Michiel,
Glad to be of assistance.
The responses are in-line.

Michiel wrote:
Hello Matt,

First off, thanks for your reply. I'm very glad to get feedback here.

On Thu, 24 Nov 2005 15:57:19 -0500, Matt Colie
wrote:


Michiel,

I am and on the wrong side of century, allow me to give advice based on
some hard won experience.

Polyester is cheaper
is more available?

Epoxy is expensive
has to be ordered

There is little difference in the actual mechanical properties (has
matter relative to the glass) = it will not be any stiffer, you can not
use mat because epoxy does not disolve the binder.

Get someone's good epoxy and pump set and sleep well.


You haven't given any advantages of epoxy over polyester for this. If
it's similarly strong, but more expensive and can't be used with mat,

No - but you can used stitched biax or triax and have better strength to
weight ratio.

why would I use it? It seems that polyester would be ideal because:

- I'm going to need a lot of it to build up thickness (price becomes
important)

The mix ratio of Polyester is ~1:32 or 64, and a small error means it
begins to cure while you are mixing or maybe never. This varies from
annoying to expensive to clean up. - I waited a week for the material
to cure once, only to have to peel off and scrap the glass and then wash
the entire work area with solvent.

There is also a very real working difference in working the two
materials. Polyester tends to cure quickly when it trips, often giving
very little warning - it might get grainy - it might not just turn into
a single glob all at once. Epoxy will get more viscous slowly and since
it can be over coated, put it aside and start a new mix.

It is always best to have two people - one to stay dry and clean and
pass tols and such to the wet and sticky pesron.

- existing deck is polyester, so adhesion should be good

Polyester is never good at adhesion even to itself, a thick section must
be assembled in one operation and cannot be broken by delays between
layers. - I had done a the complete through preparation for the hull
repair of a small boat, launched it in a local lake and set the rig.
There was a snap on the out bound reach, I gybed and headed back (good
thing) the boat had too much water in it to recover it to the trailer so
I sailed it up on the swimming beach. (You can guess how this went
over!) A group of us pulled th boat up higher and rolled it. One in the
group put a finger in the crack and pulled out the entire patch with
surpizingly little effort. The patch was perfect - except that it not
attached to the hull.

- entire boat is polyester and I would be staying with the same
material

So What? as the poly will not bond to old poly - why bother. (per above)

- the water resistance of epoxy is not needed.
It is a boat - right?

These things seem to outweigh the drawback of having to work with
toxic materials.

When I last some time ago) read all the MSD epoxy was less hazardous
because of the lack of aeromatic solvents involved. I know many more
people that have developed sensitivity to polyester that have to epoxy,
but that is anacdotal and you should do your own reasearch.

If you want maximum stiffness with an un-cored structure, get as much
glass (or kevlar/carbon) into it as you can and learn to do vacuum
laminating (bagging).


Hmm.. I'll be laying up against the existing deck. How could I use a
bag?

If your situation is typical, you will cut open the inner layer of the
deck and remove junk core and allow the area to dry. Cut a replacement
core and then decide - new or reuse - in several places I put the
original inner layer back in and used 2in. (50mm) glass to seal the cut.
In any case, the glass that remains has to be sanded/ground to a taper
to make the joint. You are going to bed the upper side of the core in
thickened resin in any case. If you are going to reuse the lower skin
it has to be preped or you have to have to cut glass to replace it.

When you are real ready, mix the stuff, coat everything that needs
coating, soak everything that needs soaking and put it all up.

This is all on top of : a piece of break away cloth (peelply), a blotter
layer to catch extra resin, a bleeder layer to leat air come to the pump
from everywhere and finally the film that is air tight.
This is all resting on a small piece of plywood that allows you to hold
it up there while you get the film sealed off and the vacuum started.

Tape the edges of the film down (or up) with some good tape and seal all
the folds the same way. Have a hole or to that you can tape a funel
over to attach the pump hose.

Watch it suck itself flat and wait for the cure to start.....

This is how I did the deck of my S2 and it worked like at charm.


I worked polyester resins for years. I went to epoxy about just over 25
years and 50+ gallons ago and have never though about going back.

If you want to know all about re-laminating a cored deck from the
underside- say so I'm here a pretty often.

Matt Colie


Of course I do! Tell me everything you know, please!

Michiel

Now - do a little figuring;
How much money will you save with the cost difference between poly and
epoxy?
Will it pay for one premature trip or one non-cure?
How important do you think the bond strength will be in your application?
How much is your time worth and what will be the final value of the
project?

Did I answer all the questions? otr just start some new ones?

Either case - I'm still here

Matt Colie