Gel coat removal - water sanding vs. straight line sanding

On Feb 12, 12:26*pm, Brad wrote:
On Feb 12, 6:27*am, JJ Sinclair wrote:





On Feb 11, 5:21*pm, Brad wrote:

On Feb 11, 5:11*pm, Papa3 wrote:

On Feb 11, 4:52*pm, JJ Sinclair wrote:

On Feb 11, 9:20*am, Brad wrote:

On Feb 11, 6:56*am, JJ Sinclair wrote:

On Feb 10, 9:55*pm, Brad wrote:

On Feb 9, 7:42*pm, shkdriver
wrote:

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.

--
shkdriver

Scott..............Prestec isn't a PU product is it?

I'll be looking at a total paint job of the HP-24 sometime soon. Right
now it is all bare carbon. Can't decide if I want to go with Simtec
products or use a 2-pack PU. a-la PPG concept.

Brad- Hide quoted text -

- Show quoted text -

I recommend PPG Concept (90288 super white) with PCL polyprimer (907
white) for primer. You must be very careful when spraying acrylic
urathane, this stuff can kill you! Get a respirator with hose outside
the spray booth, use plastic gloves, hat and glasses leaving no
exposed skin. You will need about 3 gallons of mixed product which
means 2 gal of paint, 1 gal of catalist and half gal of thinner ($1000
bucks or so). Spray on 4 medium coats or until you get good orange
peal everywhere which is an indication you have enough paint on. Let
it cure out for 24 hours at 70 degrees, then block sand (wet) with 600
followed by 800. *I spray on guide coat (spray can) before hitting it
with 600 then use the black powder rubbed on in the area before
hitting it with 800. Then let it cure out for a good 3 more days
before buffing with a wool pad and liquid rubbing compound.
Hope this helps,
JJ

Hey JJ,

This sounds like what I'll end up doing. I'll probably spray the
Polyprimer myself (this is a polyester right?). Then..........I'll
sand the primer, fill pin holes, repeat as needed, then take it to a
pro to have the top coat/PPG sprayed on.

My backyard tarp shed probably won't work!

Brad- Hide quoted text -

- Show quoted text -

Brad, Have a talk with the painter to make sure you're both on the
same page. An auto paint shop will normally give it 2 coats and it
should come out bright and shinny and that might be all you want. In
this case you want to do final sanding with 220 grit. If, on the other
hand, you wish to wet sand it as in my earlier post, you need 4 coats
with orange-peal. The painter will think your nuts, just tell him you
need lots of paint so's you can sand one coat off and have it
perfectly smooth, which his car paint job isn't. For a *4 coat job,
the final sanding can be done with 80 grit on a long board followed by
a pass with 150 (hand sanded) to knock down the high scratch marks.
This gives your paint good 'tooth' and you shouldn't be pulling any
paint when removing wing tape. The 80 grit scratch marks will
disappear after the second coat of paint is applied. Many auto paint
shops aren't ready to do a 25' wing and will probably end up with lots
of over-spray...........not a problem if your going to wet sand later.
I think 4 coat then wet sanded and buffed is the way to go. Williams
Soaring has a paint booth and Rex can deliver whatever you wish. I saw
an RV-8 he painted with 2 passes and it looked great.
Have fun,
JJ- Hide quoted text -

- Show quoted text -

Hey JJ,

Scratching my head a bit on this one. * I think what you were driving
at is that the final primer coat is left at 150 grit, followed by the
four coats of top coat. *Or did I miss something?

P3

I think JJ was referring to using 80 grit followed by 150 on the
Polyspray primer, as you said.

A final coat at 80/150 would be ah...........not so good!

Brad- Hide quoted text -

- Show quoted text -

There's two schools of thought here guys; Auto painting and sailplane
re-finishing. The auto painter is going to sand his light primer coat
with no less than 220 and probably more like 320, then spray on two
medium coats, then he's done. Its shiny, cure it out and give it to
the customer!

The sailplane re-finisher breaks all the above rules. He primes real
heavy, maybe 4 coats, depending on what he has to fill to end up with
a good block sanded surface. He jumps on this with his 18" sanding
board with 45 left/ 45 right action and hopes it comes out smooooth as
a baby's bottom without going through the primer and show raw glass.
When all is good, I hand sands it with 150 just to remove any rough
edges, but I'm going to spray on 4 coats of paint and then wet sand
it, so I don't need the 220/320 action. In fact I dont want to do that
because my paint won't have killer good adhesion (AKA tooth) and it
will peal paint from the finished product when Mr. Customer peals off
his wing tape. The 80 grit scratches will disappear with the second
coat of paint, but even if they don't, your first pass with 600 wet
will make them go away.
That's what I have done for the better part of 35 years,
JJ
PS; Oh , yeah body putty. If you have little pin-holes showing through
your primer, wipe in medium body putty and hit those areas with 150.

