Dry vs. wet sanding

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.

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.
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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/16434...paint-in-body-

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?

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

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

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.

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