Dry vs. wet sanding

[[email protected]]

Is there any reason that PPG concept can't be sanded dry? I need to knock down some bad orange peel (because I'm still learning how to paint). I was thinking about using some 500 to knock down most of the orange peel, and then move to finer grits (wet) take out the sanding scratches before polishing. It seems like everyone is sanding wet, but why? It's much harder to see what you've done because everything gets covered with white goo. If I sand dry, I can blow the dust away and see what I've got immediately. I do know about guide coat and all of that, but I'm wondering what can go wrong if I make the first pass with 500 dry, and then switch to a finer grit wet?

Thanks,

John

[Andrzej Kobus]

On Monday, February 15, 2016 at 10:30:50 PM UTC-5, wrote:
> Is there any reason that PPG concept can't be sanded dry? I need to knock down some bad orange peel (because I'm still learning how to paint). I was thinking about using some 500 to knock down most of the orange peel, and then move to finer grits (wet) take out the sanding scratches before polishing. It seems like everyone is sanding wet, but why? It's much harder to see what you've done because everything gets covered with white goo. If I sand dry, I can blow the dust away and see what I've got immediately. I do know about guide coat and all of that, but I'm wondering what can go wrong if I make the first pass with 500 dry, and then switch to a finer grit wet?
>
> Thanks,
>
> John

Your health would be one. During dry sanding isocyanates will be released, regardless how old the paint is. The newer the paint the more isocyanates will be released. You risk developing asthma, not really good for pilots :(. PPG Concept is a great paint but it requires proper precautions.

[Charlie M. (UH & 002 owner/pilot)]

Additionally, most materials are better wet sanded to NOT build up stuff in the paper grit. This (buildup) can lead to scratches (even gouges) in the surface.
The water helps float removed material away and provides a small amount of heat dissipation.

If you want to "check your work", an inexpensive red rubber squeegie works well to make the surface dry again (as well as helping remove "sanding sludge").
The dry surface you're left with makes it a lot easier to look for "shiny" vs. "dull" to see where more sanding may be needed.

I wouldn't wetsand a lot of "natural materials" (wood, paper, bamboo, leather) unless they had a coating of something or were sealed.

[Craig Lowrie]

Apply a Red disclosure coat then wet sand and you can immediately see
where you need to sand and where you have sanded enough... Sanding
wet extends the paper life and tends to prevent it clogging... Use good
quality paper (in UK Mirca is good)... Maybe start with 400 or 600 and
stop just before the last of the orange peel is gone... Then apply more
red disclosure and shift to 800, then 1200, then 1500.. Polish with
Farecla G3 then Wax... Craig...

At 05:24 16 February 2016, Charlie M. UH & 002 owner/pilot wrote:
>Additionally, most materials are better wet sanded to NOT build up
stuff in
>the paper grit. This (buildup) can lead to scratches (even gouges) in
the
>surface.
>The water helps float removed material away and provides a small
amount of
>heat dissipation.
>
>If you want to "check your work", an inexpensive red rubber squeegie
works
>well to make the surface dry again (as well as helping remove
"sanding
>sludge").
>The dry surface you're left with makes it a lot easier to look for
"shiny"
>vs. "dull" to see where more sanding may be needed.
>
>I wouldn't wetsand a lot of "natural materials" (wood, paper, bamboo,
>leather) unless they had a coating of something or were sealed.
>

[ND]

On Monday, February 15, 2016 at 10:30:50 PM UTC-5, wrote:
> Is there any reason that PPG concept can't be sanded dry? I need to knock down some bad orange peel (because I'm still learning how to paint). I was thinking about using some 500 to knock down most of the orange peel, and then move to finer grits (wet) take out the sanding scratches before polishing. It seems like everyone is sanding wet, but why? It's much harder to see what you've done because everything gets covered with white goo. If I sand dry, I can blow the dust away and see what I've got immediately. I do know about guide coat and all of that, but I'm wondering what can go wrong if I make the first pass with 500 dry, and then switch to a finer grit wet?
>
> Thanks,
>
> John

if you dry sand with 320 or finer, you'll sand for 10 seconds and your paper will be loaded/chalked up. you must wetsand young padawan. for wet sanding i recommend a plastic soda bottle with several small holes drilled in the cap. that allows you to use less water wit the same results. also, get a squeegee from lowes or walmart. that gets the surface clean and dry in seconds without all the mess. google "california water blade" and get that kind of squeegee, as you can clear a curved surface much easier, and check your progress more often.

