I have a concrete patio. It holds water when it rains, and then turns green in the middle. My husband seems to think that the builder did not put a barrier (plastic) underneath it. How can I fix this or keep it clean? Thanks for your help.
You don’t put plastic under patios. You only use plastic under floors inside your home, like when cement slabs are poured into basements and crawlspaces. For patios, you want water to drain off.
Your problem is that your patio doesn’t slope properly, and unfortunately, this is almost impossible to fix at this stage of the game. You could put on an additional layer of epoxy compound to reslope the uneven surface for proper drainage, but it's a difficult and messy undertaking, and the effects probably won't last long.
If I were in your shoes, I'd accept the current maintanance issue until you're ready to replace the patio in full. And when you do, make sure your patio crowns in the middle – that is, comes to a slightly higher point – so any moisture or debris runs off.