Sunday 14 June 2020

Painting and Plating

When I started restoring motorcycles many years ago I decided that I would do my own painting rather than go to a professional paint ‘shop. Why? Well, as a 15 year old school boy living in the Isle of Wight when I first discovered motorcycles and pulling them apart and making them go, I thought I would have a go at spraying.

I didn’t have any spray equipment so went about building a spray kit. It consisted of a fridge compressor (2 cylinder!), a length of plastic tubing and a small scent spray type of atomizer on top of the lid of a jam jar. At that time (mid 1960s), cellulose paint was used and, luckily, it is relatively benign if inhaled.  Nevertheless, spraying in a small garden shed at home would produce a vapour cloud so dense that it was impossible to see the opposite side of the shed about 8 feet away. So, a heater blower from a truck was installed as an extractor fan with a length of polythene tubing poking out of a window. It was pretty useless but at least gave my mother some reassurance that I wasn’t asphyxiating myself in the shed. 

In fact, spraying became so successful that a friend of mine and I set up a schoolboy business “Motorcycle Services” and started spraying bikes and scooters for “customers”. Our greatest claim to fame must be that we sprayed a Norton Dominator that was sold to Des Norman, one of the founders of Britten-Norman Aircraft Company based in Bembridge. It looked pretty smart with a non-standard British Racing Green tank ….but I digress.

Now, I spray 2-pack, often referred to as “2K”. The advantages of 2K are that a superb gloss finish is achievable and it is petrol resistant. The disadvantage is that it contains isocyanates and, according to UK Heath and Safety Executive:

“Spraying 2-pack isocyanate paints is the main cause of occupational asthma in the UK and, for years, vehicle paint sprayers have been the group most at risk. MVR paint sprayers have about a 90 times higher risk of getting asthma compared with the UK working population. Every year around 50 sprayers are diagnosed with isocyanate asthma and most have to leave the industry.” 

It is absolutely vital to breath using a supply air respirator. I therefore use 2 compressors, one to supply air to the paint gun and the second, located a long way from the spraying area, suppling fresh air to a full face-covering respirator. The importance of an air-fed respirator cannot be over-emphasized. A passive respirator, like a mask, is NOT sufficient. How do I know? I tried it once and coughed and wheezed like a 50-a-day smoker for a week!

The process I use is: etch primer (from a rattle can); 2K primer followed by 2K top coat. The number of coats of 2K depends on the flatness of the original surface. I do not apply lacquer on petrol tanks because it often reacts badly with waterslide transfers; they "crinkle up".

A lot of parts show the scaring of 90 years of age which is not easy to eradicate without applying excessive amounts of primer-filler. More recently I have started hand painting frames using coach enamel and this can produce a high gloss providing the surface is prepared thoroughly. 

The pic below shows a pair of mudguards hardening off in the garden after spraying.

I also now use powder coating for many parts. Luckily, we have an excellent powder coater a short drive away and I am increasingly using his services.

Up to about 1930, nickel plating was used for  ”brightwork” on cars and motorcycles. Some years ago I bought a nickel plating kit from Frosts and I have used this for plating small items (ie those that fit in a 10 litre bucket) on many restorations, eg  nuts and bolts, oil and petrol pipes, levers, gear-change and brake trunnions etc. The advantage of doing your own plating for small components is that you can retain their identity from each labelled packet (see previous post) and it reduces the chance of small parts being lost at the plater. 

The process is quite straightforward: polish the parts to the finish that you want to see; scour with scouring powder and a toothbrush (I use “Vim” bath and sink cleaner from a hardware store); rinse and “fondle” the parts with clean hands and soap, which acts as a surfactant, (I use hotel soap bars that I appropriated during my working life); rinse with clean water and suspend in the plating bath using stainless steel wire and with a crocodile clipped wire that attaches to the bus bar. I usually plate at around 2 amp and leave them in the bath for 12 – 18 hours. It is important that the surface is polished to a fine finish before plating. Surface imperfections will be plated exactly as they go into the plating bath; unlike painting, plating cannot be used to "fill in" imperfections.

When the parts are removed from the bath, wash with clean water and polish on a polishing mop. It is important to use “dull nickel” rather than “bright nickel” plating. The former, when polished, is correct for the period; the latter (which uses a different electrolyte) is far too shiny and looks completely wrong.

The bucket ends up being quite crowded with, in addition to the parts being plated, 2x nickel anodes on opposite sides, an aquarium heater (it is very important to keep the temperature up, especially in the winter) and an aquarium air supply that bubbles air through the electrolyte to dislodge hydrogen bubbles sticking to the surface of the parts (this causes a crater-like appearance on the surface after plating). I cover the whole lot with a thick towel, which absorbs condensed vapour from the heated water, and leave overnight.

Larger parts, such as the exhaust and handlebars, have to go to a professional plater for the simple reason that they don’t fit in the bucket.

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