For bad stains it may be necessary to wean the timber with an oxalic acid timber wash, which is biodegradable, so any run-off from your deck cleaning will break down naturally and rot kill all your plants! Apply the mix to the surface with a stiff scrubbing brush. After about 15 minutes it will have done the job of removing dead timber cells and the residues of old oil finishes. It will have opened up the cellular structure of the timber surface ready for a fresh intake of protective oil. Wash the acid off with water, or better still with the high-pressure cleaner.
If your timber work has gone black
Many people over the years have mistakenly finished their timber decking with linseed oil, thinking it will protect the timber. But linseed oil is mildew food so when used on exterior timber and exposed to moisture it will eventually turn black. Linseed oil also offers little resistance to UV and is not particularly durable for surfaces under foot. Fixing the problem is not easy:
Multiple applications of a commercial timber wash product may be necessary to remove many layers of built-up linseed oil, or you can make up a solution using oxalic acid flakes purchased from a hard-ware store. Be sure to test one or two timbers before proceeding with the whole deck.
As a follow-up, or if your decking only requires a light treatment, you may also consider washing all the timber work with a strongly mixed oxygen bleach solution like NapiSan.
Once the deck is washed (or if you’ve just laid a new deck), I’d recommend that you leave it to dry out and allow the natural mildew-killing action of the sun to work on it before applying a new finish.
Make your decking go ‘silver’
If you replace some old rotting timbers with new boards, they may not match your existing boards, which possibly will have that grey silver look from exposure to the weather. The silvered look is a result of the natural tannins that give timber its colour leaching out and washing away, leaving the surface to become sun bleached.
If you don’t finish the new boards at all, they won’t take too long to silver off and be indistinguishable from the original boards. If you’re in a hurry, this process can be accelerator by mopping the new boards with a mixture of baking soda and water. One box of baking soda to a half bucket of water should do it.
If you have a whole deck you want to silver, repeated treatments of an oxalic-acid-based timber wash, followed by cleaning with high-pressure water cleaner, will help. Once the timber does form the silvered surface you’re after, no further protection will be required to maintain it In much the same way as tarnish works on metal, the silvery layer of dead timber cells provide a protective surface for the timber below, Don’t be tempted to oil that surface or it will just turn it black. From time to time you can reapply the timber cleaner with a stiff scrubbing brush to keep the surface from becoming too rough.
Making your silvered deck look new!
To return deck timber to its original c dour, the deck can be sanded in the same way as a timber floor:
1 – Make sure you clean the deck really well, and remove all the debris that’s collected in the cracks.
2 – Then make sure all nail heads are embedded below the surface with a nail punch and hammer, or the sandpaper will catch and tear.
3 – Use a belt sander if its a small deck, or hire a floor sander if it’s large. Begin sanding across the wood’s grain with a coarse belt, then diagonally with a medium belt, and finish with a fine belt going with the grain.
4 – Once the deck is sanded it can be left to silver off again evenly if you like that look, or you can use the opportunity to apply tinted decking oil.
Refinishing the deck
Keeping the coatings up to your deck is your best defence against its early demise. There are many choices of finish available, from clear oils to opaque acrylic paints. As you’ll know by now if you’ve read the rest of this book, I’m a great fan of oil-based products on outdoor timber as it’s a natural waterproofing agent. But you should choose a product that also contains pigmentation as a UV inhibitor.
Staining a treated pine deck
Treated pine timbers can be stained, but for best results wait three months to a year after installing if you can. This allows any excess resins to leach out. The slightly faded timber will also give a truer colour to the stain you choose, Most of the timber finish companies consider the colour of raw treated pine in their colour sampling, and if you have a look at the colour swatches at a hardware store you’ll see the different colours applied to treated pine. The best bet would be to test stain a few off-cuts for you before purchasing all the stain required. Use a tinted decking oil rather than a straight stain; it’s easy to apply and will help preserve the timbers of your new deck. It’s also easy to reapply to high wear-and-tear areas, like stair treads.