Bricks, Masonry, Asphalt and Concrete - Help! Yellow stain on new concrete

I found some yellow stains on my freshly resurfaced porch(MAINLY ON THE CORNER OF MY FRONT STEP).My contractor had to cover the porch with his plastic tarp because of forcasted rain. I removed the tarp the next morning and noticed a yellow oily substance that seeped under the wet tarp and what appears to be vegetable oil.Now,I tried to remove the stain with a concrete stain remover with no success since I think its imbedded in the new concrete.My question..Is the contractor to blame because of not making sure his equipment was clean? My neighboor said I should paint the entire step with a soupy mix of water and cement to make it white again.Any ideas? Thanks

Contractor should return to identify cause of stain and clean the concrete step. Concrete is porous and will absorb oil. Oil could have been on the plastic tarp used to cover the wet concrete. Attempts to paint over oil stain would likely create adhesion problems. Concrete cleaners for oil stains usually require keeping concrete wet with cleaner and allowing to soak into porous concrete and using brush to agitate. Check the concrete cleaner you used to see if it recommended for oil stains on concrete.

Since the concrete is fresh and the problem could have been caused by the contractor, I'd call him before trying anything myself.

Thank you all for your quick replies.. Cleaned the stains with a wire brush and they vanished.I was lucky this time.

Whatever was on the concrete apparently was not oil. Must have been soil. Now that concrete is clean, you might want to seal with a couple coats of penetrating sealer to keep out stains.