Acid staining is an excellent way to add color to existing concrete. One of the reasons this method is so popular is that it does not require a great deal of renovation expertise. There are, however, some issues of which you should be aware if you are undertaking this project yourself.
Many factors may affect the way that your concrete absorbs stain. Concretes can be mixed in different proportions using different fine and coarse aggregates that "grab" the stain at different rates. In addition, how old or new the concrete is often determines how easily it will accept the color. There is no way to perfectly predict what a stain will look like on your particular concrete surface without performing a test patch.
Variations in your stain color can be due to several things. The concrete that makes up the surface that you are staining may not have been mixed correctly before it was poured, leaving spots of different colors that will cause the stained finish to look different from one area to the next. Also, your concrete may be stained with oil or other chemicals. If you do not clean the concrete well, these stains may prevent the concrete from absorbing the stain over them or may actually change the chemical makeup--and therefore the appearance--of the stain. Finally, if the stain is not applied evenly, or some areas are dryer than others when a second application is added, the color may appear uneven.
Many people are aware that it is a bad idea to paint on days that are very warm or humid. But those same people may not think twice about attempting to stain their concrete in the same conditions. Stain is, essentially, a very thin paint that is allowed to soak into the surface of the concrete. If you apply stain when it is too hot or there is a high precipitation rating, it is almost guaranteed that the stain will never dry correctly, and may not dry at all.
Once concrete has been etched with acid in preparation of absorbing the stain, it must be rinsed thoroughly. It is important not to rush and apply the stain directly to the damp concrete. Water will thin the stain, causing the finish to be marred and possibly causing the stain to sit upon the surface without absorbing or drying. Once the concrete has been rinsed, it will take at least a full 2 days for the concrete to be sufficiently dry for staining.
Applying concrete stain is fairly straightforward. Stain should be applied in straight lines, just like paint. However, stain must be applied in very thin layers. Many people are tempted to slap down a thick application and be done with the job, and you can often get away with this when you are painting. But when stain is applied too thickly it will not absorb or dry properly and will simply cause a big mess. Each thin layer of stain should dry completely before another is added to deepen the color. It is most important that you always work from the interior of a room toward an exit; it is very frustrating to ruin a good job by walking all over it because you are trapped.
Lack of Sealer
All finished concrete projects should be sealed for protection. A concrete or masonry sealant will protect your stained concrete from damage due to the elements, accidents or heavy surface usage. Concrete stain should dry at least 48 hours before being sealed to ensure that it is completely dry. When concrete is initially sealed, you should use two coats. Maintaining your concrete will only require adding one additional coat each year.