How to Install Moisture Resistant Drywall: Best Practices for Wet Areas

Most moisture failures in moisture resistant drywall installations are installation failures, not product failures. The sequence below is the one that keeps a wet-area wall performing from handover to year fifteen.

Step 1 — Check the Substrate and Framing

• Framing must be dry, straight and free of standing water.
• Stud spacing: typically 600 mm centres maximum for 12.5 mm board, reduced to 400 mm for ceilings.
• Allow a 10–13 mm gap between board and finished floor level to prevent wicking.

Step 2 — Store, Handle and Cut Correctly

Store panels flat and off the ground, under cover. Cut with a fine-tooth blade and seal every exposed cut edge and core with a moisture-resistant sealer before installation in wet zones. This single step prevents the most common failure we see on site, and it costs almost nothing.

Step 3 — Fix the Panels

Use corrosion-resistant screws at approximately 200 mm centres in wet areas and 300 mm in dry zones. Recess heads just below the surface without breaking the paper. Butt joints should be tight but not forced; a 1 mm gap improves compound penetration.

Step 4 — Treat Joints and Corners

Use a setting-type compound with embedded tape in wet areas. Standard drying-type compound is unsuitable where sustained humidity is expected. Reinforce internal corners with tape and use pre-formed corner beads at external corners.

Step 5 — Seal, Then Waterproof

Seal fasteners, joints and cut edges, then apply the waterproofing membrane across the whole wet-zone substrate before tiling. The board resists moisture; the membrane stops liquid water. Treating one as a substitute for the other is the mistake that shows up two years later.

Pre-Tile Inspection Checklist

Where the Checklist Comes From

The points above are drawn from site reports on hotel, hospital and residential projects. On those jobs, the recurring defects were consistent — unsealed cut edges, over-driven screws, missing membranes above shower heads — and none of them originated with the board. Installation guidance we issue follows ASTM C840 and GA-216, and where a local code is stricter, the local code governs. Photographs of a completed substrate can be reviewed before tile is applied, which is a far cheaper checkpoint than corrective work after tiling.

Frequently Asked Questions