We use Glaze-n-Seal stripper,[black can]on all concrete to remove sealers.very powerful stuff.it will etch concrete serface as well.so be easy.use a chip brush 1.00 each HD has them.go to your concrete supply they will have 1/2 pint samples.READ ALL LABLE.glove up, it will burn.It might take 2 coats to remove polyurethane.leave stripper on 1 minute at a time or less it drys faster in sun.use water with stiff brush to remove all stripper,let dry completely befor 2nd coat if needednow you have a very clean small area of your concrete patio.you may have to put a sealer over the clean area now.if it is a texured concrete,stained patio it wont hurt the finish.just pressure wash all of patio,put a high end sealer over.good luck.ken
We all no alot but can onlydo a little-----

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