JJ....................my glider bits came out of the mold with no
primer, paint or anything, just black carbon with probably a million
little pin holes. My plan is the sand the surface of everything with
150 grit, clean all the dust and bits of sanding debris off with air
and.........(insert suggestion here)................then, if I flood
the surface with polyprime, will that fill the pin holes and give me a
good base to work with?

thanks,
Brad- Hide quoted text -

- Show quoted text -

It will bridge across many pinholes. You will sand thru bridging- more
pinholes.
My suggestion is light coat of filler. don't sand yet. squeegee in a
coat of filler to fill pinholes. Then sand.
That will get 90% on first try from my experience.
UH

On Feb 12, 9:26*am, Brad wrote:
On Feb 12, 6:27*am, JJ Sinclair wrote:





On Feb 11, 5:21*pm, Brad wrote:

On Feb 11, 5:11*pm, Papa3 wrote:

On Feb 11, 4:52*pm, JJ Sinclair wrote:

On Feb 11, 9:20*am, Brad wrote:

On Feb 11, 6:56*am, JJ Sinclair wrote:

On Feb 10, 9:55*pm, Brad wrote:

On Feb 9, 7:42*pm, shkdriver
wrote:

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.

--
shkdriver

Scott..............Prestec isn't a PU product is it?

I'll be looking at a total paint job of the HP-24 sometime soon. Right
now it is all bare carbon. Can't decide if I want to go with Simtec
products or use a 2-pack PU. a-la PPG concept.

Brad- Hide quoted text -

- Show quoted text -

I recommend PPG Concept (90288 super white) with PCL polyprimer (907
white) for primer. You must be very careful when spraying acrylic
urathane, this stuff can kill you! Get a respirator with hose outside
the spray booth, use plastic gloves, hat and glasses leaving no
exposed skin. You will need about 3 gallons of mixed product which
means 2 gal of paint, 1 gal of catalist and half gal of thinner ($1000
bucks or so). Spray on 4 medium coats or until you get good orange
peal everywhere which is an indication you have enough paint on. Let
it cure out for 24 hours at 70 degrees, then block sand (wet) with 600
followed by 800. *I spray on guide coat (spray can) before hitting it
with 600 then use the black powder rubbed on in the area before
hitting it with 800. Then let it cure out for a good 3 more days
before buffing with a wool pad and liquid rubbing compound.
Hope this helps,
JJ

Hey JJ,

This sounds like what I'll end up doing. I'll probably spray the
Polyprimer myself (this is a polyester right?). Then..........I'll
sand the primer, fill pin holes, repeat as needed, then take it to a
pro to have the top coat/PPG sprayed on.

My backyard tarp shed probably won't work!

Brad- Hide quoted text -

- Show quoted text -

Brad, Have a talk with the painter to make sure you're both on the
same page. An auto paint shop will normally give it 2 coats and it
should come out bright and shinny and that might be all you want. In
this case you want to do final sanding with 220 grit. If, on the other
hand, you wish to wet sand it as in my earlier post, you need 4 coats
with orange-peal. The painter will think your nuts, just tell him you
need lots of paint so's you can sand one coat off and have it
perfectly smooth, which his car paint job isn't. For a *4 coat job,
the final sanding can be done with 80 grit on a long board followed by
a pass with 150 (hand sanded) to knock down the high scratch marks.
This gives your paint good 'tooth' and you shouldn't be pulling any
paint when removing wing tape. The 80 grit scratch marks will
disappear after the second coat of paint is applied. Many auto paint
shops aren't ready to do a 25' wing and will probably end up with lots
of over-spray...........not a problem if your going to wet sand later.
I think 4 coat then wet sanded and buffed is the way to go. Williams
Soaring has a paint booth and Rex can deliver whatever you wish. I saw
an RV-8 he painted with 2 passes and it looked great.
Have fun,
JJ- Hide quoted text -

- Show quoted text -

Hey JJ,

Scratching my head a bit on this one. * I think what you were driving
at is that the final primer coat is left at 150 grit, followed by the
four coats of top coat. *Or did I miss something?

