Powder Coat vs Epoxy Paint

[Martin Sullivan]

Hi,

An interesting question, I think.

I’m interested in the different ways of painting the underbody components and the protection against the effects of stone chips, scrapes, spray and horrible salty roads.

In my ongoing mini restoration I am (was?) using a combination of the two. Epoxy for the chassis and powder coating for anything I can take off.

Powder coating is quite a “thing” at the moment. Everyone I have spoken to has regarded powder coating as the most effective way to paint and protect car components and this is the path I was going down.
However, I thought I’d just question it.
The issue with powder coating appears to be in its longevity. Once chipped (and we’re talking the underside of a car here) water can and will get under the paint and spread, causing flaking, blister spots and consequently rust. I’ve certainly noticed this on the Zed, but it is 20 years old.

Epoxy appears to be harder wearing and less prone to chipping. From what I gather, if it does chip it won’t allow water to spread under the coating as much therefore reducing the scale of blistering.

I have the various bits in the picture away being shot blasted at the moment which is costing about £55.
I’ve been quoted about £85 to have it all powder coated which will be easier than painting (ignore the fact the components aren’t fully broken down).
2.25litres of Epoxy paint from Rustbuster is roughly £60 and will be enough to do all of this, all the chassis and most like all the back end.

What are people’s thoughts and opinions?
Epoxy or powder coat?
What are your views on the amount I’ve been quoted?

Thanks
Martin

 

[RonA]

Hi Martin
I restored a TR6 around the time of the millenium, and got a lot of suspension parts (including springs) powder coated at the time, they still look like new under the dust but they haven't really had a hard life. The powder coating was quite a soft resilient type which probably would survive better on suspension parts, I have seen some powder coatings which look hard and glossy so it looks like there are different grades of powder coating. Also good powder coating needs good grit blasting. I've had little experience with epoxy, I found it gave a nice hard surface that looked good but possibly would chip easier than the powder coating.

 

[colb]

In my experience powder coating is only as good as the preperation of the parts to be coated and the thickness of the coating applied. It bakes hard and as you say quite easy to collect chips which then allows moisture to get underneath the covering with the coating starting to lift over time. I have always had fair results with Hammerite paint but once that gets chipped it will allow moisture in and lift the coating after time just the same as powder coating. Mate always uses red oxide paint followed by black hammerite on his Z's seems to stand up to wear and tear ok.

 

[DrWong]

No experience of powder coating, but used Lechlar epoxy on my chassis rails, sills (inner/outer), ARB + mounts, x-brace, wheel arches etc. It's great for DIY and hobbyists because it's cheap and versatile. I just mix up small amounts to use as and when I need to. No special equipment needed other than proper PPE and you can just brush it on. It's pretty tolerant of less than perfect preparation (I've got drops of the stuff stuck fast to the concrete of my back yard) and easy to touch up if need be. I did my inner chassis sills two years ago and they still look perfect, despite year-round (albeit light) use.

 

[gookah]

my thoughts are :
most BMW springs are powder coated, grit punctures the coating when the bottom spring support gets small pieces on it, that then allows salt water in, and spring eventually rusts and snaps.

Powder coating will be ideal if you dont drive in winter or in the wet very often.

Otherwise might be best with normal paint that you can touch up.

 

[Woodsta888]

The paint can be touched up with spare paint, which is the ultimate argument for - the paint.

The rear trailing arms just aren't worth prepping any other way than shot-blasting, unless you like a dremel workout. I started prepping mine, and in the end sent them to be shotblasted for £50. The mainbeam I prepped myself, and in hindsight, whilst possible for a good DIY job timewise, next time I'll pay someone else.

Painting - well a brush wont beat a spray considering it's suspension, so unless you have access to a spray setup then, finish wise - we're back at powder.

The question is - does epoxy paint positively or negatively, affect powder coating if applied to it?

If positive fine. Negative? - (some chemical incompatibility) then, well, no.

I've done it by hand.

Next time; I'd grind the spatter off the rear beam - get the rest shotblasted- and for the price - powdercoated. I'd keep an eye on chips with external silicone by Dow Corning if, epoxy paint isn't compatible with powder coatings.

Actually, next time I'd prolly spend a day at the Z-shed and get a pre coated one from @Lee installed and enjoy helping.

 

[Lee]

We’re still not sure if the Powder coat is the best option we’ll have to see how it fairs over the coming years. I can say though the coating is very thick and won’t chip easy.

The subframes look very pretty finished.

 

[Delk]

I used to off road a lot and had big Jeeps that had very hard life being smashed on rocks and covered with mud.

Powder coating looked very nice when new but didn't last long. As you said once chipped it would starts to corrode underneath and flacked off in sheets. Items that were painted lasted longer as the damaged was more centralized.

 

[hard top]

I used to off road a lot

I used to enjoy doing that in a SWB 1966 Land Rover ....

