QUESTION

We are getting tile discoloring on our new walk in shower floor,,,,the installer found that the base was tiled over before the cement had cured, thus trapping moisture. They pulled the tiles off to check it our, and found the cement base was still wet.

The contractor removed the tile completely, placed fans to dry out the base and wants to re-tile over the now dry base. I feel the improperly cured concrete may have gone granular as it sat for 3 wks. before we saw the problem and was still wet. There was discoloration before shower any use by us.........I think the entire base should be replaced with fresh cement, then retiled,,,,your thoughts please??

ANSWER

ANSWER -  Normally installing tile over damp mortar doesn't cause staining.  We call that a wet set method if the mortar is installed at the same time as the tile is installed.  A thin-set adhesive is applied to the back of the tile and embedded into the fresh mortar.  So not sure how your tile was discolored or why it happen.

Some natural stones or some more porous tiles will darken at first if the underlying mortar bed is wet.  If it doesn't dry out it is normally due to plugged weep holes in the drain.

As far as whether it is necessary to replace the mortar bed, as long as the mortar is hard and free of cracks, then there should be no reason to replace it.   If the mortar base is not hard and is crumbling then it might need replacing.