Refinishing: Who has tried a shortcut?

I have refinished an old Mosquito that had badly cracked
wings. I did it with Glasurit 2K and high build epoxy
primer.

We took off enough old gelcoat that the surface looked
good, we did not remove all old gelcoat.

We took lots of time removing grease/oil/dirt from
cracks in order that the paint surface would not be
damaged by grease causing the paints not to stick well.
Used lots of degreasing agent, acetone I think.

The epoxy primer took very well and was sanded back
for smoothness then painted with the top coat 2 pack.

I haven't seen it for a couple of years but last time
I did the paint was still holding up and not showing
any signs of crack propagation through the primer and
top coat.

When it was finished, I was very pleased with the results
and the glider flew much better having got back a great
portion of its laminar flow.

The gelcoat, although cracked, was NOT peeling off.
It still was a suitable surface to paint on.

John

If old gelcoat is left behind, would not it eventually
crack and propagate to the surface? Also, and I have
googled RAS on this subject, is UV penetrating through
the cracks to the structure harmful? IE, will refinishing
a ship as soon as cracks appear save time and money
in the long run?

After operating a glider repair station for 20 years, I can truly say, "been
there, done that" We probably refinished at least 20 sailplanes. What have I
learned?

1. It's one hell of a lot of work.

2. All cracks, loose material, chips and flakes, MUST be removed. Notice I
didn't say *everything* must be removed. Should everything be removed? In my
opinion, No, it's not necessary. I would say that we removed about 50% of the
gelcoat on the ships we refinished. How have these ships held up? Quite well
with the exception of those ships that were left out all the time (FBO
operations) The gelcoat (Prestec) showed paint failure within 4 years. Cracking
and checking appeared from the outside, NOT cracks that reappeared from the old
gelcoat.

3. I have refinished my Genesis 2 with acrylic urethane (PPG Concept 70) and I
think this is the way to go, especially for ships that will be left out. I
would only use Prestec for spot repairs of gelcoated gliders. By the way, the
*brown ring* around paint repairs is caused by not removing the oxidized old
paint. I recommend the edge of the old paint be lightly sanded with 220 grit
and then control the edge of the new paint, so that the *fether edge* occurs in
the middle of the 220 sanded area.

4. We need some way to get our 20 year old ships refinished for less than
$10,000 US bucks. It just doesn't make good sense to spend any more than that
on an old ship. Some shops will welcome *owner assisted refinishing*. I have
done this. It might well be worth considering taking your vacation at the
local repair shop. The shop doesn't want your project to linger on for months,
but if you offer to work full time for a month, things will move along
satisfactorily. Can you do it at home? Probably not. You need some specialized
equipment, a good air compressor to start with + air boards, spray booth,
respirator, not to mention a cooled, heated and well lighted place to work.

5. Did I mention that it is one hell of a lot of work?
JJ Sinclair

Do you know what was used for the new finish? Is it gel-coat or 2 part
polyurathane paint? If it is paint, what kind of primer went on underneath
it?

Ian

It is not a 2 part polyurathane paint. I suspect it is Gel Coat on top
but I can't say for sure.

Brian

The composites industry has many years of experience and good understanding of
gel coat cracking mechanisms. To address a few of the comments:

1) A gel coat fracture must be removed to the extent of its depth; otherwise
the crack propagation mechanism is in play and will eventually affect the
surface again.

2) A thick and/or flexible secondary coating will delay the re-appearance of
cracks, but not the effects. There must always be concern about an underlying
(but now covered) crack propagating into the laminate.

3) UV penetration of the laminate is a non-issue unless the crack is huge. In
that case the crack itself will be a structural issue.

4) To date, there is not a viable method of "filling" cracks. This is a
function of the inherent surface tension of the potential liquid materials. If
one could fill cracks there is a fair chance two micro-cracks would appear on
each side of the original crack and eventually propagate into larger cracks.

5) To date, no one in the composites industry has come up with a workable
shortcut. A quick fix solution would be worth big bucks, with gliders being a
tiny portion of the overall application.

Hope this helps.

Bob Lacovara

Time for a round up.

I started this thread 4 days ago and I asked:

There has been quite a bit on refinishing on RAS recently. Most people
advocate that when gel-coat starts cracking up, it is essential to remove
it ALL.

There has been lots of advice and theory as to why the above is true. No
doubt it is the recommended approach - recommended by many who are not in a
position where they might have to pay for the work!

However there was little response to my question:

Does anybody out their own a ship which was refinished without removing
all the gel-coat? What is the service history of these gliders?

So far there have been two postings of problems with re-finishes. Neither of
these involved a polyurathane finish. Gliders re-finished with extensive or
complete removal of the old gel-coat have held up - at least as well as the
original gel coat.

