PDA

View Full Version : Powder Coating versus Galvanising



Cobrarob
29-09-11, 09:21 PM
Has anybody any experience of powder coatings cracking on chassis and then flaking off after water has got in?

wilf
30-09-11, 07:49 AM
If they do, then it was down to poor prep in the first palce, most likely inadequate degreasing.

Clarkson
30-09-11, 08:18 AM
Has anybody any experience of powder coatings cracking on chassis and then flaking off after water has got in?

Yes, roll on 20 years and that's why I have re powder coated my chassis.

russell_ram2
30-09-11, 08:22 AM
No, mine is coming up to 20 years old and looks as good as the day it was done.

What Wilf said . . .


Russ

dingocooke
30-09-11, 09:06 AM
As was said by the other posters, preparation is the key; a lot of fabricators just wipe down the chassis and get it powder coated, so you still have the scale on it from the rolling mill; this flakes off over time anyway so whatever you put on it, it will come off.

There are two solutions, start with BDMS (bright drawn mild steel) that has been de scaled at the mill, or (preferably) get the complete chassis blasted, then clean all blasting media and dust off it with an airline and then a thinners wipe, before getting the powder coat done.

I know JK at Crendon does the latter procedure, but it's expensive and time consuming; Ive not seen a crendon with a flaky paint, and my RAM chassis was almost perfect after 18 years or so, I have seen a couple of RAMs with flaky powder coat, one can only assume the prep was missed.

If your chassis paint work is good, it is worth spraying WD40 on the welds and any junctions with crevices that the paint wont have covered so well, as these are the places the rot/water ingress and flaking will start

Cobrarob
30-09-11, 09:48 AM
Thanks for the info. It appears if you are buying the chassis already coated from the kit manufacturer you are in the hands of the gods!

chesterak
30-09-11, 10:18 AM
Thats exactly why I had my chassis supplied un-coated. I sorted out welds not to my liking, welded on additional brackets/pads, drilled most holes for brake clips etc, then had it powder coated....

capcobra
18-12-11, 02:47 AM
No reason for paint to flake off, so long as your shirly bassey is properly blast cleaned / degreased, given an undercoat and then powder coated with a decent quality powder. Having said that, no reason why you cant powder coat straight over galvanised chassis (or whatever parts you have in mind) so long as the powder coater you go to knows what they're about. I think the guy I go to has to use some type of special brew powder mix to coat galv.
For anyone based in the South West, I can recommend Keynsham Powder Coatings (Bristol)

JonnyT
19-12-11, 10:47 AM
I wouldn't pay the extra for the Dax powder coating again - it was flaking off before we got to the IVA. However there is a huge variety in qualities that I hadn't realised with prices to match. A mate of mine is a fabricator and was doing some bits for a house in London. For one lamp standard he got prices varying from £75 to £600. Given the location they went for the £600!

Everything I do now gets two coats of thinned red oxide and two coats of tractor enamel. Finish is fine (particularly if you spray it) and because it is old school enamel it has some self healing properties because it doesn't set rock hard like other paints. My oldest experience of this method is 6 years on a set of callipers and the paint is still pretty much as it was when I did it.

Cobrarob
19-12-11, 07:44 PM
I wouldn't pay the extra for the Dax powder coating again - it was flaking off before we got to the IVA. However there is a huge variety in qualities that I hadn't realised with prices to match. A mate of mine is a fabricator and was doing some bits for a house in London. For one lamp standard he got prices varying from £75 to £600. Given the location they went for the £600!

Everything I do now gets two coats of thinned red oxide and two coats of tractor enamel. Finish is fine (particularly if you spray it) and because it is old school enamel it has some self healing properties because it doesn't set rock hard like other paints. My oldest experience of this method is 6 years on a set of callipers and the paint is still pretty much as it was when I did it.

thanks for the info. I have heard that powder coating is OK if it is prepared and applied correctly but you will nit know the answer until 3 or 4 years down the line.

craggle
19-12-11, 07:56 PM
If you have the option and intend to use the car in all conditions then get it galvanised. It is a bit of a risk as the temperature involved in molten zinc can cause distortion of metals, especially thin sheet areas but it will provide the best protection possible. Powder coat will rust and flake off if it is damaged enough to expose the base metal, Galvanise is a sacrificial protection so scratching or chipping it won't actually make it rust, it just accelerates the "corrosion" of the zinc.

My Dax chassis still looks perfect after 6 or 7 years but then it stays dry and has done only 1000 miles since it's been on the road which is now about 4 years.
TVR chassis were powder coated too I think and there are plenty of very rusty versions out there now so not just kit car manufacturers having an issue.

Craig.

labeline
19-12-11, 08:09 PM
My powder coating came off in sheets before I even had the bodywork on. I had to take everything off and send it back to be done again and it is still coming off now albeit 17 years later. Having looked at the metal under the coating it is obvious to me that it was entirely down to poor preparation. If it is done properly, degreased, shotblasted and coated then I am sure it is good stuff but if not then its a real pain. I am not sure how many operations have the ability to powder coat something that big and heavy. In the case of the first one above, I was blamed for breaking their equipment. As I had had to completely strip the chassis down again I was less than sympathetic.

kdavies3
19-12-11, 10:37 PM
The powder coat on my contemporary chassis is at least 12 years old.
Still perfect, but it hasn't seen a road yet. :D