney717]

use a saw toothed small notched trowel 1/8 inch
squeeze out some PL Premium Construction adhesive
Use the trowel to lat down beads on the keel bottom

When it has set up, fill in with a smooth trowel.
It will swell up slightly but it will be a flexible permanent water barrier and those worms wont be able to get thru it.

When I tore off the worm shoe, tar paper had been stapled to the bottom of the keel, And some worms had gone thru the paper.

[Undaunted]

You're

[Undaunted]

You're suggesting construction adhesive as the bedding?

[sdowney717]

do a test.
It is permanently waterproof.
All you need is a barrier.
If this boat is going to be scraped over stuff, then also attach a new peice of sacrificial wood on top.

[Bob Cleek]

Henry's.... it's called, "Henry's." It is a brand of "wetpatch." This stuff is basically some sort of non hardening tar with asbestos, or maybe glass, fibre mixed into it. Comes in a gallon paint can. Used to have a purple label. Probably still does. A gallon can will last you for a LONG time unless you are building a big boat. Cheep too!

[Thorne]

Dunno about PL Premium as a bedding compound for a false keel -- it is really strong and permanent.

I used Dolphinite on mine, but now I might consider using Vulken116 -- stays reasonably flexible and could be cut free with a hot wire passed between the false bottom and real bottom planks.

But the Henry's should work as long as the boat isn't propped up on stands at a wooden boat show in hot weather.

[Undaunted]

I'm going to look into the Vulken 116, I need something a little more robust than Dolfinite as I drag the boat up the beach and stones and sand are getting into the bedding and pulling it apart... Thanks for the suggestion!

Scott

[Undaunted]

Thorne,

Do you have an opinion on 3M 5200 for this use?

Scott

[ron ll]

My 28,000 lb boat still has a couple of drops of black tar squeeze out between the keel and shoe where it is blocked when hauled out. It's just a couple of small drops but it is still soft and tarlike and I'm pretty sure these pieces haven't been apart or rebedded in many years, maybe even since it was built in 1943.

[Thorne]

In my somewhat inexperienced opinion, there seems to be some general classes of sticky stuff -- often the differences are a bit of a grey area and open to interpretation.

Bedding compound is different from glues with a different function, but you might be able to use some of the tube SEALANTS (as opposed to glues) that are designed to fill gaps and remain flexible as a bedding compound -- as long as you can deal with the adhesion issues when the time comes to replace/reseat the bedded object/material.

Here's a thread with an in-depth discussion of this issue -
http://www.woodenboatvb.com/vbulletin/upload/showthread.php?t=7068&highlight=4300

I'd guess that these sealants include Vulkem116, 3M 4200, Sikaflex 291, and other tube sealants/glues that remain soft rather than harden over time.


Here's info from one of Bob Smalser's posts on this subject -

http://www.woodenboatvb.com/vbulleti...ead.php?t=6799 (http://www.woodenboatvb.com/vbulletin/upload/showthread.php?t=6799)

General Notes on Glues and Goos

Resorcinol: The marine standard. If you can get 70 degrees F or higher for an overnight cure and consistent and high clamping pressure with no gaps, you won’t go wrong using it. Likes wood at 10-15% EMC, according to Navy tests. Long open time. Repairable with epoxy. Ugly red glue line.

Marine Epoxy: The repair and restoration standard. Bonds well to a wide variety of materials, and usable in almost all flexibility and temperature conditions. Needs no clamping pressure, only contact…fills gaps well. Likes wood below 12% EMC. Repairable with itself, joints can often be broken apart for repair with using heat. Clear glue line and can be dyed to match the wood. Controllable open time with different hardeners. Slightly permeable to water vapor and there are reports of failures in fully saturated wood and with White Oak. Very sensitive to UV, requiring protection.

3M 5200: A rubbery, polyurethane sealant in various colors with adhesive properties sometimes used as a glue. Fails as a glue under water saturation without high clamping pressure, and without the proper strength testing I couldn’t do here, it’s not recommended as a stand-alone marine glue. Repairable with epoxy.

