Re: [Paddlewise] Coaming Adhesive: FG yaks

Dave wrote;

-(SNIP)


>Considering the stresses I have applied to the coaming/deck joint, I'm
>not upset about the failure.  It's not too bad a job, though the
>fiberglass itch nails me for a week or so on projects like this, and
>it's tough to get to all the surfaces which need sanding/grinding.
>
>I am curious, though, why Eddyline chose a putty which was NOT
>epoxy-based, and why there was no chopped glass in the mix to improve
>its strength.  I'd think both of these would improve the durability of
>the joint.

There may be chopped glass in the mix although the fiber length may be
short so they are not easily discerned. Also, polyester adhesive mixes are
not unusual and do hold up quite well when the resin used is flexible
enough for the job. With time polyesters do get more rigid and maybe the
resin Eddyline used was not as flexible as it could have been. Production
demands often eliminate epoxy as a practical adhesive.

>
>Anybody else know what adhesive/filler combo is used to keep the
>coaming/deck joint intact on their FG yak?

Since kayaks are rather flexible the coaming joint can be the stiffest part
of the deck. This invites failure so the best adhesive is one that has
enough elongation to accomodate the flex of the deck. Sikaflex 292 is a
good flexible adhesive for polyester joints. I would rate it better than
epoxy since it allows movement. There are other similar adhesives but those
I am familiar with are industrial materials and not readily available.

(SNIP)

>I'm finding that sanding/grinding a little ways into the deck material
>seems to be necessary to get a good "tooth" for the repair.  When I did
>this five/six years ago, I used polyester resin and a couple layers of
>mat to reinforce the seam, and that seemed to be pretty strong.  (Did
>not know epoxy was better, then.)

You would need a good "tooth" for the epoxy too and you should be sure all
the brittle filler is removed or the joint will fail again at the
epoxy/polyester filler interface.


>To prevent a reoccurrence, I'm going to make sure the tangs which extend
>down from the coaming are supported by the hull.  I think the separation
>started when there was a little gap between the end of the tang and the
>hull inner surface, so when I used the coaming rim to lift myself out of
>the yak, I over-stressed the coaming/deck joint.  Finally got so bad a
>couple weeks ago, there was a FLOOD of water entering the cockpit when I
>did leaned turns on that side!  That's what initiated the repair.

The flooding is a bummer. Be cautious with the support to the hull. You may
cause a hard spot that could cause a hull failure. Sea kayak hulls and
decks tend to thin and joints should give a bit and not cause "Hard" spots.

Cheers,
John Winters
Redwing Designs
Specialists in Human Powered Watercraft
http://home.ican.net/~735769/


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