[Rhodes22-list] Polyester casting resin over Epoxy

[Kroposki]

Juan,
	After reading Roger's reply, you know that you got an accurate
and professional reply to your question.  If you want to learn more
about this subject, I recommend reading Fiber Glass Boats, by John A.
Roberts.  A book written in 1984, but gets the subject into language and
concepts for those of us who are not yet at Roger's level.
                         Ed K

-----Original Message-----
From: rhodes22-list-bounces at rhodes22.org
[mailto:rhodes22-list-bounces at rhodes22.org] On Behalf Of Roger Pihlaja
Sent: Monday, October 06, 2003 10:07 PM
To: The Rhodes 22 mail list
Subject: Re: [Rhodes22-list] Polyester casting resin over Epoxy

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
>
>
>
> __________________________________________________
> Use Rhodes22-list at rhodes22.org, Help? www.rhodes22.org/list
>
>
>


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