ALUMINIUM FRAME REFURBISHMENT
THE EMPEROR'S NEW CLOTHES
Michael Stenning takes us through the structural and cosmetic reinvention an aluminium frame. Despite steel’s revival and carbon fibre now distinctly mainstream; aluminium alloy remains a popular frame material. Excellent performance to weight ratio, ease of mass manufacture coupled with favourable pricing give it lasting appeal. Even repainting isn’t too tricky, so long as you follow some simple rules. Michael got some help from the experts at Maldon Shot Blasting and Powder Coating, Chris and Graham, Co-Directors and craftsmen, and their father, Trevor.
Aluminium frames are not created equal and are alloyed with other metals to provide the desired characteristics. Some manufacturers experimented with 5000 series marine grade aluminium but it’s really a choice between 6061 (blended with magnesium and silicone) and 7005 (zinc and magnesium). Economies of scale are great news for end consumers. However, dents, cracks and similar structural damage spell scrapheap.
That said; with lateral thought, replaceable derailleur hangers can be whipped up by machine shops long after that model ceased production and OEM spares evaporated. Decent bike shops can repair stripped derailleur hangers, carrier mounts, brake posts and other small threaded parts. Bottom bracket shells can also be recut (usually to Italian) which restricts choice of unit, though much better than binning an otherwise serviceable frame.
Fatigue is another popular anxiety. True, cracks and other stress damage can appear very suddenly, so keep a watchful eye on anything suspicious between washes. Nonetheless, mid to upper end rigs can clock up massive mileages and deliver surprisingly compliant rides on and off road.
Aluminium doesn’t rust … yup; but it corrodes and benefits from a decent protective painted, anodized or lacquer finish.
This Specialized arrived at Maldon Shot Blasting & Powder Coating for refinishing. Structurally sound, there is some obvious flaking and surface oxidisation forming around the bottom bracket shell.
Stage 1 Testing, Testing
Aluminium alloys are easily damaged by the wrong blast media. Back in the mid1980s, Cannondale made it explicitly clear that sandblasting would cause structural damage and void the warrantee.
This remains an absolute no-no on contemporary frames, regardless of brand. Previously powder coated examples should slosh around in an alkaline stripper first, to avoid deep and extensive pitting. Methyl chloride was once the active ingredient in better quality DIY strippers and extremely effective. Alas, it’s also highly carcinogenic, so largely restricted to commercial use.
Factory finishes still vary in type and quality. Aqua blasting is the least aggressive procedure and combines a light powdery abrasive with fine mists of water. However, years of experience sees Graham head straight for the Iron Oxide Cabinet.
This is an efficient, though still compassionate process that will lick a stove enamelled steel frameset clean in around three to four minutes. Being a softer metal, patience is paramount, so after 90 seconds Graham stops to inspect a small test area, which is clean but dull grey.
Stage 2 Blast! Blast! Blast!
Fifteen painstaking minutes later it’s essentially bare - save for residual shadows.
Graham transfers to the shot blaster, tickling the tubes to a lightly etched sheen - ideal for sharpest results.
Inevitably some residual grains will rattle around their inner sanctum. These eventually drain harmlessly via bottom bracket shell, breathe holes, head and seat tubes. However, a thirty second chase through using compressed air keeps squatters in single figures.
Since we’re on the subject, ensure your project is stripped of all components/fasteners. Degrease threaded sections and have the courtesy to mention if something oily is lying dormant in the tubes - it could suddenly come alive, scalding the sprayer, or ruining new livery.
Stage 3 Primer
Detractors offer powder coating’s weight as a deal-breaker. This has prompted some firms to skip the next stage and explains why industrial painters can keep the prices lower. Ultimately, we only get what we pay for. Aluminium alloys are porous, meaning moisture can develop during the curing phases, resulting in unsightly blemishes/bubbling often referred to as “gassing out”.
Even if you’ve dodged this particular bullet, stone chips encourage moisture and corrosion to flourish unnoticed, until the powder coat begins flaking/peeling away in chunks. With primer beneath, superficial battle scars are easily retouched using hobby enamels or car type paint sticks.
