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.

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).

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


Michiel wrote:

Hello,

I'm going to need to do some work with polyester and fiberglass. I
will probably be replacing the core in my deck with solid fiberglass.

I've previously only worked with epoxy. It seems that this should be
straightforward?

Polyester resin and fiberglass cloth are available everywhere. Are
there any important differences in quality/properties or could I just
get the stuff sold at Home Depot (Evercoat, I think) and work with
that?

Also, does anyone have data such as:

- how do you get maximum stiffness, and how stiff will 1/4" be?
- how much resin and mat does it takes to build up a certain
thickness, say 1/4" or 1/2".
- and then of course, where to get resin and mat inexpensively.

Thank you,

Michiel

"Michiel" wrote in message
...
- existing deck is polyester, so adhesion should be good

The general consensus is that epoxy adheres much much better to cured
polyester than polyester does.

Meindert

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

Michiel,

There are some interesting problems with foam-in-place core (i.e. why do
you think Boston Whaler is almost alone in this.) The local pressures
that the expanding foam can cause can be significant. I have used
expanded in place urethane foam for several different purposes and it is
not as easy to work with as you might expect.

Think about the job you just proposed. . . .
You are going to have to do almost everything that the vacuum job
requires and you will still have to support the inner surface somehow
during the operation. And, now you have to patch the fill holes you put
in the weather deck.

If you are going to cut the deck open from inside. (The only advantage
this has is saving the non-skid molded into the surface.) Just put
core back in - plastic or balsa is little different - I find the balsa
to bind better to the epoxy, but places with lots of holes might want
plastic. Do Not use plywood at all. It has an inherent capaability to
migrate moisure along the grain. Balsa core is all end grain and
plastic? I did use plywood in some places of one job I wanted more
stiffess - the difference was not noticable from balsa - and have had to
replace some of it already.

It takes at lease 8lb core to be the same stiffess as balsa. The core
is the center of a beam structure. If you do not get the minimum
stiffness there, the beam will not be stiff. Plastic core is way more
expensive than balsa, but this comes back to the job cost/value
discussion that you need to decide.

Is this enough answer?

Matt Colie


Michiel wrote:
On Fri, 25 Nov 2005 11:54:18 -0500, Matt Colie
wrote:


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


(instructions for replacing the core with vacuum bagging)

Ouch.. that's more then I'm ready to take on now, in terms of work,
skill and supplies. I can see the point being made about the amount of
work.

Maybe yet another option:

I came across a web site that showed a pourable urethane foam:
http://www.shopmaninc.com/foam.html

How about cutting out the inner skin, scraping out the balsa core,
glassing the inner skin back in place and then pouring in that
urethane foam through holes in the outer skin? That 8lbs foam might be
perfect for it. I wonder what the viscosity is like.

Michiel

Micheal,
I was about to ask if the boat were somewhere that freezes, you just
answered that.

You should know that it is -way- harder to effectively diagnose core
problems when the structure is frozen.

The up side is that, if you can warm the boat up in freezing weather, it
will dry out real fast (it still takes a significant time for the balsa
to completely dry) because the absolute humidity is sooo loow.

I like the sight you found, I saved it to pass to the next person to ask.
?Did you notice that the Acrylic and balsa are pretty close at the same
density?

The freeze-thaw cycle is part of what causes the delamination, but the
other bad-guy in the action is the original polyester resin that failed
to bond the core in the first place. What you have found is a common
problem. There is no easy fix. (I have been asked countless times if
it were posible to repair this be injecting some magic solution.) The
answer is know. I have seen the results of more than a few attempts.

If the core is not rotted, there is no reason you cannot open the area
up, dry it out and relaminate it. (I have done this successfully.) You
will find that those who worked from above have sand or shot bags all
around the room. It takes 1~3psi to effectively laminate. So, unless
you can unless you can jack the deck up 2~500lbs worth, find a vacuum
pump. Start shopping. It was more that a few years ago, but I bought
a pump and motor from a surplus house and screwed them both to a board.
I got the coupling parts from either Mcmaster-Carr or WW.Grainger (I
forget which) as well as a cheap A(15$) vacuum gage and a by-pass valve
to regulate the vacuum. All was less than 100$ cash-out-of-pocket.

Surplus Sales http://www.surpluscenter.com
C&H http://www.candhsales.com
American Scientific http://www.sciplus.com
Grainger http://www.grainger.com
McMaster http://www.mcmaster.com/

Remember - Thinking is the most effective and the least expensive thing
you can do.

Matt Colie

Michiel wrote:
Matt and everyone else who responded to my questions:

Thanks again for sharing your experience and knowledge. Very cool!


