Chem instead of secondary epoxy bond

Chem instead of secondary epoxy bond

Post by Frogwatc » Fri, 16 Feb 2007 01:36:56


Reading Skip Gundlach's discussion of fixing "Flying Pig" and having
built 4 boats with epoxy, the issue of primary rather than secondary
bonding is often on my mind.  A primary, (chemical) bond is much
stronger than a secondary mechanical bond.  There ought to be a way to
promote a chemical bond (polymerization) with the underlying
material.  I wonder if treating it with something like epoxy paint
remover first would do this.  I need to get back in touch with a
polymer chemist friend of mine about this cuz I think it'd be a good
product if it'd work.
 
 
 

Chem instead of secondary epoxy bond

Post by KLC Lewi » Fri, 16 Feb 2007 01:43:43


Quote:
> Reading Skip Gundlach's discussion of fixing "Flying Pig" and having
> built 4 boats with epoxy, the issue of primary rather than secondary
> bonding is often on my mind.  A primary, (chemical) bond is much
> stronger than a secondary mechanical bond.  There ought to be a way to
> promote a chemical bond (polymerization) with the underlying
> material.  I wonder if treating it with something like epoxy paint
> remover first would do this.  I need to get back in touch with a
> polymer chemist friend of mine about this cuz I think it'd be a good
> product if it'd work.

Is it ever possible to get a primary bond between polyester resin and epoxy?
I don't know, but I've been told "no" by so many people over the years that
I tend to act as if I believe it.

 
 
 

Chem instead of secondary epoxy bond

Post by Roger Lon » Fri, 16 Feb 2007 02:42:20

Quote:

> Is it ever possible to get a primary bond between polyester resin and
> epoxy? I don't know, but I've been told "no" by so many people over
> the years that I tend to act as if I believe it.

"They" always told me to use epoxy on old polyester because it would be
stronger than new polyester to old.  Maybe not a primary bond but strong.  I
remember gazing at my navel over a transducer through hull backing block
that wouldn't have much mechanical connection because the fitting was the
flush type with very little shoulder.  I wanted to use 5200 because of the
difficulty in fitting a block tightly and working with epoxy at arm's length
in a small space.  According to the published tensile strength numbers, the
6" x 6" block would lift the boat.  Now, I wouldn't stand under it if I
tried it but it seemed like plenty of strength for the job to me.

Some perspective on strength may be in order.  If "Flying Pig" had been a
classic wooden boat, the total tensile strength of her hull would have been
the area of the frames or about the same as less than 3/8 inch of wood.  The
static caulking and swelling pressure would already load up these structural
members significantly. Her bulkheads would have probably landed on a frames
and had two screws in each plank, maybe 80 screws in all and each close to
the end of the plank they held.  Boats of this construction have weathered
many storms and circumnavigations.  Most of them had some rot somewhere by
the time they were really tested.

It's true that, if FP had been a wooden boat, S&L probably would have been
standing in the water long before the chopper arrived.  It would also be
nice if the restored boat was as strong or stonger then when built.
However, there is also the question of how strong it really needs to be.
Stronger is always bettter but, if that was the only consideration, we would
all be sailing steel boats.

If the best tabbing job that can be done without stripping the boat fails
down the road, it's highly unlikely the boat would sink, even in a major
storm.  They might have to ease off on the sails and limp a bit but the
worst probable case isn't that dire.   The most likely failure mode would be
for the localized high stress areas to start to open up.  The big gun
repairs could then be concentrated on those in a year or two.

Remember, this boat was pounding on c***with all these structural members
loose and she still came off watertight.

--
Roger Long

 
 
 

Chem instead of secondary epoxy bond

Post by capt.bill1 » Fri, 16 Feb 2007 06:35:07


Quote:

> > Is it ever possible to get a primary bond between polyester resin and
> > epoxy? I don't know, but I've been told "no" by so many people over
> > the years that I tend to act as if I believe it.

> "They" always told me to use epoxy on old polyester because it would be
> stronger than new polyester to old.  Maybe not a primary bond but strong.  I
> remember gazing at my navel over a transducer through hull backing block
> that wouldn't have much mechanical connection because the fitting was the
> flush type with very little shoulder.  I wanted to use 5200 because of the
> difficulty in fitting a block tightly and working with epoxy at arm's length
> in a small space.  According to the published tensile strength numbers, the
> 6" x 6" block would lift the boat.  Now, I wouldn't stand under it if I
> tried it but it seemed like plenty of strength for the job to me.

