3M 5200 Adhesive question

[baliano]

Does anyone know how thin a bond thickness I can use and maintain the 3M 5200 bond strength?? Is it 0.005", 0.10", even thicker? I've asked 3M about clamping pressure but haven't received an answer. In terms of joining flat sides like in a frame build-up, the thinner I can keep it the more stable the joint should be.

[Hughman]

3M must have specs on this. Keep at 'em.

My gut feeling is .10 or thicker.

What are you building in them thar hills?

[ 11-02-2004, 10:00 PM: Message edited by: Hughman ]

[Bob Adams]

I'd agree much more than .10....I've taken apart a few bad repairs (with difficulty!)where this wonder googe was 1/4 to 1/2 inch thick. Really tough stuff. If using for a construction adhesive (it's only proper use),I'd think too thin of a glue line would be weaker.

[Ross M]

A most excellent question, Baliano - the archives appear to be silent on the issue. I too have contacted 3M and recieved no response.

The nearest thing to a recommendation that I have found is within Don Danenberg's book "Runabout Woodworking/How to Restore Your Wooden Runabout".

In the section where the author discusses the depth of chine rabbets, he appears to allows for a 5200 bond line thicknesses of 1/16" (1/8" total; 1/16" between the chine and the first layer of planking + 1/16" between the first and second layer of planking).

Granted, this is not a frame lap joint. I intend to query him on his website's forum, as regards frame laps, but haven't gotten around to it yet.

In the mean time, I think I can say this: The stiffness of the joint is probably inversely proportional to the bond-line thickness.

At one extreme - say .005", the joint is going to be stiffer and somewhat more likely to shear wood fiber under impacts/heavy deflections.

At the opposite extreme - say .125", the joint is going to be very elastic; offering little risk of wood fiber shearing, but significantly higher risk of failing the (presumably associated) mechanical fasteners.

I am still thinking about what all this means. If I figure anything out, I will post.

If we are lucky, one of the more knowledgeable members will happen along and enlighten us!

Ross

[Dan McCosh]

5200 isn't a glue--it's a flexible sealant that happens to have a high adhesive strength. The material itself doesn't have most of the characteristics you probablly would want for a structural joint. This would weaken more as the material gets thinner--i.e., with clamping loads and a thin coat. I have used it for bonding trim, but wouldn't think it would be good for a bond with structural loads.

[JormaS]

They also have a glue. It´s called 5230.

[George Roberts]

baliano ---

Since epoxy does not bond aluminum to anything ...

I have been using 3M 5200 to bond aluminum to fiberglass. I try for a very thin glue line - certainly under .06" but more than .01". I find it works well.

Like everything else you need to keep the stresses on the joints below the failure strength of the parts.

[baliano]

Thanks all. Hughman, I'm building an old Science & Mechanics design called the Buddy, a 13' utility OB with a short cowl at the bow. By the way, those old magazine sponsored designs require a lot of thought and planning to address what isn't said in the articles or is misleading in the drawings. It's been fun so far.

I don't want thick glue joints on my frame laps for obvious structural stability reasons so I might use Resorcinol instead. I'm using 18-8 SS woodscrews for all the joints but if the glue line is thick and flexible there will be an excess load on the screws.

I do intend to use the 5200 for the plywood to frame joints where a little flexibility is OK to help maintain watertightness under variable loads. More of a sealing application than structural adhesive since the plywood is screwed down every few inches. It should also eliminate the need for cloth embedded in the glue between the bottom sheets and the keel and chines.

[N. Scheuer]

The ideal bond thickness for 3M 5200 depends on the application; the more joint movement expected, the thicker the 5200.

Commonly used as a bedding adhesive/seal, along with mechanical fasteners for deck fasteners, I should think something on the order of .03inches, or .8mm would be ideal. In fact, I'd wouldn't go much thinner for any reason.

For fine wood joinery, wouldn't epoxy be better?

For sealing plexiglas portlights on a hull (dare I say fiberglass?) where the plexiglas is likely to expand and contract, applying 5200 in the area of .06 to .1 inches would be appropriate.

