Fix uneven paint area

[DMM]

My friend came over to help me paint the ship, he accidentally touched the wet paint and then repaint it, now it looks like this. How do I fix it? 

[bruce d]

Bummer. 

It would help a lot to know a some more such as what paint, was it brushed or sprayed?  It looks like a plastic model so hopefully it will stand a bit of handling during the repairs.

 

Bruce

[Jack-in-the-Blue]

41 minutes ago, DMM said:

How do I fix it? 

I suggest that you strip it all off the plastic with IPA and start over with thinned paints in multiple coats giving plenty of drying time between layers. 

[SkiBee]

Instead of stripping off the paint, why not just use some wet sandpaper and get it smooth then repaint the whole area again.

[DMM]

2 hours ago, SkiBee said:

Instead of stripping off the paint, why not just use some wet sandpaper and get it smooth then repaint the whole area again.

What grid should I wet sand with?

[DMM]

6 hours ago, bruce d said:

Bummer. 

It would help a lot to know a some more such as what paint, was it brushed or sprayed?  It looks like a plastic model so hopefully it will stand a bit of handling during the repairs.

 

Bruce

It was sprayed and yes, plastic model

[Bob Cleek]

With help like that, who needs friends?

 

Sprayed with what? Oil-based enamel or water-based acrylic?

 

I would not advise trying to strip the paint off of plastic.  Isopropyl alcohol will remove some types of acrylic paint, but not all. Stripping the paint with any other sort of solvent runs the risk of softening the plastic. Your best bet is to wait until the paint is thoroughly hardened. Then sand, wet or dry doesn't matter. Wet is messy. Dry is dusty. There's no free lunch there.

 

That said, from the picture you posted it looks like your plastic hull isn't smooth, but rather has some raised surface lines there that look like they may be armor plating belts or the like. If that's the case, forget what I said about sanding. It would be very difficult for you to sand that area smooth and preserve the raised surface detail there. If the hull has surface detail, then chemically removing the paint is the only way to do it and preserve the surface detail. You will have to ascertain what solvent will remove the paint. If there is any instructions on the can about what solvent to use to clean up with, that will give you a good hint. Otherwise, call the manufacturer if you have to and ask them. Don't use any solvent until you are sure the plastic can withstand it. You can test solvents on some sprue material. If the solvent makes the plastic sticky, it's too "hot." One solvent that may work and is always worth having on hand anyway is called "Goof-Off." It will remove oil-based paint and acrylics if the acrylics haven't been curing for weeks. You can find it at any hardware store. It's sold for wiping up paint spatters. If you have to strip the surface, make sure that it's completely clear of any solvent residue afterwards because the solvent may react adversely to the paint you will be applying. Ignore the following information about sanding and start up again at the step where you apply your boot stripe masking tape. 

 

If you are sanding instead of stripping, you should sand the surface down until it is completely fair. Use a foam sanding block which will avoid your developing flat spots that you'd get from a hard block... or use your fingers. The goal is not to sand the "goof" fair at the expense of the surrounding area. You want to sand the whole surface fair without simply developing a smoothed "divot" in the overall surface. This is important because it will really show up when the whole surface is repainted if it's not perfectly faired into the whole surrounding surface. It looks like you have a fairly thick smear there, so you may wish to start with somewhere around a 320 or 400 grit paper and once you get it faired with that, then go over it again with a 600 grit. You want to get the whole area "smooth as a baby's bottom." Don't forget to carefully attend to the detail sanding around the through-hull on the side of the hull there, It needs it, too. Don't sand too aggressively with the larger grit sandpaper. If you sand too aggressively with heavy grit, you will likely see sanding swirls and scratches on the painted surface that will be difficult to remove with your finer grit paper.

 

After you've sanded it smooth dust it well and wipe it down with a "tack rag" which can be bought at any paint store. If you haven't encountered one of these before, it's just a piece of cheesecloth that is covered in some sort of slightly sticky stuff. They're cheap. Wiping the surface with a tack cloth will remove all traces of sanding dust on the surface. (Did I mention that sanding at your workbench and then immediately painting thereafter is asking for dust specks all over your paint job? Sand in one room. Paint in another.) If you fold your tack cloth carefully, you will see that it provides a lot of tacky surface and can be used a folded square at a time for a long time if you keep it sealed in a zip lock bag between uses. If you don't, it will dry up in a week or two. Don't apply your boot stripe masking tape until you've tacked the area well. Dust under the tape edge may cause paint to wick under the tape. (For this same reason, never lay a roll of masking tape on its side, especially on a dusty workbench top. It will pick up dust on the edge of the roll and you'll have dust all along the line you mask with it. Store masking tape in a zip-lock plastic bag and it will stay clean and not dry out over time.)

