Sammyboy

My son and I have been working, forever it seems, on a Holdsworth for him. Using wire brushes on a drill, we've stripped 90% of the paint, but getting it out of the corners and joints is proving really hard. I read here somewhere that there's no need to go back to bare metal everywhere, but what really DOES need to be done before we can start spraying? How good does it need to be?

Pompiere

It doesn't need to be bare metal, but the surface needs to be scuffed up so the paint has something to hold on to. Use a primer coat to help find any imperfections, then sand them out and prime again. The single color of the primer makes rough spots really stand out. You may have do this a few times, but preparation is the key to a good finish.

iab

I also agree stripping to bare metal isn't necessary. You just have to watch the transition from bare metal to paint. If it isn't feathered, you will see the stair-step in the final paint. Hand sanding at those transitions should be sufficient.

The frame should be clean before priming, absolutely no oils from your hands or the paint can chip in those areas. Use a sandable primer and I sand to 600 grit but 320 is probably fine. Clean the primer of oils before you put down color.

roccobike

Sammy, I just completed a rattle can paint job. I always wash the surface with HOT water before painting to be sure I've removed any oils from my hands or inadvertant grease from the surface. This rinse is also effective in removing any stray particles from sanding.
BTW, do you have one of the spray can holders that attach to the top of the can and allow the painter to apply the paint by use of a trigger in holders handle? Sorry, I'm at work and can't post a link here, but these devices allow you to spray the paint as if it was from a spray gun providing much better control of the flow of paint and direction.

piwonka

it needs to be smooth, any texture you can see will show through the paint. i think it's easiest to just strip all the way to bare metal and start fresh. i use nasty chemicals to do that...

AEO

a tack cloth does a very nice job of cleaning the surface of any dirt and grease.

stringbreaker

Have it sandblasted. A powdercoat place should do it for a reasonable fee.

Noah Scape

Years ago, I took a frame to a machine shop and had it bead blasted for $10. I really liked the results. Has anyone done this lately? And, what is the going rate?

pumpy schwartz

i paid around 20 bucks just recently

stringbreaker

There ya go then you can sand it smooth or maybe have it powdercoated instead of a rattlecan job. Powdercoat is really reasonable and its tough and way better than rattlecan spray job IMHO of course

Dr.Deltron

Dirt, dust, particles..yes.

Grease/oil...not so much!

For THAT there's PPG's DX330 Wax & Grease Remover.
Or warm soapy water with a good rinse.

redneckwes

You can't beat sandblasting for a good start, should say media blasting as sand is mostly obsolete. Then sandpaper, and a wipe down with mineral spirits on a lint free cloth.

dbakl

I've used Windex between sanding and coats to remove fingerprints etc with good results.

WNG

If powdercoating is available, check the pricing, it can be competitive with even a rattle can job. Given that you must have several cans of base color, several cans of primer, and several cans of clearcoat.
It all adds up. There's a guy in the South Shore of MA who will do a frame for $50.
And the powdercoat will be way more durable.

Fred Smedley

Wax and grease remover at auto paint stores is pretty cheap.

graywolf

My informed opinion is:

First your remove everything that can be removed.

Then you use a good oil and wax remover.

Next you clean any rusty spots down to bare metal.

Leave no rust at all.

Then you prime the bare spots with a good anti-corrosion primer.

Use a spot filler to fill any low areas including where you removed the rust.

Sand things level.

Use a primer filler to remove small imperfections, you will need to do several coats, sanding it almost off between coats.

When the surface is a perfect as you can make it, Spray with primer sealer.

Spray finish coat (If your are doing a fancy paint job there may be several steps to this).

Let the paint dry thoroughly before replacing components, this could take up to a month or six weeks if you do not have some forced drying method available.

BTW, if the frame has been touched between steps go over it with the oil and wax remover before continuing.

This is basically the technique I have used on hotrod paint jobs in the past, you know the 24 coats of hand rubbed black lacquer thing. It probably will not be up to Dr Delton's standards, but it will be better than most body shops do. In most cases the manufacturer had far better anti-corrosion and priming techniques than an individual can come up with (especially from 1970 on), so if you do not need to remove down to the metal I recommend not doing it.

