Paint coming off after sanding with high grit

[hkisthebest]

This is the first time I'm trying to build a model car, and I want the body to be as shiny as possible. So here's the step I planned on doing. Prime - sand with 600, 800 grit - 4 coats of paint - wet sand with 1500, 2000, 3000 grit - layers of clear coat - sand and polish. 

However, some of the color paint started to come off when I was sanding the paint with both 1500 and 3000 grit. Am I doing anything wrong here? 

FYI, the paint I'm using is Tamiya lacquer spray paint.

Thanks in advance. 

[gman]

Is the paint coming off of high spots and edges/seams on the body, or is it coming off in sheets where you are sanding?

If it is coming off on high spots, edges and seams, you could be sanding through the colour coats. If it is coming off in sheets, there may not be enough bond between the primer and the colour coat.

Ideally you would have good mechanical/chemical adhesion between primer and plastic, and between primer and colour coats. You'd lightly smooth any dust or fuzz out of the colour coats and then lay on enough clear coats to provide a layer you can then wet sand and polish. With that said, you have to go light with the wet sanding and polishing so as not to cut through clear coats into colour coats, and colour coats into primer.

Are you using primer, colour and clear that is all Tamyia lacquer?

[jaymcminn]

If I'm reading correctly, you're sanding out the color coat now before applying clear? If so, you will absolutely be seeing color come off. Sanding color coats by definition means removing paint and it's perfectly normal. If you remove too much you'll start seeing the primer come through. "Too much" is largely dependent on how many coats and how thickly they were applied in the first place. Color sanding is good practice for solid colors, not so much for metallic or pearl colors. Many builders don't color sand at all, preferring to do all the sanding in the clear coat stage.

If you're getting color coming off while sanding clear coats, STOP. You've burned through the clear somewhere and you're probably about to hit primer. Try to figure out where you've gone through the clear. If it's something like trim that's going to be painted or foiled anyway don't worry too much about it. If it's an edge or a shut line, you might be alright if you go easy around the area. 1:1 detailers will sometimes tape these areas off to avoid burn through.

[bobss396]

Tamiya spray goes on very thin and is relatively softer that most model paints. I always started out color-sanding at 3200 grit. But go easy, always use the pads/cloths dipped in water (with a little dish soap in it) so the pads/cloths don't clog up. 

How many coats of paint did you give it? I like at least 2 or more.

[Big John]

Hopefully you are wet sanding to keep the paint from building up on your paper. Once paint starts to stick to the paper change paper or you will just mar the paint surface.  Wash down the model to remove any dust that will act as a resist for the following coats and keep them from sticking. Repeat.

[hkisthebest]

On 8/18/2024 at 11:01 AM, gman said:

Is the paint coming off of high spots and edges/seams on the body, or is it coming off in sheets where you are sanding?

If it is coming off on high spots, edges and seams, you could be sanding through the colour coats. If it is coming off in sheets, there may not be enough bond between the primer and the colour coat.

Ideally you would have good mechanical/chemical adhesion between primer and plastic, and between primer and colour coats. You'd lightly smooth any dust or fuzz out of the colour coats and then lay on enough clear coats to provide a layer you can then wet sand and polish. With that said, you have to go light with the wet sanding and polishing so as not to cut through clear coats into colour coats, and colour coats into primer.

Are you using primer, colour and clear that is all Tamyia lacquer?

I am using 2 layers of primer, and 3 layers of coat with Tamiya lacquer. I think my color coat should be thicker, so I don't sand through it. 

[hkisthebest]

20 hours ago, jaymcminn said:

If I'm reading correctly, you're sanding out the color coat now before applying clear? If so, you will absolutely be seeing color come off. Sanding color coats by definition means removing paint and it's perfectly normal. If you remove too much you'll start seeing the primer come through. "Too much" is largely dependent on how many coats and how thickly they were applied in the first place. Color sanding is good practice for solid colors, not so much for metallic or pearl colors. Many builders don't color sand at all, preferring to do all the sanding in the clear coat stage.

If you're getting color coming off while sanding clear coats, STOP. You've burned through the clear somewhere and you're probably about to hit primer. Try to figure out where you've gone through the clear. If it's something like trim that's going to be painted or foiled anyway don't worry too much about it. If it's an edge or a shut line, you might be alright if you go easy around the area. 1:1 detailers will sometimes tape these areas off to avoid burn through.

