[missycat]

I've been given a greenhouse for my allotment but the metal plinth it stands on is rusty but not rusted through. Can I paint over it say with Hammerite or similar?

[monsta]

ofcourse might pay to clean it with a wirebrush first 

[Lardman]

You can do, but it depends on what its made from as to how long it will last and what protection it will offer.  Any protection is better than no protection.

If the base is galvanized it shouldn't have rusted, but you'll also have problems getting paint to key to it. If you just paint over the rust chances are it will continue to rust away and leave you with rust marks in your paint.

You can get stuff that 'fixes' rust so it can then be painted over (check your car parts suppliers) if its badly rusted to be honest by the time you've gone to all the trouble to fix it you'll probably be close to the price of a new galv base.

[pairofacres]

A decent coat of Hammerite generally stabilises existing rust and stops it developing further, as long as you knock off any loose stuff first. If you're spraying a frame, their MetalMaster gun is quite neat and stops a lot of wastage. Bit of a pricey investment in the first place, but if you're into "toys", it's quite a cool bit of kit to have around 

[missycat]

Thanks for responses, I found some old hammerite in the shed so will probably give it a go (may buy a hammerite primer if not too expensive). If it lasts a season it'll give me time to save up for a new plinth.