Drawbacks to Acid Staining Green Concrete

By Chris Sullivan – ChemSystems, Inc.

Question:

What is the drawback of acid staining a residential concrete floor the day after the concrete is placed, rather than waiting the suggested 28 days? Is this recommended waiting time the same for both acid and water-based stains?

Answer:

As soon as water meets cement, a chemical reaction starts and it takes approximately 28 days for concrete to achieve 90% of its strength. During this period, crystals start growing, which are the glue that holds concrete together. You don't want to bother those crystals with any distractions while they are developing and hardening. Stains, especially reactive acid stains, are one such distraction. The other factor to consider in the first week after the concrete is placed is moisture content and how that might affect color development. The higher the water content, the more the stain (whether it's water or acid based) will be diluted and the lighter the color. Goofy side reactions can also take place with excess water in the concrete, possibly resulting in funky color development.

All that being said, will staining destroy concrete if applied 24 hours after placement? Probably not. Will it be a roll of the dice what the color looks like, how permanent the color will be, and whether a weak surface will develop? Probably.

I usually take a middle ground on these issues. Typically 10 days to 2 weeks is enough time for a good cure before staining, especially in warm, dry conditions. Wet, cool conditions will slow things down. Applying a sample of the stain to the actual surface is the only way to really see what you're going to end up with.

Applying acid stain to green concrete can weaken the
surface and result in extreme marbling and color variations.