If you wipe the grout off too soon, the grout may come out from between the tiles. Wiping off grout immediately after it has been applied is generally not recommended. So, after applying the grout, wait 15-30 minutes before wiping the grout off by using a dense grout sponge. It is also important to rinse the sponge frequently and wring it out well to ensure it is not spreading the grout around.