I need some help with what product I can use to repair 6 concrete steps leading up to the front door of a period building. The steps are heavily pitted with undulations and dips that vary from 4mm to 10mm. I've used various forms of latex in the past, for interiors, but need some help in dealing with this as its exterior. Needs to be waterproof and hardwearing. Would like to avoid tiling them or building them up in concrete screed as assume it would need a minimum of 1" thickness. Cheers..