Matte paint - Porous?

yep, better to have a slightly gloss finish....

Doki ( snipped-for-privacy@gmail.com) gurgled happily, sounding much like they were saying :

No.

Matt paint is, however, "less smooth" than gloss (the fact it reflects light less is what makes it less shiny), so you won't get the water beading in the same way, which may make you think it's porous. It isn't.

Oh good. Just wondering as Matte is the factory finish for something I've got to paint and I don't want it rusting away. That and primer being matte and porous had me wondering.

Primers and unprotected metallic matt finishes are porous in the sense that they do require a protective layer like varnish, lacquer, gloss etc. In an unprotected state the paint will absorb impurities simply because they lack oil or resins which gloss finishes do not.

Although they are not porous like a sponge or blotting paper they are however an open finish that requires closing with a material that seals the porosity.

You can add a gloss to a flat matt paint and add a matting agent to a full gloss, semi-matt offers better protection than a full matt finish and is easier to clean.

Steve.

Gloss paint can be porous too though right? That's why people use wax etc to seal the paint??

( snipped-for-privacy@yahoo.co.uk) gurgled happily, sounding much like they were saying :

Wax polish isn't to seal porosity in paint. It's to make it look shiny.

If paint was porous, water would get through to the steel and your car would rot to bits in short order.

I guess they used that paint on fiats and toyotas then.

Fiats maybe, but Toyotas are not noted for rot. Not modern ones anyway; I've had lots of them and the only ones that rotted were those made in the 70s.

Fiats were no worse than any other mainstream 80s car for rot and since about 1990 they've been significantly better than most.

SteveH ( snipped-for-privacy@italiancar.co.uk) gurgled happily, sounding much like they were saying :

Quite. Got to buy a Ford these days to get real rot.

The message from snipped-for-privacy@italiancar.co.uk (SteveH) contains these words:

But in the 70s they were staggeringly rusty. I patched a Fiat sill with some Mini roof once. Left it ground and sanded flat but unpainted overnight. Next morning the patch was still shiny but all the original Fiat had gone red.

Guy King ( snipped-for-privacy@zetnet.co.uk) gurgled happily, sounding much like they were saying :

It might be as much to do with the age of the Fiat as anything - '77-'78 was notorious for a shortage of decent steel, and everybody had to use Soviet recycled (s)crap. Hence the real shortage of anything R-S-T reg left on the roads.

The message from Adrian contains these words:

Nothing wrong with recycled steel - very good stuff provided it's blown for long enough in the convertor.

Guy King ( snipped-for-privacy@zetnet.co.uk) gurgled happily, sounding much like they were saying :

It wasn't. Hence the S being in brackets.

Cit had a similar problem on later CX turbo diesel engines - the blocks were cast in India, and weren't for long enough - so loads of impurities were left, which dissolved if the cooling system was filled with 'orrible British tap water. Many cars didn't suffer from porous blocks - usually those that used distilled water or nice tap water (one CX expert living near Aberdeen swore he'd never seen one affected car), but most did.