Just a thought. Filled a hole with plaster the other day outside. Looked at it this morning and its cracked!!! Guessing I should just rub it back and put some more filler in it!!! Any advise from anyone who knows would be appreciated, ta.

The hole was too big! Plaster shrinks slightly as it dries out: for small holes this is not noticable but for big ones it will result in cracks showing.

You could certainly rub it back and apply more filler, but for larger holes you can buy a plastic mesh for the plaster to key into which ensures that the shrinkage happens uniformly across the plaster and doesn't result in a noticable crack.

As expected from BE, a prompt and precise reply.
Thank you x