Millboard decking

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What is Millboard decking?

Millboard is a resin-and-mineral composite decking board, sold as a premium alternative to timber and wood-plastic composites. It is a brand name, so “Millboard decking” and “Millboard composite decking” both mean the same range. The UK collections page lists four lines:

What joist spacing and gaps does Millboard need?

Millboard’s installation guide, which we read as hosted by Cladco and MKM, is specific.

• Joist centres: 400 mm for residential use, and 300 mm for commercial use, bridges, balconies, moorings, doorways and steps. Boards laid at 45 degrees need 300 mm residential and 240 mm commercial. A cut board needs at least three joists under it.
• Gaps: 4 mm between board sides (6 mm if you use DuoFix side fixing), 1 mm at butt ends, and 10 mm to any solid surface so water can drain. Unsupported overhang is limited to 50 mm.
• Load: 2.5 kN per m² residential and 5 kN per m² commercial on the spec sheet.
• Fall: a slight fall away from the building is recommended.

What screws does Millboard use?

Durafix, which is also a warranty condition. They are A2 stainless with a six-point torx head and a wax coating, in three sizes: 4.5 by 60 mm for top-down fixing into timber, 4.5 by 45 mm for DuoSpan and Plas-Pro joists, and 4.5 by 35 mm for fascia. Millboard says no pre-drilling or countersinking is needed and to use a standard driver rather than an impact driver.

Fix two screws at each joist crossing and three at board ends, with end screws 20 to 25 mm from the end and 20 mm from the side. Board ends need at least 20 mm of support. Cut with a carbon-tipped blade and put each cut over a joist. Visible cuts on edging profiles must be coated with Millboard’s touch-up coating.

What are DuoSpan and DuoLift?

DuoSpan is Millboard’s aluminium joist and beam subframe, sold as DuoSpan 51 and DuoSpan 99 joists. Its page gives no span figures. DuoLift is a pedestal system for levelling a deck over an existing surface:

• height adjustable from 15 mm and self-levelling from 35 mm, with a maximum combined height of 350 mm
• a joist cradle for joists 15 to 60 mm, a 20 mm self-levelling joint that corrects a slope of up to 5 degrees, a 45 mm riser and a 45 mm foot with a 220 mm base
• no load rating on the page
• made from 30 percent glass-filled nylon 6 with 100 percent recycled content, according to its NBS listing, which says it suits roof terraces and ground-level terraces on a solid, stable base and not directly on soil

How long is the Millboard warranty?

Millboard’s UK warranties page gives a 25 year limited structural warranty for residential use and 10 years for commercial. You register within 90 days of purchase and must use Durafix fixings. A Cladco page describes the warranty as limited to a single-family home and gives 10, 12 or 25 years depending on the application and subframe, and a Millboard guide FAQ we read gives 5 years commercial. The documents don’t agree, so ask Millboard for the current one.

How do you clean Millboard?

Water, mild detergent and a cloth or brush. No solvents, chemicals or abrasive cleaners are needed. Remove berries and animal droppings quickly. A pressure washer is allowed at or below 2,000 psi with a 40 to 60 degree fan tip about 250 to 300 mm away, though it may make screw holes more visible; test somewhere hidden first. Our cleaning guide compares it with other makers.

New boards can look oily or shiny from a manufacturing release agent, which weathers off in 6 to 8 weeks. In winter, a small amount of granulated white salt is fine; rock salt isn’t advised. Put fire bowls and braziers on a porcelain or cement slab extending about 1 m beyond, and keep sharp furniture feet and metal planter bases off the surface. Patio heaters aren’t known to affect the boards.

What does Millboard cost?

We have no Millboard board price: the online shop sells boards individually but showed no price when we checked. A large 300 by 200 mm sample was listed at £10 on the Weathered Oak page. Our prices page shows the boards we can price.

See the Millboard AU page for the Australian range, and our boards comparison to line it up against other makers.