-andy

[[email protected]]

On Monday, February 15, 2016 at 10:30:50 PM UTC-5, wrote:
> Is there any reason that PPG concept can't be sanded dry? I need to knock down some bad orange peel (because I'm still learning how to paint). I was thinking about using some 500 to knock down most of the orange peel, and then move to finer grits (wet) take out the sanding scratches before polishing. It seems like everyone is sanding wet, but why? It's much harder to see what you've done because everything gets covered with white goo. If I sand dry, I can blow the dust away and see what I've got immediately. I do know about guide coat and all of that, but I'm wondering what can go wrong if I make the first pass with 500 dry, and then switch to a finer grit wet?
>
> Thanks,
>
> John

Slow down.
Put guide coat on and start with 1000 or finer.
When you scratch it with rough paper you ensure you will need to do a lot more sanding with finer grits to get the scratches out.
You are also much more likely to sand through.
Sand very wet and use a squeegee to clear the gunk off.
Take your time Grasshopper.
UH

[Craig Funston]

On Tuesday, February 16, 2016 at 6:12:51 AM UTC-8, wrote:
> On Monday, February 15, 2016 at 10:30:50 PM UTC-5, wrote:
> > Is there any reason that PPG concept can't be sanded dry? I need to knock down some bad orange peel (because I'm still learning how to paint). I was thinking about using some 500 to knock down most of the orange peel, and then move to finer grits (wet) take out the sanding scratches before polishing. It seems like everyone is sanding wet, but why? It's much harder to see what you've done because everything gets covered with white goo. If I sand dry, I can blow the dust away and see what I've got immediately. I do know about guide coat and all of that, but I'm wondering what can go wrong if I make the first pass with 500 dry, and then switch to a finer grit wet?
> >
> > Thanks,
> >
> > John
>
> Slow down.
> Put guide coat on and start with 1000 or finer.
> When you scratch it with rough paper you ensure you will need to do a lot more sanding with finer grits to get the scratches out.
> You are also much more likely to sand through.
> Sand very wet and use a squeegee to clear the gunk off.
> Take your time Grasshopper.
> UH

Also use a block that's on the harder side. A soft sponge type block with fine grit sand paper will just shine up the undulations.

Cheers,
7Q

[[email protected]]

Yep......what Hank said! I use a 12 " Dura-Block with paper folded in half the long way. Wear gloves and dip the block in a bucket of warm water (to clear the residue.......warm to be kind to your hands). I do start with 800w after 24 hours at 70f. Comes off very easy while the paint (or gelcoat) is green. Buff it out after a week or so.
Have fun,
JJ

[[email protected]]

Thanks for the suggestions!

John

[[email protected]]

During dry sanding isocyanates will be released, regardless how old the paint is. The newer the paint the more isocyanates will be released. You risk developing asthma, not really good for pilots :(. PPG Concept is a great paint but it requires proper precautions.
------------------------

Can someone confirm this? I understand the dangers while polyurethane is
being sprayed, and perhaps also in the early stages of curing. But I
thought the material was pretty much inert after it cured. I haven't
been able to find any warnings beyond the spraying process on the
internet. Can somebody supply more information? I'd like to be as
safe as possible. Or at last understand the dangers.

Jim Beckman

[[email protected]]

I have read this as well however the dispersion is not nearly what it would be when sprayed. Most if not all hardeners are iso based. I would love to know if there exists a 2k system for AU that doesn't use them, but even water based systems rely on isocyanate hardeners. Non catalyzed systems exists but the finish is not nearly as durable. 1k clears basically suck. For sanding I would think wet sand with gloves, mask and a suit ideally outside.

