Avoid Deck Cupping Occurring With Wilson Timbers

Boards that have propensity to cup usually do so for a variety of reasons, none of which have to do with the fastening systems. No fastening system can prevent, delay, or otherwise stop a board from cupping except over the joists - by virtue of the fact that the cupping occurs between the joists.

The main reason boards cup is from moisture, either within the board or the immediate surroundings. Ventilation of the deck is a key factor. If the deck is low to the ground and the ground does not drain fast enough, the evaporating moisture rises and is trapped underneath the deck.

When the bottoms of the boards, especially hardwoods, dry more slowly than the top of the board which has free air flow and sunlight, the boards will cup. Hardwoods need to be fully seasoned before building the deck!

The best prevention is to allow ventilation by spreading a healthy layer of coarse gravel over a plastic membrane that allows the rain water to run away and then dry.

Skirting the lower sections of the deck also enables moisture to be trapped under the deck. Tops dry, bottoms don't = Cupping. Well ventilated + seasoned board = less opportunity.

But, if a board is beginning to cup - it will. All you should do is design the project to diminish the opportunities. Boards which are dimensional unstable, 140 x 19 Australian hardwood for instance, are more likely to cup and more severely. Most hardwoods have the characteristics of absorbing moisture and expanding in such direction and strength to shear 10 ga. wire screws. When the deck fasteners fail due to the abnormal movement from moisture absorption, nails pull up, screws shear and it's 'decks gone wild!'.

Design and execute your project to avoid expensive and labor intensive repairs.

Use narrow 75mm or 90mm decking boards in areas where ventilation and moisture could be a problem, your boards might still cup, but it will not be as noticeable!

Pre-oil your decking boards all round prior to installation!