It is one of the oldest questions ever asked among do-it-yourselfers and construction newbies: “Can you grout over old grout?” The right question is probably, “Should you?” There are many factors that dictate whether you could apply grout over old grout lines while regrouting tile or if you will have to do the backbreaking work of removing old grout to make way for a new one.
The key thing to remember is that new grout does not bond to dried or cured grout well, although it may seem as if it does. After a while, the new grouting material will simply crack and separate from the old one. Here are a few scenarios and solutions you might want to consider before grouting over grout:
Grout Over Grout Scenarios
New, shallow grout, unsealed
If grout is relatively new, shallow and has not been sealed, it is perfectly okay to re-apply new grouting material over it. By “shallow,” we mean a depth of 1/8 inches maximum. It’s better if the depth is at 1/32 or 1/16 inches. If it is higher than 1/8 inches, the grout has to be scraped off and the joints cleaned before new material is added to replace it.
If grout has been sealed, do not attempt to put new material over it since this will not adhere to the dried surface. Instead, remove as much old grouting as you can, clean up and allow to dry before applying a fresh layer of grout.
Damaged grout lines
If old grout is crumbling, cracked or damaged, do not try to fix it by applying new material over it. Once the material dries, it will only crack and crumble away, wasting your precious time and effort. Remove the old material so you can replace it with a new layer.
Dirty, discolored grout lines
If the problem is just dirt and some discoloration, there may be no need to replace the grouting. Instead, try cleaning out the gaps first with a good cleaner. If the results are satisfactory, you may not have to apply new grouting material at all.