Cracking grout on pebble shower floor
A contractor installed a pebble stone (river rock) floor in our shower last year. We had to wait a year to save and install glass doors before we could use the shower. Unfortunately, a month into using it, the grout started to flake and crack. I repaired the problem areas but then started to notice, when the grout was wet, micro-cracks running along grout lines (these appear more as faint lines). When I started scrapping away at the wet grout, I discovered that water had seeped right through the grout and that the adhesive was spongy in parts. I later found out that the contractor hadn't applied a sufficient amount of sealer down. He used Polyblend sand grout and grout and tile sealer from the TileLab. I'm pretty sure he bought these at Home Depot. The tile sealer says porous surfaces need more than two coats, but the contractor had stopped at two coats. Can I get away with simply applying more sealer to the floor? When dry, the shower floor pebble tiles seem very solid; however, they have a bit of soap scum on them. Is there a super water tight sealer I could put over the existing sealer?