I painted my first exterior coat on my 73 f-100 last night and had a couple of runs. It started getting cooler out so I was afraid of solvent pop, which happened to the bed when I refinished it, so I am going to wait until tomorrow. My question is, if I wait until tomorrow, the paint will have set about 20hrs would I be able to light sand those runs out and then put the second coat on without any problems? By the way the paint is PPG omni acrylic urethane enamel. One more thing there were a couple of spots where it turned out like a bowling ball finish, which I believe is maybe where the paint was not mixed thourougly. Does this sound right? Thanks for any advice.

Byron

 

you should be fine with sanding those runs out. Only problem is you can't sand out the runs on your last coat with the acrylic enamal or you won't have a shiny finish (unless you clear coat).

On the bowling ball finish, it could be paint that is not mixed really well or could be some contaminate getting past your filter in your air line.

The hardest thing about being a good painter is patience, you really have to take your time and put just enough to get good coverage but not overdue it and gets runs, also proper equipment is very important.

I have painted a few cars, trucks, tractors, etc. and I still really feel like I could learn some more. I would love to intern with a really good professional and learn everything that he knows.

Oh and preparation is a really big issue, you can be the greatest painter in the world but if your vehicle isn't properly prepared and cleaned then it will turn out like crap.

hope that helps

 

I figured I would lose my shine if sanding after the final coat, so hopefully if all goes well get the runs out now and not have any noticable ones when I am done. I do not think the marks are contamination because I prepped real well and I am using a turbine paint sprayer.

 

Don't spray the truck without sanding after 20 hours! Your final coats won't adhere for long. Scuff the entire job quickly with a (clean, new) Green Scotch-brite pad, wipe it down again with your pre-paint solvent (wax and grease remover), then respray.
Good luck & take pics!

 

The solvent will soften the paint ,maybe to the point of the rag sticking to the finish ,if you are going to scotch brite it ,,just blow it off & re tack it ..

Hopefully , you catalized the paint ,,

You may also want to find out if there is a re coat window for the product you are spraying ..

 

If this is really a urethane like you stated, then you should be able to sand it down and repaint it the next day and maybe not have any problems. Is this the mtk au urethane?
Waiting longer, or cutting the surface by sanding, and letting it get some sun to cure up a bit would be safer. You will have to sand for adhesion like etech said. I would probably use something in the neighborhood of 600 wet and do a thorough job of sanding, and use a block backing of the paper for the run areas. Depening on how thick they are, they also may want to stay soft a little while. I personally don't feel comfortable just having the scratch of a scotchbrite pad, but it may work for others just fine. Won't touch runs though, you will have to sand them. You might also get by da with 320, but it is a little bit courser then the mtk recommends,(believe they say 400 by da, most likely in case using a light metallic color). But from what I remember last time I tried da sanding with 400, it didn't work all that well sanding with it, but that was many years ago, and they may have better papers now.
I painted a beater of mine a few years back with the mtk urethane, and repainted a quarter panel without problems, but it was likely a few days by the time I got to repainting it. Also buffed it without problems, a solid color you should be able to buff, but its not a given you won't get blotchy pigment by wetsanding. I would have suggested try blocking out the runs and buffing a shot first, if you had put on more coats, and didn't have whatever the discoloration problem you have. But since you only have one coat, you should probably sand and apply more. Even an enamel if you activated it you should be able to buff back to a shine if you wait long enough to do so, and the pigment isn't effected doing so.
If its really an enamel on the other hand, such as the mae, you could have more likelyhood of problems, specially if an activator wasn't used with it. Its been quite a long time since I sprayed an enamel, but believe Enamels are Pretty fussy about recoating either need to recoat in a certain number or hours, or have to wait quite a long time and sand before recoating. If done at the wrong time, likely you could get recoat lifting.
You can go to ppg refinish and look for the tech info for your product, although I don't think omni has the greatest tech sheets.
Wish I knew more about the turbines, have never used one. Hey least your getting a learning experience with the redo's, lol.

