Best glue & technique for adhering brass to GRP?

TSB240 said:
If the GRP is that thin why not through bolt it with countersunk m4 screws.
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I'd like to, it would be my first choice...but as I said earlier, the floor in the forepeak, isn't directly behind the hole I'd be drilling through the keel-line...so it's not possible to blank-off the inside where the bolt would come through. Quite apart from the difficulty of securing the bolt inside, there would be flooded sections of hull-cavity and a continuation of my leak problem. Plus, the keel-band is only 9mm wide...put a 4mm dia hole through that, and I'd be picking the pieces off the slipway before the first launch.

I really didn't choose glue out of faith or preference - but because drilling holes has definitely not worked. Frankly I'll prefer to risk having the glued keel band drop off, than have the leaking screw-holes as an ongoing problem.

Thanks for the ideas though.
 
dancrane said:
I'd like to, it would be my first choice...but as I said earlier, the floor in the forepeak, isn't directly behind the hole I'd be drilling through the keel-line...so it's not possible to blank-off the inside where the bolt would come through. Quite apart from the difficulty of securing the bolt inside, there would be flooded sections of hull-cavity and a continuation of my leak problem. Plus, the keel-band is only 9mm wide...put a 4mm dia hole through that, and I'd be picking the pieces off the slipway before the first launch.

I really didn't choose glue out of faith or preference - but because drilling holes has definitely not worked. Frankly I'll prefer to risk having the glued keel band drop off, than have the leaking screw-holes as an ongoing problem.

Thanks for the ideas though.
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My brass keel band is 1/2" x 1/8" . it is fixed with 1/2" x 6 screws at 4 1/2" centres, The screws were dipped in resin and the tips resined over .

If necessary you might find shorter screws but it might be a good idea to thicken the centre line ( inside or outside or both ) with glass tape to give the screws something more substantial to hold on to. It is available only 1/2" wide for a few pence per mtre.

No 6 screws require a hole half the width of a gnat's cock more than 3mm If that's still to large for you then no 5 screws can be found

I too think attempting to glue it on will fail.
 
Thanks, Vic...but I'm inclined to hope I can solve the problem by the way I haven't tried, after definitely failing by the way I have.

It seems to me a very odd way to construct a boat - using thin GRP at the keel join. I think there is one of those hollow 'ribs' along the keel, strong enough for its principal purpose of stiffening the hull, but very vulnerable to puncturing by the keel-band screws. And somewhere along the length of the hollow 'rib' are other holes, allowing the water gradually to flood the forward chamber.

There's nothing to stop me using screws above the waterline, all the way up the bow. Hopefully that'll save the brass from sinking if the glue does fail.
 
dancrane said:
Thanks, Vic...but I'm inclined to hope I can solve the problem by the way I haven't tried, after definitely failing by the way I have.

It seems to me a very odd way to construct a boat - using thin GRP at the keel join. I think there is one of those hollow 'ribs' along the keel, strong enough for its principal purpose of stiffening the hull, but very vulnerable to puncturing by the keel-band screws. And somewhere along the length of the hollow 'rib' are other holes, allowing the water gradually to flood the forward chamber.

There's nothing to stop me using screws above the waterline, all the way up the bow. Hopefully that'll save the brass from sinking if the glue does fail.
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Paper rope perhaps ??
 
What's that, Vic?

I've actually got a slightly longer section of brass than last time, I think; so it may be possible for me to secure both the bow section, and the aftmost point where it reaches the division around the centreboard case, which I suspect is tougher stuff for its demanding purpose. So it could only be the middle 'sagging' section which the glue will need to hold.

I'm really not very pessimistic about my chances of making it work - just wondered what people thought was a good glue for both metal and GRP.

Maybe there's something I can first bond thoroughly onto the brass, which will later serve as an easier dry surface to glue to the GRP keel?

Apologies if that has already been suggested - it might have gone in between my ears and only just registered.
 
Although epoxy is excellent stuff for a wide variety of purposes, in general it is not very flexible. I suspect that the attachment of a keel band needs to have a certain amount of 'give' in it and epoxy, even if filled, will crack. There are some more flexible epoxies, the one used for Araldite Rapid is one, but I don't know whether it would be sufficient. Foam polyurethane was a good suggestion but when attached in a thin film it may suffer the same problems as epoxy.

My preference would be for something more elastomeric, Sikaflex or one of the hybrid polymers. Never having seen CT1 on sale I have used Toolstation's Stixall (probably very similar) for several jobs and found it pretty good, although it takes a long time to cure when applied fairly thick. The same could be said for Sikaflex 291 and Puraflex 40, but I assume there is no big rush?

I'm not too sure about the adhesion of any of them straight to brass. I have tried unsuccessfully to coat a manganese bronze (brass with a bit of manganese) with Coppercoat (epoxy) but it had mostly fallen off at the end of the season, despite not having been dragged up a beach. Hammerite special metals primer sticks to it well, which suggests you might need to use some sort of etch primer, although I have my doubts that any adhesive would stick well to any primer paint.
 
vyv_cox said:
The same could be said for Sikaflex 291 and Puraflex 40, but I assume there is no big rush?
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No great rush; but while I'm a fan of Sikaflex for sealing, I know well that 291i isn't primarily an adhesive, so I won't try that.

It only occurred to me since starting this thread, that the keel of the boat is gelcoat rather than GRP...will that make any difference?

I wonder if there'd be any value in drilling lots of shallow diagonal holes in alternating directions, into the flat side of the brass strip, in order that when the adhesive cures, it would effectively form dozens of little locking barbs, rather than just a flat slippy surface?
 
dancrane said:
No great rush; but while I'm a fan of Sikaflex for sealing, I know well that 291i isn't primarily an adhesive, so I won't try that.

It only occurred to me since starting this thread, that the keel of the boat is gelcoat rather than GRP...will that make any difference?

I wonder if there'd be any value in drilling lots of shallow diagonal holes in alternating directions, into the flat side of the brass strip, in order that when the adhesive cures, it would effectively form dozens of little locking barbs, rather than just a flat slippy surface?
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Sikaflex 292 is a structural adhesive and should be better than 291i. The non marine equivalent is Sikaflex 252.

The Sikaflex users guide leaflet gives details of cleaning and priming of brass and other materials. See http://www.kjhowells.com/hres/sikaflex_a_users_guide_1_.pdf
 
dancrane said:
but while I'm a fan of Sikaflex for sealing, I know well that 291i isn't primarily an adhesive, so I won't try that.
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Tell that to the fittings on my boat! Getting anything apart that has been attached with Sikaflex 291 is an appreciable job, as is often discussed in these pages. I have seen a keel that was attached with Sikaflex that, after having all its bolts removed, took considerable attention with big hammers and wedges before it could be persuaded to detach.
 
vyv_cox said:
Tell that to the fittings on my boat! Getting anything apart that has been attached with Sikaflex 291 is an appreciable job, as is often discussed in these pages. I have seen a keel that was attached with Sikaflex that, after having all its bolts removed, took considerable attention with big hammers and wedges before it could be persuaded to detach.
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+1 The wooden bracket that holds my shore power connectors is held on with 291i. It's only about 7" x 4", and sometimes it takes a bit of force to connect and disconnect those plugs, been on there 2 years without falling off.
 
3M 5200 has always been my go to for sticking things down that don't want to come back up again.

I probably wouldn't use epoxy since ensuring a good bond with the brass would be tricky and the end result could be a bit brittle for groundings and the like.
 
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