With regards to urethane, I ran into this:

http://www.azom.com/details.asp?Arti...ison_of_Core_1

Judging from this page polyurethane foam might not be very suitable
for a deck, although I'm not sure if the writer had the higher
densities in mind. It seems to me that the expansion of the foam would
help to make a good bond?


I did a few things this weekend to find out what state things are in.

I went around the deck with a rubber mallet to try to figure out the
extent of delamination. I think it's very widespread. Only at the
edges, things sounded hard. But I guess that it this point that's
good, because it'll make it easy to take out the old core.

I also cut out a small patch, from the inside. It was frozen when I
cut it. It's almost dry now. It doesn't look or feel rotten at all,
but it looks as if frost may have caused some damage (some cracks in
the wood). the balsa is still firmly bonded to the inner skin. It
seems the delamination is just between the outer skin and the balsa. I
can take a photo of this if it would help.

I think I may be able to reuse the existing core. The procedure I'm
thinking of now is: Cut out the inner skin, let it dry thoroughly,
Remove core in areas where deck hardware will be mounted and fill with
resin as suggested by another poster, then smear a fat coat of resin
around (be it polyester or epoxy), maybe thickened with some
microballoons and prop the whole mess up and then when it all dries
glass over the cuts.

Michiel
PS: vacuum bagging sounds like a wonderful technique, but I just can't
afford the investment now.

On Mon, 28 Nov 2005 09:24:46 -0500, Matt Colie
wrote:

If the core is not rotted, there is no reason you cannot open the area
up, dry it out and relaminate it.

While this is technically correct, once you've opened up an area I see
no point in "recycling" old balsa, given that balsa WILL wick up water
given the opportunity. It was used back in the day due to ease of
handling (cut into little tiles it will conform to complex curves in a
resin matrix) and low price.

But it's a wooden sponge. Lithium is the lightest metal, but you don't
see girders of it because its other properties are lousy for
structural applications.

Use marine plywood, encapsulated, for through deck mounting points,
and then use CoreCell, Airex, whatever for the core. They don't wick
up water and won't rot if wet. You may still have delamination if your
deck is leaky, but that's a function of the job you do next.

Along with others, I question the economics of doing this, but if you
like and want to sail the boat, you might as well do the best job
possible if you go to the trouble of taking the deck apart, which is
labour-intensive and a dirty, tedious job. The payoff is that when
it's all back together and the deck gear is backed by load-spreading
backing plates and sealant-covered bolts through epoxied holes in
encapsulated plywood, you feel very confident that the cleats will
give before the deck does, that you can jump on the deck without it
"giving" and that it will be dry and safer below, irrespective of the
weather.

I used to have fender washers. Now I have custom-cut (by me) 1/4"
backing plates on all through-deck gear. Nothing moves and only the
portlight (this winter's project!) leak. From that perspective, the 32
year old boat's "better than factory", because we have a very good
historical idea of the benefits and problems of balsa coring. And by
the way, there are some boats where thanks to attentive owners, the
balsa has never been wet, and the through-bolts pass through
water-proof epoxy "bushings". Those boats are absolutely sound.

But doing what is necessary won't add a penny to the resale value.
That's why in some cases it makes more sense to buy a beat-up bigger
sailboat with a delaminated, sad deck for a few grand and just strip
the top layer off the bugger and go for a total redo.

R.

Michiel wrote:

Matt and everyone else who responded to my questions:

Thanks again for sharing your experience and knowledge. Very cool!


With regards to urethane, I ran into this:

http://www.azom.com/details.asp?Arti...ison_of_Core_1

Judging from this page polyurethane foam might not be very suitable
for a deck, although I'm not sure if the writer had the higher
densities in mind. It seems to me that the expansion of the foam would
help to make a good bond?


I did a few things this weekend to find out what state things are in.

I went around the deck with a rubber mallet to try to figure out the
extent of delamination. I think it's very widespread. Only at the
edges, things sounded hard. But I guess that it this point that's
good, because it'll make it easy to take out the old core.

I also cut out a small patch, from the inside. It was frozen when I
cut it. It's almost dry now. It doesn't look or feel rotten at all,
but it looks as if frost may have caused some damage (some cracks in
the wood). the balsa is still firmly bonded to the inner skin. It
seems the delamination is just between the outer skin and the balsa. I
can take a photo of this if it would help.

I think I may be able to reuse the existing core. The procedure I'm
thinking of now is: Cut out the inner skin, let it dry thoroughly,
Remove core in areas where deck hardware will be mounted and fill with
resin as suggested by another poster, then smear a fat coat of resin
around (be it polyester or epoxy), maybe thickened with some
microballoons and prop the whole mess up and then when it all dries
glass over the cuts.

