Finish TradesQuestion 225 of 700
A tile setter spreads thinset mortar but leaves it too long before placing tile, and a skin forms on the ridges. What is the MAIN risk of setting tile into skinned-over thinset?
a.The tile will set faster and stronger
b.The grout joints will be wider
c.Poor bond because the skinned surface no longer transfers adhesive to the tile
d.The mortar color will change but bond is unaffected
Explanation
Once thinset skins over (passes its open time), it can no longer wet out and grab the back of the tile, so bond strength drops and tiles can debond. The setter should remove the skinned mortar and re-spread fresh. It does not set stronger, does not widen joints, and the skin is a real bond problem, not just color.
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