Wooden Decking Stains, Treatments & Oils : Part 2 – Problems & Cures


Following on from Part 1 of our Decking Guide, in Part 2 Wood Finishes Direct talk about some of the more common problems that can affect decking maintenance. We also take a look at the various types of decking treatments on the market and the differences between them.

Common garden decking problems

  • Wood blackening happens when fungus forms on the surface of the wood, usually because water has penetrated the wood and reacted with the brown tannin it contains. Different woods have different levels of tannin, but fungal blackening can be removed with a special Mould and Mildew Cleaner.
  • Greying or Silvering occurs when the wood has been water and sun-damaged, but the effect can be reversed with oxalic acid. There’s a great product from Osmo called Wood Reviver Gel, which contains the acid, which helps to restore the natural colour of the wood. Just like magic – it’s such a amazing transformation!

Grey decking is a common issue that can be quickly and easily resolved

How long does garden decking finish last?

Decking is one of the most difficult areas in a garden to keep in good order. During the year it gets a lot of foot traffic, in all weathers, and it’s open to the elements, insects, leaves and mud, all of which can remove the finish a little at a time. When the biggest contributing factor is the weather, life becomes very unpredictable. Which is why it’s difficult for manufacturers to give accurate timescales about how long a particular finish will last.

As a general rule, the most exposed parts of your wooden decking suffer the worst weather damage, needing more maintenance and more frequent attention. The bottom area of decking spindles get all dry or go black or grey, suffering more than the top because of running water and gradually wearing the finish off. Decking oil comes into its own here, with the affected areas easily rubbed down with steel wool or sandpaper and repaired seamlessly by treating with fungicidal wash (if required) then using more oil.

Once it’s finished, one of the easiest ways to extend the life of your decking is regular sweeping. Other than that, regular use of a specialist decking cleaner will do the trick.

Decking treatment terminology

The wood finishing industry’s terminology is full of inconsistencies. Most people don’t know that a lacquer and a varnish are the same thing, for example, and pigments are often confused with dyes. So we thought it’d be useful to clear up a few popular misconceptions:

Decking Stains – A normal water-based wood stain is purely a colour, usually a liquid. It doesn’t give the wood a sheen or protect it, it just colours the wood, and you need to add a protective finish on top. Decking stain is different. It’s more than a colouring liquid, with added protection. But there’s more…

Take Ronseal. They’re one of Britain’s leading suppliers of decking finishes, yet they have two different decking products, both called a stain but both very different.  The product they call Ronseal Decking Stain falls into the sealer category, a paint-like material which does nothing to enhance the grain and over time, will likely start to peel and flake as the product degrades. Their Advanced Decking Stain is far superior and oil-based. In our opinion neither of them are decking stains.

  • Ronseal Decking Stain is actually a coloured decking treatment
  • Ronseal Advanced Decking Stain, now discontinued, was actually a coloured decking oil

What is decking oil? – If it’s called a decking oil, it is probably exactly that. In our experience it’s always a good choice when made by a reputable company like Barrettine or Ronseal.

What is wooden decking treatment? ‘Treatment’ can mean either an oil or a surface coating. Be sure to find out which to make sure it meets your requirements.

What is a garden decking finish? As above, a ‘finish’ could mean more or less anything. Proceed with caution.

Next time, in the final part of our complete garden decking treatment guide, we’ll take a look at how best to apply decking treatments, plus top tips about decking maintenance and making the most of your beautiful decking all year round.


  1. Hi there. Last year we treated and coloured a large south-facing deck with Manns Premier UV Decking Oil, Dark Oak. It looked great but after a winter with several ‘sahara sand’ rainstorms it needs washing off before re-oiling with the same Manns product. The issue I have is that when we washed off the deck last summer, it left limescale stains because we are in a hard water area (Hampshire). Any thoughts on how we can clean it without leaving stains or should we just go ahead an re-oil it after a thorough sweeping?

    • Morning Paul, thank you for getting in touch.

      When it comes to cleaning decking, we would normally recommend a decking cleaner as these products are designed to help clean decking. Our friendly experts will be happy to give you further advice.