 

I have hit the re coat window twice in my career ..not good either time .(Only with urethane enamel),complete stripping and had to re do the body work also ,4 weeks of free labor & materials ,,& two really unhappy customer's

One was within days ,,the other was 2 weeks later ,,,

& one of them was a 3 stage pearl....

The last one ,,I repainted it , one panel at a time I was so unsure it would work out ...

Both times it was using hardener (activator)...

Do your self a favor ,,,do a test area first ...

If you have never seen a perfectly restored(black) Lincoln, lift all over ,(every inch of it ) right before your eyes ...

do a test ...

 

I agree ,,although, 400 will also be sufficient ,, given the right sanding technique...(Circular last )

Especially using enamel..

 

If I had to guess ,,what you are seeing is called mottling ''metalling sliding within the binding clear.. you may need to put it on a little dryer ,& double coat it ...

 

Well I got the second coat done. The paint had set for about 21hrs. The tempature dropped last night to about 55 degrees, so I think my time between coats could have been extended because of the cooler weather. I fixed the one run I had with some 600 grit dry, wiped it down and sprayed the second coat. It turned out good. I did have a small spot where I had sanded, so I am going to wait a few weeks and let the paint cure and fix that one spot and repaint. Other than that, after about an hour everything still looks good. I will take some pictures tomorrow and post them. The paint was Omni MTK AUE grabber blue. Thanks for the help and if anyone has any other suggestions, I still have to refinish the bed.

 

If it has set for about an hour and a half and is drying good and also still looks ok, does this mean that the lifting is not going to happen? After hearing about these stories I am nervous.

 

i don't see why it would lift.

 

If it hasn't lifted after an hour, you most likely are safe. Lifting usually occurs during application, when solvent attacks a sensitive substrate or cut through area you are painting over and lifts it. Really would be more of a likely problem if you had used an unactivated enamel.
Hopefully you are safe after that amount of time, having recoated it without sanding it all. Mtk tech sheet says nothing about maximum time between coats. But there 160 urethane clear says mtk has up to 1 week to clear, so gives some hope you will be okay. Not a chemist and know if the resins and chemistry are the same, but urethane clearcoat is basically a urethane single stage without the pigment in it. I personally wouldn't make a habit of it not knowing for sure, maybe something you could find out an answer calling there technical support.

 

I have another question about this single stage acrylic urethane enamel. After it dries, will I be able to fine sand and buff the finish for a smooth look, or am I going to have to live with the way it looks now?

 

I believe the grabber blue (used on both mustangs and mavericks from what I remember) is a solid color-no metallic, isn't it?
If its a solid color and you used mtk urethane, then yes you might be able to buff it. If a metallic or pearl, no, you would have very little room before you cut through the thin layer of clear resin that floats to the top and get into the metallic and end up with blotchy uneven color.

I would still do an inconspicous spot first with a solid color that hasn't been clearcoated, or paint a test panel or spare piece, and experiment on that, just to make sure the eveness of the pigment isn't effected from color sanding and buffing.

Another thing that would kinda concern me is it sounds like you painted in two sessions, painted a coat, and then applied a second coat 24 hrs later. Does that mean you have 2 coats of material to play with when color sanding, or only one (with the time between the two coats being applied) and if you happen to cut through that somewhere on an edge or with heavy sanding, you end up with a noticeable difference in that spot. I just don't know for sure. If you apply urethane clearcoat in two seperate sessions, and cut through the layers you applied last into the first coats of clear you applied, you'll have a very noticeable spot where you cut through them. Urethane won't reflow, and those layers don't melt in with the first layers after a certain amount of time has elapsed. That may be something to field to ppg tech support and explain the time elapsed between coats. Or duplicate what you did and time elapsed on a test panel, and see what happens if you cut through the top layer of color. If you only really only have one layer to play with I would be real carefull, and not do very heavy sanding (like if you have a decent sized run or defect to get out) and be very carefull around edges and bodylines (or even go as far as to mask those areas off to protect them) 1 layer doesn't give you alot of room for color sanding and buffing.