Learn why you should fill your bathtub with water before caulking. Find out how your bath tub expands and contracts, and how filling it before caulking will prevent cracking and crumbling grout.
LESLIE: Carol in Missouri, welcome to The Money Pit. What can we do for you today?
CAROL: Hi, I need to have a question answered about caulking around your tub .
LESLIE: Sure, how can we help?
CAROL: Well, I had my bathroom remodeled  and they put tile around the tub but it doesn’t seem to go all the way down to the tub itself; the tile. Of course there’s grout in there. Well that has since eroded away and every time I caulk it it just doesn’t stay.
TOM: Ah, because you don’t know the secret way to caulk your tub .
LESLIE: Yeah, there’s a secret trick.
TOM: Yeah, a good tip.
CAROL: Oh, good. I was hoping somebody would help me.
TOM: No problem. First of all, when they put tile in they just always grout down to the tub lid but the tub is always moving, Carol; it’s always expanding and contracting and especially as it gets filled up with water or if you step inside of it for a shower. It kind of pulls down and stretches down.
CAROL: I thought that was my imagination.
TOM: No, it is absolutely not. It is absolutely not. So what you can do is sort of fake it out. Here’s what you do.
First of all, get rid of all the old grout , the old caulk; make sure it’s really clean.
TOM: Then fill the tub up with water. Fill it up as much as you possibly can. Water is very heavy.
TOM: It weighs eight pounds per gallon.
LESLIE: Yeah, and make sure that that area where you pulled that grout or the existing caulk out of, make sure it’s really dry in there before you go and refill it because you don’t want that extra moisture back there for when you do recaulk it.
CAROL: What if there’s not enough of that green board all the way – going down all the way behind the club. See that’s what I think is a problem, too.
TOM: Then what you want to do is caulk that gap and you do it with the tub filled with water because this way after the caulk dries you can let the water out and the tub will sort of go back up and compress and when you step in the tub to take a shower it’s not going to pull down again; it’s not going to pull out. So clean it really good; fill the tub up with water; caulk it, Carol, and then let the water out and you will be good to go and you’ll have a caulk joint there that’s really going to last a long time.
CAROL: Wonderful. There had to have been a secret. I thought, “Why is it doing this all the time?”
TOM: There was a solution.