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PhilC
07-22-2007 14:43:00
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Re: what is wet sanding in reply to 5020s rock, 07-21-2007 21:46:21
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At the risk of being smart, it's sanding with water by hand or by special tools and equipment designed for that purpose. Definitely not an orbital or belt sander!
The purpose of wet sanding is generally to remove excessive texture, whether in surfacer or sealer prior to topcoat or afterward. Either way, it removes unwanted texture.
There are two basic approaches to removing undesirable texture, wet or dry sanding. I have used both, but not with Ag paints, only automotive paints. For quite some time, I blocked surfacer with wet or dry 600 grit paper (I prefer Norton or Mirka) prior to the car going into the booth for sealer, base, and clear. At the time, the cars were sprayed in a heated air make up donwdraft paint booth with bake feature. I rarely ever dealt with dirt nibs in post paint prep and texture was controlled with gun speed, distance and air pressure.
The place I work at now does not have a downdraft paint booth, instead it's an older cross draft that isn't as airtight. As a result, I now have to "cut and buff" dirt nibs on a regular basis. Texture, again, is controlled by gun speed, distance, and air pressure. If the painter gets it wrong, I have to save his butt in post prep, and occasionally, I have to do that.
I now prefer to dry sand vs wet sand, it's faster and cleaner. When I de-nib a car, I'll use 1500 grit wet to knock the nibs down and then follow-up with 1500 grit and an interface pad on a 6" DA. Once I've gotten things where I want them, I buff with 3M Extra Cut and a white wool pad on an electric buffer. Depending on color, I may follow that with a swirl remover and lastly, 3M UltraFina polish. I usually only do that on darker colors as the lighter colors don't show the swirls as much.
Wet sanding is as effective, but I don't care to have my hands in water all the time anymore. As I age, my skin dries out too much using thismethod and in winter, my skin literally splits open which is very painful. Add a few drops of car wash soap to your bucket of water when wet sanding, it adds lubricity to the water and will help draw the "slurry" off while you sand. Also, make sure you soak your sandpaper for a minimum of half an hour prior to use. Longer is better (an hour is plenty long) but you don't need to worry about over soaking either.
I think your texture issue is coming from a couple sources. Air pressure is to be set at the gun, not at the wall. You have to account for line loss through your air hose which should be as short as possible yet long enough to get the job done. Hoses in paint booths are no longer than 50' and most often not much more than 25'. The longer the hose the greater the line loss.
Your air pressure should be according to your paint and spray gun mfr's recommendation. I typically set my pressure at the gun and note what reading I have at the wall. Once done, (assuming a consistent and sufficient air supply) I can then use the wall regulator for setting pressure. Having said that, most people don't have the stable air supply a body shop does, so the best practice is to always set at the gun. Another source for texture will come from your spray technique. It takes time and practice to learn a consistent technique that minimizes texture.
There are other things that could contribute, but generally, it comes from the ones mentioned above.
I'm not familiar with the different brands of tractor paints, but I'm going to assume they are some form of acrylic or alkyd enamel. We no longer use these in the automotive industry, all we use are urethanes. Not knowing what kind of paint is on your tractor, I don't know how much you can wet sand to remove texture without causing problems. General rule of thumb, the least amount possible. You don't want it perfectly flat anyway, Ford sure didn't.
Hope that helps.
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