Yes, I am sanding the color paint, not clear coat. I think I need some more layers of color coat before wet sanding it, and be careful for the edges. Normally when sanding color coats, what grit should I start with? And is it normal for it to not be shiny after sanding with 15000 grit? 

[hkisthebest]

9 hours ago, bobss396 said:

Tamiya spray goes on very thin and is relatively softer that most model paints. I always started out color-sanding at 3200 grit. But go easy, always use the pads/cloths dipped in water (with a little dish soap in it) so the pads/cloths don't clog up. 

How many coats of paint did you give it? I like at least 2 or more.

You mean start wet sanding with 3200 grit on color coat? 

[hkisthebest]

3 hours ago, Big John said:

Hopefully you are wet sanding to keep the paint from building up on your paper. Once paint starts to stick to the paper change paper or you will just mar the paint surface.  Wash down the model to remove any dust that will act as a resist for the following coats and keep them from sticking. Repeat.

Ahhh, good to know! The paint did stick onto the sand paper. Thanks!!

[jaymcminn]

1500 grit is fairly harsh to start with. I actually prefer not to clear coat solid Tamiya lacquers and will sand and polish the color coats. I start with 2000 grit automotive sandpaper, move to 2500 and finish with 3000 grit before moving to automotive rubbing compound and polish. I follow the traditional 3 mist coats, 3 wet coats rule and usually don't have a lot of orange peel in the finish to start. Below is my 1/12 Tamiya Porsche 934 painted in Tamiya Camel Yellow without clear coat...

And my 1/12 Tamiya Fairlady 240ZG in Tamiya Racing Green.

[bobss396]

15 hours ago, hkisthebest said:

You mean start wet sanding with 3200 grit on color coat? 

Yes, 3200 grit is a good place to start. If you start with too coarse a grit, it cuts the paint quicker. Too fine a grit, the cloth or paper clogs up fast. I work by the sink and have a container of water with a few drops of soap in it. 

With each grit, you want the model to be "uniformly dull". You are knocking the peaks off the rougher finish, it will get shinier as you progress. Stay away from edges, crown lines, etc. Experience will tell you when you are ready for the clear coat. The TS-13 is one I like with the TS line of paints. Anything I color sand, I will quit at #4000 or #6000 grit and go to clear.

Edit: What are you sanding with? I like the Detail Master DM9000 set. I also have some other of their cloths, from #800 to #2400. The abrasive pads, they are thick and I find it easier to sand through edges.

Edited August 20, 2024 by bobss396

[hkisthebest]

20 minutes ago, bobss396 said:

Yes, 3200 grit is a good place to start. If you start with too coarse a grit, it cuts the paint quicker. Too fine a grit, the cloth or paper clogs up fast. I work by the sink and have a container of water with a few drops of soap in it. 

With each grit, you want the model to be "uniformly dull". You are knocking the peaks off the rougher finish, it will get shinier as you progress. Stay away from edges, crown lines, etc. Experience will tell you when you are ready for the clear coat. The TS-13 is one I like with the TS line of paints. Anything I color sand, I will quit at #4000 or #6000 grit and go to clear.

Edit: What are you sanding with? I like the Detail Master DM9000 set. I also have some other of their cloths, from #800 to #2400. The abrasive pads, they are thick and I find it easier to sand through edges.

When you say "shinier", shinny, but not like a gloss finish, right? Cause I've sanded a spoon to see what is achievable through sanding, and it did not make it glossy. The gloss comes after the clear coat, correct? 
 

I'm using regular sanding paper only

[peteski]

Sanding will always result is smooth but hazy surface. To get the paint glossy after sanding (and not using clear coat), you have to polish/wax it.  Some people use automotive polish/wax. others use stuff made for models. Yet others use Novus line of polishes.

[Matt Bacon]

On 8/18/2024 at 1:55 AM, hkisthebest said:

This is the first time I'm trying to build a model car, and I want the body to be as shiny as possible. So here's the step I planned on doing. Prime - sand with 600, 800 grit - 4 coats of paint - wet sand with 1500, 2000, 3000 grit - layers of clear coat - sand and polish.