So I will extend the question. Does anybody anybody know of gliders that
have been refinished with polyurathane and subsequently experienced
problems?

I can answer that by saying I know of one glider that was re-finished with
polyurathane about 10 years ago. There is some localised paint cracking on
the tailplane and rudder which suggests that there were some areas of poor
preparation during the refinish. I suspect that the glass skin on these
areas is thiner more flexible which results in a finish that is more
susceptible to cracking. This was not an "expensive" refinish job, for
example the ailerons and flaps were not removed during the respray. But
overall the glider still looks very neat and I think I can say this finish
has lasted as least as well as many factory gel coat finishes.


Ian

Greg,
Because most sailpanes are waxed throughout the year.
Reuben
Greg Arnold wrote in message news:BdREb.20434$J77.19108@fed1read07...
Bob, why do sailplanes (which spend most of their time in the trailer)
have such a problem, while sailboats (which spend most of their time in
the sun and weather) usually have a good gelcoat?



B Lacovara wrote:

The composites industry has many years of experience and good understanding of
gel coat cracking mechanisms. To address a few of the comments:

1) A gel coat fracture must be removed to the extent of its depth; otherwise
the crack propagation mechanism is in play and will eventually affect the
surface again.

2) A thick and/or flexible secondary coating will delay the re-appearance of
cracks, but not the effects. There must always be concern about an underlying
(but now covered) crack propagating into the laminate.

3) UV penetration of the laminate is a non-issue unless the crack is huge. In
that case the crack itself will be a structural issue.

4) To date, there is not a viable method of "filling" cracks. This is a
function of the inherent surface tension of the potential liquid materials. If
one could fill cracks there is a fair chance two micro-cracks would appear on
each side of the original crack and eventually propagate into larger cracks.

5) To date, no one in the composites industry has come up with a workable
shortcut. A quick fix solution would be worth big bucks, with gliders being a
tiny portion of the overall application.

Hope this helps.

Bob Lacovara

Ian,

With respect, you cannot establish good practice by
totting up numbers of for and against contributions
to RAS. Bob Lacovara's contribution says it all.

If you come to resell the shortcut refinished glider
will you make clear to potential purchasers that the
condition of the glider laminate is unknown and can
only be checked by removing the new and underlying
old finishes?

John Galloway


At 09:36 20 December 2003, Ian Forbes wrote:
Time for a round up.

I started this thread 4 days ago and I asked:

There has been quite a bit on refinishing on RAS recently.
Most people
advocate that when gel-coat starts cracking up, it
is essential to remove
it ALL.

There has been lots of advice and theory as to why
the above is true. No
doubt it is the recommended approach - recommended
by many who are not in a
position where they might have to pay for the work!

However there was little response to my question:

Does anybody out their own a ship which was refinished
without removing
all the gel-coat? What is the service history of these
gliders?

So far there have been two postings of problems with
re-finishes. Neither of
these involved a polyurathane finish. Gliders re-finished
with extensive or
complete removal of the old gel-coat have held up -
at least as well as the
original gel coat.

So I will extend the question. Does anybody anybody
know of gliders that
have been refinished with polyurathane and subsequently
experienced
problems?

I can answer that by saying I know of one glider that
was re-finished with
polyurathane about 10 years ago. There is some localised
paint cracking on
the tailplane and rudder which suggests that there
were some areas of poor
preparation during the refinish. I suspect that the
glass skin on these
areas is thiner more flexible which results in a finish
that is more
susceptible to cracking. This was not an 'expensive'
refinish job, for
example the ailerons and flaps were not removed during
the respray. But
overall the glider still looks very neat and I think
I can say this finish
has lasted as least as well as many factory gel coat
finishes.


Ian

I know of wings on a Phoebus that was sanded and then sprayed with
Polyurethane.
After a couple of years, the wings looked like surface of El Mirage Dry Lake
in Southern California.
The old gelcoat pieces were not coming off but the cracks and fissures in
the paint were obvious to the most casual observer.
However, this Phoebus is still flying and it has been probably 15 years since
sprayed.
GA

Good report, Bob
I would only add one data point. You saidThere must always be
concern about an underlying
(but now covered) crack propagating into the laminate.

I have ground out literally hundreds of cracks in gel-coat that went right down
to the fiberglass laminate. To date, I haven't seen any gel-coat cracks that
entered the underlying structure. Not saying it can't happen, just haven't seen
it in going on 30 years of smelling fiberglass dust. BTW, I'm talking about
pure gel-coat cracks, not surface cracks that were caused by laminate failure
underneath. That is the first question that a repairman asks, Is this a
gel-coat crack or has the underlying structure moved?
JJ Sinclair