Acrylic passenger car sides - paint before assembly or after?

[nickelplate759]

I'm building some passenger cars from American Limited core kits and laser-cut acrylic car sides.  In the past I've always assembled the car with most of the masking still on the sides, then carefully removing the mask from the outside, painting everything after the car is assembled, and completing the lettering before finally removing the window masks and interior masking.     I'm thinking of trying a new approach - paint the sides, roof and ends first, then assemble.   It should make masking for multi-color paint jobs easier.   

Has anyone here tried it that way, and if so do you have any words of wisdom on the subject?

[thomasjmdavis]

George,

I made one attempt to do it that way (my first car done with those 'laserkit' sides, IIRC, 25-ish years ago), and would list mine as a failure.  The key issue for me was that I had some adhesive get onto the painted surface, and a couple of joints that were not quite perfect.  I ended up having to do some sanding and filling, then repainted. In the end, it was OK, but I went back to doing full assembly, and then the additional masking to mask off the roof, etc. for future cars.

On the other hand, there was at least one manufacturer who did what appear to be injection molded sides for SP cars, that marketed completely painted and lettered sides for SP daylight cars (I have a few I've never built).  So...someone must have had success doing decorated sides over core kits.

The one recommendation would be to check the fit of the sides to the roof of the core kit.  My experience with the core kits is that on some roofs, the 'rabbet' on the edge to accept the side is deeper on one side than the other- this was the main problem with the attempt I made that resulted in sanding on the joint on one side and filling, then sanding  on the other.

[Sokramiketes]

I also have better luck assembling the car body in full.  The solvent glue needed for acrylic to styrene is more aggressive, so I get that joining out of the way and then proceed to painting.

Couple other oopsies from early builds:

1) Leave most of the masking on the back side of the acrylic car side.  You'll have to trim some off to glue the sides to the core kit, but leave the rest so that you don't get overspray on the inside of the car side (which is also the inside of the clear windows later... oops.
2) Always remember that the first color you spray on the car side is going to be the interior color.  So pick your primer coat wisely...
3) The window masking has to stay in place until decaling AND CLEAR COAT is applied, at least if you're not doing a full gloss top coat.  Otherwise the windows get foggy and dirty for your flat or satin finish application. 

[nickelplate759]

Thank you both.   I've built several, and made at least two of the mistakes that @Sokramiketes mentions (NP dark-green interior anyone?).

I'll continue with the assemble-first and then paint method.

ESMC also offered pre-painted (styrene) sides at one time, and I've successfully built several of those, but as you point out styrene is easier to attach to the core kit.

[robert3985]

When I paint mine, I always paint them first, then assemble.  I don't have problems with the glue getting everywhere for some reason, and painting the parts before assembly makes putting them together much easier IMO.

I got about a dozen kits I need to get finished up...thanks for the reminder!

Cheerio!
Bob Gilmore

[nickelplate759]

It turns out that some of my acrylic sides are soooo ooold that the glue on the original masking has deteriorated.  On those, I can't remove the masking neatly and there's lots of glue residue (others are just fine).   So I think I need to take all the masking off - including the windows - and remask.

Fortunately, there's a nice groove around the windows, so I think I can:
1.  Clean the sides very well to get off all the old masking and glue residue.
2.  Apply fresh masking over the window areas.
3.  Trim the masking with a sharp blade, following the grooves around the windows.
4.  Paint and letter as per normal, removing the window masks when I'm done.

Looking for suggestions on what to use for re-masking the windows.  It needs to cut cleanly and easily on the car so the knife doesn't slip.
Current thoughts are
A.  Tamiya masking tape
B.  Scotch clear "Magic" tape.

Thoughts and/or experience to share?

[nkalanaga]

Clear tape (mine is 3M from at least 12 years ago) works fine as masking tape, but getting it off in one piece can be a pain.  It comes off neatly enough, no residue, but it likes to tear, so comes off in pieces. 

For items with distinct edges, especially grooves, I've had good luck with ordinary hardware store masking tape.  In my case, literally, "Duck Tape" (the brand name).

If you have the Tamiya, I'd go with that.  You know how it will work.

[peteski]

It turns out that some of my acrylic sides are soooo ooold that the glue on the original masking has deteriorated.  On those, I can't remove the masking neatly and there's lots of glue residue (others are just fine).   So I think I need to take all the masking off - including the windows - and remask.

Yes, old adhesive on the protective paper can be problematic.  There used to be a liquid available from plastic distributors to moisten the paper and soften the adhesive.  But I just used Naphtha (VM&P Naohtha or Ronsonol lighter fluid).  Just let it soak for some time. You might have to apply it couple of times (because it keeps evaporating).  Just use a pipette or paint brush to apply it.  If you use Tru-Color paints they should not be affected is some Naphtha gets on their surface, so you should be able to leave the masking paper on the windows until after painting.

I also did a quick search https://duckduckgo.com/?q=removing+old+backing+paper+from+acrylic&t=h_&ia=web and there are plenty of hints on how to remove the paper.  Heptane is one possibility (it is similar to Naphtha), and  using an hair dryer is another possibility.