Grooved vs smooth composite decking

What is the difference between grooved and smooth composite boards?

Two things get called “grooved”: the slots along the board edges, which take hidden clips, and ridges on the top face. They’re separate features. A US installer sums up the edge difference: grooved boards take hidden clips, solid-edge boards are face-screwed, and there’s no difference in warranty, maintenance or lifespan, by his account.

Even on a hidden-clip deck you still need solid-edge boards for the picture frame, stair treads and any rail cap. He prefers to face-screw grooved boards too, using colour-matched screws, pilot holes and flush heads, because he says it ties the frame together better, though hidden clips are quicker and cheaper.

How do the gaps differ?

Eva-Last says grooved boards take clips that give a standard 5 mm gap, while square-edge boards need spacers for a consistent gap. Cladco lists its Signature and ProDeck boards as woodgrain effect or grooved, and its recycled plastic as grooved, while Millboard’s Enhanced Grain is a premium oak effect with no grooved option on the Cladco listing. Millboard’s Modello is a grooved range in Linear and Contour designs.

Which face goes up?

It depends whether the board is reversible. Guardian’s boards are double-sided with two finishes you can mix or reverse. Eurocell says its step edging only matches the grooved side. On timber, one UK DIYer lays boards smooth side up because debris and algae collect in grooves and oiling is easier on a flat face, while noting most UK people choose grooves up. If the maker’s print is on the smooth face, that’s a hint it goes down.

Smooth or grooved for grip?

Grip depends on the surface and how clean it is, so ask for the wet pendulum value. Millboard’s Modello Linear, a grooved board, has wet values of 48 to 62 in a SATRA report. See non-slip decking.

Which is easier to clean and cheaper?

Smooth faces are quicker to sweep. Hidden-clip grooved boards cost more to fix but look cleaner. One US presenter notes that wood-based boards can swell at cut ends if water gets in, and mineral-based boards don’t, in his supplier-linked view. Our boards comparison lists the verified boards.