Plaster finish prior to new tile installation
by Phil Edwards
I have removed ceramic tiles from a shower enclosure and have exposed a sand/cement render that is mostly sound (there are some areas that will need to be made good) and approximately 50% covered with the remains of old tile adhesive. In order to make the wall perfectly flat and plumb in preparation for new ceramic tiles I intend to plaster it. Plaster depth required varies from approximately 1 to 5mm. My questions are 1) how do I ensure a good bond between new plaster and old render that will take the weight of the new ceramic tiles? and 2) which plaster should I use?
Looking forward to hearing from you
If the surface you are plastering is rough rather than smooth, of varying depths and ridged then you already have a good key. However to be on the safe side a coat of diluted PVA (follow instructions but a milky consistency is good) will ensure a good bond. New plaster should be applied when the PVA is tacky.
Sand & cement mixed in the ratio of 4:1 or 5:1 (with a drop of plasticiser) may work best. The gypsum based Bonding Coat will live up to it's name and provide great bonding qualities - but, if there is any water ingress due to any defective tiling/cracking etc. then Bonding Coat will absorb as much water as it can - creeping up the wall and eventually turn to a Mush. Whereas sand & cement will remain unaffected.
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