Question
Hey Mr. Goulding-

I have an acid stained exterior patio that has started to fade.  It is about four years old and I'm fairly certain it was never sealed (my fault).

I was wondering if it is possible to use an acrylic stain over the acid stain.  If so, what is the best way to clean/prepare the colored concrete prior to applying the acrylic stain.  The masonry cleaner/etcher I looked at said not to use on colored concrete?

Also, how well does an acrylic stain hold up in your opinion?

Thanks for any help or advice.

-Ben

Answer
Hey Ben. Great question. I will be very upfront here. I have limited technical knowledge in this area as I am more specialized in the use of natural stone. Also, I find a lot of controversial issues in dealing with concrete. We all do things a little bit differently and I don't think you will ever get everyone to agree on how to handle something like this. There really are a lot of variables here. I try not to use acrylic sealers because I don't find they penetrate into the concrete enough.(Depending on the porosity of the concrete and your prep work), but, maybe there is a product that I also haven't found yet that is better?
With that being said, here is my answer of what I would do in this case, and ask you to investigate it a little further as well. Sometimes you have to gather as much information as you can and weight the pros and cons on a piece of paper to come up with your solution.
First. I would go with an acrylic sealer instead of stain. If you like the look of the concrete now?, you are killing 2 birds with one stone and saving money. This will actually enhance the faded stain that you now have darkening the color and bringing it back to life (wetting things as an example). It's a patio right? I would use something that is going to cut the grease like TSP to clean it.(You probably had a bbq on it?)
Make sure you use a clear, UV stable, acrylic sealer that is breathable. The breathable part is to allow any moisture vapour that is sponged up through the concrete to escape.
It really depends on the amount of foot traffic you have on it for how long it will last. It's a maintenance issue for sure. Yes, you will have to re-apply this. It could be in a year? or it could last for 10 years if there is little or no traffic on it.
Another good place to post this question is http://www.concretenetwork.com/ again, gather as much info as you can. I have a pretty full computer of bookmarks to cross reference everything, even if it is something I have been doing it for years. New ways, techniques, and products are introduced every day. Best of luck to you. Wish I really could help you more.