A local contractor (Alberta, Canada) is suggesting to put down a polysapartic coating on top of my outdoor patio (after grinding to remove surface flaws, etc.). Says that he can put a fine dusting of sand or quartz between layers to give it slip resistance. Have been reading up on polyaspartic coatings, but generally only find info for them for interior use. I also have read that they might not allow water vapour to move through the concrete itself (as a regular sealer might). Has anyone had experience with these types of coatings for outdoor use?