 

Once your hull is sanded and taped, tack it again immediately before you paint it. Then paint it. Good luck if you are using a "rattle can" to spray the paint. If you are lucky, you won't get spits and spatters out of it. wiping the nozzle with a clean rag and a bit of solvent before spraying is a good idea, as is testing your spray pattern on a piece of cardboard or the like before aiming it at the model to make sure it's working okay before committing to the real job. Spray it on in light coats. Begin the spraying beyond the end of the model and let up on the nozzle beyond the other end, holding the can level and at a right angle to the surface being sprayed. Don't bend your wrist to "brush" it with the spray pattern. This will vary the distance between your nozzle and the sprayed surface and result in an uneven application of paint. Don't apply too much paint. A thick coat runs the risk of runs or "curtains." It is best to apply several very light coats, letting them dry before applying another. 

 

It may be just the lighting, but it appears that you may not have even color coverage on the hull as it is. It's difficult to cover grey plastic with a red paint. You end up with a somewhat darker color red when the red paint doesn't fully cover the grey plastic. covering any dark color like grey with a lighter color is very difficult and if the top coat is not evenly applied there will be color differences noticeable. If the top coat is is applied thickly enough to cover the dark color below it completely, it may have to be so thick that it obliterates surface detail or causes other problems when drying such as a "crackle" finish. If your red bottom paint color didn't cover the grey completely the first time around (and you didn't apply way too much red to try to accomplish that) you should consider applying a neutral opaque undercoat to ensure an even color. This paint has a high volume of pigment and is designed to cover very well without applying an excessively thick coat. Spray opaque undercoat is available anywhere the paint you are using is sold.

 

You may well be aware of all these little details, but I added them while I was at it because others with less experience may be reading this post and the whole "tutorial" may be helpful to them.

 

Good luck with it. "Goofs" just go with the territory. Don't beat yourself up over it, but maybe you might want to keep that friend out of your modeling shop in the future, though.  

Edited September 12, 2023 by Bob Cleek

[DMM]

7 minutes ago, Bob Cleek said:

With help like that, who needs friends?

 

Sprayed with what? Oil-based enamel or water-based acrylic?

 

I would not advise trying to strip the paint off of plastic.  Isopropyl alcohol will remove some types of acrylic paint, but not all. Stripping the paint with any other sort of solvent runs the risk of softening the plastic. Your best bet is to wait until the paint is thoroughly hardened. Then sand, wet or dry doesn't matter. Wet is messy. Dry is dusty. There's no free lunch there.

 

You should sand the surface down until it is completely fair. Use a foam sanding block which will avoid your developing flat spots that you'd get from a hard block... or use your fingers. The goal is not to sand the "goof" fair at the expense of the surrounding area. You want to sand the whole surface fair without simply developing a smoothed "divot" in the overall surface. This is important because it will really show up when the whole surface is repainted if it's not perfectly faired into the whole surrounding surface. It looks like you have a fairly thick smear there, so you may wish to start with somewhere around a 320 or 400 grit paper and once you get it faired with that, then go over it again with a 600 grit. You want to get the whole area "smooth as a baby's bottom." Don't forget to carefully attend to the detail sanding around the through-hull on the side of the hull there, It needs it, too. Don't sand too aggressively with the larger grit sandpaper. If you sand too aggressively with heavy grit, you will likely see sanding swirls and scratches on the painted surface that will be difficult to remove with your finer grit paper.

 

After you've sanded it smooth dust it well and wipe it down with a "tack rag" which can be bought at any paint store. If you haven't encountered one of these before, it's just a piece of cheesecloth that is covered in some sort of slightly sticky stuff. They're cheap. Wiping the surface with a tack cloth will remove all traces of sanding dust on the surface. (Did I mention that sanding at your workbench and then immediately painting thereafter is asking for dust specks all over your paint job? Sand in one room. Paint in another.) If you fold your tack cloth carefully, you will see that it provides a lot of tacky surface and can be used a folded square at a time for a long time if you keep it sealed in a zip lock bag between uses. If you don't, it will dry up in a week or two. Don't apply your boot stripe masking tape until you've tacked the area well. Dust under the tape edge may cause paint to wick under the tape. (For this same reason, never lay a roll of masking tape on its side, especially on a dusty workbench top. It will pick up dust on the edge of the roll and you'll have dust all along the line you mask with it. Store masking tape in a zip-lock plastic bag and it will stay clean and not dry out over time.)

