How to Prep Your Decking Before BBQ Season
The summer holidays have a way of arriving without much warning. One day it's still early mornings and school drop-off routines, and the next you're dragging the garden furniture out and realising the decking is green with algae, slippery underfoot, and weathered to a dull grey where it was once rich and warm.
Getting your decking ready for BBQ season doesn't need to take a full weekend, but it does need to be done in the right order. Rush it or skip steps, and you'll find that oil or sealer won't bond properly, algae will be back within weeks, and the surface will remain a slip hazard even after all your effort.
This guide walks through everything you need to do, in the right sequence, to have your decking clean, safe, refreshed, and protected before the first guests arrive.
Why Decking Takes Such a Battering Over Winter
Decking is one of the hardest-working surfaces in any garden. It sits flat, horizontal, and usually at least partially shaded, which means it stays wet long after rain has dried off the rest of the garden. That moisture, combined with leaf fall, organic debris, and cool UK temperatures, creates ideal conditions for algae and green mould to colonise the surface.
By the time summer arrives, most decking is carrying a biological load that goes well beyond what you can see. The green or black film on the surface is only the visible part; algae and mould spores are already embedded in the grain of the wood. If you simply brush or jet wash the surface without treating it chemically, you're removing the top layer but leaving behind the roots, which means the growth returns often faster than before.
Cold temperatures also take a toll on the timber itself. Moisture that soaks into untreated or under-maintained wood expands when it freezes and contracts as it thaws, gradually opening up the grain and micro-cracks in the surface. Over successive winters, this leads to splitting, warping, and the grey, weathered appearance that's so common on neglected decking.
The good news is that even decking that's been left alone for a few years can be brought back to excellent condition with the right products and a bit of patience.
Step 1: Clear the Deck Completely
Before you apply anything, remove everything from the surface including furniture, plant pots, outdoor rugs and lights. Algae and mould will have developed underneath anything that's been sitting in place all winter, and you need full access to every board.
Give the surface a sweep to clear loose debris, paying particular attention to the gaps between boards where leaves and organic matter accumulate. A stiff brush or a purpose-made deck tool works well for this.
Check the deck's structure while you're at it. Press down on boards across the whole area to check for any that feel soft or springy, which can indicate rot beneath the surface. Inspect fixings for rust or corrosion. Identifying any structural issues before you start cleaning and treating means you won't be sealing in a problem.
Step 2: Treat Algae and Green Mould
This is the most important step, and it needs to happen before any physical scrubbing or jet washing.
Apply GK Decking Cleaner 5Ltr directly to the surface and allow it to dwell, this may need to be left overnight. The formula works by penetrating the timber and breaking down biological growth at its source, killing the algae and mould spores embedded in the grain rather than simply shifting surface staining. This is what stops it coming straight back.
Follow the product instructions for dwell time, and don't rush this step. On decking that's been heavily affected or neglected for more than a season, you may want to consider a second application of GK Concentrated Fungicidal Wash to deal with persistent fungal growth and mildew before moving on.
Once the treatment has done its work, rinse the surface thoroughly. At this stage, a pressure washer on a moderate setting (working along the grain, not across it) will shift the loosened biological material far more efficiently than scrubbing by hand. The chemical treatment has done the hard work; the rinse is just clearing the residue.
Allow the deck to dry fully before proceeding.
Step 3: Restore Weathered or Greyed Timber
If your decking has lost its colour, turned grey, lost its warmth, or looks flat and tired even after cleaning, cleaning alone won't fix that. The greying is caused by UV degradation of the timber's surface fibres and weathering that goes beyond what a standard cleaner can reverse.
GK Wood Restorer 5Ltr is the right product for this stage. It works by opening up the timber grain and restoring the natural colour of the wood, bringing it back to a condition close to how it looked when it was new. This is also a critical preparation step if you plan to apply any oil, stain, or sealer afterwards as restored, open-grained timber will absorb and bond with subsequent treatments far more effectively than weathered, closed-off wood.
Apply to a clean, dry surface following the product instructions, and allow it to work before rinsing. The transformation on heavily weathered decking can be significant.
Step 4: Deal With Any Oil Staining
If your decking is near a barbecue area, or if you've applied decking oil in the past and had an uneven result, runs, or dark patches, you may be dealing with oil staining that resists standard cleaning.
GK Oil Out Oil Stain Remover 5Ltr is formulated specifically for this: lifting oil penetration from timber without the bleaching or discolouration that harsher treatments can cause. Apply to the affected areas, allow to dwell, then rinse clean.
This is also worth doing proactively around the BBQ station before the season starts, so you're starting from a clean base before the inevitable drips begin.
Step 5: Seal and Protect the Surface
Cleaning and restoring your decking without sealing it afterwards is like painting a masterpiece and skipping the varnish; all that effort remains vulnerable to the elements.
GK Invisible Wood Sealer 5Ltr is the recommended final step for most decking. It's a penetrating, water-based formula that soaks into the timber and creates a moisture-repelling barrier from within, causing water to bead and run off the surface rather than soaking in.
Critically, it dries completely invisible with no sheen, no change in tone, and no surface film, so the restored natural colour of your decking is what the eye sees, not a coating on top of it.
The formula also incorporates an algae-repelling action, which means you're not just protecting the timber from moisture; you're actively making it harder for biological growth to re-establish during the season.
Apply to a clean, dry surface using a brush, long-pile roller, or low-pressure sprayer. Two wet-on-wet coats give the best result. Apply the second coat before the first has dried to maximise penetration. The sealer is touch dry within two hours and ready for foot traffic within 24 hours, so you can have the furniture back out and the deck in use by the following day.
One 5Ltr bottle covers up to 25 square metres, enough for a generous decking area.
Step 6: Finish the Details
With the main deck surface sorted, a few finishing touches make the whole space feel genuinely ready for the season.
Composite decking and surrounding surfaces: If you have composite decking panels, plastic furniture bases, or hard outdoor surfaces around the deck, GK Multi-Surface Cleaner & Sanitiser handles all of these cleanly and without the need for specialist products.
Furniture: Bring garden chairs and tables out of storage and give them a once-over with a suitable cleaner before guests arrive. Metal furniture can show rust streaks from damp storage; check fixings and frames while everything is out.
BBQ area: Clean down the grill area and surrounding boards before the first use of the season. A clean base around the BBQ makes any subsequent oil stain treatment faster and simpler.
How Long Will This Take?
Depending on the size of your decking and its condition, the full process: cleaning, restoring, and sealing, typically takes two-three days:
Day one: Clear the deck and apply decking cleaner.
Day two: Treat any persistent mould or oil staining, rinse and allow to dry.
Day three (once dry): Apply Wood Restorer if needed, allow to dry, then apply two coats of Invisible Wood Sealer wet-on-wet.
By the morning of day four, the deck is fully sealed and ready for use.
Products Used in This Guide
All products mentioned are available from GK Products UK with free delivery on orders over £60:
GK Concentrated Fungicidal Wash 1Ltr
GK Oil Out Oil Stain Remover 5Ltr
GK Multi-Surface Cleaner & Sanitiser 5Ltr
Got a question about your specific decking type, or not sure which products are right for your situation? Get in touch with the GK team at sales@gkproductsuk.com or call 07557 111 297. We're happy to advise!