Liquid Polyurethane: Gorilla Glue, Elmer’s Probond, Elmer’s Ultimate, and others. Versatile in temperature and bonding wet wood with moderate open time, these glues aren’t rated for below waterline use but initial use shows potential as a marine glue. Likes high clamping pressure and fits similar to resorcinol…it won’t fill gaps. Will successfully glue green wood at 30% EMC. Repairable with epoxy. Noticeable, yellow-brown glue lines.

PL Premium Construction Adhesive: This polyurethane goo shows promise as a marine glue with further testing and use. Works like 3M 5200 but cures and behaves like liquid poly. Appears to bond well to everything epoxy does, and more where epoxy and liquid poly won’t, perhaps because of a higher isocyanate content…it bonds to difficult surfaces only cyanoacrylate super glues will bond to. The only general-use glue I’ve found that will bond difficult aliphatic-contaminated surfaces. Appears flexible to temperature and moisture content with gap-filling ability, but as a construction adhesive, its open time is shorter than liquid poly. Appeared to like high clamping pressure, and unlike other glues, wouldn’t bond at all without at least some. Repairable with itself and epoxy. Glue line as in liquid poly.

Urea Formaldehyde Plastic Resin Glue: Weldwood, DAP and others. The old interior furniture standard, and in older marine applications that required well-blended glue lines. Still preferred by many, as it is a no-creep glue easily repaired using epoxy. Long open time, it needs tight fits and 65 degrees F or higher for an overnight cure…it doesn’t fill gaps. Best glue line among them all and moderate water resistance still make it useful for protected marine brightwork applications. A relatively brittle glue and UV sensitive, it requires protection….but its brittleness is an aid to repairability, as joints can be broken apart for repair. An inexpensive powder with a short, one-year shelf life.

The Titebond Family of Aliphatics: Convenient. No mixing, just squeeze. Short open times, fast tack, and short clamping times. Fast, and an acceptable long-grain layup glue…in heated, commercial shops, I’ve had rough-cut Titebond panel layups in and out of the clamps and thru the planer inside of an hour. Flexible in temperature and to a lesser extent in moisture content, but the bottled glue can freeze in unheated shops. A flexible glue, it has been reported to creep under load, sometimes several years after the joint was made. The latest “Titebond III” appears to be a stronger glue than its two predecessors. Difficult glues to repair, as they won’t stick to themselves and no other glues will except cyanoacrylates, which are too brittle for general use. Epoxy and fabric aren’t bonding to aliphatic glue lines in marine strip construction, compounding repair difficulties. While not definitive, the new PL Premium appears to bond well to Titebond III residue and is worth pursuing by those repairing old white and yellow aliphatic joints.

[Undaunted]

Thank you Thorne, very helpful. Looks like 3M 4300, Silkaflex 291 or Vulken 116 might have enough adhesive and flexible qualities I am looking for as a below the water bedding compound that someday will need to be removed. I'll have to look into these further...

Scott

[Thorne]

Not mine -- was part of Bob's post, sorry that I didn't make that clear.

Good stuff! I find that this forum is a goldmine when used with specific questions that are searched carefully.

[Undaunted]

Based on everyone's help, study of manufacturers specifications and the observatons by JORMA below, I decided to use Sikaflex 291 LOT over 3M 5200, to bed my sacrificial keel to my 12' dory. Previous owner seemed to use Dolfinite and it didn't hold up. We'll see how this works! Thanks for everyone's help!

Scott Glenn
Sea Bright NJ

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Senior Member

When cured, the Sikaflex 291 is reported to have a hardness of Shore A 40. 3M 5200 is Shore A 60, which is considerably harder and less elastic. 3M 5300 is 50, and 3M 4300 is 40 I think. For comparison, the Sikaflex 290 DC seam compound is 35 to 40 as I remember. The most elastic seam compounds used in construction have a hardness of Shore A 15. 3M 5230 (if I remember the figures right) is Shore A 80 I think, which makes it an outright glue. I did not find any such data concerning the PL products on their web site.

If the compound is to "give" under the ribs, it must have some minimum thickness. I don´t know if that is prescribed by the manufacturers. Clearly, 2 mm of compound will be more forgiving than, say, 0.5 mm. Without the use of spacers, one would assume that the latter is the more probable thickness if heavy wheights are used to press the ribs down. That would call for a more elastic compound. This may be the reason why Sika have decided to make it Shore A 40 for this application. But I´m not sure.