P3

I think JJ was referring to using 80 grit followed by 150 on the
Polyspray primer, as you said.

A final coat at 80/150 would be ah...........not so good!

Brad- Hide quoted text -

- Show quoted text -

There's two schools of thought here guys; Auto painting and sailplane
re-finishing. The auto painter is going to sand his light primer coat
with no less than 220 and probably more like 320, then spray on two
medium coats, then he's done. Its shiny, cure it out and give it to
the customer!

The sailplane re-finisher breaks all the above rules. He primes real
heavy, maybe 4 coats, depending on what he has to fill to end up with
a good block sanded surface. He jumps on this with his 18" sanding
board with 45 left/ 45 right action and hopes it comes out smooooth as
a baby's bottom without going through the primer and show raw glass.
When all is good, I hand sands it with 150 just to remove any rough
edges, but I'm going to spray on 4 coats of paint and then wet sand
it, so I don't need the 220/320 action. In fact I dont want to do that
because my paint won't have killer good adhesion (AKA tooth) and it
will peal paint from the finished product when Mr. Customer peals off
his wing tape. The 80 grit scratches will disappear with the second
coat of paint, but even if they don't, your first pass with 600 wet
will make them go away.
That's what I have done for the better part of 35 years,
JJ
PS; Oh , yeah body putty. If you have little pin-holes showing through
your primer, wipe in medium body putty and hit those areas with 150.

JJ....................my glider bits came out of the mold with no
primer, paint or anything, just black carbon with probably a million
little pin holes. My plan is the sand the surface of everything with
150 grit, clean all the dust and bits of sanding debris off with air
and.........(insert suggestion here)................then, if I flood
the surface with polyprime, will that fill the pin holes and give me a
good base to work with?

thanks,
Brad- Hide quoted text -

- Show quoted text -

Flooding doesn't get all the little buggers, but a light prime will
expose them all and then do like UH says and wipe in body putty. I
like the blue stuff that has body, the red stuff is a mite thin for
pin-holes. If Bob did a good job on his molds, you won't need too
heavy a prime......maybe around the L/E, T/E, spoilers, etc, but the
rest may get-er-done with one prime coat. Your local auto paint store
has all the sanding boards and sticky back paper roll in 80 grit, etc.
JJ

On Feb 12, 12:41*pm, JJ Sinclair wrote:
If Bob did a good job on his molds...

You ought to come and see for yourself. We're convening the next
Akaflieg Douglas Flat in early March, Doug and Brad are coming down to
close a set of wings.

One thing that I've done with the high solids primer is to mix in some
micro balloons, might give that a try to fill the pin
holes............I'll rough up the surface, and squeegee in the
thickened goop.

When I painted the wings on my Russia, I was horrified to see hundreds
of little pin holes appear......seemingly out of nowhere. But, that
was my first experience with composites, sure have learned a bunch
since then!

Brad

(big snip)

Prestec products,
For my mostly wood SHK, After sanding CAREFULLY down to bare wood (discovering original pencil marks!) Prepped bare wood with 3 coats EV-400 epoxy varnish, then Prestec 2081 white epoxy primer/filler, "block" sand with 5 foot long fiberglass sanding block, also used 18 inch long sanding board and various smaller hand pads, final sanding primer/filler with wet 400 3M then used randolph ranthane.
Prestec 2081 primer/filler is marketed for Wood or composite surfaces (radomes) sombody with a glass ship would pick another prestec product maybe?
For pinhole filling I also used activated "Auto body" products at first, However Prestec supplied me with their White epoxy filler product, Less viscous, more liquid, and after a short learning curve, Much superior to car products.
BTW, when using air tools, be judicious with the air tool oil, I sometimes wrapped a shop rag around the tools exhaust to minimize oil spray on my surfaces. also meticulous intercoating surface cleaning ensured good adhesion.
P.S. the 5 foot long sanding block was a section of fiberglass U channel used to make ladders. A local buddy is an aerodynamacist at a wind generator company and supplied me with it, they use them for mounting electrical components.
Good Luck!
Scott W.

[quote=shkdriver;721144](big snip)

Prestec products,


Hey, Also for what it's worth,
It probably goes without saying, Work Closely with your A&P IA, and the maker of your aircraft concerning methods and products.
During my project I was told about a guy who Repaired a Dart and could not get it inspected because of the adhesive he used. OOps!

Scott W.