Chassis paint of powder coating?

[Bob Purton]

What is your preference when restoring a microcar chassis [thats if the car has a chassis] Do you prefere a couple of coats of finaganes smoothrite or powder coating and why?

[Jim Janecek]

paint over powdercoating if you use a paint that has a urethane base so it won't crack or chip.

Powdercoating seems like tough surface but if you do not bake the heavier pieces of the frame long enough it will chip off easily.
I've seen a number of Isetta frames that were powdercoated but they were not properly baked, either at a high enough temp or long enough and they did not hold up to dings and scrapes as well as a good urethane (read: flexible base) paint like POR15 or something.

also- the powdercoating can add a thickness that may be a problem depending on tolerances involved.  Small holes and passageways can become constricted, requiring the use of a drill to enlarge them to proper spec.

of course the urethane paints can do the same thing if you are not careful.

[cuscus47]

I also prefer POR after a good sandblast or heavy scrape.  It is a moisture-cure urethane and so helps prevent further rust even if a tiny layer of rust is present.  It cannot do this rust prevention if it goes over old paint, though it will still stick.  It dries extremely hard, waterproof and has a large elasticity coefficient and so is ideal for flexing.  The only problem is that it is dear and it will cure once opened (because of the moisture in the air) and so use in small containers.  Buy pints or quarts, not gallons.  Quite often I will use only a half of a quart can, and in six months, if you then break though the skin with a chisel and hammer (about 1/4 thick by now), you still have half a pint or so of still good stuff. Spray is ok, but if you brush, it will dry brushmarkless. Use toluol to clean up, nothing else works as well. Once fully cured, 2-3 days, nothing will stick, primer, paint or even more POR, unless sanded with 600 and plenty of elbow grease. You can buy though POR primers and fillers that will etch it.  If I am going to paint over it, I flash a quick spray of selfetch over it after a few hours dry time, and then it will stick and so will any top coats.  I prefer it to an epoxy primer/filler. Good luck Bob.

[Bob Purton]

Ah! I'm not alone then! The whole of the uk has gone powdercoating mad! Everyone I talk to is saying I powder coated this and powdercoated that, has everyone forgotten how to use a paintbrush? I have seen a lot of powder coat flaking off once the seal is broken by a chip or gouge, the moisture appears to get under it and it comes off in huge chunk's. Thats a gross generalisation I know,  the process varies and some companies are better than others. I'm sure its got its uses but I prefer a good chassis paint. Ten years ago I painted the underside of my Messerschmitt wings with two coats of hammerite, ten years later barely a mark on them! My Isetta chassis was smoothrited eighteen years ago and again still in tact. I have heard good things about POR15 especially the tank sealant but have never tried it mainly because I prefer to use home grown products and I think all that pints and quarts would confuse me over here that all went out with groats and bushels! Sorry cuscus, couldnt resist it and only joking! Thanks for the benefit of your experience and maybe I will try POR15 sealer in my Motobi tank. Have been asked to do someones Isetta chassis, I think I will stick to sand blasting and Smoothrite. The downside is the fumes when using it, must have plenty of ventilation. Has anyone had good experiences with chassis powdercoating IE still in tact after long useage of the car?

[cuscus47]

I understand Bob, that you prefer to put a UK product on a German vehicle  .  That's your perogative.  I haven't talked of a groat for years, however I believe that Lizzy still gives them out on Easter in the Maundy money.  So they are are still minted, though not for general circulation.  I realize that you may be confused with pints, quarts and gallons etc, especially since they are different sizes this side of the pond, but however packaged, it still is a great product.  Since you've had good success with Hammerite/smoothrite, stick (no pun intended) with it.  From the description, Smoothrite seems it may also be a moisture cured urethane, where as Powdercoat is a heat cured dry urethane.  It makes a good hard surface, but is limited to poorer mechanical and chemical bonds with the substrate and so rust can still form and spread if damaged, whereas a moisture cure removes continually the potential for rust forming, even if damaged.  Rust will form in the location of the damage, but is inhibited in its spread.  Use the old paintbrush method, like you have before, and what ever you use it will be better than nada. And you always do it perfectly with love and talent.   Ian.

[Bob Purton]

No Ian, I prefer to put a UK product on a UK built Isetta,  built in good old Brighton. I think smoothrite is of the nature you describe, it also has rust converting ability but I prefere to start with clean bare metal anyway. I used it on my rusty trailer, just having used a wire brush to remove the worst of the rust, the trailer stays out in all weather and I have to repaint it over the rust about every eight years so it is a good product. Seriously though I would like to try POR15 sometime, its available in the uk through the Frost catalogue I think but we pay a premium for these US products, where as I would pay 10 grouts for a tin of Hammerite I would have to pay at least 15 grouts for POR15! All the best Ian, nice to hear from you!

[Jim Janecek]

if "smoothrite" is a UK brand of moisture-cured urethane based paint then it is basically the same thing as POR15

I'm not sure what -if any- differences there are between them.

[Big Al]

Hammerite and Smoothrite used to be enamel paint for brushing. Then Finnigan's was bought out, by an American company?, and the paint was made available in spray tins. I think you will find it changed formula at this time as the whole lot of products was relaunched. Certainly 'modern' Hammerite does not cover like old Hammerite used to. However for restorations this is irrelevant in most cases since you should not be using it unless doing a budget job! Smoothrite was always for a better finish even in Finnigan's day but it certainly can give a nice coat. I am not sure it is a urethane based product though. For Hammerite I found the cheapo deal Aldi stuff is better than Hammerite - and it would appear to be German. Of course the Germans were happy to sell cars with hammer paint finished dashboards etc since they have a clearer feel for engineering or something, see Goggo saloon dash for instance. Hammerite will not equal this finish but ape it. Meanwhile the Brits glued bits of wood and cloth over things and charged extra for it.
One reason for interest in powder coating is the availability of a home kit for around £100 from Machine Mart in the UK. I am attracted to it myself but what is not made clear is you need a stove to heat the treated item. The wife might grumble on finding a suspension unit in with the Mutton so an old cooker or something might be needed. I wondered if the old Aga was up to the job. However a chassis is a bit big for controlled home heating so this method is really only good for small bits.

[Bob Purton]

Hi Al and welcome back.  Do I understand this correctly? Since you have been away you have married an old woman named Aga? 

[AndrewG]

How hot does the powder coating need to go?  For curing laminates, a lot can be achieved by building an 'oven' out of foam insulation and putting a 'black' heater or two inside (the sort of thing sold for greenhouse use).  A fan heater works well though then you are skating near the limits of safety.

[Rob Dobie]

I found this on the web ... "powder coated items are placed in an oven and heated to temperatures that range from 160 to 210 degrees C (depending on the powder)."

This is from Australia ... http://www.finishing.com/Library/pennisi/powder.html

[Big Al]

Hi Al and welcome back.  Do I understand this correctly? Since you have been away you have married an old woman named Aga? 

I wondered if related to the Aga Kahn but on the basis she can't I suspect not. Hot stuff though. (I assume our chums abroad know an Aga is a sort of stove cooker or this will all be meaningless).

[marcus]

I use Powder Coat on quite a number of my products but I would not choose it for any exterior car part. Although it is a good coating for many purposes, there is usually a little edge or nook which does not get coated. Even a microscopic hole in its surface will let in some moisture. This will cause rusting, which will spread under the powder coat like buddleia roots / shoots spread between brick and plaster. Suddenly a big flake of PC will fall off, letting in more damp. It is baked onto the metal, but does not chemically bond onto it like etch primer. Also PC has a very low surface energy, meaning anything (like paint) applied over the top is unlikely to stick very well.