A Step-by-Step Guide

Step 1: Prepare the Ground and Subframe

Whether you’re installing your first deck or you’ve already built dozens, the foundation and subframe largely determine how straight and stable the finished deck will be.

Install the subframe on a flat, stable surface. If this isn’t possible, provide adequate support at intervals of no more than 400 mm. When storing the boards, stack them face-to-face and back-to-back. Never drag boards across one another when removing them from the pallet, as this can cause scuff marks or damage to the surface.

What Joist Spacing Should You Use?

• Residential applications: maximum 400 mm centres
• Commercial or public applications: maximum 300 mm centres
• Joists at a 45-degree angle: maximum 300 mm centres for residential applications or 240 mm for commercial/public applications

Where board ends meet, make sure both ends are adequately supported by the same joist. You can find the complete installation instructions on our website.

Step 2: Lay Out the Boards Before Installation

Lay the boards loosely in position a day before installation, exactly where you intend to fit them. This allows you to create a natural mix of grain patterns and colour variations across the deck while giving the boards time to acclimatise to the outdoor conditions before fixing them in place.

Step 3: How Much Space Should You Leave Between Decking Boards?

One of the most common questions when installing decking is how much space to leave between the boards.
For Millboard, use the following spacing:

• Between the sides of the boards: 3–6 mm
• Between board ends: 1–2 mm
• Between a board and a fixed surface such as a wall or upstand: 10 mm to allow adequate drainage

Don’t want to measure every gap individually? Millboard Multi-Spacers make the process easier. Simply place them between the boards to maintain a consistent 6 mm gap.

Step 4: Fix the Decking Boards

With Millboard, there’s no need to pre-drill or countersink. The Durafix® screws can be driven directly through the board.

Use a standard drill/driver with the supplied bit. Avoid using an impact driver or hammer drill, as this can damage the bit or screw head. For the best finish, apply silicone spray to the screws before installation and maintain light downward pressure while driving them in. This helps prevent a gap from forming beneath the screw head.

Once the screw has been driven into position, Millboard’s Lastane® surface closes back over the screw head. The fixing sits at least 5 mm beneath the surface, leaving it virtually hidden from view.

After every four or five boards, use a string line to check that the deck is still running straight. A few minutes of checking during installation can save hours of correction later.
Want to see exactly how it’s done? Watch the installation video before driving your first screw.

Step 5: Cutting Millboard to Size

Millboard can be cut using many of the same tools used for natural timber. For the best results, use a saw blade with hardened teeth. Millboard has very low thermal expansion, so a gap of 2 mm at the board ends is sufficient.

A mitre saw generally gives the cleanest result for straight cuts. For edges, curves and cut-outs, you can use a hand saw or jigsaw. Always wear appropriate safety glasses and gloves when cutting.

For a clean corner detail, mitre-cut the boards and bond them together. Finish exposed cut ends with the appropriate touch-up paint to restore a consistent appearance.