I have an aircon unit on my balcony. It has had a slight leak, over a long period, where the pipes are connected to it. Now it's been moved and regassed, but it's left behind a nasty stain on the concrete floor. I've tried white spirit and thinners but they don't touch it. Any ideas on how to remove the stain, please ?

Try bathroom/toilet cleaner in the purple bottle, Vixol. Give the area a good soaking and let it sit for a couple of minutes then scrub it with a brush. Be careful, it contains 10% hydrochloric acid.

Thanks for your quick and helpful response, WayneD - I'll try that.