Yet Another Cycling Forum

General Category => The Knowledge => Topic started by: andyoxon on 13 February, 2020, 12:03:16 pm

Title: Paint repair - smaller frame areas...
Post by: andyoxon on 13 February, 2020, 12:03:16 pm
I seem to have an area of ~50p coin on the BB shell, which has lost it's paint, and now bare metal (531ST); just seems to have flaked off.  What is the best procedure and paint product for reapplying / repairing?  I have used a small tin of similar colour (metallic darkish grey/bronze) Humbrol metalcote for small touch-up jobs, but given the BB area gets all the general road crud frequently applied - probably need something robust.

Thoughts?
Title: Re: Paint repair - smaller frame areas...
Post by: spesh on 13 February, 2020, 12:13:02 pm
I'd say treat it like a superficial rust patch on a car - remove all loose paint and rust, apply rust treatment, then prime it, colour coat, and finish off with several coats of clear lacquer.
Title: Re: Paint repair - smaller frame areas...
Post by: andyoxon on 13 February, 2020, 12:23:20 pm
Quote from: spesh on 13 February, 2020, 12:13:02 pm
I'd say treat it like a superficial rust patch on a car - remove all loose paint and rust, apply rust treatment, then prime it, colour coat, and finish off with several coats of clear lacquer.

Ok, thanks.  Think I have most of the w&d sandpaper, spray kit, from when I once did a whole wing of an old car.   Reckon I could use a hair dryer as a paint quick drying/hardening aid?  Or, black smooth hammerite at a 'temporary' quick fix?   ;)
Title: Re: Paint repair - smaller frame areas...
Post by: Canardly on 13 February, 2020, 12:29:56 pm
Hammerite is not what it once was. Takes forever to dry out remaining finger nail soft in the interim.
Title: Re: Paint repair - smaller frame areas...
Post by: mrcharly-YHT on 13 February, 2020, 12:39:30 pm
If you are applying rust treatment (vactan or similar), don't remove all rust. Just wire-brush off the loose rust.
Title: Re: Paint repair - smaller frame areas...
Post by: andyoxon on 13 February, 2020, 02:04:16 pm
Quote from: mrcharly-YHT on 13 February, 2020, 12:39:30 pm
If you are applying rust treatment (vactan or similar), don't remove all rust. Just wire-brush off the loose rust.

Think I have a pot of Kurust somewhere... Tho fortunately the exposed metal looks pretty clean atm.
Title: Re: Paint repair - smaller frame areas...
Post by: orienteer on 13 February, 2020, 06:11:03 pm
I sandpaper any rust off then use primer before applying a top coat. Can usually find a car touch up paint in Halfords that matches, brush or spray can.
Title: Re: Paint repair - smaller frame areas...
Post by: andyoxon on 14 February, 2020, 07:20:23 am
Somewhat worse, after an initial cleanup...  Fortunately pretty much out of sight underneath BB/DT.  Probably have to guess-match the colour, thought it doesn't need to be that close.

(https://live.staticflickr.com/65535/49532250606_878526491b.jpg) (https://flic.kr/p/2isZJqN)IMG_20200213 (https://flic.kr/p/2isZJqN) by ao (https://www.flickr.com/photos/145942400@N06/), on Flickr
Title: Re: Paint repair - smaller frame areas...
Post by: Gattopardo on 14 February, 2020, 07:56:30 am
Touch it up with cold gavinising spray, high zinc content stops the rust and makes a good metal to paint key.
Title: Re: Paint repair - smaller frame areas...
Post by: mrcharly-YHT on 14 February, 2020, 08:10:54 am
IME, paint *really* doesn't like adhering to anything galvanized, so is it really a good idea to use a cold galvanizing spray? I've never tried it, mind, just painting galvanized stuff is never successful. Paint flakes off.
Title: Re: Paint repair - smaller frame areas...
Post by: Gattopardo on 14 February, 2020, 08:21:29 am
Works fine with rattle cans and humbrol touch up tins.
Title: Re: Paint repair - smaller frame areas...
Post by: LittleWheelsandBig on 14 February, 2020, 09:34:31 am
Painting over hot-dip galvanising can be done successfully but is a bit tricky. ‘Cold-gal paint’ is quite a different beast to galvanising and overcoating is much easier, with a compatible coating.
Title: Re: Paint repair - smaller frame areas...
Post by: andyoxon on 14 February, 2020, 10:40:31 am
Thanks all.

Have some kurust rust converter, also left over grey zinc primer, clear laquer spray, picked up some black & silver halfords touch-up paint to mix to approx colour.  Plan to get all the paint margin smoothed nicely.

Is it a bad idea to 'speed dry' thin primer/paint coats with warm air dryer?
Title: Re: Paint repair - smaller frame areas...
Post by: Brucey on 14 February, 2020, 12:29:24 pm
gentle warmth will be OK, but severe heat may provoke a variety of paint flaws.

Word of warning; you may be intending to use a mixture of paint types, e.g. acrylic and cellulose based paints.  This can easily go horribly wrong on you, and even if you 'buy everything in halfords so it should be OK'. 

