Gel coat removal - water sanding vs. straight line sanding

On Feb 8, 5:29*pm, bildan wrote:
On Feb 8, 2:51*pm, JJ Sinclair wrote:





On Feb 8, 12:40*pm, Tim Taylor wrote:

On Feb 8, 12:34*pm, bildan wrote:

On Feb 8, 12:05*pm, wrote:

On Feb 7, 10:54*am, bildan wrote:

On Feb 7, 7:26*am, wrote:

On Feb 6, 7:57*pm, bildan wrote:

On Feb 6, 10:54*am, LS3 Pilot wrote:

Trying to do some work on my ship. *Does anyone that reads this forum
have experience in the best way to remove gelcoat? *I've got an area
thats too big to hand sand on the wing that needs some work. *A friend
suggested I buy a water sander that continuously feeds water to the
sander (similar to a pneumatic powered straight line sander).

What's the best tools to safely and effectively removing the old gel?

There's a thing called an "air file" auto body shops use.

http://www.pivco.net/index.php?main_...roducts_id=171...

It's a linear oscillating compressed air driven sander about 18" long
and 2.25" inches wide. *I've been told they work pretty well with 80
grit and they have less chance of digging into the fiberglass than a
rotary grinder. *Since it's air driven, I suppose you could safely use
wet sanding and avoid the dust.

I have used the following in order to find the "best"(for us) tools
fo gelcoat removal.
3 inch air rotary disc sander.- Too small- blows dust all over- noisy
7 inch electric disc sander. Too harsh for us and not easy to control.
Quick but likely to do damage easily.
18 inch air powered linear sander. Noisy. Not good except single
contour. Blows dust around. Need big compressor.
4 inch belt sander. Fast. tricky to use.
4 inch grinder with disc sanding attachment. Fast, fairly easy to
control. inexpensive. Slings dust everywhere.
5 inch electric orbital sander. Very uniform controllable removal.
Lowest dust generation in room. Easiest to use by unskilled or
learning helpers.
Only ones we use now are last 2 with last one doing 90% of the work.
Feel free to relearn the lessons already learned- we all seem tempted
to find the better way that nobody has found. Understand from the get-
go, there is no easy way to do this job.
Have "fun".
UH

It's still early and I'm working on my first cup of coffee but....

Might it be possible to make a support block that would limit the
"exposure" of the cutting surface on more aggressive sanders so as to
prevent it digging in? *It would work sort of like a block plane.
The idea is to use a fast cutting tool but limited to a very shallow
cut.- Hide quoted text -

- Show quoted text -

Might work if the surface we are sanding is straight and uniform over
significant distance.
And the surface we are sanding to is straight and uniform.
And the abrasive medium doesn't wear.
None of these occurs on the projects I work on.
Finding the "easy" way that all the folks that have done this before
is seriously tempting. By the time you develop and test the tool, you
can learn how to use the proven tools pretty effectively.
Well known shop scenario- voice is the worker:
This whizbang (grinder, sander insert tool here) really does much
better than the hard way I keep reading about.
Goin' pretty good- this isn't so tough.
One more pass and it'll be just right.
Damn!
RAS- How do I fix a hole in my(substitute part) skin?
Another thread!
Been there- done that.
You can't buy experience, but you DO pay for it.
FWIW
UH

Yep, I'm sure it takes a lot of experience.

Another thought struck me. *Are you familiar with "rivet shavers" that
cut countersunk rivets flush with an aluminum skin?

They have a sharp rotary cutter inside a micrometer adjustable housing
that lets the user adjust the depth of the cut to produce a perfectly
smooth rivet 'shave'. *Maybe something like that....

I expect the idea would be to quickly and accurately remove all but a
few thousandths of gelcoat which would then be removed with the 5"
orbital sander.

I think this is what you are talking about Bill:

http://www.gelplane.co.uk/gelplane/product.asp

I have thought about both the plane as well as testing bead/sand
blasting. *Never got around to having the time to test both. *Used the
7" rotary sanding technique like everyone else.

