Fig 1(a) Nailed

Fig 1(b) Glued/nailed

Fig 1(c) Glued

Plywood flooring attached directly to concrete

When headroom is at a premium, the only possible solution to installing a plywood floor over concrete is to fix the plywood directly to the concrete slab. Three construction options are presented and in each case it is assumed that the slab has been laid over a properly installed vapour barrier and levelled using a proprietary mortar (if necessary) as shown in Figure 1(c).

Case 1 (a)

The preferred construction procedure to be followed if a vapour barrier has been provided under the slab and the plywood is to be connected using mechanical fasteners, is shown in Figure 1(a). The nails and nailing pattern specified in Table 1 should be used to fix the plywood to the concrete.

Case 1(b)

This option is suitable if a glued/nailed solution is sought when a vapour barrier has been provided under the slab. It is illustrated in Figure 1(b). This system results in the plywood face veneer receiving minimum damage due to nailing. It is thus appropriate if the plywood is to be used as a feature floor. Fixing the plywood to the concrete can be effected using the nails specified in Table 1.

NOTES:

1. Using this technique the plywood will be required to span across the adhesive beads which will result in some 'give' in the floor.
2. Apply only sufficient adhesive to lay two sheets of plywood at a time.
3. When using this construction, end matching is desirable for best results.

Case 1(c)

The final option, shown in Figure 1(c), provides a glued only solution. The method has the advantage of preserving the face veneer of the plywood. To fix the plywood to the concrete refer to Table 1.

NOTE: Apply sufficient adhesive to lay only two sheets of plywood at a time.

Finishing

Sanding should produce the desired surface finish. For a high quality finish it is recommended that a professional sander be used. It must be remembered that a veneer is being sanded not a solid piece of timber. To protect the quality of the wood surface from deterioration due to weathering or construction dirt, it is recommended that a 20% strength coating of the final finish be applied to the surface as soon as possible after laying. This is particularly important in new buildings in which the flooring is exposed to finishing trades. This protective coating is sanded off prior to the final finishing coat leaving a high quality surface ready for finishing.

Reference: Plywood Association of Australia brochure "Timber tops for concrete slabs"

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Timber Research Unit
Department of Architecture
University of Tasmania