I'm recaulking a shower which has a plastic base that flexes a bit when stepped on in certain spots. This caused the caulking to pull away the last time I recaulked.
If this was a tub, I'd fill it with water to weigh it down while caulking/curing. But it's a shower. Any ideas on items to use to achieve the same effect? The best I've come up with so far is bags of water softener salt. I don't have a set of weight plates or anything like that.
What could I use to weigh down the shower?
There's no need to go buy, haul, move and store heavy, scratchy things. Find some buckets or totes or jugs and fill them with water. They won't risk damage to your tub, are free, and can be easily handled.
Pick up 5 or 6 8"x 8" x 16" cinder blocks at your home store. They weigh about 35 pounds each. Position them around the shower on top of a towel and caulk with a quality silicone caulk after removing all the old caulk. Afterwards, you can always find some use around the house for the blocks. Good luck.
Since you have water, the easiest would be a big bucket full of water.
That said, if your plastic shower base flexes, this means it was installed incorrectly. These shower bases are quite flexible, so normal practice is to put something between the bottom of the shower base and the floor, for example plaster or mortar, then set the shower base on it. It is then well supported from the bottom. Another reason for your issue may be that the floor itself flexes, but that's less common.
You should first investigate why it flexes. You can do that by kneeling in the shower, setting your weight on the shower base, and looking at the joint between the base and the wall tile.
If the entire shower base lowers by a few mm (ie, it moves vertically and down) INCLUDING THE EDGES then there is a problem with the floor, or the edges are not touching the floor. Since the shower base's edges are its lowermost part, they normally rest either on the floor or on some mortar. If they don't, you have a problem.
If the edges of the shower base do not move DOWN but instead retract towards the inside of the tub, widening the joint gap when you step inside, then the shower base's edges are properly set on the floor but whoever installed it did not put support material below the center of the tub. So it flexes and that pulls the edges in, cracking your caulk.
In this latter case, there is an easy fix: if the empty volume under the shower base isn't too large, you can drill a small hole in the side and inject a can of expanding foam, which will harden and support the shower base from below. Don't drill from the top, of course... that would cause a leak. And don't forget to leave something heavy in the tub while the foam expands... otherwise it will probably lift itself off. Mortar would of course be better, but it's much harder to inject through a tiny hole.
It sounds from your description that the floor is not straight. Thefore a weight helps temporarily to cauke it but later you have the tension to the other way when there is no weight and the cauke will crack. I would recommend to make the floor perfectly straight first .
