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Old 04-25-2011, 08:10 AM
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Wet or Dry sanding primer

I've been in/around the autobody business for roughly 20 years, now just doing jobs out of my garage/shop, about 3-4 a year. I've always sanded my primer dry with 400 and then maybe go to 600 if its a silver or something with lots of metallic without any issues at all but I keep seeing and hearing things about people wetsanding the primer , what I want to know is what are the advantages to wetsanding versus dry besides the obvious dust, does it cut better ? Am I missing the boat on something here ?

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Old 04-25-2011, 09:29 AM
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When you wet sand you are continually flooding the sanding surface with water which allows sanding debris to float away from your sandpaper. Dry sanding the paper loads up with sanding debris and hard spots can develop which leads to an uneven surface. It is hard for me to believe with 20+ years experience that you have never wet sanded primer.
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Old 04-25-2011, 08:50 PM
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The paper lasts longer too.

I like to use a bucket of water and add
a few drops of dishwashing detergent.

While the panel's wet, you can see
imperfections better.
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Old 04-27-2011, 07:31 PM
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Well 13 of my years were at a shop that had no idea of how things should actually be done, so we were stuck doing things the "old fasioned way" but not so old that we used the ol' Red oxide laquer. I've been doing my own jobs on the side now for about 6 years and always sanded dry but I am seriously thinking of trying to do it wet and see how well it works , just wanted some input first.
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Old 04-28-2011, 06:32 AM
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Quote:
Originally Posted by outlaw17
Well 13 of my years were at a shop that had no idea of how things should actually be done, so we were stuck doing things the "old fasioned way" but not so old that we used the ol' Red oxide laquer. I've been doing my own jobs on the side now for about 6 years and always sanded dry but I am seriously thinking of trying to do it wet and see how well it works , just wanted some input first.
Once you do the wet sanding you'll wonder why you never tried it before. Just the $aving$ alone in paper will be enough to sway you, then the benefit of not breathing the dust will help and of course with flooding the surface clean you can easily see (and feel) where it needs a bit more scuffing.

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Old 05-12-2011, 04:06 PM
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I'm reading up on this process, it's my next step.

Nebie question:
Arn't you worried about the moisture (wet sanding) working it's way thru your primer?
I thought that primers arn't really waterproof.

Thanks
Thom
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Old 05-12-2011, 04:31 PM
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i see this all the time and never understood why the 400 & 600 on primer.
if you use sealer before paint
dry sand w/220, seal, paint, clear.
you will never see a sand scratch.
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Old 05-12-2011, 04:32 PM
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Quote:
Originally Posted by Thommyknocker
I'm reading up on this process, it's my next step.

Nebie question:
Arn't you worried about the moisture (wet sanding) working it's way thru your primer?
I thought that primers arn't really waterproof.

Thanks
Thom
Not a bit worried about either 2K urethane epoxy. While the urethane is not waterproof, it is still water resistant, but don't expect that it will protect the steel surface outside in the rain and over several months. Epoxy - which is by far the best IS waterproof and is what most of us here will recommend --- and many of us use the SPI epoxy as you can sand it much like the 2K, tho it is a bit more difficult.

This car of mine was painted in 2009( this photo is with no final hand buff and polish/wax ):

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Old 05-12-2011, 07:20 PM
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ogre,

Quote:
i see this all the time and never understood why the 400 & 600 on primer.
if you use sealer before paint
dry sand w/220, seal, paint, clear.
you will never see a sand scratch.
What are you using as a sealer - reduced Epoxy Primer or a specific Sealer?

Thanx,

Tom
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Old 05-12-2011, 07:47 PM
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I have been wetsanding 2K for about 20 years with zero rust.. but as was said, I would not leave it in the weather for an extended period.
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Old 05-13-2011, 01:38 PM
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Quote:
Originally Posted by TucsonJay
I have been wetsanding 2K for about 20 years with zero rust.. but as was said, I would not leave it in the weather for an extended period.
Sounds reasonable to me.

Thanks guys.
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Old 05-14-2011, 08:03 AM
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Quote:
Originally Posted by ogre
i see this all the time and never understood why the 400 & 600 on primer.
if you use sealer before paint
dry sand w/220, seal, paint, clear.
you will never see a sand scratch.
I totally disagree. You will see this unless you bury it with sealer. That's like saying to poly prime over an 80 scratch. Sure I can do it but I'm no longer priming for coats, I'm now worried about covering scratches which makes priming more of a hassle, and there's a risk of having scratches still there down low or in areas where you MAY not be as thorough. The lowest I go for final prime app is 260- 320 but it's ALWAYS reguide coated with 400-600 depending on what's sprayed. You also have to consider that if you're piling on sealer to cross link it's not cured when you're looking at it fresh. It will then settle and reveal scratches later. If it's a metallic you will notice your scratch patterns RIGHT AWAY due to the flakes laying funny, and it will only get worse. I say to make that possible you must be sealing with a 2k, which I've seen from time to time, but I don't recommend that at all. You want your sealer thin cause you're covering it before it's cured.
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Old 05-14-2011, 04:33 PM
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from my experience finish all repairs in 180 followed be by 3 coats of high build primer. rubbing primer will depend on next coat
water basecoat 320 then 400
solvent basecoat 320
high or medium solid (2k) 240
sealer 240

i would never and have never preped using water because its un required work, dry sanding is faster and cleaner, occasionaly the da pads may clog but have never seen it damage primer/paintwork.

i cant believe people still use wet and dry for anything more than denibbing/polishing, i though wet sanding primer went out
in the 80s
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