The old Sailplane Racing Association web pages were great information
on refinishing. Not sure if that information was moved to a new site.- Hide quoted text -

- Show quoted text -

The Gel-plane looks interesting, but the photo shows gelcoat being
removed from a boat that has mat structure (chopped fibers & resin)
and it doesn't matter much if you cut the top off the fibers. In a
sailplane the structure is cloth and it matters a whole bunch if you
even nick a few fibers. The real problem is the depth of the gelcoat
isn't uniform. Remember how it is built, gelcoat is sprayed into a
prepared mold and experience has shown that extra gelcoat is needed at
all edges and openings, spoilers, etc. Now start grinding it off and
you soon see that you must stop here, but keep going deeper over
there. I have tried sand-blasting (went right through in a heartbeat)
and paint remover ( just turned everything brown). Alas, I have found
nothing to beat good the old orbital sander. One can train high school
kids to do it, but they soon move on to more interesting work. We are
taliking about a mind-knumbing boring, filthy dirty, noisy, nasty,
activity that nobody is his right mind would do for a few worthless
dollars. Speaking of the worthless dollar, this is a good time to buy
a sailplane.................its got to be worth more worthless dollars
in the future because our national debt will keep eroding the value of
our already worthless dollar. Does everybody realize that every US
taxpayer owes $140,000.00 as his/her part of out national debt? *OK,
enough of that..................Go out and buy a sailplane today, it
will never cost less than it does today.

JJ * *Who can make you a good deal on a fine little 2-place ship that
was owned by a little old lady who only flew it on Sundays, but she
accidently flew it into a tree..........not to worry, it has been
expertly repaired and refinished by a master abrasives technician.

The thing is, there's a bunch of nice airworthy old gliders out there
with bad gelcoat. *Right now, replacing gelcoat costs more than
they're worth. If an economical way could be found to redo the
gelcoat, that would be a good thing, wouldn't it?- Hide quoted text -

- Show quoted text -

The economical way is owner with more time than money guided by a
knowledgable helper who has done it before.
A couple guys have done that in our shop.
UH

The economical way is owner with more time than money guided by a
knowledgable helper who has done it before.
A couple guys have done that in our shop.
UH

Forgive the obtuseness, but how long does it take to strip the gelcoat
off, say a 15 m wing?
I guess that would be the easy part, because then one needs to build
it back up and check the profile, yes? How long for that?

I'm probably not going to like the answer... I'm very glad that the
gelcoat on my mistress is in great shape.

"jsbrake" wrote

I'm probably not going to like the answer... I'm very glad that the
gelcoat on my mistress is in great shape.

I can't imagine a reason to remove all of the gelcoat off of anything. In
refinishing, you get down as deep as needed in problem areas and then build
it back up, scuff up the rest, and shoot a new thin even coat on the whole
thing, and be done with it. Thin is the key; don't put on more than you
took off.
--
Jim in NC

On Feb 8, 7:00*pm, "Morgans" wrote:
"jsbrake" wrote

I'm probably not going to like the answer... I'm very glad that the
gelcoat on my mistress is in great shape.

*I can't imagine a reason to remove all of the gelcoat off of anything. *In
refinishing, you get down as deep as needed in problem areas and then build
it back up, scuff up the rest, and shoot a new thin even coat on the whole
thing, and be done with it. *Thin is the key; don't put on more than you
took off.
--
Jim in NC

I have seen several examples where someone attempted to remove only
the "bad gelcoat" layer. In a year or two it looked terrible!

"mike" wrote

I have seen several examples where someone attempted to remove only
the "bad gelcoat" layer. In a year or two it looked terrible!

Oh, yes, the devil is in the details, isn't it.

There are degrees of bad. If the bad is cosmetic, i.e., scratches and
oxidation, a removal of the surface and reapplication of a compatible (ah,
more details that can be the devil) new layer will look fine.

If there is degradation of the jelcoat to fiberglass/carbon fiber/Kevlar
bonding, then the detail is the devil. Nothing to do but to take it all
off.

