Where client is
not wanting to remove a tile bed to apply a waterproof membrane, waterproofing membrane
can be applied over the existing tiles prior to laying the new tile again. But,
technically there are N number of issues that need to be considered before carrying
out this procedure.
This type of
application can be done in internal areas only, as the size will be limited,
controlled temperature, quality of application can be maintained (as area will
be small). Never try this application at external situations, commercial
applications and is never-ever in pools or water tanks.
Existing tiles
should have joints in between and filled with grouting material. The tiles must
be in sound condition and securely bonded to the sub-floor. If tiles are loose, then
the existing tiles shall be removed, and a complete re-installation shall be done
as one loosely bonded tile may have allowed the water or any contaminants
through the tile bed and may fail in very short time.
Always note that
the installation of an impervious membrane over existing tiles will de-stabilize
the old tiles which may become loose later time line.
The tiles must
be cleaned and made free of contaminants. Wash and scrub the surface down with
a film less detergent and rinse thoroughly. Mild grinding the glaze on the tile
surface to provide a better key and surface shall be vacuumed afterwards.
Remove any old sealants out of the corners. Skim coat needs to be applied at
all grout lines joints.
It will be always
better go with sheet applied membrane, if not liquid applied membrane can be
installed considering the above mentioned points with protection over them. A
small movement in the substrate will make the existing tile to pop up and thus results
in failing of entire system.
In case of
external situation, always use exposed grade / under tile grade sheet waterproofing
membranes.
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