I just finished grouting my kitchen floor with unsanded dark gray grout (near-black "charcoal" according to the box, also it contains portland cement). Not long after the first section I started noticing some efflorescence forming in a few places. At this point everything is done and it is a day old. Despite some attempts to mitigate, there is still quite a bit of efflorescence (very splotchy, but in many places).
Things I have tried:
- Sponging sooner and with shorter waits in between, to try and reduce the total amount of time the grout was wet. Did not seem to make a difference.
- Letting the grout sit and dry out longer in between passes with the sponge (10-15 min). Did not seem to make a difference.
- Using a brass wire brush after curing. This worked well (aside from some mild depth to the grout lines, but the grout beneath was revealed to be much lighter than the "charcoal" color. A bummer but this got the most uniform result.
So 2 questions:
For next time, what stategies are the most effective at mitigating this?
- Are there types of grout that don't have this problem (or to a lesser degree)?
- Can I buy some kind of additive?
- How likely is it that something I am doing during application is the issue? What should I be mindful of?
For this time, what can I do now?
- The wire brush works, but the grout underneath is lighter than the untouched areas without efflorescence (not sure why). Also, if I brush an area without the efflorescence, that is lighter underneath too. I realize I may have to live with that, which is unfortunate but I'm cool with it.
- Would using muriatic acid get me different results, or would it more or less be similar to the brush method (perhaps without removing as much material)?