This is a case where working with someone that can teach the ins and outs of
fiberglass work can be invaluable, or valuable enough to save many man-hours
and material bucks.
--
Jim in NC

On Feb 8, 10:11*pm, "Morgans" wrote:
"mike" wrote

I have seen several examples where someone attempted to remove only
the "bad gelcoat" layer. In a year or two it looked terrible!

Oh, yes, *the devil is in the details, isn't it.

There are degrees of bad. *If the bad is cosmetic, i.e., scratches and
oxidation, a removal of the surface and reapplication of a compatible (ah,
more details that can be the devil) new layer will look fine.

I can't imagine a reason to remove all of the gelcoat off of anything.

This is a case where working with someone that can teach the ins and outs of
fiberglass work can be invaluable, or valuable enough to save many man-hours
and material bucks.
--
Jim in NC

You mentioned, " I can't imagine a reason to remove all of the gelcoat
off of anything."

and then in a following post,

" If there is degradation of the gelcoat to fiberglass/carbon fiber/
Kevlar
bonding, then the detail is the devil. Nothing to do but to take it
all
off."

I was addressing your first dictum.

Mike

"mike" wrote

You mentioned, " I can't imagine a reason to remove all of the gelcoat
off of anything."

and then in a following post,

" If there is degradation of the gelcoat to fiberglass/carbon fiber/
Kevlar
bonding, then the detail is the devil. Nothing to do but to take it
all
off."

I was addressing your first dictum.

You got me on that one.

OK, how about, I can't imagine removing all of the jelcoat unless it was
already trying to remove itself. g
--
Jim in NC

Hello,
Having refinished only a shk which is primarily wood construction with fiberglass cockpit and leading edges, IMHO if you decide to purchase a pneumatic (air) driven sander, dual action orbital or "air file" there is a world of difference between quality tools and Harbor freight cheap imports.
I recomend Hutchins brand tools, powerful, smooth action, and easy on air demand. also you can use a water flood with air tools.

For heavens sake wear a high quality air mask, that previous comment of not needing one because the particles are too big is B.S. and dangerous!
As an ICU RN I work with pulmonologists every day and ran that one by them, one simply stated "I wouldn't breath that with your lungs"

As far as time required, I removed three complete top coats of paint (about 75 lbs worth) and primers and fillers. brought up the new coatings and used polyurethane top coat, 18 meter wings, 4 foot wing root, big constant taper fuse, about 1100 hours.
B.T.W. prestec products ROCK!
Good luck and best wishes!
Scott W.

As far as time required, I removed three complete top coats of paint
(about 75 lbs worth) and primers and fillers. brought up the new
coatings and used polyurethane top coat, 18 meter wings, 4 foot wing
root, big constant taper fuse, about 1100 hours.
B.T.W. prestec products ROCK!
Good luck and best
wishes!
Scott W.


1100 hrs... divide by 20 hours/week = 55 weeks , just over a year of
working in the shop after the full-time job.

YIKES! I'm really, really glad I've got good ol' Scwabbelack
(spelling?) on my Kestrel... original 1972 gelcoat in great shape.

On Feb 10, 1:27*pm, jsbrake wrote:
As far as time required, I removed three complete top coats of paint
(about 75 lbs worth) and primers and fillers. brought up the new
coatings and used polyurethane top coat, 18 meter wings, 4 foot wing
root, big constant taper fuse, about 1100 hours.
B.T.W. prestec products ROCK!
Good luck and best
wishes!
Scott W.

1100 hrs... divide by 20 hours/week = 55 weeks , just over a year of
working in the shop after the full-time job.

YIKES! *I'm really, really glad I've got good ol' Scwabbelack
(spelling?) on my Kestrel... original 1972 gelcoat in great shape.

650 man hrs for club members to refinish ASK-21. Gelcoat off, fill,
contour, respray in acrylic urethane.
About 1/2 that for ASW-19 in gelcoat.
Good news is no need to go to gym for upper body exercise. My doctor
says that, for a fat guy, I have pretty good arms and shoulders.
LOL
UH