Boat Building Forum

Find advice on all aspects of building your own kayak, canoe or any lightweight boats

Re: Fiberglass cloth all stressed out
By:Dale Frolander
Date: 6/28/2001, 9:36 pm
In Response To: Re: Fiberglass cloth all stressed out (John Michne)

The dots are bright white and it is surely delamination from too much stress. I think that you both have provided me with the answer though. The key is that I didn't know that epoxy shrinks when heated instead of expanding. I had put more epoxy in the forward end than the aft end and I also did the forward end first. I think the more epoxy and the warmer water is what caused it to happen on the forward one, and I haven't yet seen it on the aft one (I pulled the aft end out of the bucket just before I took off and haven't been back home yet). The shrinking of the epoxy would be able to suck in the sides more than the top and bottom because the end shape is like a vertical oval 0. The stress pulling in on the sides would put the outside in compression causing the dots. That also would explain why the dots run forward and aft (Hoop stress).

Hopefully a fix for the future would be to put in the wooden pipe in the end of the kayak before doing the end pour, instead of after. The wooden pipe would help keep the sides from being pulled in. Also, I might use a little cooler water (I used warm water of around 100 degrees or so - shower temperature).

Thanks for the info.

: Dale - What you probably saw was so-called thermal curing of the epoxy. This
: happens when the cured epoxy gets heated to around 120 - 130 degrees. It
: shrinks some, causing the weave of the cloth to print through. The effect
: is quite noticeable on new boats after their initial trip in the hot
: summer sun. A few weeks ago, I took my latest boat out of the shop into
: the bright sun for a few pictures. The total time in the sun was less than
: a half hour. When I brought it back inside the shop, I noticed the weave
: bumps. On a finished boat, wet sanding and a couple more coats of varnish
: fixes the problem. I have heard more than a few times that some
: professional builders purposely heat their newly epoxied hulls to cause
: the thermal curing, even before sanding. The finished boat then doesn't
: get the problem. I have never seen a good reference to the procedure,
: though. Also have been thinking of trying to do it on my next boat.

: You don't have to sand the glass off. Just sand the epoxy fair before
: varnishing, although you may still get it on the rest of the boat.

: Hope that explains it......

: John

Messages In This Thread

Fiberglass cloth all stressed out
Dale Frolander -- 6/28/2001, 3:54 pm
Re: Fiberglass cloth all stressed out
Doug K. -- 6/29/2001, 11:17 am
Re: Fiberglass cloth all stressed out
Dale Frolander -- 6/29/2001, 9:58 pm
I think I have the answer.
John Monfoe -- 6/29/2001, 5:18 am
Re: I think I have the answer.
John Monfoe -- 6/29/2001, 5:26 am
Repair Discussion Link
Ted Henry -- 6/28/2001, 11:26 pm
I missed that discussion before.
Dale Frolander -- 6/29/2001, 2:18 am
Re: Fiberglass cloth all stressed out
John Michne -- 6/28/2001, 8:00 pm
Re: Fiberglass cloth all stressed out
Dale Frolander -- 6/28/2001, 9:36 pm
Re: Fiberglass cloth all stressed out
Ted Henry -- 6/28/2001, 6:45 pm