hi all, I am in the midst of grouting my project and this morning I applied white grout to a portion of it. When I lifted the tape off the parts I didn't want white, I noticed some grout leaked underneath. No problem, I took an exacto knife to it and scrapped it back and then vacuumed. My question is, when I apply the black next will it just run up to the white or leak over it? Anybody have any experience with this? Thanks