IRRC (and do double check this to be sure) it is (say) normally OK to use acrylic over cellulose base coats but not the other way around.  Annoyingly the paint incompatibility may manifest itself only after hours days or weeks, as a cracking in the painted area.

Even with some kowledge and experience I can still get caught out; they don't always say what type of paint it is on the can, so when (after two different primer layers) you rub down and need to repair a primer area, the feathering in may result in cellulose over acrylic, and consequent problems.

cheers
Title: Re: Paint repair - smaller frame areas...
Post by: Gattopardo on 14 February, 2020, 01:39:26 pm
Quote from: andyoxon on 14 February, 2020, 10:40:31 am
Thanks all.

Have some kurust rust converter, also left over grey zinc primer, clear laquer spray, picked up some black & silver halfords touch-up paint to mix to approx colour.  Plan to get all the paint margin smoothed nicely.

Is it a bad idea to 'speed dry' thin primer/paint coats with warm air dryer?

Would not bother with kurust stuff, learnt that from playing with rusty cars.
Title: Re: Paint repair - smaller frame areas...
Post by: Gattopardo on 14 February, 2020, 01:44:20 pm
Quote from: LittleWheelsandBig on 14 February, 2020, 09:34:31 am
Painting over hot-dip galvanising can be done successfully but is a bit tricky. ‘Cold-gal paint’ is quite a different beast to galvanising and overcoating is much easier, with a compatible coating.

Yep LWAB is right, cold gal spray is basically the same stuff as Davids 182 zinc (https://www.u-pol.com/files/7671/z182m-TDS-EN-UK) but cheaper.
Title: Re: Paint repair - smaller frame areas...
Post by: andyoxon on 18 February, 2020, 11:21:45 am
In the end, I applied kurust, 3 coats of zinc primer, 3 coats of halfords repair paint, 1 coat of laquer.  I was fortunate to be able to get a reasonable paint match by adding a drop of silver to black topcoat.  Also had to extend the repair up the DT, as when I was adjusting some masking tape a large flake of paint detached.  For primer & laquer I had to spray them into a jar & then use a paintbrush.  I could have spend more time sanding between, matching the colour, working  the margins etc, but see how long the repair lasts...  Certainly thicker than the original   ;)

(https://live.staticflickr.com/65535/49552329897_fa7fba113e_w.jpg) (https://flic.kr/p/2iuLDit)IMG_20200217b (https://flic.kr/p/2iuLDit) by ao (https://www.flickr.com/photos/145942400@N06/), on Flickr

Pic.  Before final sanding & lacquer.

Title: Re: Paint repair - smaller frame areas...
Post by: Brucey on 18 February, 2020, 12:11:36 pm
that looks OK to me; more than good enough appearance considering where it is on the bike. 

When the flake of paint detached, how did it look? Was there any sign of corrosion underneath the paint?  If so, there could be other similar areas, and that may result in a need for further repairs down the line.

But you know how to do them now, so it won't be a major event if it does happen.

BTW if you don't have one, I would suggest fitting a long front mudflap; corrosion of the sort you had is very likely if you don't have a decent mudflap fitted.  The ones that come with mudguard sets are almost all pretty useless.

cheers

Title: Re: Paint repair - smaller frame areas...
Post by: Gattopardo on 18 February, 2020, 12:23:42 pm
Quote from: Brucey on 18 February, 2020, 12:11:36 pm
that looks OK to me; more than good enough appearance considering where it is on the bike. 

When the flake of paint detached, how did it look? Was there any sign of corrosion underneath the paint?  If so, there could be other similar areas, and that may result in a need for further repairs down the line.

But you know how to do them now, so it won't be a major event if it does happen.

BTW if you don't have one, I would suggest fitting a long front mudflap; corrosion of the sort you had is very likely if you don't have a decent mudflap fitted.  The ones that come with mudguard sets are almost all pretty useless.

cheers

Er are you forgetting dry weather bike, wet weather bike. 
Title: Re: Paint repair - smaller frame areas...
Post by: andyoxon on 18 February, 2020, 12:40:04 pm
Quote from: Brucey on 18 February, 2020, 12:11:36 pm
that looks OK to me; more than good enough appearance considering where it is on the bike. 

When the flake of paint detached, how did it look? Was there any sign of corrosion underneath the paint?  If so, there could be other similar areas, and that may result in a need for further repairs down the line.

But you know how to do them now, so it won't be a major event if it does happen.

BTW if you don't have one, I would suggest fitting a long front mudflap; corrosion of the sort you had is very likely if you don't have a decent mudflap fitted.  The ones that come with mudguard sets are almost all pretty useless.

cheers

The metal under the flake was pretty clean. 
I remember when I bought the bike new (90s), thinking that some areas of paintwork were disappointingly not the best. e.g. one area of chainstay had what appeared to have a kind of bubbly-imperfection.  (made the mistake of not asking to see the frame, prior to custom build). That section already has a 'humbrol' repair, which could at some stage be improved. 

yes, could think about mudflaps, as bike is used all year round*, bridleways included...
 
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