Michiel
PS: vacuum bagging sounds like a wonderful technique, but I just can't
afford the investment now.



You can prop up under the side deck with garbage bags of air and
other junk. It may be easier then sealing vacuum bagging. When I
tore up my side deck, I observed that where seepage had frozen, it
broke the bond with the end grain of the balsa, and allowed water to
progressively advance, freeze and thaw, cycle by cycle, year by
year. Once the bond is broken, by expanded frozen water, the open
end grain allows the balsa to get wet. If it freezes, it then tears
the bond to the next adjacent healthy core section, and the cycle
progresses. If the balsa is not rotton it can be dried and
rebonded. Otherwise, it progresses from light and strong to dark and
mushy. The mush must be removed and replaced, and must be groped
out inch by inch. I used a couglins folding camp saw with a couple
of extra teeth filed in the curve outside the end. Is it ever
wicked looking, now! If the cycle is stopped, any core will do, so
long as it stays dry. The cycle is started only by leaky stanction
bases, etc.

Seal up your side decks now! stop this cancer before it starts,
it's a lot less cure than otherwise.

Working under the side deck is only possible if there are no
cabinets, etc in the way. The amount of work counts for more than
technique or materials.

Terry K

http://www.cncphotoalbum.com/doityou.../rotrepair.htm

http://www.cncphotoalbum.com/doityou...rotrepair2.htm

Simple with great diagrams.

Mic wrote:

http://www.cncphotoalbum.com/doityou.../rotrepair.htm

http://www.cncphotoalbum.com/doityou...rotrepair2.htm

Simple with great diagrams.


-----------------------

REGARDING THOSE LINKS - we don't recommend 'squirting' any sort of
solvent containing liquid into any sort of confined space (such as
inside your deck).

Use 100% solids (solvent free) products and epoxies designed to bond to
wet or damp surfaces.

paul oman
progressive epoxy polymers

--

Micheal,
This is why I figured out how to do it with vacuum after my first failure.
I replaced about 20 sqft of my S2's deck and about 8 sqft of hull.
Matt Colie A.Sloop Bonne Ide'e S2-7.9 #1

Michiel wrote:
Hello,

Back in November I posted here about my balsa cored deck, which had
delaminated and had some rotten balsa in it. I got some great input
here and a variety of opinions.

I've just completed the repair and I thought I'd share my approach.
Sorry, no photo's - I was too lazy for that. I have not kept careful
track of my time and expenses, but I imagine I spent 40 or 50 hours on
it and about $300 in supplies.

Only part of my deck is cored, so the extend of the repairs was
limited. Perhaps about 10 square feet.

The balsa on the starboard side had let go of the outer skin, but was
completely dry. The port side was wet and most of the balsa was wet
and rotted. I found this out by drilling a lot of holes from the
inside and inspecting the wood that came out.

I repaired the delamination on the starboard side by injecting epoxy
thickened with glass microballoons, into holes drilled through the
inner skin and core about every 7 or 8 inch. This was very easy. I
filled caulk tubes with the epoxy paste and used this to be able to
quickly fill syringes. It would have be cool if someone would make
caulk tubes with narrow tips, so the syringes can be eliminated. The
result of this is excellent. The epoxy spread well inside the deck and
the deck is very stiff.

On the port side, I cut out the inner skin and replaced the core.

I used a rotozip saw with a carbide tile cutter bit to cut the skin
out, in pieces no bigger then about two by three feet. The balsa core
was attached to the inner skin, but entirely loose from the outer
skin.

I removed the old balsa from the inner skin with a chisel and then
ground the inner skin down with a 4.5" grinder. I also ground the
inside of the outer skin clean this way. This was an extremely dusty
process, with very fine dust.

For replacement core, I used scored Divinycell. The scoring helps it
to conform to contours. I first laminated this to the loose pieces of
inner skin. Trash bags filled with sand helped to apply pressure. I
left voids around holes for hardware, which I filled by injecting
epoxy after the deck was back together..

After I had these pieces of inner skin with new core laminated and
carefully trimmed to be the same size as the skin and with the scoring
facing up. I then laminated this to the outer skin from inside the
boat. I tried to use truck tubes to apply pressu this did not work
well. The tubes didn't press hard enough - they would just expand the
other way. Instead I used many strips of wood cut to the right length.

After this, filled voids between the panels and glassed the cuts, then
faired a bit and finally painted with a two part epoxy paint.

It looks pretty good. The shiny paint shows surface irregularities
much more then the headliner did.

Michiel