Great question. I have a friend with a similar issue on their bathroom counter top. Would love to hear what you find out!

If your concrete countertops are changing color when they get wet and the stains disappear, then the sealer that was applied has worn off, or it was never put on proper to begin with. The purpose of the sealer is to create a barrier between the material (concrete) and the surface, when you are getting it wet, the counter is absorbing the water which is giving you the glossy look. When using sealers there are basically two types, penetrating and topical. Penetrating as implied go into the actual surface and pores of the material and bond with the counters to give protection. Topical sit on top of the counters to protect. As far as resealing, you must first know what type of sealer was originally used, as some sealers will not adhere to previously treated surfaces, or actually can counter- react and cause additional problems. I personally do not like using epoxy type topical sealers as you lose the natural beautiful feeling of the concrete. When I first started working with concrete countertops, I practiced for a couple years on many different sample pieces and studied the many aspects needed to be understood to work with concrete before venturing out to market them. I know this doesn't particularly help you now, but for future endeavors or for others reading this dilemma and considering using concrete, make sure you find a quality artisan who can produce a professional product. As far as your top, if you can not find out the specifics of what went into the tops and sealer used, you also should try to contact a local artisan to help you solve your dilemma. As far as the glossy wet look, there are sealers that will produce this look and is a favorite of mine personally and I recommend it to the majority of my clients. Hope this helps, and if you have any follow-up questions, feel free to ask, I would be glad to try and help.