 

[Oddly Godly]

I used epoxy mastic in the late 90s on my mx5. It did a great job of protecting the wishbones etc that I treated. Powder coating looks nicer but if you can't see the treated parts does appearance matter.

 

[Delk]

I used to enjoy doing that in a SWB 1966 Land Rover ....

I had a 61 2A for fifteen years. It spent 10 years as my daily driver. My last Jeep followed me from the West Coast of the States down to the Islands then to the UK. Used it for awhile but it became less and less so it moved on for the Z3.



I owned the Jeep from new and the first few years all the and parts were powder coated. Even living in the mountains of Washington State and Oregon where rust isn't an issue it was all flaking off because of the damage. After that it had normal paint applied for the rest of the 20 years I owned it. I didn't have near as much trouble and could just touch up spots as required. I built the front bumper above and it wasn't just for show. It took a good amount of abuse through the year. In the winter I could touch it up or repair it myself unlike powder coating.

 

[137699]

One of my other cars I had all the subframe, axles & bits powdercoated 4 years ago.
I used it all year round and it's done around 40,000 fairly hard driven miles since that work was done including 3 trips to the scottish highlands - yet it still looks like new under there.
Pretty pleased with the results.

 

[Oddly Godly]

When used epoxy mastic back in the 90s the advertising said it was used on North Sea oil rigs.if it was good enough for them I thought its good enough for my MX5

 

[Lee]

One of my other cars I had all the subframe, axles & bits powdercoated 4 years ago.
I used it all year round and it's done around 40,000 fairly hard driven miles since that work was done including 3 trips to the scottish highlands - yet it still looks like new under there.
Pretty pleased with the results.

This is good to hear. The last 10 cars out the Zedshed have been leaving with an extra thick powder coat on everything. Looking forward to seeing how this fairs on our roads over the coming years.

 

[Pingu]

"Differential aeration corrosion" is one of the terms from college that stuck in my head. We used to call it "the other name for rust".

It is the (mostly) hidden damage caused by flaked/broken protective layers. Some of the examples of this type of corrosion from the North Sea were quite frightening. One piece of metal that looked well painted was reduced to 50% of its original thickness about three inches from the small speck of damage. The steel directly beneath the damage was metalurgically well protected, but three inches away were some inclusions that were a gateway to poorer quality steel. We were told to use a hammer to test the coating using sound and feel, unless we had access to X-rays, etc. It looked near perfect after a quick wash, but was rotten underneath.

 

[Martin Sullivan]

I’ve had a few bits powder coated now. I used a company who does a lot of bits for a motor fabricators I know.

All of the parts had been sand blasted. The majority of it had been done by a company but the engine brace I did myself.
The brake dust covers were new. I sand blasted them back to bright metal before new powder coat as when they were supplied they were scratched.

The wheel hubs were pretty good. The areas where the dust covers bolt down the powder coat was flaky. It’s as though where there is a sharper angle the paint has adhered well.

The front anti roll bar took a slight knock from the jack I was using and the opposite end fell into the slate drive from about 5 inches off the ground. Both very minor and I expected to be inconsequential but the powder coat has been scratched through to bare metal.

Ive taken quite a lot of care reassembling the car so as not to scratch the fresh powder coat but I can’t say I’m too impressed so far.
It cost me £60 for blasting and £100 for the powder coat. Full quoted cost was £220 if all done by a business rather than some cash and mates rates.

I don’t know if I’ll get anything else powder coated. It looks good but I’m far from convinced.
I suspect I’ll have some more bits powder coated but certain, harder working parts will be painted in 2 part epoxy.
Roll bar and chassis brace I’ll probably powder coat as it can come off. Wheel hubs (knuckles) I wish I had painted.

 

[Chris Hunter]

We have had several Lotus Elises, Exiges, a
Europa S all powder coated cosmetically it looked well but was easily chipped. I have just finished a rear end refurbishment on my 3.0 but plumped for rustoleum for longevity.
Chris

 

[IainP]

Epoxy.
I had an old bloke go off on a right rant about powder coating a few years ago. It used to be his business, he was absolutely raging that the coating had cracked when he bent a steering tube on his hillclimb car.

In summary:
Grit size and blast pressure is critical, he said most places use the same for ali and steel. They shouldn't.

Temperature. The Metal MUST be heat soaked to the melting point of the powder. It'll flow long before that, BUT, it won't bond to the metal, or get into the micro mechanical retention that should be provided by the correct grit size.

If the metal is not heat soaked, the coating WILL crack, chip or flake.

My guy said very few coating places heat their items up high enough for long enough, it's expensive in energy cost and takes longer to cycle.

I use epoxy or Hammerite every since. I now also know now why the powder coating place I used when I was into bikes went out of business, they did it right, but were undercut by several others.

Iain