 

Once your hull is sanded and taped, tack it again immediately before you paint it. Then paint it. Good luck if you are using a "rattle can" to spray the paint. If you are lucky, you won't get spits and spatters out of it. wiping the nozzle with a clean rag and a bit of solvent before spraying is a good idea, as is testing your spray pattern on a piece of cardboard or the like before aiming it at the model to make sure it's working okay before committing to the real job. Spray it on in light coats. Begin the spraying beyond the end of the model and let up on the nozzle beyond the other end, holding the can level and at a right angle to the surface being sprayed. Don't bend your wrist to "brush" it with the spray pattern. This will vary the distance between your nozzle and the sprayed surface and result in an uneven application of paint.

 

I figure you may well be aware of all these little details, but I added them while I was at it because others with less experience may be reading this post.

 

Good luck with it. "Goofs" just go with the territory. Don't feel too bad. Maybe you might want to keep that friend out of your modeling shop in the future, though.  

Thank you for the nice explanation, very helpful to newbie like me  

[Jack-in-the-Blue]

I was a plastic modeller of fifty years experience (and an airbrush user) who only recently became a novice in wood kits. I’ve stripped acrylic paint dozens of times so I’m speaking from experience here. I’ve also tried and failed with abrasives. 
 

Stripping the paint = thirty minutes and no damage to plastic. IPA is not toxic or even unpleasant. It’s also cheap. A few sheets of alcohol wetted kitchen roll will wipe away even thick paint like yours. You may need a toothbrush in heavily recessed details such as around the prop shafts and rudder. 
 

Abrasives will clog straight away, take ages and destroy the plastic surface details. You will need lots of paper. You won’t be able to sand around the details. 

 

If you do decide on sanding use wet and dry paper with lots of water, under a shower perhaps. And let the paint dry and cure really well - several days!
 

I suggest trying both methods on a small inconspicuous areas before committing yourself. 

 

Good luck. Let us know how you get on. 🙂

Edited September 12, 2023 by Jack-in-the-Blue

[Bob Cleek]

2 hours ago, Jack-in-the-Blue said:

I was a plastic modeller of fifty years experience (and an airbrush user) who only recently became a novice in wood kits. I’ve stripped acrylic paint dozens of times so I’m speaking from experience here. I’ve also tried and failed with abrasives. 

 

He hasn't told us whether he is painting with acrylic paint or oil-based enamel. Acrylic paints don't sand worth a damn. 
 

Stripping the paint = thirty minutes and no damage to plastic. IPA is not toxic or even unpleasant. It’s also cheap. A few sheets of alcohol wetted kitchen roll will wipe away even thick paint like yours. You may need a toothbrush in heavily recessed details such as around the prop shafts and rudder.

 

I agree with you completely, if he is using acrylic paint. Isopropyl alcohol will remove acrylics but may do little to remove enamels. 
 

Abrasives will clog straight away, take ages and destroy the plastic surface details. You will need lots of paper. You won’t be able to sand around the details. 

Yep, no question about that. This is one reason why I've avoided acrylics over the years. They cure to a relatively soft and flexible surface. Rubber doesn't sand well at all. 

2 hours ago, Jack-in-the-Blue said:

 

If you do decide on sanding use wet and dry paper with lots of water, under a shower perhaps. And let the paint dry and cure really well - several days!

The drier the better. Acrylic paint continues to harden slowly after an initial curing to a tack-free surface. The harder it is, the more easily it will sand. Again, this is one of the disadvantages of acrylic coatings.

2 hours ago, Jack-in-the-Blue said:

I suggest trying both methods on a small inconspicuous areas before committing yourself. 

Excellent advice always. But before anything else, I'd urge him to determine what type of paint he is using. Any chemical removal of the paint he has on there now has to be compatible with not only the paint he is removing, but also the plastic it's painted onto.

2 hours ago, Jack-in-the-Blue said:

 

Good luck. Let us know how you get on. 🙂

 

Edited September 12, 2023 by Bob Cleek

[Canute]

Tamiya makes good primers in rattle cans/spray bombs.  I believe they're lacquer based. Tamiya have figured out how to make good spray nozzles. I'd use the Fine gray primer under both yellow and red. As a heads up, they make 2 different grays. A gray and a fine gray. The fine will show blemishes, the plain gray is more of a filling primer. Choose accordingly.