Sheer Clamps

[David]

Tim,

I'm curious why you attached them with bolts and 5200 versus gluing in thinckened epoxy and bolting. Are you planning to saturate the installed clamps with epoxy as a preventative? Also wondering how thick the topsides are at the bolt attachment--it's hard to tell from the photos.

As a more general question: It seems that you used resorcinol glue at the stem (based on your photos) and expoxy elsewhere (of couse)--what determines which you use for a particular application?

David

[Tim]

I used 5200 partly because of its strength (not that epoxy lacks strength, of course), but mostly because of its easier application and the long open time it allows. Trying to mix the amount of epoxy required to the proper thickness, spread it, and get the wood secured in place in time could have been tough. I was able to hold the two halves of each section together temporarily with screw clamps against the hull, which pressed the epoxy in the joint together while I installed and threaded the bolts and nuts, which really pulled everything together. Doing this whole job in epoxy, with a good-sized pot of mixed stuff and a fair bit needed, would have been more difficult, I think.

Also, the photos don't show it that well, but because the clamp is installed where the deck used to be tabbed to the hull--and where the old tabbing still exists--there is some serious unevenness of the laminate there. I guessed it would be easier to apply sufficient 5200 than epoxy. The bolts are effective at clamping the pieces in place and drawing it as tightly into the hull as possible,where the thick 5200 makes up for the undulations.

As to choice of glue, if you're referring to the sheer clamp, all sections use epoxy to secure the two boards together. The reddish color you see in the photo below, if this is the one that led to the question, is actually because the two halves of the clamp sections have slipped by one another during the bending and securing, leaving a shadow line that appears highlighted because of the overall dark color of the end grain. Other color variations on the boards are just resin residue.


The hull thickness is mostly about 1/2" or so at the sheerline, between the hull itself and the heavy tabbing that remains from the old deck.

Ultimate protection of the clamps from routine condensation amounts is to be determined. Paint will work fine, and is probably what I will do. Let's not forget what a fine boatbuilding material wood is even without the miracle of epoxy. Not all wood requires epoxy coating in order to succeed in boatbuilding. I also intend to run a bead of sealant along the outside (hullside) edge of the clamps to ensure that no moisture can penetrate behind.

[David]

WRT the 5200-glued sheer clamps, could you remove the bolts at this point and continue constuction? That's the definition I always have in the back of my mind with the possible use of epoxy (not that you will ever remove the bolts--but could you--is the 5200 that strong?).

So, do I take your response to mean you never use resorcinol glue? I kind of thought you did on occasions. I have read that while it is not gap filling, it is more resistant to UV, and easy to mix in small batches. I have used it for years with great success, but I don't know the relative strength of it versus epoxy.

David

[Tim]

I also like resorcinol glue--I feel it is an outstanding product that has been neglected in the face of "the epoxy revolution" (my term). It is extremely strong, 100% waterproof, and more UV resistant than epoxy. One should never overlook resorcinol when working with wood in a marine application.

I am using resorcinol in the deck beam laminations, and will use it in other applications as well. It's definitely not the choice where gap-filling is needed, but for basic gluing and laminating, it is well worthy of consideration for anyone. It can be tough to find locally; my local hardware store doesn't carry it, so I have to plan ahead. I now order it in larger quantities to keep on hand. I also like it particularly for its use in smaller batches, as you said. Sometimes the dark glue lines left by resorcinol can be a problem; other times highlighting the joint is appropriate, or the joint may be hidden in the first place.

5200 is incredibly strong. It's not a sealant, it's a flexible adhesive. At full cure, there's no question that I could remove those bolts--if indeed I could even force the bolts back out against the tenacious grip of the 5200 in the boltholes. (Note that it does take a minimum of 7 days to reach full cure, and longer than that depending on temperature.)

I hate to keep dragging out the same old example, but I have seen a ballast keel on a 42 foot sailboat remain firmly affixed, held only by 5200, after all the keel bolts were removed and the boat lifted in a Travellift, ostensibly to lift the hull off the keel. Eventually the ballast was broken free and removed, but not without some serious effort. I call that pretty impressive. It's not a product you want to use where you don't want permanance, that's for sure.

I also like epoxy, of course. But I like to consider different materials at any given time for any particular job.

Just out of curiosity, what in my previous response gave any impression that I never use resorcinol? I don't read anything of the sort into it myself. Actually, I might have considered using resorcinol instead of the epoxy holding each of the clamp sections together, except I didn't have any at the time (I was waiting for a shipment). Resorcinol would have also worked well in that application, since no gap filling was required.

In any event, the job's done now!

[David]

Sorry, you didn't really say whether you did or didn't in your post, just that what I was looking at was a shadow, so I kind of took it to mean that you didn't use resorcinol.

David