Decking repair: what can be fixed and what can't

Signs your deck needs attention

Walk the whole deck slowly. Boards that feel soft or spongy underfoot, flex more than their neighbours or sound dull when tapped are the first warning. Look for boards that have split along their length, screws that have lifted proud of the surface, and gaps that have closed up so water can no longer drain between boards.

Underneath, if you can see, look for dark, damp timber where joists sit on the ground or on blocks, and for any post that has moved. A deck that rocks or bounces when someone walks across it has a problem in its frame, not just its boards.

Replacing rotten or split boards

A damaged board is unscrewed and lifted, and the joists it sat on are checked while they are exposed. The new board is cut to length, ideally running between joists so its ends are supported, and fixed with decking screws at each joist. New boards look brighter than weathered ones at first, and a matching treatment or stain helps them sit in.

• Lift the damaged board and check the joists underneath
• Cut new boards to break over the centre of a joist
• Leave a drainage gap between boards
• Use proper decking screws, not nails or short fixings
• Treat cut ends before fixing them down

Checking the joists and sub-frame

The joists are the real test. A sharp screwdriver pushed into the timber should meet firm resistance. If it sinks in easily, the joist is rotting. Rot tends to start where timber touches soil, sits in standing water, or butts up against a house wall where rain runs down.

One or two damaged joists can sometimes be strengthened by fixing a new length alongside, known as sistering, or by adding an extra support post. Widespread rot across the frame is a different story. At that point the boards are only as good as what they sit on, and repair stops making sense.

Loose screws, movement and bounce

Lifting screws and creaking boards often come from timber moving with the weather. Backing out the old screw and refixing with a longer one into fresh timber, or adding a second screw, usually cures it. A deck that bounces across its middle may have joists spaced too far apart for the board thickness, and extra noggins or a mid span support can stiffen it.

Movement at the edge of the deck, where it meets the house or a step, should always be checked properly, because that is where people put their weight going in and out.

Slippery decking and cleaning

Green, slippery decking is caused by algae growing on damp, shaded timber. A stiff brush with a suitable deck cleaner, or careful pressure washing that does not tear up the surface, removes the growth. Clearing the gaps between boards helps the surface dry out, and cutting back overhanging plants lets in light. Anti slip strips or a grip treatment on steps add another layer of safety.

Regular cleaning in spring and autumn does more to keep a deck safe than anything else, and it makes rot in the boards easier to spot early.

Repair or replace?

Repair when the frame is sound and the damage is limited to boards, fixings or one corner. Replace when several joists are soft, the posts have moved, or the deck was built too close to the ground with no airflow. The decking installation page explains how a new deck is built so the same problems do not return, and the decking vs patio guide is worth a read if you are wondering whether to swap timber for paving altogether.

Decking repairs are part of the landscaping and carpentry work CRF Services Ltd takes on for modest gardens around Rochester and Medway.

Frequently asked questions

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