Perform a White Glove Test
To make sure that you have removed all stain residue from the surface, perform a “white glove” test. Dampen a white terry cloth rag or T-shirt in a bucket of water and ring it out. Then gently rub it across the concrete surface. If the rag stays clean, the surface should be ready to accept the sealer without any adherence problems. If the rag becomes contaminated with stain residue, clean the floor again until it is fully clean. Although it may be difficult to obtain a totally clean rag when using certain stain colors on certain substrates, the majority of the rag should stay clean.
(Source: Bob Harris’ Guide to Stained Concrete Interior Floors)
Neturalizing the Concrete after Staining
Why you need to restore the pH balance
It is very important to clean the concrete slab thoroughly after applying an acid-based chemical stain to remove any stain residue that could inhibit bonding of the sealer and to “neutralize” the surface. By applying an acid stain, you take concrete from a basic pH state to an acid state. You need to return the concrete to a basic state, while removing any unreacted stain. Typically, you should wait to remove stain until the chemical reaction is complete, generally a minimum of 3 to 4 hours after stain application.
Here are the basic steps:
- After the surface has completely dried, scrub off the stain residue with a mixture of water and a neutralizing agent, such as an alkaline soap, ammonia, or baking soda. Use a broom with medium-stiff bristles or a slow-speed floor scrubber with a soft scrub brush attachment. Multiple scrubbings may be needed, especially with darker stain colors.
- Rinse the surface with clean water, and remove all water and stain residue from the concrete with a wet vacuum, mop, or squeegee.
Note that if you are using a water-based stain, these cleaning steps aren’t necessary. Water-based stains don't require neutralization or rinsing, and application tools can usually be cleaned with mild soap and water.
After applying an acid stain, be sure to scrub the concrete with an alkaline soap to neutralize the surface and remove any stain residue.