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  1. #1

    Quick Pergola Timber Question

    Have my timber delivered today and a chippy outside waiting to knock up my Pergola but they've delivered treated C24 instead of untreated.
    I'm going to stain/coat with something but not 100% sure if the tanalised stuff is "fish safe".
    Anyone around with a quick bit of "yes, that'll be fine Gaz opinions?



  2. #2
    panic over...they're dropping over the right stuff

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  4. #3
    Senior Member Rank = Grand Champion andikoi's Avatar
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    yes, that'll be fine Gaz,all my wood has been tanallised,mainly due to me being slow at building and not wanting it rotting while i do it lol,andi

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  6. #4
    Senior Member Rank = Gosai Brandlin's Avatar
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    I cant answer for the 'fish safe' bit, but i'm presuming it isn't actually IN the pond?

    Remember we all walk around on tanailised decking in bare feet and handle the stuff often especially when building. So I do understand the concern regarding toxicity, and i do recognise that a closed water eco system like a pond can amplify chemical effects but i'd be very surprised if a treated pergola would effect water quality. I'd be more concerned with any spillages of the relevant coatings you're going to apply every year to protect it if it isn't tanalised.

    On the other hand, I wouldn't be building anything outdoors with C24 without it being tanalised, especially if its coming into contact with the ground or concrete surfaces?

    As i say, I'm not the fish expert, but i know a bit about wood

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  8. #5
    well, I'm going to "treat" it with a sealant of some description so maybe worrying unnecessarily

  9. #6
    Senior Member Rank = Gosai Brandlin's Avatar
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    Sorry to be negative, but there is simply no comparison between a 'sealant' (your words) and pressure treated (tanalised) timber. I suspect there is a reason that the timber yard sent you treated timber - and that's because you told them you were building outdoors, so they sent you the right stuff.

    Yes you will get some protection from the elements with a brush on treatment but you will need to do it at least every year and it will be next to useless in any areas where you get trapped permanent water - ie where the timber contacts the ground, or a wall, or even where you have joints between two pieces of wood where water can be drawn in with capillary action and stay.

    There are a whole range of treatments on the market. They fall in 3 categories.

    1. oil based - such as danish or tung oil - natural oils that penetrate into the surface of the wood and harden when they dry, quite robust best of the options, but need to be reapplied. Best option if you have parts in contact with ground or any standing water is to soak the cut ends in a bucket of the oil. Will need reapplying yearly. If you are going to use untreated softwood outside then this is really the only option you should consider. There are many different formulations but in general you wont want any of this splashing in your pond

    2. water/ acrylic polymer solutions - usually advertised as 'water based' because you can clean your brushes with water rather than white spitrits, but far inferior to oil based treatments for wood. Water solution evaporates, leaving a very thin clear plastic coating on the wood, better ones are UV stable and dont degrade as badly in sunlight as the non UV stabe ones. Either wears heavily in normal weather conditions and will need retreating at least annually. Some are marketed as pet-safe.

    3. water / wax based.... things like thompsons waterseal - basically a solution of wax suspended in paraffin, when the paraffin evaporates it leaves behind a thick wax coating that looks great because water beads well. it wears quickly in normal light and weather exposure and definitely needs regular re-treatment - due to the paraffin its also toxic. These are IMO a marketing gimmick as they look great the moment you aply them with the wax beading but they wear very poorly and you HAVE to keep reapplying because the wax repels other products - its a marketers wet-dream!

    The difference is tanalising is a treatment that is applied under extreme pressure and penetrates the surface of the wood far deeper than anything you can brush on or soak in, and in its treated and dry form (unless you are soaking whole beams of it in your pond) pretty much safe. Tanalised timber will last you easily 20 years or more even if you never treat it again. Applying oil to it will also retard the rate at which it goes silver. Untreated softwood - worst case, with ground or concrete contact and untreated joints, you might be unlucky and see failure in 2-3 years. Best case 5-7.

    If you are proceeding with untanalised softwood, then i strongly recommend that you thoroughly soak all the cut surfaces of joins and all end grain of component parts and let it dry before you assemble. That will at least ensure that you offer 'some' protection to the most vulnerable areas that you cannot get to with a brush.

