On Tue, 11 Jan 2011 18:58:03 +0000, Red Green wrote:
Can't say if it will flake off over time.

I did our septic tank caps a year or so ago, and they're flaking quite
badly. I just gave those a quick spray (with a view to doing something
better if needed) and figured I'd see how it went; the answer seems to be
"not well" :-)

Like you say, some surface prep - light sanding and then primer - is
probably a good idea.

cheers

Jules