On 2006-06-24 03:26:42 -0400, ray lunder said:

And don't forget to put a sheet of plastic between the core and resin
if you're working next to the core. (the foam reacts with the epoxy
and gasses, leaving voids).

This is rather bad advice. In almost all cases, you WANT THE RESIN AND
PATCH TO BOND TO THE CORE. Putting plastic between the core and the
resin leaves a void too, just not one filled with gasses. Most cores
DO NOT react to Epoxy by dissolving and gassing off... especially if
the core is a good end-grain balsa, which it is on the better boats. If
the core is not bonded to the repaired area, you have effectively
created a section that is pre-delaminated. DUH.

On the OP's question, smallest piece first will be stronger
(assuming a good bond). Depends on what you want. You can
also put down more than 3 layers wet-on-wet, I've done five
or six at a time (using slow set resin) and it works just
fine. The prep work is the key.


And don't forget to put a sheet of plastic between the core and resin
if you're working next to the core. (the foam reacts with the epoxy
and gasses, leaving voids).


???

Isn't the point to bond the core to the surface? If you're
getting that much reaction & gas, you're doing something wrong.


dog wrote:
This is rather bad advice. In almost all cases, you WANT THE RESIN AND
PATCH TO BOND TO THE CORE. Putting plastic between the core and the
resin leaves a void too, just not one filled with gasses. Most cores DO
NOT react to Epoxy by dissolving and gassing off... especially if the
core is a good end-grain balsa, which it is on the better boats.

Not tostart an argument, but there are many foams to choose
from and some are lighter & stronger than balsa.

... If the
core is not bonded to the repaired area, you have effectively created a
section that is pre-delaminated.

Yeah, that was kind of what I thought too. But you have to
keep in mind, everybody wants something different.

DSK

dog wrote:
This is rather bad advice. In almost all cases, you WANT THE RESIN AND
PATCH TO BOND TO THE CORE. Putting plastic between the core and the
resin leaves a void too, just not one filled with gasses. Most cores
DO NOT react to Epoxy by dissolving and gassing off... especially if
the core is a good end-grain balsa, which it is on the better boats.

Not tostart an argument, but there are many foams to choose from and
some are lighter & stronger than balsa.

... If the core is not bonded to the repaired area, you have
effectively created a section that is pre-delaminated.

Yeah, that was kind of what I thought too. But you have to keep in
mind, everybody wants something different.

DSK

Yes, there are many foams to choose from, but few have the same
characteristics that make end-grain balsa such a good core material.
Few of the foams bond and wick epoxy resin as well as end-grain balsa.
Few of the foams have the compressive and sheer strength and resistance
that end-grain balsa has. Few of the foams have the high temperature
resistance to softening and deforming that balsa has. To date, nothing
that I have seen is better than a good end-grain balsa for most
applications. There are a few high-tech honeycomb materials that are
almost as good, but they're generally far more expensive and difficult
to work with than end-grain balsa.

dog wrote:
Yes, there are many foams to choose from, but few have the same
characteristics that make end-grain balsa such a good core material.
Few of the foams bond and wick epoxy resin as well as end-grain balsa.

Are you looking for bond strength / peel resistance? Some
foams are better in this regard.


Few of the foams have the compressive and sheer strength and resistance
that end-grain balsa has.

Now that's just plain wrong, it is very easy to find foam
that is better in these characteristics. The question is,
can you find better foam that is still lighter, and also
doesn't cost a lot more?

Look into the specs on foam in the 20# and up range.


... Few of the foams have the high temperature
resistance to softening and deforming that balsa has.

Considering the temp characteristics of epoxy, I don't think
this makes much difference. OTOH it is possible to use
fire-retardant foams... balsa is wood after all, and will burn.


... To date, nothing
that I have seen is better than a good end-grain balsa for most
applications.

That statement leads me to wonder how far you've looked.

... There are a few high-tech honeycomb materials that are
almost as good, but they're generally far more expensive and difficult
to work with than end-grain balsa.

It's true that balsa is relatively inexpensive and easy to
work with. I like it... but for my ownpersonal super boat
project, I picked a type of foam that a friend used in
airplane kits. Has some drawbacks, but I have no doubt that
it will be lighter and stronger than balsa... and it won't
ever ever ever rot.

Fresh Breezes- Doug King

dog wrote:

Yes, there are many foams to choose from, but few have the same
characteristics that make end-grain balsa such a good core material.
Few of the foams bond and wick epoxy resin as well as end-grain balsa.

What a crock of crap.

The only time someone uses balsa as a core material on a boat is
because they don't know any better or can't afford anything else.

Lew

What Lew said.

"Lew Hodgett" wrote in message
ink.net...
dog wrote:

Yes, there are many foams to choose from, but few have the same
characteristics that make end-grain balsa such a good core material.
Few of the foams bond and wick epoxy resin as well as end-grain balsa.

What a crock of crap.

The only time someone uses balsa as a core material on a boat is
because they don't know any better or can't afford anything else.

Lew