Water came through and now my gypsum false ceiling is stained and sagging — patch it or replace the board?

Your instinct is right — painting over it is hiding an active leak, not fixing it. A brown stain and a sag mean water got in and the gypsum board has taken on moisture; stain-blocking and repainting a wet, sagging ceiling just buys a few weeks before it bleeds through again. The order is non-negotiable: find and STOP the source first, dry it fully, THEN decide patch vs replace.

How to handle it: - Stop the source first: a stain that's still spreading, or a sag, means water is likely still getting in — usually a failed waterproofing layer, a leaking pipe, or an AC drain/condensate issue above. Fixing the source often needs the waterproofing membrane above sorting — products like Sika are what a proper repair uses. Don't skip this or you'll redo the ceiling. - Patch vs replace: once it's genuinely DRY — a small, firm, lightly-stained area can be cut out and a new piece of board let in, taped and skimmed. But board that has sagged, gone soft/crumbly, or grown mould has lost its integrity — replace those sections, don't patch. - Mould: in a warm, humid ceiling void, wet gypsum grows mould fast. If you see or smell it, that board comes out — you don't paint over mould.

So: stop the leak, dry it, replace what's soft or mouldy and patch what's sound, and only then paint. A painting services in Dubai crew that insists on drying and source-fixing before finishing is the one you want — the one offering to just stain-block a sagging ceiling is the one to avoid.