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Friday, December 3, 2021

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HomeTechnicalAsk the ExpertsCan tile be set over a substrate with 90% relative humidity?

Can tile be set over a substrate with 90% relative humidity?

ANSWER

This RH level likely should not affect the bond of ceramic or porcelain tile to a concrete substrate when using a cementitious bond coat, provided that the substrate and back of the tile are clean and free of any bond breakers, the concrete is properly prepared for tile, and correct bond coat coverage is achieved. For a high RH application 95%-100% bond coat coverage is beneficial.

Other considerations will factor in the long-term appearance and performance of the installation. For example, water or vapor percolating through the concrete substrate could result in visible efflorescence in the grout or the body of the tile. A vapor barrier, waterproof membrane or uncoupling membrane will help to reduce the potential of efflorescence. Selection and application of the correct membrane will be critical to ensure it can handle the water or vapor pressure coming from the concrete to which it is adhered.

It is beneficial and sometimes necessary to reduce the amount of RH in the substrate. To do this, the source of the humidity has to be discovered and mitigated. Sometimes landscaping, roofline water runoff management systems, etc. need to be designed and installed to redirect the water from flowing to or residing beneath the concrete slab. Water barriers can be installed beneath the slab before it is poured. 

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