All of the above is to be ignored if you are using some high tech finishing system, then follow the manufactures directions exactly so you can make them reimburse you if it does not work as advertised.

Dr.Deltron

Au contrare!

What you stated so succinctly is pretty much what I do.

Except...between the Primer/Sealer and the final coat (clear), I add some color(s).

And the other note, I just spray lots of primer and sand it all off at once, rather than sanding it between coats. If the area being filled is deep, I sometimes mask close to the effected area to take the overspray.
Sands more quickly that way.

Charles Wahl

I'm not whining, but he just quoted me $95, and I wasn't asking for anything special. The days of the $50 powdercoat job may have gone the way of the subprime mortgage.

OLDYELLR

I've been using rattle-can paint jobs for decades on everything from scale models to motorcycle parts to furniture. The biggest problem I've always encountered is wrinkling of the primer when the colour coat is applied or wrinkling of the colour when the clear coat is applied. I've experimented with different and similar brands and types and there seems to be no clear solution. What's the secret? Is it timing?

Dr.Deltron

That's the likely culprit. Some paints say recoat within 4 hours OR AFTER 72 hours.
This is important!
If you spray one coat one day, and another coat the next day, you could have problems. And wrinkling is just one of them.

And if you waited the 72 hours, you should lightly scuff & tack before the next coat.

Another, less likely problem, could be a rapid change in ambient temperature, especially downward.
If you were to spray a coat a 5 p.m. on a Winter day at 55 degrees, and then the sun goes down and the temp drops 10 or 15 degrees, you can have real troubles.

Rattle cans work best at 65-75 degrees F.
Low humidity is good too.

dbakl

Yeah, timing is everything! I've done a lot of stuff with spray cans, its not too hard to spray a good job, but how it holds up is something different; spray can paint tends to be a little soft and brittle. Keep to the same brand of primer and color. They state something like recoat in 20 minutes or 4 days! I only spray when its hot, dry and still. Throw the spray can in a sink of warm water before you start, makes it spray smoother. Final coats I only do from a new can so it has plenty of paint and pressure, ie, no spatters. Once I finish the color coats I usually put the piece on top of my shed in the summer here in Oakland to bake for a few weeks before starting the clears.

I've been experimenting with spraying gloss clear Varathane over enamels, seems to work well but takes a long time and a lot of coats to build up any density. Lacquers spray easier and smoother and rub out better but don't stand up to solvents. Haven't tried the Varathane on lacquer yet but I might on a motorcycle fender I have going.

graywolf

I think that is part of the "there may be several steps to this". Besides, I am an old coot from before clear coat finishes, although I seem to remember something called Candy Apple Pearl, or something like that.

Yes, I can understand why you would do a heavy primer/filler coat, you have to make a living at it and can not be waiting for each time for several coats to dry for sanding. I think if time is not a problem the multi-coat process is a bit easier to do properly for us amateurs. Every time I have tried to do the heavy coat thing I have had big problems. That may be because it is hard to get an heavy even coat with spray cans.

Wino Ryder

Was meaning to ask you doctor, or anyone else that my know, if a sufficiant paint hardness could be had from letting a frame sit out in the sun and 'cure' for a determined amount of time. I mean like after you spray it with rattle cans. I was thinking about repainting my wife's "girlie bike', which I posted a while back
https://www.bikeforums.net/showthread...748&highlight=

The main thing I'm concerned about is getting the paint to harden good, where its not so easy to scratch.

Any ideas?

Dr.Deltron

The test for hardness is your fingernail.

I usually test somewher inconspicuous, like the face of the drop-out. The axle/QR will be making impressions there anyway.

If you can make an impression, it's not "cured" yet.

Even the sunny day treatment may take a couple of weeks. Depends on how many coats there are too.

In the past, I have also used a "hot box" to help speed hardening.
Simply split some 2x4's, frame a 4'x5'x1' box and cover with 1/4" plywood. Hinge one of the large sides. Install 2-3 outdoor flood lights. Put a cross piece in the ceiling of the box. Install a bike hook and hang the frame from the BB shell.
Ideally, the temp should be about 80*-90* F
Bake until done.

nlerner

And then move into it once you've amassed too many bikes for good relations with the spouse.

Neal