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I pulled up kitchen vinyl to put down ceramic tile (w/ backer board), and found 1/4" Weyerhauser Structurewood underlayment OSB.

Is this sufficiently for laying mortar and Hardie backberboard, or do I need some surface prep other than smoothing and cleaning?

This is kitchen with pretty solid, 3/4", TG solid board subfloor below the underlayment, so this not a question about waterproof or structure issue or OSB vs exterior grade plywood for underlayment, but whether mortar will bond reliably to this specific OSB underlayment.

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isherwood
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codechimp
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1 Answers1

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OSB, by nature is not a good surface to lay floor tile on and not particularly something that should have mortar directly on it. It is suitable as an underlayment for hardwood or engineered wood floors.

It is manufactured with wood chips and glue. Therefore it is unstable when subjected to water and will lose cohesion. I would never tile directly over OSB.

For tile you are better suited to a cement based underlayment like Perma-base or HardiBacker The 1/4" boards could go over the 1/4" OSB. But a better solution would be the 1/2" cement board.

The cement boards are screwed to the subfloor, not installed with mortar.

isherwood
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RMDman
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