"Stuart Noble" wrote in message
...
Bob Mannix wrote:
"geoff" wrote in message
...
In message , news.virgin.net
writes
Hi,
I fixed up some pending structural rust on my bike with hammerite
red
undercoat but don't really feel the need to colour match the bit I did
(underneath). Can I just leave the undercoat exposed ? will this do the
job
? I'm always seeing cars driving about will only undercoat.

Hammerite undercoat, I don't know, but I thought that normal undercoats
absorbed water

Primers stick to surfaces but don't cover and have no surface themselves,
either flat or protective
Undercoats stick to primers, cover, and have surfaces that are flat but
not protective
Top coats stick to undercoats, don't cover, are only as flat as the
surface underneath but have a protective surface.

Combination paints (eg primer/undercoats, "one coat" for decorating)
muddy the water, but the above is close enough!



Most undercoats are the same as topcoats except they have a higher solids
to resin ratio

Errr, so they are not the same! Higher solids, lower resin means better
cover and flatter/matter nad no protective surface. More resin less solids
means worse cover but a hard protective coat which is, I believe, what I
said. There is a sense in which all paints are "the same with different
ingredients" of course!


--
Bob Mannix
(anti-spam is as easy as 1-2-3 - not)