Priming Aluminium Body

[diplomat2.6]

Does anyone know the Audi recommended primer for bare aluminium?

Secondly, where is the plug for the SAT nat receiver positioned. I am thinking about repainting the boot lid when the weather improves!

All help very welcome

[HPsauce]

The GPS aerial "puck" has a captive lead maybe a foot or so long that makes a connection inside the boot lid to the cable that comes through one of the grommets.

[diplomat2.6]

Thanks - the previous owner had the boot painted without removing it, leaving a nasty edge. I am wondering whether to remove the boot lid to paint - is it a multiplug for all electrics do you remember?

Now there is also horrible microblistering that has appeared in the winter.

[HPsauce]

GPS aerial is a separate (coax) lead; never looked at the others.
It's only held on from below by one big nut so no excuse not to remove it when painting!

[diplomat2.6]

I can't understand why they didn't - the job is shoddy from start to finish. Luckily they didn't paint anything big!

[David's8]

A quick google using "aluminium car primer" throws up a number of recommended etching primer tho' which one (or other) that an Audi bodyshop would use I am not sure.... which was, of course your real questtion I guess?

[pete-p]

I have a page from the A2 study which may or not help

[diplomat2.6]

Thanks. I have had a look on Youtube and they seem to suggest a chromate converting layer for painting aluminium body aircraft called Alodine.
I've contacted a regular poster on Youtube called The Gunman who works in a commercial bodyshop. No reply yet.

The problem I've got is that there are so many badly repaired D2s but I can't understand why the paint finishes are often so dreadful. I think it is because there must be an 'official' technique that is really time consuming, so the only people who provide sensible quotes are low end bodyshops without a booth. Perhaps people don't think it's worth spending the cash. Well, you haven't got to worry about rust have you?

I had a quote of £3500 for the rectification of two rear wings, a front wing, two doors, two bumpers - the materials cost is likely to be £200. But, I want to make sure I invest the time is researching how to do it 'by the book' to avoid having to do it again.

Will keep the post updated as I go

[diplomat2.6]

I went on the Jaguar forum for the X350

his is from the X350 body repair guide:

Galvanic Corrosion and Housekeeping

Galvanic corrosion is the ‘cross-contamination’ of dissimilar metals, in this case aluminium and steel. Avoidance of galvanic corrosion is an important issue to be considered in the repair of aluminium bodied vehicles.

Precautions to prevent the contamination of exposed bare aluminium surfaces should be taken.

Good housekeeping / cleanliness should be adopted throughout repairs and especially prior to welding, pre-treatment and adhesive bonding.

The repair environment requires control and protection from dust and debris from conventional steel body repairs. All equipment used must be clearly identified and used solely on aluminium. Tools should be kept clean and in good order. Steel fastenings are coated to prevent galvanic corrosion.

Fastenings should be examined during repairs and where damaged or suspect must be renewed. The use of graphite, ‘penetrating’ oil or copper based anti-seize compounds upon the steel fastenings is not recommended.


And for the painting process:

Following completion of appropriate panel repairs carry out the following actions:

– Clean original paint surfaces with soap and water, rinse and wipe dry.
– Preclean with Prepsol 3919S, or 3910WB Waterborne Degreaser.

Dry sand with P280 – P320

Sand bare aluminium surfaces using Grey Scotchbrite with 3608S to remove all traces of oxidisation.

Degrease with 3920S or 3911WB Waterborne ‘Final Clean’.

Wipe dry and tack wipe before priming.



Epoxy Primer Coat
Product Preparation Mix:
– 4 parts 830R Epoxy Primer.
– 1 part 835R Epoxy Activator.
– 2 parts 3871S Thinner.

Apply 1 full coat of 830R Epoxy Primer. Flash until ‘flat’ before baking. Bake for 45 minutes @ 60°C.
Recommended Film build: ± 35μ dry.

Once the epoxy primer is cured, dry sand mechanically with P280 – P320.
Degrease with 3920S or 3911WB. Wipe dry and tack wipe.

Note:
If bare metal is exposed during sanding, repeat epoxy
primer process.



Primer Surfacer Coat
Preparation Mix:
– 2 parts 3240S UHS Primer.
– 1 part 3206S Activator.
– 3% 3289S Accelerator.

Apply 2 full coats 3240S UHS primer surfacer.

Flash for 10 minutes between coats and for 15 minutes before bake.
Bake for 20 minutes @ 60°C.
Recommended film build: 50 – 100μ dry.
Dry sand, initially with P320 finishing with P400 – P500.
Degrease with 3920S or 3911WB. Wipe dry and tack wipe.



Basecoat / Clearcoat
Basecoat preparation is not required as Cromax® (a water based basecoat colour) is supplied from formula ready to
spray.

Apply 2 coats wet – on – wet, followed by optional ‘mist’ coat for metallic and pearl.

No flash time required between coats.

Flash until completely dry (if required, use suitable air blower system) before application of Clearcoat.

Clearcoat Preparation Mix:
– 3 parts 3800S Chromaclear® HS Clearcoat.
– 1 part XK205 Low Emission activator.

Apply 2 coats, allow to flash for 5 – 10 minutes between coats and for 0 – 5 minutes before bake.
Bake for 30 minutes @ 60°C.

[diplomat2.6]

This is quite interesting too - particularly the part on achieving the ultimate paint finish.

http://www.pistonheads.com/gassing/topic.asp?t=1225405