[Andrzej Kobus]

On Wednesday, February 17, 2016 at 7:38:10 AM UTC-5, wrote:
> During dry sanding isocyanates will be released, regardless how old the paint is. The newer the paint the more isocyanates will be released. You risk developing asthma, not really good for pilots :(. PPG Concept is a great paint but it requires proper precautions.
> ------------------------
>
> Can someone confirm this? I understand the dangers while polyurethane is
> being sprayed, and perhaps also in the early stages of curing. But I
> thought the material was pretty much inert after it cured. I haven't
> been able to find any warnings beyond the spraying process on the
> internet. Can somebody supply more information? I'd like to be as
> safe as possible. Or at last understand the dangers.
>
> Jim Beckman

Jim, the release of isocyanates is caused by heat from sanding. The higher the heat the more isocyanates will be released. The amounts we are talking about are not large but almost all of us have been exposed to isocyanates over our lifetime and the effects of this chemical are cumulative so it is wise to avoid it as much as possible. If you use water you are generating very little heat plus isocyanates bind to water which is a plus in this case.

There are paint out there that are water based and since isocyanates bind to water they are much safer to use. Isocyanates will always seek water molecules to bind to so if you spray make sure you use full body cover.

PPG Concept for example can be painted with a roller or brush and then wet sanded like gel coat. It is very easy to repair single stage AU.

Wet sanding is the way to go (don't save on water) and if you sand dry do it very slowly and play really slow music :)

If you like to read here is the science http://www.pubfacts.com/detail/16434466/Determination-of-airborne-isocyanates-generated-during-the-thermal-degradation-of-car-paint-in-body-

[[email protected]]

As an aside question sort of related to the subject, has anyone finished a sailplane with Interlux Brightside Polyurethane? And if so were you pleased with the results?

[[email protected]]

My paint supplier told me there were much cheaper urethane paints available, so I sent a note to PPG. Told them we loved Concept, but it was getting hard to get (in my county) and very expensive. Asked if other urethane paints would be a suitable substitute for Concept? Got a nice reply that stater poly-urethane paints would become brittle with age. Concept is acrylic-urethane (not poly-urethane) and remains slightly flexible throughout its life span.
JJ

[[email protected]]

On Wednesday, February 17, 2016 at 6:22:51 PM UTC-5, Andrzej Kobus wrote:

> Jim, the release of isocyanates is caused by heat from sanding. The higher the heat the more isocyanates will be released. The amounts we are talking about are not large but almost all of us have been exposed to isocyanates over our lifetime and the effects of this chemical are cumulative so it is wise to avoid it as much as possible. If you use water you are generating very little heat plus isocyanates bind to water which is a plus in this case.

Thanks for the reference. The study in question considered "workers'
exposure to isocyanates during cutting, grinding and orbital sanding
operations." So it sounds like we're talking about a lot less heat
when we're just color sanding by hand. Still and all, there's no
reason to take chances, and I can't see any real advantage to dry
sanding. We've color sanded one set of (Grob 103) wings painted
with polyurethane, and it was wet sanding all the way.

(I'll admit that I have, on rare occasions, sanded out a run
or two in polyurethane that I caused.)

Jim Beckman

[Surge]

On Thursday, 18 February 2016 16:48:19 UTC+2, wrote:
> My paint supplier told me there were much cheaper urethane paints available, so I sent a note to PPG. Told them we loved Concept, but it was getting hard to get (in my county) and very expensive. Asked if other urethane paints would be a suitable substitute for Concept? Got a nice reply that stater poly-urethane paints would become brittle with age. Concept is acrylic-urethane (not poly-urethane) and remains slightly flexible throughout its life span.
> JJ


When you guys mention polyurethane are you referring to acrylic or polyester?

From what I've read regarding automotive 2K paints, you get polyurethane with acrylic polyols or polyester polyols.
So it's actually acrylic polyurethane or polyester polyurethane.

I am aware one also get's acrylic urethane which is more elastic than acrylic or polyester based polyurethanes.

[Andrzej Kobus]

On Thursday, February 18, 2016 at 9:48:19 AM UTC-5, wrote:
> My paint supplier told me there were much cheaper urethane paints available, so I sent a note to PPG. Told them we loved Concept, but it was getting hard to get (in my county) and very expensive. Asked if other urethane paints would be a suitable substitute for Concept? Got a nice reply that stater poly-urethane paints would become brittle with age. Concept is acrylic-urethane (not poly-urethane) and remains slightly flexible throughout its life span.
> JJ

There are modifiers available to make the polyurethane paint flexible. These modifiers are used when painting plastic parts on cars to allow paint to flex with plastic. AU is however the best paint all around for application and sanding/polishing