I’m trying to install a set of North Water D-Rings with vinyl bases on the underside of my (North Shore)composite kayak’s front deck which I’ll then string with bungee cord to hold a bilge pump, etc… I used Weldwood contact cement which I used when padding out the thigh braces with great success. However, the contact cement does not seem to be creating a permanent bond in this case. What bonds vinyl to fiberglass? Is vynabond the answer? How about Lexel, Goop, or some 3-M product?
I have used it
Although some have stated that vinyl adhesives like Vynabond will only adhere to vinyl, I have used them on composite boats with good success.
For my Clipper Viper I used Vinyl-Tec 2000, which is a vinyl adhesive similar to Vynabond, to glue in all the anchors, including knee and thigh strap anchors, and none show signs of loosening.
Contact adhesive will separate over time when subjected to significant distracting forces, as you found out.
4200 fast cure, if you might want to remove someday. 5200 if you want it to be around forever…either way, rough up the vinyl with 150 grit, and wipe down with lacquer thinner or acetone.
My D-Rings On Round Vinyl Seats/Pads
Are still glued to the fiberglass deck of my Ocean Kayak surfski, which I installed over 20 years ago using 3M Scotch-Weld 3532 B/A Urethane Adhesive. Unfortunately, you can’t buy an individual 2 component kit anymore. You got to buy a case of 6 kits now. Cheapest case I could find was $28 from Pack-N-Tape.
is what has been holding my North Water under deck bags in place for several years in my composite boats. Proper surface prep of the pads & under deck surface and sufficient cure time are key.
vinyl adhesives won’t affect the resin
or cloth, but those adhesives apparently contain not only solvent, but small amounts of vinyl, or something very like it.
So when it is painted on the inside of the hull, it will at least form a mechanical bond with the surface. And the vinyl will be “sticky” to form a bond with the vinyl patch when it is applied.
If the inside of the hull weren’t rough to begin with, and cleaned, and roughened somewhat to raise some fibers, I don’t think the bond would hold very long.
Of course, I prefer bonding with epoxy, which is very compatible with the resins used to make the boat. But nothing succeeds like success.
I have been reasonably pleased with Vynabond. I actually attached to a Kevlar boat, but I think it's the resin (vinylester, in my case) that matters, not the cloth. I bonded in vinyl-backed daisy chains, to which I attach cord to hold my flotation bags in place. People have told me that the bond isn't strong enough to withstand serious pressure from whitewater, and I believe them. But I don't paddle any significant whitewater, and the bond is strong enough for me to do rescue practice without forcing the bags out.
The only aspect that made me unhappy is that after five or six years, the bond failed, and one daisy chain started flopping around. As far as I know, no pressure was needed to make this happen; the bond just wore out. Presumably it would have failed earlier if I had put pressure on the bond at the right time. I repaired with more Vynabond.
So I wouldn't recommend Vynabond on a composite boat for a life-critical application or an application where lots of force will be applied. For my more casual use, I am okay with it, and your use sounds even more casual.
I agree that it forms only a mechanical bond. As far as technique, I combined the manufacturer's advice for use on composites (on their website, not on the can) with advice I got on this board (maybe from Clarion). Unfortunately, I can't remember exactly what I did. I know I used sandpaper and acetone to prepare both surfaces. I seem to remember using my camp stove to heat (gently!) the vinyl surface after the Vynabond had dried. But that might have been some other crazy project -- don't quote me. For the more recent repair, I didn't use heat; I just prepped the surfaces, smeared thinly but thoroughly, let dry, and pressed together. That was in the fall, so I don't have long-term data; so far so good.
vinyl adhesive bond may weaken in time
Vinyl patches bonded to composite boats or Royalex boats may come off in time. In my experience, it takes years for this to happen and it usually occurs on a warm day. They can easily be bonded back in place with vinyl adhesive a second time.
The way I use vinyl adhesive is to mark the position of the patch on the hull with pencil, lightly sand the hull surface using 100-150 grit paper, clean the hull and patch with acetone, and allow both to dry. Vinyl adhesive must be applied to both surfaces and allowed to degas some before the patch is approximated to the hull. On a warm day, that happens in 10-15 minutes. On a cooler day the process can be sped up by using a heat gun or hair drier on patch and hull. Be careful not to overheat a Royalex hull.
Even if the vinyl adhesive appears to be degassed, I will often waft a heat gun over the patch and hull surface just before approximating. It is a good idea to use indexing marks on the patch and hull to assure the correct placement and orientation before the two are approximated because the patch can’t usually be realigned once the two come together. It is a good idea to go over the patch with a plastic roller (sometimes called a tile roller) which can be purchased at your local hardware store.
The thing I like about vinyl adhesive is that patches can be removed without damaging the hull and often without damaging the patch. You might need to reposition a patch or replace one if a D ring rusts or if you reoutfit the boat. To do this, warm the patch with a heat gun, peel an edge up with a paint scraper, grab the edge with a pliers or similar instrument, and slowly peel it off as you gently warm it. Patches glued in with 3M Scotch Weld structural adhesive, epoxy, and many other agents can not be easily removed without hull damage.
No Damaged With 3M 3252 B/A
Scotch-Weld product. There are different varieties of 3M Scotch-Weld products, and the 3252 B/A is somewhat flexible and the vinyl pads do peel off. However, yes, there is the adhesive residue that requires a 2 part process of removal: soak a rag with paint thinner and leave it on the dried adhesive, use elbow grease, finish off with Acetone and more elbow grease.