  2. hi there

    I would REALLY appreciate your help after googling and finding not much help anywhere else! We had decking laid in May (UK summer time) and now in October the last couple of months we have seen the wood has gotten water logged in various patches, and is blackening and white specs of fungi are growing on top of these water logged patches. I just cant seem to get the wood to dry out, which I think is what is causing the white fungi to grow.

    We did seal it twice with a ronseal wood oil, so I don’t understand what we have done wrong. The only thing I can think is that our neighbour who laid the decking, cut pieces in half so I wondered if the freshly cut ends have got water in them and that is what is causing them to never be able to dry out, and then the white mould/black spots start appearing?

    Do you have any advice as to how to fix this problem? We have tried using two types of algae/mould cleaner and its not solving the problem. It just keeps returning. And we are not even in the depths of winter yet so I can only imagine the problem getting much worse.

    We are doing everything we can to prevent wood rot and don’t want to waste money spent on this lovely decking we have been looking forward to enjoying for so long!!

    Thank you so much in advance for your help.

    • Good Afternoon Joanna,

      Decking is one of the hardest areas of exterior wood to protect and keep looking good. It is usually totally exposed to all the elements, sun which causes UV damage, rain which causes moisture ingress that leads to mould or rot, wind which leads to foliage bowing onto and decaying on the surface and lots of other factors on top of this.

      As well as good, protective treatments we also recommend regular sweeping and cleaning to help protect the wood from as much as possible. If you would like to get in touch via our contact us page with details of the type of wood and the exact product you have used and I can advice further. Also if you are able to send any photos in of the decking this may help.

      Kind Regards Samantha.

  3. hi, I am about to oil my decking but I cant decide which oil to use. I have read that the Ronseal oil has good reviews however whenever I have purchased paint from that manufacturer I have been most disappointed.

    I recently purchased some Barrettine and I found the quality to be very good although the coverage wasn’t great and I needed several coats to achieve the colour promised on the tin.

    what brand of oil would you recommend for my decking ?

    • Good Afternoon Greg,

      Thank you for getting in touch with your enquiry, the Barrettine Decking Oil is very popular and a good choice for sure. It is solvent based and will nourish and protect the wood. It also has UV stabalisers to slow down UV damage and even more so if you use a coloured oil.

      Another good alternative is the Manns Premier UV Decking Oil that is suitable for both softwood and hardwood.

      The Barrettine comes in a 1 litre tin also unlike the Manns and so gives a little bit of variation in coverage requirements.

      I hope that helps, as always test areas are recommended and if you have any questions please get in touch via our contact us page.

      Kind Regards Samantha.

  4. Hi .l have decking which was laid last year . I have just jet washed it and it’s come up like new . I now want to treat it for the first time , my wife wants it coloured slate grey and l want to treat it with oil , any help advise would be very much appreciated . Kinds regards Chris r

    • Good Afternoon Chris,

      Thank you for getting in touch with your enquiry. Grey is a very popular colour choice this year and one of the few brands that have twigged on to this is Osmo and there is a grey in their Osmo Decking Oil range which may suit your needs. It just requires two thin coats for application and as always I do recommend a test area first to ensure that you like the finish to be achieved.

      For further information or to order please feel free to call in an speak to one of our friendly team on 01303 213838.

      Many Thanks Samantha.

  5. Hi,
    I laid a deck down around 18 months ago to cover my flat concrete courtyard.
    Unfortunately, during the winter months, the area doesn’t get enough sun and certain areas take a looong time to dry, this is made worse by my poor decision to go for wider, 140mm boards which seem to encourage water pooling..
    I went for a local hard wood, spent a lot of money on the construction and oiled thoroughly, but unfortunately the finish has deteriorated very quickly! Now have fungus marks and a lot of faded areas. What can I do to prolong its life apart from mopping every time it rains (which is driving me crazy) and re-oiling? Whats the best way to protect the specific areas that consistently pool during winter and need extra protection?
    thanks for any help, Chris

    • Hello Chris,

      Decking is the hardest exterior wood to protect, it is exposed to every element and because it is horizontal surface is susceptible to surface water resulting in water ingress. Even the best products have trouble standing up to all weather battering that decking gets. The key is keeping the decking swept and clean and then regular maintenance with the oil and this will all help to keep the wood looking fresh and protected.

