Green Treated Decking Problems and How to Avoid Them

Green treated softwood is a widely used, affordable decking material. It also behaves like any softwood: it moves, weathers and needs sensible installation. This guide explains the common problems, why they happen and how to reduce them. See our green treated decking kits and decking boards.

What “green treated” means

Our product page describes the boards as A/B grade Scandinavian Redwood, pressure-treated with Tanalith E for protection against decay, UC3, in green, reversible with one grooved or reeded face and one flat. The kits are described as pressure treated to BS 8417 at our own treatment works. The treatment protects against rot and insects. It does not stop movement or surface weathering.

Problem 1: Splitting and surface checks

Why it happens. Softwood dries unevenly, and fine cracks (checks) appear on the surface as the timber settles to its surroundings. Treated timber often arrives still damp from treatment.

How to avoid it. Store boards flat, under cover, with air around them. Pre-drill near ends and keep screws away from the board edges. Small surface checks are normal and rarely affect function.

Problem 2: Cupping and twisting

Why it happens. Boards take up and lose moisture unevenly on their two faces. Wide boards cup more readily, and the 145mm boards are on the wide side.

How to avoid it. Fix with two screws per joist, leave the boards to acclimatise, and ensure water can drain from the surface and from below. Fixing a face that holds water increases cupping risk, so follow the fitting guidance for the board you buy.

Problem 3: Shrinkage gaps and tight boards

Why it happens. Boards fixed when damp shrink and leave larger gaps. Boards fixed dry and tight swell and press against each other.

How to avoid it. Leave a consistent gap, set with a spacer. Think about the season you are laying in.

Problem 4: Green colour that fades or looks patchy

Why it happens. The green tint comes from the preservative and gradually weathers towards grey-brown, unevenly in sun and shade.

How to avoid it. Expect colour change. If you want to keep colour, clean first, let the timber dry and apply a deck stain or oil suitable for pressure-treated timber, following the maker’s instructions on when to apply it.

Problem 5: Algae, moss and slippery surfaces

Why it happens. Shaded, damp, poorly ventilated decks grow algae, which is slippery.

How to avoid it. Sweep leaves and debris, clear the gaps and wash down. Improve airflow and drainage, and cut back overhanging plants. For steps, ramps, slopes or wet areas, consider anti-slip decking; our anti-slip decking guide explains the options.

Problem 6: Cut ends left bare

Why it happens. Pressure treatment penetrates the outer part of the timber, so a fresh cut can expose less protected wood.

How to avoid it. Treat cut ends with a suitable end-grain preservative, and keep cuts to a minimum. Our kits arrive cut to length, which keeps site cutting down.

Problem 7: Rust and staining from fixings

Why it happens. Copper-based preservatives are corrosive to some metals, and cheap fixings rust and stain the surface.

How to avoid it. Use suitable stainless screws. The product page for the loose boards recommends 4.5 x 65mm stainless steel decking screws, and the kits include A2 stainless decking screws in the size listed on each kit page.

Problem 8: Standing water and rot at the frame

Why it happens. A deck that cannot drain, or sits on soil, stays damp, and any timber will decay sooner.

How to avoid it. Build on firm, level, well-drained ground, with a weed membrane and a ventilated gap underneath. Support joists clear of the soil. Kits do not include membrane or joist supports.

Problem 9: Handling treated timber safely

Why it happens. Preservative-treated timber produces sawdust that should be handled carefully.

How to avoid it. Wear a dust mask, gloves and eye protection when cutting, and dispose of offcuts and sawdust appropriately. Do not burn treated offcuts, and follow the treatment manufacturer’s safety guidance.

Problem 10: Expecting hardwood-like looks

Why it happens. Softwood is knottier and moves more than denser decking timbers.

How to avoid it. Choose the material to suit the budget and the use. If you want a different look, compare options such as thermowood decking. Order a free sample first.

Trends to watch

Anyone choosing decking weighs the initial cost against upkeep. If grip matters, see our anti-slip decking guide.

FAQ

Will green treated decking rot?
It is treated to resist decay and insects, but poor drainage and ground contact shorten any timber’s life.

Why is my deck splitting?
Small surface checks are normal in softwood. Pre-drilling and good storage reduce them.

Does it need staining?
Not necessarily. It can be left to weather, or finished to hold colour.

Is it slippery when wet?
Any timber can be, especially with algae. Keep it clean, or choose anti-slip boards.

Talk to us

Request a quote, order free samples, book a site meeting or call 0161 504 0011.