The most frequent phone call I receive out of the phone book usually goes something like this, “Hi, I have a back patio that I wanted to stain and I went up to __________(fill in the blank with one of your local chain home improvement stores) to pick up some “concrete stain” and now it’s flaking off. Is there something I can do to stop the flaking?”
Some customers have even gone to the extent of contacting the company to complain about the product and most of the companies will send a “stripper” and more product to re apply. I am not here to trash those companies, but to explain the very important difference between an ACID stain and a concrete stain. An acid Stain is a chemical reaction. Any other generic stain (that I’ve seen) from your home improvement chains are coatings.
So, I’ll usually take a drive out to the home of the disgruntled caller. I’ll measure up the patio and give a quote on how much it will cost to grind the coating completely off and acid stain the new canvas. That’s usually the last time I talk to them, because what started as a project that would have cost no more than a few hundred dollars and a weekend, turns into a labor intensive, relatively costly, fix. However; the result from staining a freshly ground surface, is beautiful. The aggregate in the concrete becomes slightly exposed, leaving a terrazzo like finish.
In any case, if you are going to stain your concrete, get out a phone book or get online and look up local concrete supply stores. Make sure that the stain you buy is an acid stain. Once you’ve done that, you have to carefully execute the steps in the right order. The most common problems I hear about with actual acid stain results are as follows; white foggy areas in the sealer, wrong color, areas where the stain did not react, and the acid stain not even taking at all.
White Foggy areas in the stain are caused from a few different things that I know of. The most common cause is that the person who applied the stain either neglected to neutralize the acid, or did not neutralize the acid at all. To neutralize the acid, you can go get some ammonia and cut it with water, then mop it all over the concrete or put it in a sprayer and coat the concrete. Then hose it off, or if you’re inside, mop it up. You should be able to rub a cloth across the slab afterward and pick up hardly any residue. Next, let it dry completely. That can be another reason for flaking cloudy sealer… If you are trying to fix sealer that is already ruined, go get some cheap bedsheets and some xylene. Lay the bedsheets flat across the concrete and soak them in xylene. Let them dry and crust up and then dispose of them. If you need to, do it again. Then neutralize and seal. Make sure you get a sealer from the concrete supply store that has a high solids content. If the foggy marks return in the sealer you are probably facing a more serious problem. Sometimes concrete slabs are poured over ground that retains too much moisture and if there is no moisture barrier the moisture can actually be drawn up through the surface of the concrete and weaken the sealer. At that point, I would go with tile.
WRONG COLOR… Acid Stain is a chemical reaction with the cement in the concrete. The actual color is based on many variables. Some of them are controlled variables and others are not. This is important to understand. You can only apply acid stain so many different ways. The concrete has more control over the color than the person executing the application. If you are going to get on the ground with a color chart and compare, you are not going to be happy. Start light with diluted acid stain and get darker from there. The stage immediately after staining was designated the “freak-out” stage by my old boss. When the concrete stain has dried and the sealer has not been applied, it often looks like rust. Don’t worry about it. To see something close to the color that will be achieved through sealer, just get an area wet again.
STAIN DID NOT REACT. Since Acid Staining is a chemical reaction, anything in the pores of the concrete or on the surface will either block the stain from reacting completely, or change the reaction. Often people pull up there carpet, do a little floor sanding, and stain. This is fine if you like the result, but some people hate it. Paint,carpet glue, chemical spills, and other things on the concrete, never completely go away unless you grind them down…or you can overlay, and that is another article at another time. I would give the same advice for finding an overlay as I would an acid stain. Stay away from generic resurface products.
If the stain did not take at all anywhere, there is probably a cure and seal product on the concrete. You’ll have to strip it or grind it or overlay… If it is an outside slab, chances are it has just been suspect to the elements for too long. Often the pores are clogged with dirt and the cream has worn off the top leaving small aggregate and sand exposed. Sand will not stain. The result achieved through staining a slab in this condition would be the same result as if you hosed it down. Same advice here, grind down or, if it’s not cracked and shifting, find a good over-lay. Then start over.
Source by David Council