Small hairline cracks in shower base [Archive] - Ceramic Tile Advice Forums - John Bridge Ceramic Tile


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03-05-2007, 08:42 AM

I was religious about following directions while installing a new shower base and walls. After the top layer of bedding mortar was dry I worked on tiling the walls. Now I noticed I have two small hairline cracks in the shower base. My next step is to lay the floor tile. I hope these small cracks are not the end-of-the-world for me. Is there anything I can do to repair these cracks before I lay the tile? Or are they too small to worry about. They are thinner than a piece of paper.



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03-05-2007, 10:32 AM

A picture would be helpful as well as any specifics on the material of the shower base. Any crack that goes through the thickness, even smaller than the thickness of a paper, can allow water to leak. Some pros might know of patching methods but again that would depend on the material.

03-05-2007, 12:33 PM
I used a pre-blended mortar to be used for mortar beds (mostly portland cement). I have the two layers separated with a 40-mil plastic membrane. The sub base is a concrete slab. I had to build a fake subfloor to raise it for some plumbing. The faux subfloor is made with 3/4" plywood and reinforced with flat 2x6's.

It seems the membrane is my first line of defense. Does anyone think using Redbond waterproofer on the base before laying the thinset and tile will give me any added insurance? Or am I guaranteed to have problems. I will get a picture tonight.

Thanks for advice.

Chris :bang:

03-05-2007, 12:51 PM
Now I'm really confused...

When you said "shower base" I was thinking about one of those preformed, one-piece decorative units with drain attached. Are you talking about a mortar bed shower floor with PVC/CPE liner constructed via methods disclosed in the liberry?:

If so, then hairline cracks in the mortar bed are a non-issue.

What exactly you got?

03-05-2007, 01:58 PM
Yes, it is a manually poured mortar bed shower floor. Sorry for the confusion.

03-05-2007, 02:09 PM
I used a pre-blended mortar to be used for mortar beds (mostly portland cement

Uh-oh Please describe the sand to cement ratio or the brand name and usage indicated on the bag. :)

03-05-2007, 08:10 PM
And tell us how thick that top layer is to.

My initial guess would be all that wood business you laid down on the slab, especially those 2x6's laid flat, is the culprit. Might even be pressure treated lumber which is worst yet. It's likely that wood is twisting and bending some as it dries out, causing the cracks.


03-06-2007, 01:55 PM
The top mortar bed is about 1 inch thick (uniform). I was not happy about adding all the wood since I have a cement floor. The plumbers routed two lines directly behind the old PVC shower insert. So I had to raise the floor to get by (above) the water lines to get a nice square bed and walls.

I used regular 3/4 inch plywood and used a bunch of screws to fasten it to a 2x6 frame and then screwed it to the joining wall studs. Then I mounted the drain on a hole in the faux wood floor and then progressed with the mortar bed. I understand wood can move and such, but this platform I built is much stiffer than any wood subfloor built on 16" centers, even with sisters.

My opinion now after reading the article in the library is if water seeps down through a hairline crack in the bed to the membrane and out the drain then everything is working as it is supposed to.

03-06-2007, 03:02 PM
if you have wood sitting on concrete then this is only the beginning. Sorry. :cry: Even if water doesn't seep through from above it will almost certainly wick up from below. Have you read about why you don't build wood curbs on slab?