[Rhodes22-list] Polyester casting resin over Epoxy

[Roger Pihlaja]

Juan,

You heard correctly, polyester casting resins do NOT adhere well to epoxy
resins.  Therefore, I would recommend not using polyester casting resin for
filling the void spaces between the lead shot inside the  keel cavity.
Instead, I would recommend using WEST system 105 epoxy resin with 209 extra
slow hardener.  Be sure to wipe the amine blush off the repaired epoxy
surfaces & scuff sand the cured epoxy with #100 sandpaper to provide a good
"tooth" before you start backfilling with lead shot ballast & epoxy.  Use
acetone & clean cotton rags to wipe the amine blush off the surfaces.  I
would pour in about a 1" thick layer of lead shot, pour epoxy over the layer
& spread it around with a paint scraper to get good coverage.  Add another
1" thick layer of lead shot, more epoxy, & spread it as before.  Continue
this procedure until the keel cavity is full.  By the way, you will get more
lead into the cavity if you use a mixture of large & small diameter shot.  A
mixture of 75%wt 1/2" OD lead shot with 25%wt 1/8" OD lead shot is about
ideal.  The little balls fill in the void spaces between the larger balls.
Use the WEST 209 extra slow hardener so that you will not have any problems
with heat build-up in the keel cavity during the curing process & so that
you will have plenty of time to complete the job.

Good luck!

Roger Pihlaja
S/V Dynamic Equilibrium

----- Original Message -----
From: "Martinez, Juan" <JMartinez at JVC.com>
To: <rhodes22-list at rhodes22.org>
Sent: Monday, October 06, 2003 6:33 PM
Subject: [Rhodes22-list] Polyester casting resin over Epoxy


> I own a 1981 Rhodes 22.  I joined the list about a year ago. I find the
> list very informative. I am repairing damage to the keel of my. I
> speculate that freeze damage caused hour-glassing of the centerboard box
> and longitudinal cracks following the seam line where the centerboard
> box and the keel were originally bonded (bottom of the keel).  I cleaned
> out all the ballast from the keel cavity down to the inner fiberglass
> roving wall. The ballast was chunks of lead (about 100lbs), some resin /
> sand mixture and the rest cement that had loosened up to the consistency
> of packed wet sand. I am planning to repair the longitudinal cracks from
> inside the keel cavity overlaying several layers of fiberglass and West
> 105/205 epoxy resin.  After the repair is complete, I need to fill the
> keel cavity again with ballast. I am planning to use polyester casting
> resin and lead shot.  I have read that polyester resin does not adhere
> well to epoxy.  Is there anything I can do to improve the casting resin/
> epoxy bond?  Are there any mechanical or chemical alternatives that may
> promote good adhesion of the casting resin to the epoxy?
>
>
>
> Juan Martinez
>
>
>
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