Hello guys

I'm restoring an old bike and I'm thinking to spray the spot where the paint chipped off just to protect it from rust. Do you think it's a good idea?

I think a lot depends on what bike you're talking about. If it's a collector then I'd say no. But if it's just a towner then by all means paint it for protection.

Unless the spot is huge there's no need to spray it. A small dab of model enamel or even a dot of varnish or almost anything that dries to a protective film is all you need. Spray is so messy for a small touch up.

The most important thing to do is get out the rust that is there, carefully scraping and sanding it to clean metal. Then treat the clean metal with a rust inhibitor and some sort of coating to prevent further rust. Leave as much finish intact as you can. Then you have to decide whether or not to try to match the original finish to cover the defect. That's where artistry and a good paint match comes into play. I've had good results using professionally matched paint from a local autobody shop and an airbrush (with careful masking and building up the painted area to match the surrounding paint). It is tedious and even my best work is detectable if you look really close, but it looks pretty darned good from a foot or more away.

Something to watch for when inspecting a frame are little paint blisters. These always indicate subsurface rust, so I like to pry these open and clean out the rust and treat the metal underneath. These blisters are treacherous. If you ignore them, they will spread, since the rust procedes under cover of paint. Sometimes (in the worst case scenario) they represent rust that began inside the frame tube and are emerging to the surface.

I just went through this. I have a few steel bikes, none worth much, but i ride them. 2 are hybrids, rest are road bikes. I used sandpaper used for metal that i got at home depot to sand small rust spots down to bare metal. Then i painted those areas with Rustoleum auto primer (came in spray can.) One first bike i spray painted using masking tape. Next bike i sprayed some primer in a cup and used a small brush. Then I used Rustoleum spray paint to cover up the primer (sprayed a little in a cup and used little brush to brush on.) I have made no effort to match color, the 2 bikes i am working on so far are a dark green and a medium blue and rather than buy all differnet colors of paint to try to color match (never work well) I decided i am just going to use black paint and the heck with it. I am not "restoring" the bikes, i am just painting over some metal so the bike wont rust so i can continue to ride them.
I havent done this yet to the better of my bikes, i may decide to try to paint match color, or i may take some other approach ie maybe use clear nail polish to protect the "value" of the original finish or maybe have the entire frame powder coated i havent decided. But for my really low end utility bikes i am happy with what i have done with the piecemeal approach with Rustoleum auto primer and spray can paint.

Been known to use spraypaint on my old trek; however as noted by Gary surface prep is paramount if you want to do it right.
Fortunatly for me the trek is gloss black so matching is not an issue.

Thanks a lot for your responses guys! I'll take them uder consideration.

The bike is an old mercier and it's quite beautiful.

I purchased and use a wire brush and I must say that's such a great tool for rust scraping or generally steel polishing. Way better than sand paper if you ask me.

Also I think the paint work always will be visible if you try to cover just some spots and not paint everything from scratch because time wore away the old paint and made it very difficult to duplicate.

If you're going to paint the whole frame then that's a whole other story of course. The problem with that is that you ruin all the nice highlights, if any, and the decals.

Need to reconsider anything abrasive: wire brush, steel wool, or sand paper. All remove everything, rust, chrome, paint, or whatever. They cannot distinguish between what you want to get rid of, and what you want to keep. Lots of threads already on rust removal, and touching up paint.

Depending on the size of the nick or chip sometimes is not a good idea to spray the paint, specially if is something really small but deep that u can see the metal shining big time. In those cases u have to sand a little bit then apply some primer using a small brush and then the paint using the brush. Or u can go straight using the brush. Wait until is dry, then sand to get the surface even and polish.

Brush- in- the- cap touchup paint is simpler.

I just wanted to add that it is possible to touch up nicks, scrapes, and rust on a bike frame and have it come out looking really good. Art and antique restorers do something similar all the time. The problem is that this requires two things: 1) the ability to exactly duplicate the paint color and texture; and, 2) the skill to apply the paint so that it matches the rest of the frame. Most folks just go to the auto parts store to by a can of Dupli-Color that comes close and the brush or spray it on. The result is usually awful (though it will usually stop rust progression).

People have brought this up in other threads and it works pretty well for most colors. Testor's Model Enamels come in numerous shades and hues and usually you can get a pretty close match.

- clean and degrease all around the area you will be working. PrepSol or similar paint prep cleaner/solvent will remove any wax or silicone from previous polishings which can cause "fish eyes" in new paint.
- remove any loose paint
- using a rubber auto body sanding pad (3M makes a 3 pack for about $2) and some 800 grit or finer sandpaper carefully feather the edges of the damage and get the exposed metal clean
- wipe with PrepSol or similar cleaner
- using a brush, cover exposed metal with a coat of rust inhibiting primer and allow to dry for 24 hours (get yourself a couple of decent soft artists brushes, don't use the 39-cent plastic brushes sold in hardware and hobby stores)
- sand the surface lightly with 1,000 grit sandpaper on the rubber backing pad just until smooth and satiny
- wipe the surface with a clean piece of cotton t-shirt or microfiber cloth to get rid of any dust
- paint a coat of your matching enamel over the primer and a couple of mm onto the surrounding paint. Don't overwork the paint by repeatedly brushing over it. Try to get it on in a thin consistent layer in just a few strokes. Then feather the edge to leave as small a ridge as possible. If you have an air brush, you can use that at this stage and give it a few coats.
- This is important, allow the paint to dry 24 hours before using the bike but do not do anything to smooth or blend it for at least a week. Two weeks is better if the weather is cool and moist. You can ride the bike during this time but let the paint completely cure, which is different than just drying to the touch.
- After plenty of curing time, take 1,000 or 1,200 grit sandpaper and the rubber backing pad, slowly and gently smooth any minor imprefections and feather the edge into the surrounding paint. Don't overdo it, the paint layer is very thin and you need to leave enough for the polishing step that is next.
- Use an automotive polish which is a wax/silicone with a micro fine abrasive (not rubbing compound which is more aggressive) and a microfiber cloth or piece of cotton t-shirt and gently buff the area over and around the repair finishing by giving the entire frame tube a light buff, then wipe it down with a clean cloth and give the entire frame a wax with a regular wax/silicone that has no abrasive quality.

If you're like me, you'll still see the repair and feel like you could do better, but the vast majority of other people will never spot it even when you point it out. By the time the finish ages a bit and goes through a few washings, the repair should be undetectable when standing beside the bike. In any case, even if the paint is not an absolutely perfect match, the frame will be protected and it will look a heck of a lot better than a big scratch.

Thanks a lot guys, I think I got the right information to start!

Wow, Myosmith incredible post!

Just two last questions.

How do you prepare the edges of the area (the rusty one that's just cleaned from the rust-paint) where you want to paint? I mean, having the almost scraped off old paint underneath around the edges of the clean metal patch, can I apply primer on top of it?

And
Is there a specific type of paint that works best on metal and outdoor heavy use (rain, air etc)?