Finish TradesQuestion 464 of 700

When cement backer board is used as a tile substrate on a floor, how should the board joints be treated before setting tile?

a.Taped with alkali-resistant mesh tape and filled with thinset mortar
b.Left open with a wide visible gap
c.Sealed with ordinary painter's masking tape
d.Covered only with drywall joint compound

Explanation

Backer-board joints are reinforced with alkali-resistant mesh tape embedded in thinset so the joint moves as one plane and does not telegraph cracks. Leaving joints open, using paper masking tape, or using water-soluble drywall compound would all fail under a tile floor's moisture and movement.

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