Frame earthed; Graham selects a grey epoxy zinc phosphate base. Generally kinder to sprayer and wider environment than chromates; this also enjoys excellent adhesion and flow rate, meaning it’s much easier for him to achieve a uniformly smooth effect. This is completed in four minutes; then oven cured.
Stage 4 Curing
The powder assumes a liquid state and fully cured in fifteen minutes at 200 degrees. Frames/components/accessories skipping primer should also be preheated this way prior to their colour coat.
Stage 5 Colour
Contrary to misinformed forum “experts”, you are only limited by your imagination and budget when it comes to powder colours and finishes.
In this instance we’re having “artic white”; which is a hybrid epoxy/polyester mix, combining durability with cosmetic allure. Standard epoxy finishes aren’t UV stable though, explaining why mass produced garden furniture dulls or fades within a year or two.
All colours, irrespective of paint family have their quirks, requiring subtly different techniques. Whites and yellows are particularly tricky given their lack of pigment.
This leads inexperienced operators to overcompensate, applying too much powder. Best case scenario we’re talking orange peel city; worst, it’ll emerge literally hanging (think thick, runny custard). Graham weaves seamlessly along the tubes like a well –coordinated dervish and within five minutes we’re oven bound again.
Home & Dry
The overall effect looks absolutely stunning but Chris spots some blemishes along the top tube. In practice, this is easily corrected but further illustrations of discerning workmanship and the slightly unpredictable nature of aluminium alloys.
Affected areas are sanded back to primer using 180grit and the frame is baked for another fifteen minutes prior to repainting.
Snagged n’ Sorted
Graham is called away, so Chris takes charge, applying the remedial coat in three minutes before it’s returned to the oven.
In this instance, the customer doesn’t want a clear lacquer applying, which allows a variety of options. As it stands, the grand total is £65 plus VAT (Price correct at time of publishing).
Several solid colour effects are very possible with powder coating; although it requires considerable skill and this carries a cost implication. Therefore, 2pac paints are more commonly used.
The temperatures involved in curing powder coat acrylic and polyester lacquers would ruin decals. However, these can be applied and sealed beneath 2pac clear coats.
Wet Stuff (Traditional alternatives)
2pac paints superseded nitro cellulose lacquers in automotive contexts during the1970s and are another favourable option. These can be oven or air cured, so safe for carbon fibre and bonded (glued) frames including Alan and Raleigh’s Dynatec series, or those using plastic internal cable guides.
Pros: Results are excellent; albeit more labour intensive and closer to high quality stove enamels.
Cons: Being a wet-spray process, there’s also quite a bit of wastage/overspray.
2pacs contain cyanide, which is extremely hazardous and must only be by professionals wearing full body suits and air fed masks. Consequently, water based coatings are now widely used within the car industry but seem unsuitable for bicycle/motorcycle applications.
Frankly, specialist/project finishers such as Maldon Shot Blasting & Powder Coating are your best bet since they’ll work to standards, not prices. Industrial “job lot” firms operating on a factory-style conveyor process can prove godsend or nemesis in equal measure.
On the plus side, this might be fine for a workhorse fixed/single speed. Frame and forks in a basic, primary colour can cost as little as £25.
Be prepared to undertake a lot of preparatory work yourself and oversee wherever possible; the prospect of entrusting someone used to blasting RSJ’s with a thin-walled bicycle frame turns my blood cold.
Many local authorities have graffiti removal teams with precision cleaning equipment. These can be adjusted to restore discoloured stonework or strip the foil from fag packets, leaving the cardboard behind completely untouched.
Masking may prove non-existent, requiring intensive, time consuming clean up.
Ask nicely, catch someone in the right mood and they might do you a big favour. Talking of which, a cycling mate who works in a car body repair shop might be able to turn a frame round at cost, on their own time but otherwise, I’d steer clear.
Materials-wise, doing it yourself sounds like a great way of saving cash but is extremely time/labour intensive. Fine if you’re looking for a summer project and/or seek to develop your spraying skills. Over the counter chemical strippers are messy, relatively expensive and slow-acting.
Some extremely high grades of aluminium might be worth stripping bare and polishing but I’d still err towards a professionally applied acrylic lacquer, which won’t yellow, crack or peel. Leftover acrylic paints and hobby enamels can achieve surprisingly satisfying cosmetic effects on town hacks but tend to be decidedly brittle.