      For cleaning the areas effected by Algae and mould I would recommend the Cuprinol Decking Cleaner. And then a fresh coat of Barrettine Decking Oil.

      I hope that helps and if you have any further questions please do let me know.

      Kind Regards Samantha.

  6. Hi just applied ronseal deck oil in cedar colour to my siberian larch deck dont like the colour can i go over it with ronseal deck oil in the dark oak colour cheers

    • Hello Leighton,

      You can apply an alternative colour over the top if you wish, it is advisable to do a test area first, as the colour result may be slightly different to expected as there is already a colour on there. Also you will need to test for absorbance levels. If you have done one coat of the Cedar, this should not be a problem, but if you have done two the wood may not absorb a third coat. I would be happy to help and advice further should you have any further questions. Feel free to get in touch.

      Kind Regards Sam.

  7. Hi Sam, I have a decking made of soft wood which has gone that silvery grey and would like to give it a new lease of life. Would it be possible to get it looking like the picture in part two that rich colour, if so how would I achieve this.
    Regards Lindsey

    • Hello Lindsey,

      The decking in that picture is a tropical hardwood, possibly Teak or Iroko. So for your decking you will need to add some colour to achieve the same type of look. If the wood is bare then the first thing for me to recommend after a good clean is the Barrettine Premier Wood Preservative. This will protect from mould, mildew and rot. Once this has dried you could have a look at the colours available in the Barrettine Decking Oil which will give colour and protection.

      There is also a great range of colours in the Osmo Natural Oil Woodstain range that are suitable for decking. If you would like to have a read up of the recommended products and let me know if you have any further questions.

      All the Best Sam.

  8. Is the Barrettine Mould and Mildew Cleaner safe to use around pets especially if it has to be left on for a while?

    • Hello Lee,

      It is advised to keep animals away from this product during application and whilst the product is left on to work, this is because it contains Biocides.

      Please let me know if you have any further questions.

      Kind regards Sam.

  9. Hi

    I have just purchased 25ltrs of Ronseal Decking Clear Oil from you but prior to using this I want to stain my decking with Manns Pine Wood stain in Jacobean Oak. The decking is soft wood.

    Before I purchase the stain from you can you let me know that it is compatible to use with the Ronseals Decking Oil?

    Many Thanks in advance.



    • Hello Kenny,

      Sorry for the delay in getting back to you. The Manns Pine Wood Stain is not suitable for use outside and to add colour to decking you would be better off applying a coloured oil. The Ronseal Decking Oil that you have has a range of colours and you could apply one coat of the colour required and one coat of the clear. Or two coats of the coloured oil. If you need any more help please feel free to call and speak to one of our advisers.

      Kind regards Sam.

  10. Hi, I’m confused about whether to use a decking oil or one that has a wax included. I cannot seem to find an answer anywhere! Many thanks

    • Hello Sally,

      If you are treating new decking then you could apply a coat of Preservative which will protect against mould, mildew and rot. And then a top coat of a Decking Oil, such as Barrettine Decking Oil, that will give water repellency and some UV protection from sun damage.

      For extra protection from the sun you could apply a coloured oil the darker the colour the more UV protection you will get and the Barrettine has some coloured Oils in its range. I hope that helps and if you have any further questions please do not hesitate to let me know.

      If you are applying to already treated decking then my recommendation would depend on the previous treatment.

      All the Best Sam.

    • Hello Joanne,

      I can’t really comment on the particular product that you have used as we don’t stock it. But as it is a surface sealer, preparation is very important before applying such products, and there are a number of issues that could cause the stain to peel and flake. If you would like to send us some photos and a brief description of your application process we can try to advice you on the best way forward. Our email is wood@finishes.direct

  11. Have used 3tubs of advanced mahogany deck stain will it be ok to put 2 Coates of ronseal deck stain on top ( the one that comes in a tin ) cheers

    • Hi Dave,

      If looking to apply additional coats of decking stain or decking oil on top of an existing one, it’s important to ensure that it is the same product. If not, check with the Ronseal to see if the two different types of product are compatible with each other. Not all products will work on top of another and you may find that the newly applied decking stain will not adhere to the old stain. Another possibility is that the two products may produce a reaction resulting in blistering, cracking or peeling of the surface coatings.


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