I'm no expert, but what the contractor said doesn't really make any sense. If concrete changed color like that over time, it seems to me that the floor you started out with would also change color over that same period of time and you would still notice the difference.
This type of exposed aggregate concrete is pretty common here in my area and many grocery stores were using it for a while. Unfortunately, while it has a lower "startup" cost the drawback is that repairs are expensive and come out looking like this. The one down the street from my house has it and you can see every repair they've done to the floor. Some of it has been done for 10+ years. So, no I disagree with the contractor. About 15-20 years ago Walmart did a study on their Sam's clubs regarding this type of flooring and hired a firm to really do a detailed investigation on the cost savings. The study found that it actually had an impact on sales if the cracks and repairs were visible. The study also showed that the level of light reflected off the concrete made the consumer perceive that the aisles were poorly lit and this also impacted sales. They compared it with other stores where they installed vinyl composition tile and found out that while they spent more to maintain the flooring, overall sales actually improved because customers felt it was a better experience and felt more comfortable in the store. Ultimately though they didn't feel it was a significant enough savings to change out all the existing stores and stayed with the concrete. They did eventually begin to use stained concrete as opposed to this type of exposed aggregate.
Sorry, just though you might be interested in that for what it's worth.
I think he's hoping that you'll just get used to it over time and accept that is the way it will look. Unfortunately, I don't know that there is a way to get it to look monolithic again outside of some type of stain or coating which kind of defeats the purpose of this type of floor.
I think I would get a second opinion. I would probably talk to someone who does commercial decorative concrete and see what options they might have to offer.
My good friend Mike Antonetti could probably say for sure. Unfortunately, I'm not sure if he's still lurking on the site or not. He deals with quite a bit of concrete grinding. If you look him up in the directory, you could PM him a message and see.
Best of luck with it.