I'm going to say that's WAY too much sanding, especially for Tamiya lacquer paint. First, make sure you've done all your clean up on the bare plastic shell -- remove al the mould separation lines, sprue attachments, fill any sink marks etc, and sand that smooth with 600, 800 and 1000 grit. You don't need to sand the whole thing... if the plastic is shiny and unblemished leave it alone. Then spray it with Tamiya Fine Surface primer, which should come up very smooth. If not, you can hit it with soft 1500 or 2000 grit sanding sponges, but again, only where it needs it. Then apply your Tamiya lacquer. You can use whatever technique works for you -- mist and wet coats, or the method I use, which is just building up multiple "splatter coats" lightly until the coverage is even. If it's metallic, apply some thin coats of TS-13 Clear. Let it cure thoroughly for a week. Then you just polish it. You shouldn't need to do any more sanding. Novus Plastic Polish Number 3 if you need it, but you probably won't, followed by Number 2 (the fine scratch remover) will bring up a glossy and realistic shine. Just polish in small circles and you'll see the colour appearing on your polish cloth and it'll start to squeak, at which point it's done. Meguiars Ultimate Compound for real cars works just as well, as I'm sure will Tamiya Polishing compounds.

best,

M.

Edited August 20, 2024 by Matt Bacon

[bobss396]

23 hours ago, hkisthebest said:

When you say "shinier", shinny, but not like a gloss finish, right? Cause I've sanded a spoon to see what is achievable through sanding, and it did not make it glossy. The gloss comes after the clear coat, correct? 
 

I'm using regular sanding paper only

Shiny to a degree. You need to knock the "peaks" down. A very rough finish reflects light poorly, it reflects more as the peaks are dismissed.

I don't recommend using sandpaper. I will use it sparingly and in small pieces cut out of a large sheet. You have to be aware of anything that the paper touches.

The DM cloths work pretty well. I cut mine into 4 equal size pieces and mark the grit on the back with a sharpie.

[Dave G.]

Much depends on the abrasive itself. In the model world it seems hard to find a standard. For instance, I use a version of micro pads. But to say 3000 is something standard seems optimistic at best. 3000 in my set seems more like 800 or 1000 in 1/1 sand paper. I'd never scuff Tamiya lacquer with it. Starting around 5500 or 6000 would be more realistic. I don't do much sanding of lacquer color coat if I intend to clear coat though. Just knock off any little dust nibs. Then put down about 5 coats of clear. Plus scuffing metallic before cleat coating can be something of a diminished return. However, if Tamiya lacquer goes on real nice, it will be very glossy if it's a gloss paint, I see no need to clear coat it on the classic cars I tend to build. Same for enamels, I've never seen the need to clear coat enamel finishes if put on right.

Paints in lacquer, like MCW or Scale Finishes is another matter. These are automotive lacquer, much hotter than Tamiya and much harder surface. They also don't dry super glossy to begin with. Most folks just plan on clear coating that stuff. It's often used as a color coat/clear coat system, perhaps rightfully so.

[bill-e-boy]

I have found that the Tamiya lacquer clear eats into the colour coats and you can get colour on your sanding pads when final sanding proir to polish. Also found that the Tamiya paint stays soft for a long time - both lacquer and acrylic. If colour sanded to soon you always get sanding scratches when starting with too coarse a grit. Even 2000 is too coarse - better to start with 3600 then move up. The finish will come up but you have to let the paint harden. 

[hkisthebest]

4 hours ago, bill-e-boy said:

I have found that the Tamiya lacquer clear eats into the colour coats and you can get colour on your sanding pads when final sanding proir to polish. Also found that the Tamiya paint stays soft for a long time - both lacquer and acrylic. If colour sanded to soon you always get sanding scratches when starting with too coarse a grit. Even 2000 is too coarse - better to start with 3600 then move up. The finish will come up but you have to let the paint harden. 

Yes, I have learnt that the hard way. I waited two days for the Tamiya lacquer paint to dry before sanding it, and it still left a bit of my finger print on it. I guess I'll just wait for a week for both the color coat and clear coat. 

[bill-e-boy]

On 8/24/2024 at 12:56 PM, hkisthebest said:

I guess I'll just wait for a week for both the color coat and clear coat.

More like a month grrrh!!!

 

[bobss396]

Having a dehydrator has been a game changer for me. I'm on my 2nd one, my modified Magic Chef took a dump on me a while back. I can color-sand in a few hours, between coats. I paint mostly rattle can lacquers and Tamiya TS sprays.