5200 is a Urethane rubber compound closely related to construction sealants like Sikaflex (if not virtually equal) where the "modulus" specification denotes how much a bond can be expected to stretch. Low Modulus means that the cured seal can stretch a great deal. However, when stretch is desired, the seal must be thick enough to be be realistic. Let's say we can expect 100% "elongation" from a given compound. Applying a .03' joint simply means that when the joint is stretched to .06", it may be expected to fail.

On the other hand, if the seal is .25", then it can stretch to .5" before failure. BTW, 5200 is not one of those "100% elongation" compounds. It's more like 20%.

In construction sealing applications, like between aluminum or PVC window jambs and masonry, joints are typically .25" thick, and sometimes .5" thick.

Good luck, Moby Nick

[baliano]

After all this discussion I've decided 5200 is not going to work anywhere on the hull exept to attach the short cowl. The article calls for Marine Glue and "C" quality Marine Glue, both. I have no idea what the "C" stands for, if anyone out there knows please tell me. I'd really like to understand the difference bewteen the two glues since it could impact the structural properties of the hull. At this point, I've pretty much decided to go with Resorcinol throughout and use cloth strips between the bottom planking and keel and chines like the article calls for.

[Venchka]

What is the copyright date on this magazine? Dollars to doughnuts the glue and techniques described on the plans are either non-existant in today's marketplace or obsolete. Or both. Unless of course, you just want to do it the old way. Nothing wrong with that, I suppose. As long as the boat holds together.

Wayne
In the Swamp. :D

[baliano]

Most of the boats in Science & Mechanics from that period used Weldwood glue which was a powder that was mixed with water. Weldwood (DAP) still makes a glue that sounds exactly like the old stuff but they claim it's interior use only. Resorcinol is now their waterproof glue recomended for marine use. It's a two part resin glue that costs about half what epoxy does and has about the same strength in that the wood will fail before the glue. I've never heard of this "C" quality glue before and the material list for the Buddy doesn't call out a specific brand of glue.

[John Blazy]

I've been staying out of this discussion 'cuz I don't use 5200 (I use PL Premium polyurethane - virtually identical but at least five bucks a tube less), although I was an adhesive chemist and can help a little with your question - 5200 is probably great for many of the glue joints like the chine joints where rough, or loose fitting surfaces contact and you need a bit of shock resistance (cloth over it though).

Also - use plenty of adhesive, and you can even add glue blocks for added surface area, or the resorcinol glue for cloth. But if you are laminating frame lumber to build up thicker frames, then epoxy or resorcinol (or even Gorilla PUR glue at worst) is best. Just remember that the Weldwood is a harder, slightly more brittle adhesive, and can be compared to glass (that can crack) vs rubber when comparing it to 5200. Epoxy is somewhere between, kindof like Lexan plastic, which makes it superior.

So I wouldn't go to the extreme of saying that you can't use 5200 on the boat at all, 'cept for the cowling. Half of my boat is PL Premium (like 5200), and I know of folks who've built their entire boat with PL Premium.

As a matter of fact, if you can structurally engineer it correctly (enough glue blocks for glue surface area), I bet you could build a successful boat with pure silicone.

A 1" wide joint in 5200 is likely going to be stronger than a 3/4" wide joint in epoxy. Its all in the engineering.

In the glue joint of frame members contacting the hull, I would use Polyurethanes exclusively due to their shock resistance and expansion upon cure. Epoxy and resorcinol may be strong, but if the joint is starved or the hull flexes under the pounding waves - you got crack city.

[Ken Hutchins]

Marine glue as mentioned in old plans was typically not much of a glue, but a compound to keep moisture out of the joints and preserve the wood while allowing movement of the joint, a common brand back the was Kuhls which was a pine tar based compound I think Jeffries is similar to Kulhs.

[baliano]

Thanks Ken and John, that makes sense based on where the two glues are used. With those two pieces of information I get a good idea what the designer was thinking. Marine glue is being used in areas subject to some bending probably to absorb the motion and maintain a seal. The "C" quality glue is used where the frame should be stiff as around the Stem, frames to keel and around the transom. Those and the lap joints are where I should use Resorcinol, the 5200 probably would work for the rest. I'll have to allow a little room for that when I cut the notches for the chines and clamps.