UKC

I'm guessing this isn't quite the done thing, but having seen how successfully the people painting my house used wood filler to fill in around a small hole in my outside wall before painting over it (I guess it's all synthetic stuff which hardens - essentially), for very small patches can one get away with putting filler straight onto gloss paint and then painting over it?

Thanks.

Tim

There are two kinds of filler: Decorator's caulk, which is an aqueous paste that never quite hardens and so retains some flexibility, great for filling small cracks between materials with differential expansion such as window frames and walls. It's easy to use, good when finished off with a wet sponge and hides a multitude of sins. 

The Polyfilla type, which is plaster of Paris or as close as dammit; can be sanded smooth and is great for filling dips and holes in flat surfaces but not cracks where there's movement or sanding will be awkward. 

Both will stick well to clean dry gloss paint in my experience. The best tool you can buy for spreading Polyfilla is a nice springy flexible decorator's spatula.

I think timmd is talking about two part wood filler, which is a resin/pu type deal.

If that is the case it should be fine, it sands nicely and will take paint easily.

It might stick - but why not just sand the area 1st with something like 40 to 100 grit, fill, sand it smooth and then repaint

Wood filler (if brown) will need undercoating before glossing over. It does stick to gloss itself. The one I use is cellulose-based.

Decorator's caulk - if you fill gaps behind skirting boards with it on walls prone to black mould you will need to paint over it as it WILL go mouldy .

If its external and the wood is dry and rotten then you can't go wrong with car filler. Worked a treat for a rotten window frame I had.