Pre-Paint Degreasing

I've a few alumium parts to paint in the near future.

I'm wondering the best way to give them a thorough cleaning before the etch priming.

Would pure isopropyl alcohol do the trick? Maybe diluted with distilled water?

If not, any alternative suggestions would be welcome, preferably household or easily/cheaply obtainable.

Cheers, Steve

Brake cleaner or acetone

Robert.

I use the dishwasher, but try it on some scrap first as I suspect it might attack ally. If doing steel get it out as soon as its done the rinse or it will rust

Grit blasting or cellulose thinners would be my first choice.

Thinners. He'll already have some to use with the primer

Depends on the type of grease, how much there is, and how clean the parts need to be.

Often as not a lightly contaminated surface can be cleaned well enough by wiping over with a clean cotton rag soaked in Acetone or isopropyl alcohol. Both should be full strength, not diluted with water.

I often wipe with Acetone, rinse under the tap, dry and then wipe over with IPA. This is because some greases are more soluble in Ketones than Alcohols and vice versa. Using Acetone and IPA in sequence is belt and braces.

If cleanliness is important, washing in Acetone, followed by washing in IPA, followed by washing in very hot water with detergent, followed by a water rinse, and finishing with an IPA rinse. This isn't always good enough.

Viewed through a microscope metal is seen to be full of tiny cracks and caves. Getting grease out of these requires stern measures, perhaps boiling in distilled water with detergent for an hour or two, followed by a sequence of Acetone and IPA washes and rinses.

Don't use alkaline degreasers on Aluminium, they corrode the metal.

Wear clean rubber gloves, and before starting make sure they aren't attacked by Acetone. It's an excellent solvent, including skin!

The best solvents are often low flash point hydrocarbons. Petrol works well, but it's very dangerous. Cellulose Thinners, Acetone and IPA are considerably safer. Diesel gets heavy grease off, but is greasy itself - more trouble than it's worth. I've had mixed results with my ultrasonic cleaner.

Dave

Dishwasher tablets are strongly alkaline and will dissolve aluminium and its alloys.

Try cellulose thinners and a toothbrush.

The use of a grease solvent is widely advocated, but it's not the best method. Think about it: the solvent produces a dilute grease solution, which spreads all over the substrate - then evaporates, leaving grease residue on the surface. If using solvents, you need to use enough to wash the substrate - repeatedly - so the grease is carried away. It gets expensives, and time-consuming. However, since it's so widely used, it is presumably good enough... Probably.

It's better to scrub the alloy with household scouring powder, and rinse with 'distilled' water (from de-icing the freezer, perhaps). Test for success by dropping water on the cleaned surface. It should completely wet the surface, with the drops forming a microscopically thin film. Any signs of the water not wanting to form a film, or frank beading, means it's not de-greased. Oh, and, of course, rinse and repeat...

I use isopropyl or thinners for cleaning. Thinners is better but the fumes are potent.

Dan Gelbart is rather dismissive of using solvents to prepare metals for painting. He says a sand blaster, bluing or Ajax, of all things, is best. After watching the video below I tried Ajax myself and it seemed to work fine, but I'm no expert.

Take a look and see what you think.

I must warn of the extreme danger of putting metal machine parts in the dishwasher, if the wife comes home and catches you the repercussions are most unpleasant!

I speak from experience........

Dave

In addition to never admitting to using the domestic oven for anything other than domestic duties.

No matter how little evidence is left after you meticulously cleaned up (even after watching lots of forensic science/police series on the telly to get some hints and tips) after temporarily commandeering it engineering/workshop purposes, she will know.....

Regards

Derek

Graham,

That video by Dan Gelbart is very informative, thanks.

Hmm...I guess I need to add 'Sand Blaster' to my Amazon Wishlist

Ches

Graham, mentions the use of Ajax. Has anyone tried getting hold of "Ajax", or "Vim" for that matter. Last time I looked, Vim seemed very pricey for what is was. Or maybe I'm just out of touch!

Worst case of this was when I was a teenager, mother returned home early to find a motorcycle engine in the bath

Suitably chosen solvents are unlikely to damage the surface, whereas abrasives do.

Maybe painting implies that scratching and pitting the surface isn't a problem, and it's often done deliberately to provide a key. But abrasives aren't smart if the object is to be anodised.

I don't know exactly what's in Ajax or Vim. They're both scouring powders and these contain an abrasive such as chalk with a degreaser such as Sodium Carbonate, and Bleaching Powder (active ingredient Chlorine). I'd avoid using them on light metal alloys - anything containing Aluminium, Magnesium or Zinc. Cleaning is good, corroding is bad!

Dave

If I remember correctly the base of Vim and Ajax is pumice powder.

Edited By bernard towers on 05/09/2023 12:10:19

Bernard,

You're probably right, and very gritty pumice powder.

A friend put his motorcycle crankcases in the dishwasher, they came out lovely and clean and he is still a happily married man.

Mike

Had to buy mine online.