> Some perspective on strength may be in order.  If "Flying Pig" had been a
> classic wooden boat, the total tensile strength of her hull would have been
> the area of the frames or about the same as less than 3/8 inch of wood.  The
> static caulking and swelling pressure would already load up these structural
> members significantly. Her bulkheads would have probably landed on a frames
> and had two screws in each plank, maybe 80 screws in all and each close to
> the end of the plank they held.  Boats of this construction have weathered
> many storms and circumnavigations.  Most of them had some rot somewhere by
> the time they were really tested.

> It's true that, if FP had been a wooden boat, S&L probably would have been
> standing in the water long before the chopper arrived.  It would also be
> nice if the restored boat was as strong or stonger then when built.
> However, there is also the question of how strong it really needs to be.
> Stronger is always bettter but, if that was the only consideration, we would
> all be sailing steel boats.

> If the best tabbing job that can be done without stripping the boat fails
> down the road, it's highly unlikely the boat would sink, even in a major
> storm.  They might have to ease off on the sails and limp a bit but the
> worst probable case isn't that dire.   The most likely failure mode would be
> for the localized high stress areas to start to open up.  The big gun
> repairs could then be concentrated on those in a year or two.

> Remember, this boat was pounding on c***with all these structural members
> loose and she still came off watertight.

> --
> Roger Long

I have to agree with Roger on this. I've seen a number of fiberglass
boats that have taken a pounding, been repaired and sailed/motored
away to be just fine.

I think it's way over reacting to say it will never be as strong so
it's time to junk it or risk dying at sea.

I say, fix the rudder, retab/epoxy it, reinforce where you can and get
on with the trip.

The boat doesn't seem to have any major holes in it for crying out
loud.

 
 
 

Chem instead of secondary epoxy bond

Post by Roger Lon » Fri, 16 Feb 2007 07:22:02

I just did a quick search for information on secondary bonds.  I don't know
how authoratitive the one site I saw is but it quoted 2000 psi for epoxy on
old polyester.  New polyester itself was only quoted at 500.  So, 10 square
inches could lift the boat except that the polyester would give up first.
It would have taken 40 square inches, 6.32 inches on a side,  to lift her
the way she was built originally.  I'm sure it's not that good in practice
but even if it's way, way, off....

--
Roger Long

 
 
 

Chem instead of secondary epoxy bond

Post by Evan Gatehouse » Fri, 16 Feb 2007 15:14:20

Looking at those pictures of the busted tabbing I see nothing that
couldn't be fixed with 10 days of solid labour, an angle grinder with
a bunch of 24 grit disks and a pile of biaxial tape.

Evan Gatehouse

 
 
 

Chem instead of secondary epoxy bond

Post by Evan Gatehouse » Fri, 16 Feb 2007 15:29:50

Quote:

> I just did a quick search for information on secondary bonds.  I don't
> know how authoratitive the one site I saw is but it quoted 2000 psi for
> epoxy on old polyester.  New polyester itself was only quoted at 500.  
> So, 10 square inches could lift the boat except that the polyester would
> give up first. It would have taken 40 square inches, 6.32 inches on a
> side,  to lift her the way she was built originally.  I'm sure it's not
> that good in practice but even if it's way, way, off....

2000 psi is about the right ballpark for epoxy in shear.  My concern
is that the tabbing is probably compromised by the damage.  If the
tabbbing just mostly peeled, it might be o.k.  If it was my boat I'd
probably take a grinder to the tabbing and re-do it with biaxial and
epoxy.

It took me about a week to redo ALL the tabbing on my last boat, a 30'
mono with a lot of lockers and compartments.  It was not that big a job.

Evan Gatehouse

 
 
 

Chem instead of secondary epoxy bond

Post by Roger Lon » Fri, 16 Feb 2007 22:03:03

Quote:

> Looking at those pictures of the busted tabbing I see nothing that
> couldn't be fixed with 10 days of solid labour, an angle grinder with
> a bunch of 24 grit disks and a pile of biaxial tape.

I looked too.

Skip,

You should take heart.  Your boat is probably as strong right now as 90% of
the vessels that ever went deep water.  Creaking, disconcerting moving of
stuff inside, etc. are other issues but you don't need massive primary bonds
to resist that.  Do the quick and dirty.  Time will show if specific areas
need a revisit and do the prioritizing for you.

The extra strength of a complete re-do could help if you let the little boat
symbol on the chartplotter strays over the green again but I bet than's
never going to happen a second time.  Even with full stength, a boat that
goes ashore like that almost anywhere else in the world is going to be
picked clean by the locals long before you can do anything.

You probably have lost a big chunk of the eventual sail price but it doesn't
sound to me like you're planning to trade up:)  That will be the least of
your worries when the time comes.

--
Roger Long