Powder coat problems
Discussion
Hi
A tale with no names.
I saw a car with a recently refirbed chassis. Chassis off, shot blast then new powder coat. In the very few years since completion it has significant rust showing through the powder coating, all over the place. The rust is incurable, unless the process is repeated, I.e chassis off again and do it right. So £10k down the drain.
The technical points here.
Powder coat is not a good rust preventer. It doesn’t adhere well to the substrate and any water in the gap will let rust track everywhere.
Shot blasting the chassis exposes all the highly reactive mild steel to the air, and increases the surface roughness, hence surface area, which makes it rust faster.
Always use a hot zinc coat before powder coating. This stops rust by an electrochemical process, the zinc is known as a sacrificial anode. It actually self heals when scratched off.
The moral points.
If your chassis is off, a few hundred quid extra will get you hot zinc. Do it!
Always check the quality of the work done, even if by 'experts'
Best
Nic
A tale with no names.
I saw a car with a recently refirbed chassis. Chassis off, shot blast then new powder coat. In the very few years since completion it has significant rust showing through the powder coating, all over the place. The rust is incurable, unless the process is repeated, I.e chassis off again and do it right. So £10k down the drain.
The technical points here.
Powder coat is not a good rust preventer. It doesn’t adhere well to the substrate and any water in the gap will let rust track everywhere.
Shot blasting the chassis exposes all the highly reactive mild steel to the air, and increases the surface roughness, hence surface area, which makes it rust faster.
Always use a hot zinc coat before powder coating. This stops rust by an electrochemical process, the zinc is known as a sacrificial anode. It actually self heals when scratched off.
The moral points.
If your chassis is off, a few hundred quid extra will get you hot zinc. Do it!
Always check the quality of the work done, even if by 'experts'
Best
Nic
Hi Adrian
That can’t be right? Zinc is used in the marine environment. It works via a well understood process of fundamental chemistry. It is galvanising. We all have know galvanising works?
I don’t deny your bad experience but struggling to understand. What happened, powder coat fell off?
Any other input or experience?
Best
Nic
That can’t be right? Zinc is used in the marine environment. It works via a well understood process of fundamental chemistry. It is galvanising. We all have know galvanising works?
I don’t deny your bad experience but struggling to understand. What happened, powder coat fell off?
Any other input or experience?
Best
Nic
Hi, indeed, but how do you know it is done right?
This quote from an employee of a large company supplying zinc
Some simple facts - it is a spraying process that melts a pure or alloyed metal (in this case zinc but could be aluminium, steel, bronze, brass, copper etc.). it is porous (circa 10-15%) but as the zinc is galvanic to the steel, it will still prevent corrosion. The contractor would be likely to be suggesting to paint or seal as this will extend the life a little longer and stop white rust (looks a bit like talc) forming. You will get white rust with bare galv too - it is the zinc sacrificing itself and protecting the steel below. It will normally wash off in the rain. If people like the grey look, a clear sealer could be used.
Explains the talc. Product if the zinc working to protect the steel. Otherwise the steel would have rusted.
Best
Nic
This quote from an employee of a large company supplying zinc
Some simple facts - it is a spraying process that melts a pure or alloyed metal (in this case zinc but could be aluminium, steel, bronze, brass, copper etc.). it is porous (circa 10-15%) but as the zinc is galvanic to the steel, it will still prevent corrosion. The contractor would be likely to be suggesting to paint or seal as this will extend the life a little longer and stop white rust (looks a bit like talc) forming. You will get white rust with bare galv too - it is the zinc sacrificing itself and protecting the steel below. It will normally wash off in the rain. If people like the grey look, a clear sealer could be used.
Explains the talc. Product if the zinc working to protect the steel. Otherwise the steel would have rusted.
Best
Nic
My finisher, when shown/I asked his opinion on my 3000S, hot zinc sprayed, with the correct wet hot zinc primer and wet black finished chassis 18 years after being done, re finshed it for free (there was light rust in the body plates to round tubes)...I had to pay for the powder coating of the wishbones, which all 'needed' to be done.
Nic, I have added a picture of the chassis after 18+ years that was redone for free...look at the powder coat on the diff frame ...the wishbones were the same hence the rebuild.
Now it is finished (you will of seen this picture before)
Nic, I have added a picture of the chassis after 18+ years that was redone for free...look at the powder coat on the diff frame ...the wishbones were the same hence the rebuild.
Now it is finished (you will of seen this picture before)
Edited by Adrian@ on Tuesday 11th July 21:44
Honestly Adrian, I think 18 years and not needing welding is darn good! The chassis I mentioned in powder coat alone has significant surface rust in 3 years. Will be gone in 18…
Hot zinc and seal is the process used on oil rigs, marine handrails, etc. I don’t think anyone can say it doesn’t work.
Best
Nic
Hot zinc and seal is the process used on oil rigs, marine handrails, etc. I don’t think anyone can say it doesn’t work.
Best
Nic
Nic, there was nothing to do repair wise, just light rusting on the body plates to round tubes... after 18 years... it had lived outside all that time.
Mike (my finisher) was the person that stopped me from powder coating over zinc and I really do understand the white powder aspect BUT when I do my Vixen body change, (I am going to do a 3 corner rebuild as I have already done the one corner hence I know what to expect on the other 3 ) I will show you pictures of the wishbones from the car. I did the chassis, zinc wet/wet, but the then owner did the wishbones in zinc sprayed and red powder coating and I will 'peel' the red powder coat off with a blade leaving a powder of zinc un-adhere to the red finish. Re the 3000S, I was going to wet paint over the rusty bits, but Mike did it again FOC, different finsher...different advice, (but it is how you stand by your work that counts). A@
Mike (my finisher) was the person that stopped me from powder coating over zinc and I really do understand the white powder aspect BUT when I do my Vixen body change, (I am going to do a 3 corner rebuild as I have already done the one corner hence I know what to expect on the other 3 ) I will show you pictures of the wishbones from the car. I did the chassis, zinc wet/wet, but the then owner did the wishbones in zinc sprayed and red powder coating and I will 'peel' the red powder coat off with a blade leaving a powder of zinc un-adhere to the red finish. Re the 3000S, I was going to wet paint over the rusty bits, but Mike did it again FOC, different finsher...different advice, (but it is how you stand by your work that counts). A@
Edited by Adrian@ on Tuesday 11th July 22:38
I had a load of parts on my track car hot zinc sprayed before powdercoating - the parts in question take a lot of beating on airfield tracks - they look like they have been blasted in places but no rust is showing - it had 10 years of hard work before I rolled it
I’d happily pay the extra again on parts that need long term protection
I’d happily pay the extra again on parts that need long term protection
Honestly Adrian, I think 18 years and not needing welding is darn good! The chassis I mentioned in powder coat alone has significant surface rust in 3 years. Will be gone in 18…
Hot zinc and seal is the process used on oil rigs, marine handrails, etc. I don’t think anyone can say it doesn’t work.
Best
Nic
Hot zinc and seal is the process used on oil rigs, marine handrails, etc. I don’t think anyone can say it doesn’t work.
Best
Nic
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