Gelcoat Sanding

Rather than pencil marks I recommend 3M dry guide coat. Even when wet sanding.

Lane

i really mean spanwise, when i worked at schempp-hirth 6 years ago they always sanded spanwise for finish sanding. and i have been doing it that way at a nationally known glider refinishing company for 12 years.

On Thursday, March 24, 2016 at 5:30:06 PM UTC-4, Michael Opitz wrote:
i take sections of wing and draw a line with pencil from leading edge
to
tr=
ailing edge every 18 inches or so. then, with 800 (you can use 600)
you'll
=
sand two sections at a time using spanwise strokes, working from
leading
ed=
ge to trailing edge.

Did you really mean spanwise and not chordwise??? When I worked at
S-H, we NEVER sanded spanwise. It was either chordwise or
alternating 45 degrees off chordwise. FWIW......

for finish sanding im not recommending that, because you are using a soft block for spanwise sanding. if you are using a hardblock for orange peel removal, or heavier gelcoat removal, you would want to support the wing in three places, or whatever it takes to keep the wing from sagging. on an LS-8, you only need two stands because they're so still they don't sag.


On Thursday, March 24, 2016 at 9:23:32 PM UTC-4, Mark628CA wrote:
So far, nobody has mentioned supporting the wing in at least three places to make sure the surface is straight spanwise. Just an inch or so of sag and your hard work will result in very questionable results as your two or three foot long sanding block exerts pressure on its ends and the center bends according to the weight on your hands and arms. You can bet that the curve (and rebound as you push and release) will make your efforts totally random if you are trying for an accurate, straight surface.

Learned this from Fidel Ramirez, a guy who has spent thirty-five years becoming a Master at 'glass repair and shiny white things that fly.

On Thursday, March 24, 2016 at 9:49:47 PM UTC-4, Mark628CA wrote:
but soapy residue also corrodes metal faster. so if oyu use any soap (we never do) make sure you take steps to protect your contol linkages, and hanges.

Another hint: Add a bit of dishwashing soap to the water you use to clean off your wet sanding paper and rinse the wing surface. It reduces the amount of residue that builds up on the sandpaper and makes it last longer.

And remember: Patience is a virtue. Take your time. And then take some more time. Good things come to those who exhibit patience.

At least with things like this. Other things require more immediate results. That's why high explosives were invented. Mining would take a LONG time if you had to use sandpaper.

guide coat is good for taking away orange peel or a spar bump, but pencil makes a much smaller mess -AND- if he uses guide coat, he'll have black lines on his wing forever, since it will wick down into any remaining crazing (unless he plans on sanding the crazing away entirely, but that may also mean sanding the gelcoat away entirely, depending on how severe it is).

The technique i am describing is only finish sanding. the pencil is there to show what section to sand in, and the chord-wise pencil line lets you know if you've removed enough material/ not missed spots as you sand spannwise..

-ND

On Saturday, March 26, 2016 at 6:51:18 AM UTC-4, wrote:
Rather than pencil marks I recommend 3M dry guide coat. Even when wet sanding.

Lane

also, for the process i describe, you'll want to use a soft finish sanding block. like the one in the attached link:

http://homefixated.flashpointstudio....lock-Round.jpg



On Thursday, March 24, 2016 at 5:05:14 PM UTC-4, ND wrote:
hi Peter, here's the finish sanding process I use on every glider we refinish. first let me say there are many ways to arrive at the same result. i'm the blonde guy hank called on near the end who was standing against the side wall.

i take sections of wing and draw a line with pencil from leading edge to trailing edge every 18 inches or so. then, with 800 (you can use 600) you'll sand two sections at a time using spanwise strokes, working from leading edge to trailing edge. each time you finish two sections, move up 1 section, so you are overlapping and hitting each section two times as you move down the wing. repeat the process for each grit. truth be told, i do 800, 1000, and 1500. change paper alot, it goes dead quickly. especially with old hard gel-coat.

now, for the literal coup de grâce: after doing sections of 1500, wet the whole wing down, and walk back and forth, root to tip, doing single strokes that last the whole wingspan using spent 1500. you won't be sorry. if you do a ton of that at the end, the wing will look buffed before it's buffed, and it will also shine up much easier.

if you want more detailed explanation on the actual process, email me: brayera at gmail dot com and i'll give you my number so we can talk. if your wing is crazed, don't wait to do this. the longer you wait, the worse off you are. sometimes, if you catch crazing **early**, you can save the finish. no matter what stage your crazing is at, polish hard and often from now on and you'll squeeze some extra years out of your finish.

-Andy

On Thursday, March 24, 2016 at 4:20:54 PM UTC-4, vontresc wrote:
So after attending Uncle Hank's presentation at the convention I have been
inspired to sand out the crazing in my gel coat. I am planning on the
600-1000-1200-1500 wet sanding process and then buffing out the finish.

I understand the basics, but does anyone have a good primer on the process?

Thanks

Peter

I often hear that sanding is only a temporary solution, and after couple of years the gel coat will lift again and now you have a thiner gel coat layer and wider cracks. If so, why sanding unless you try to sell your glider?

Ramy

On Monday, March 28, 2016 at 12:08:22 PM UTC-4, Ramy wrote:
I often hear that sanding is only a temporary solution, and after couple of years the gel coat will lift again and now you have a thinner gel coat layer and wider cracks. If so, why sanding unless you try to sell your glider?

Ramy

So you can save up for a full refinish. A "flattening sanding" helps with the aerodynamics followed by a good wax/polish can extend the life of what you have. A full refinish is not cheap.

On Monday, March 28, 2016 at 12:20:45 PM UTC-4, Charlie M. (UH & 002 o
exactomundo.

On Monday, March 28, 2016 at 12:08:22 PM UTC-4, Ramy wrote:
I often hear that sanding is only a temporary solution, and after couple of years the gel coat will lift again and now you have a thinner gel coat layer and wider cracks. If so, why sanding unless you try to sell your glider?

Ramy

So you can save up for a full refinish. A "flattening sanding" helps with the aerodynamics followed by a good wax/polish can extend the life of what you have. A full refinish is not cheap.

Hi Ramy,

i recently read an article on you in gliding international. you are an inspiration, i can only imagines some of the beautiful scenery you must have seen!

another possible reason to sand is if you can catch crazing in it's very earliest stages you can sand away the damaged gelcoat and literally remove the crazing completely. crazing most typically begins in the existing sanding scratches on the surface of the gelcoat. that's the reason they are often chordwise, because as mike opitz indicated above, the manufacturers used to sand chordwise.

On Monday, March 28, 2016 at 12:08:22 PM UTC-4, Ramy wrote:
I often hear that sanding is only a temporary solution, and after couple of years the gel coat will lift again and now you have a thiner gel coat layer and wider cracks. If so, why sanding unless you try to sell your glider?

Ramy