Fig 5


Fig 6


Fig 7

Fig 8

Wet area plywood flooring in residential uses

Tongue and Groove (T&G) structural plywood can be used in potentially wet area rooms, such as bathrooms or laundries, providing an impervious surface, and a floor system that can be suitably graded to a waste as required by state authorities. Other systems can also be effective in providing an impervious surface over structural plywood. The recommended system provides a means of bonding of the mortar bed to the plywood to form a composite and thus avoid the drumminess possible in other methods.

Additionally, the system includes a flexible flashing over panel joints and floor to wall junctions to accommodate differential movement at such joints. A shower tray must be used to form the base of any shower recess.

Requirements for wet area floors vary between states so Local Authority requirements should be checked. Australian Standard AS3740-1994 "Waterproofing of Wet Areas within Residential Buildings" provides additional advice.

FIXING

In wet areas, the T&G structural plywood must be glued with a structural elastomeric adhesive in addition to nail or screw fixing to the sub-floor. The adhesive should be applied to either metal or timber joists in a 6mm bead. Apply two beads to joists where panels butt together. The panels should be placed in position within 10 minutes of applying the adhesive. Fastener spacings shall be 150mm along panel ends and 300mm centres along intermediate joists.

The fastener types and dimensions are as given previously in Table 1.

The panels should be fully fixed within 15 minutes of placement. A further additional requirement over standard residential floors is that a bead of structural elastomeric adhesive is applied in the tongue in the tongue and groove joint.

The approved elastomeric adhesives, flashing, epoxy adhesive and sealants at the time of writing are shown in Table 3:

Table 3: Approved Adhesives and Flashings

The flashing used shall be waterproof, tear resistant and flexible enough to absorb minor structural movement and suitable for use with the epoxy adhesive. The epoxy adhesive shall be non-sag, waterproof and flexible enough to absorb minor structural movement and shall firmly bond flashings to the surfaces of timber flooring, plywood flooring or approved wall linings.

FLOOR AND WALL JUNCTIONS

All floor/wall junctions must be flashed with an approved flashing firmly bonded to floor and wall framing or walling with an approved epoxy adhesive. Flashings should be returned up the wall at least 50mm and cover the floor surface for at least 50mm. Where required the flashings can be cut to wrap around corners.

Floor Joints

All flooring joints shall be flashed with approved flashing at least 100mm wide firmly bonded over flooring joints with an approved epoxy adhesives. This is shown in fig.5.

Wall to Wall Junctions

Internal wall corner joints in shower recesses shall be fitted with flashing angle glue fixed to wall studs or wall linings with an approved epoxy adhesive from wall tile height to the bottom of the shower tray as shown in fig.6.

Sealing the Plywood Floor Surface

Prior to the laying of the mortar bed and tiling, all of the exposed plywood flooring and flashings must be sealed with two coats of approved sealant mixed in accordance with manufacturers instructions. The first coat of sealant is diluted with water and usually applied by the builder or sub-contractor. This coat usually takes a minimum of two hours to dry.

The tiler applies the second undiluted coating of the same approved sealant as a waterproof bonding agent. The 3:1 mortar bed of minimum thickness 12mm is placed over the floor while this coating is tacky. Finally the tiles are fixed to the mortar bed which has been suitably graded to wastes.

Floor Waste and Shower Outlet

Floor wastes and shower outlets shall be installed in accordance with the details of fig.7 and fig.8 The floor grate must project at least 12mm above the floor surface to allow for adequate bedding of the floor tiles.

| New Search |

| Projects | Technical Data | Specification | Environment | Education | Research | Glossary |

Timber Research Unit
Department of Architecture
University of Tasmania