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Over painting Hammerite
Neil2004 - 3/3/05 at 07:10 PM

Has anyone overpainted Hammerite? If so did you just use further coats of Hammerite (and was this successful)? Or did you apply a primer (if so which) then paint with a chassis or enamel paint?
Any help and advice would be very gratefully received.
Thanks.

andyps - 3/3/05 at 09:58 PM

I have overpainted it with just hammerite, but you have to wait a long time to do it if you don't do it within the first 24 hours. Check the tin and it will tell you how long to wait.

flak monkey - 3/3/05 at 10:11 PM

Hammerite should be overcoated within 8 hours. Though you can put further coats on after that of course...like Andy says, you will just have to give it a week to cure...

David

Neil2004 - 3/3/05 at 10:13 PM

Many thanks Andy. I should have mentioned that the chassis was painted with Hammerite over a year ago, so re-coating definately appears to be one option.

Mark Allanson - 3/3/05 at 10:15 PM

I think it is a bit more than a week - more like 3 months

britishtrident - 3/3/05 at 10:23 PM

It never fully hardens but it isn't a problem putting another coat of Hammerite on top it just sort of merges in to the existing coat.

[Edited on 3/3/05 by britishtrident]

Mark Allanson - 4/3/05 at 08:13 PM

quote:
Originally posted by britishtrident
It never fully hardens but it isn't a problem putting another coat of Hammerite on top it just sort of merges in to the existing coat.

[Edited on 3/3/05 by britishtrident]


Absolute tripe. The paint is a synthetic with a silicon additive to give the hammered effect. It cures by absorbing water molecules from the air, if you overpaint it before the previous coat has fully cured, you will trap the partially cured coat by the second, and this will then never cure. This will then react with the top coat and crinkle over time. I havent got a tin handy to read the instructions, but it is clearly stated that you cannot recoat within a given time after the initial drying time of the first coat. Drying is a totally different reaction to curing.

clbarclay - 4/3/05 at 08:33 PM

Why ist it OK to put on another coat before 8 hours, does it not start cureing initial, must be exposed for a while first.

Mark Allanson - 4/3/05 at 09:45 PM

Withing 8 hours, the carrier solvent can still interact with the initial coat and homogenise. After 8 (probably nearer 16) hours, the first few microns on the first coat have started to cure an this is then impermiable to the second coat, so you get a sandwich of semi cured and uncured paint - not a good idea.

Synthetic is a convertible paint, which simply means that it cures to a different substance to the wet, uncured product, and is insoluble in the original carrier. Unlike cellulose which purely dries out and will still dissolve in the original solvent even after 30 years after application.

clbarclay - 4/3/05 at 09:54 PM

How come cars are now being painted with water based paint, but are rain proof. Do they need a non water based laqure or am I missing something?

Mark Allanson - 4/3/05 at 10:00 PM

Exactly what you suspect. The water bourne basecoat is fully water soluble, even when dry, just like kiddies colouring paints. It is air dry and we need to use fans instead of baking the paint to dry it out. When dry, we coat with a full 2K clearcoat to give the water/UV/chemical protection, which needs an 80° bake to achieve full cure.

The main catchword in this thread is the difference between dry and cure. Dry is simply the evaporation of the carrier solvent, and cure is the chemical change in the coat itself