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Interior installation of tile over exterior glue plywood

Problem

Cause

Cure

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Delaminated plywood.

Arched or humped floor surface.

Use only exterior grade plywood. Install according to TCNA Handbook , ANSI A108 Standards and Specifications and APA Form E30.

Improper nailing (fastening).

Tile and/or grout cracked.

Excessive deflection due to joists in ex cess of 16 in. (406 mm) on center; girders/ floor joists not properly fastened.

Loose or broken tile.

Proper nailing helps restrain the plywood in shrinkage – expansion.

Springy floor.

Expansion and contraction of plywood due to moisture exposure.

Protect and properly store plywood in a dry area.

Insufficient thickness of floor.

After plywood is installed it should be protected from rain and moisture. Joists, underlayment, and supporting structure should be thoroughly dry before applica tion of tile.

Wood floor construction consists of only a single layer of plywood.

Inadequate expansion joints.

Maintain 16 in. (406 mm) on center joist spacing.

Use joists designed to support live and dead load. Use joists of larger size or move spacing to less than 16 in. (406 mm) on center. Securely fastening plywood on joists 16 in. (406 mm) on center provides joist support, stiffening the floor and limiting expansion and contraction. C–C (plugged) exterior grade plywood is a suitable material. C–D grade (sheathing) is not acceptable. Use a bonding material recommended and warranted by the man ufacturer. See page 60.

Fire rated plywood or concrete form ply wood used in floor construction.

Bonding failure.

Improper setting material and/or instal lation procedures.

Improper substrate or underlayment (see also other causes under “Thin Bed Instal lation Chapter” starting on page 185).

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NTCA Reference Manual | 2024 / 2025

Chapter 2 | Substrates