How to spray – part 2
Preparation (the boring but essential part…)
This month we look at preparation – how to, what you need and how to bear the monotony of rubbing down…
Back again? You must be suckers for punishment – but welcome! Last month we took a look at the basics of painting and if it was something that you could or would want to do at home. Economics mean that to attempt any more than using aerosols for small work means a large outlay, space and time to practice – but it’s by no means impossible. And if you get together, or have an interest in cars, tractors or other, larger toys, then it can really become a very useful skill to have.
So you’ve looked at the cost and whether you have decided to paint your parts or not, they will need preparing. We touched on this last month, so let’s see more closely what’s involved. But like we warned last month, it is laborious, and cannot – I repeat cannot – be skipped, or your bike parts will end up looking like an old hag on a Spanish beach…
Firstly, what are you painting? Our example here is a rear mudguard from a
1931 Sunbeam, a Model 90, no less. It had fallen over in a van against another bike and taken a couple of nasty two pence piece areas of paint down to the metal. Argh!
Now Sunbeam were famous for their beautiful finish and the parts would have been individually dipped in enamel, or Japanned. This would mean the whole part would need to be stripped so the paint we put on doesn’t react and cause mayhem with the finish. But on closer inspection, it was obvious the mudguard was a replica and a recent one, too. No problem; but what did they paint if with?
Most professionals would use a basecoat and lacquer, but this one had uneven stays and brackets on the piss, with metric nuts and bolts holding it all together. The stays were also painted on the mudguard; clearly not good quality work, so could they have used cellulose? The paint on the underside of the mudguard didn’t even have any primer, so to be safe, it all had to come off; only then could we be sure.
Don’t rush
I took many photos on my phone before the stays, numberplate and stand holder were taken off, so I could be sure everything would go back together. Once it was clear this rear end was a replacement, and a recent one, I knew it would be tricky to see what went where. This is especially important when everything is freshly painted, as you don’t want to scratch anything! The stays had a longer flat on one end, to hold the mudguard, and the ‘bridges’ they bolt to are just bent pieces of steel which I have re-bent. They were also bent, so I noted that – but you cannot mark them, as they are all to be rubbed down!
Rubbing down and what to use
Oh, choices, choices. There are many different ways to rub paint, filler, lead loading and metal down. For metal, files are the best, but most of the time you’ll use other methods. Most are broken down by ‘grit’, where the lower the number, the more coarse – or rough it is. So an 80 or
120 grit is really rough, will rub down paint quickly, but will leave a rough finish. 240 or 400 grit will take longer to rub things down, but will leave a smoother finish, whereas 800-1000 grit is really fine and anything higher is akin to polishing.
Start with a rough grit and work down – for a finish that is to be covered with traditional cellulose aerosol paint, 800 is a good grit to finish on – anything more rough will leave lines. If you’re using 2k (two-pack – which has a hardener added) filler primer with a gun, you can get away with as low as 150 grit, though 400 is better.
The cheapest is wet and dry paper. This can be used dry, but is best and lasts longest wet. The more you use it, the finer it gets.
Use it with a rubber or cork block and you’ll get a good finish, albeit after quite some time.
If you have a compressor you can use an orbital sander and discs. These do the same job but are used dry and I use the discs by hand as much as on the sander. 150 grit is a good level, then finish with wet and dry paper by hand as an orbital sander leaves circular scratches.
Scotchbrite pads are similar to washing up sponges, and I use the red ones, which equate to roughly 400 grit. Use them wet or dry and they leave a good key to a painted surface for paint to grip to.
Our mudguard
If we knew the paint was 2k (two pack) we could have rubbed the surface down with a block and 240 or 400 grit to get a rough finish the new paint would adhere to, this would also help show any dings or imperfections more easily. I did start filling the dents and dings, but thought better of it – there really is few things worse than spending all that time prepping, only to see the paint bubble or react.
This all seems a little drastic for two small areas of damage, but a touchup would be easily spotted and what to touch up with? The Sunbeam is an expensive bike which is in beautiful condition elsewhere, so it’s best to do our best. Norton Blaze discs in a grinder made short work of getting the paint off without attacking the metal, then 150
discs and a block took the small areas down, like the front lip and the edges. The underneath was buffed up nicely with more 150 discs by hand – this doesn’t need to be quite so immaculate and the stays and ‘bridges’ were rubbed down by hand, or with a brass wire wheel on the bench grinder. I then used 150 grit to improve any sharp edges.
Filler? You dirty girty!
Using body filler is not a dirty technique – despite the nonsense you hear from certain biking circles. In the old days, you could fill dings, dents or joins by lead loading; this is where you melt lead to use as a filler. Lead loading has its place in restoration, including fuel tanks, but it is more difficult than using body filler and there really is no need. Our mudguard had some dings, so a cushion – one of nanny’s, that she used to have on her driving seat of her Morris – or a dolly held in the vice were used with a dressing hammer to get the worst of the dings out. Ideally you’d get all the dings out and a couple we did, but you still use a small skim of the dreaded filler to make sure the repair is completely invisible. Especially as it is going to be painted black, which really shows any indentations up.
“If you hear yourself saying ‘It’ll do’ then it needs more work – painting it won’t mask it – it will make it stand out more.”
Our mudguard also had some holes in that were not being used – I have no idea where from – but they needed filling. So I popped the MIG welder out and filled them, using very short bursts and building the weld across the hole. This way helps minimise heat and therefore distortion. It needed grinding down, but the hole is filled with metal, which will be more hard wearing from the underneath. A skim of filler on both sides finished it off.
Take care of your feelings, man
Rubbing down mudguards is a pain, as they are curved both ways! And using a block seems illogical, but it does help to follow the contours. Without sucking eggs and showing you how, filler will wear away with rubbing down quicker than the surrounding metal, so a block is essential – most of the time. Sometimes you need to put a little extra pressure on a small point, or follow a tight curve, so using the shape of your hand is best. It just takes time and practice. Filler dust is rather nasty stuff, so if you can do it outside and wear a mask. But also close your eyes and rub your fingers across the filled sections to see if and where more rubbing down is needed. If you over rub, then it’s not the end of the world – make up some more filler and if you’re in a hurry/ bad mood/ late, then add a little extra hardner – you’ve less time to use it, but it’ll be ready to sand in much less time. If you hear yourself saying; ‘It’ll do’ then it needs more work – painting it won’t mask it – it will make it stand out more.
It’s not rocket science to prepare a piece for painting, nor does it cost much and involve expensive machinery; but it does take time. And the most important tool is your fingers and time – feel if it’s smooth and don’t rush it. Next month we put all this hard work to test and paint!