    You say you have a 'chippie' there working for you - I'd expect anyone who knows what he is doing with wood to be advising you of this or doing it anyway - if he isn't i'd be suspect of his skills and experience.

    Sorry to sound negative, trying to give you the best advice and knowledge, I do hope your pergola is successful.
    Last edited by Brandlin; 10-05-2018 at 01:34 PM.

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  11. #7
    Extreme Koi Member Rank = Yonsai muttley's Avatar
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    Sounds to me like you've had a result getting tanalised for the price of untreated then sent it back. ��

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  13. #8
    As it goes...had a rethink and using the treated. We have loads on site at the moment as also putting in 2 decks. Also putting posts on these so they’re not in contact with the walls. Just drilling coping now to go mover top before posts go on



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  15. #9


    Brazilian black slate patio and paving going down round back and side of house so using left over slabs for the pond coping which should tie everything together nicely. Cladding the pond with sleepers ripped into 4x25mm planks to match all the raised sleeper beds we have.


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  17. #10
    Senior Member Rank = Grand Champion voodoo_15_uk's Avatar
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    Looks lovely, is it non slip?


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  19. #11
    Moderator Rank = Supreme Champion Feline's Avatar
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    It looks like the same stuff as I used on my patio. It's brilliant for not reflecting in the pond window as a dark colour, and very easy to clean because water (and algae) don't penetrate the surface. Of course that does make installing it slightly more tricky as it doesn't stick to wet mortar very well (I used an SBR cement slurry bridge bond painted on the backs of mine, but made the job take longer).
    It should look nice as pond coping, but is fairly thin.

    I am considering building a pergola over my pond, not entirely decided yet, but I will be facing the same decisions as you've had with your timber about treated/untreated etc. I might solve the dilemma by saving up for a couple of years and do it in oak

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  21. #12
    Not surprised you’ll have to save up Feline, your pond must have set you back a fair few £££££. Mines only half the size and the cost soon builds up.

    The slate is from Black Mountain Quarries, 20mm. Can’t remember exactly how much but it’s around £28m2. We needed about 60m2 plus 10% wastage but it’s extremely good compared to a lot of the other samples we had and the wastage is pretty much zero so the left overs are being put to good use.
    Grout is Going to be Marshals 365 grey. Now that’s flipping expensive but will save 2 days labour so it pays for itself.
    Managed to get that for £33 plus VAT on sale or return and reckon we’ll need 8 tubs. Sealed the slate with 511 impregnator which rivals printer ink for cost lol. Luckily managed to get away with just under a gallon.
    The slates aren’t slippery until they’re wet then they’re a bit dicey. Probably ok if you’ve not been on the Bombay Saphire actually, Hoxtons is rather nice.
    All I all, well pleased with how it’s all turning out, shame there wasn’t enough left in the piggy bank for some Trex decking but never mind.


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  23. #13
    Extreme Koi Member Rank = Nanasai Rog.G's Avatar
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    Feline has the right idea,
    When I built my pergoda over 10 years ago I built it with green oak for the structure and Canadian cedar tiles for the roof. In all that time there has been no need for any protective coats and I understand that Canadian cedar tiles are good for at least 100years and the oak considerably longer.
    I have power washed it a couple of times and it comes up like new so I consider the extra initial expense to have been a very good investment that is actually saving me money now.

  24. #14
    Extreme Koi Member Rank = Gosai koicarpus's Avatar
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    Morning, looking good.

    Have you used breeze blocks on your pond?

    Dave

  25. #15
    Quote Originally Posted by koicarpus View Post
    Morning, looking good.

    Have you used breeze blocks on your pond?

    Dave
    3N Trenchblocks Dave.
    The lads that work for my builder are a lot younger and fitter than me. They’re bloody heavy. More expensive than standard blocks to buy but miles quicker to lay.
    I did drill some stainless rods in the corners for some extra strength as they don’t quite knit together as well as blocks laid flat. The corners either side of the window were my only real concern but with the rods in place I’m pretty confident it’s not going anywhere.
    Will find out in a couple of weeks as fibreglassing hopefully being done on 30th


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  26. #16


    Pergola up


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  28. #17
    Senior Member Rank = Gosai Goonerharwood's Avatar
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    Looking good pal a job well done

    Colin

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  30. #18
    Extreme Koi Member Rank = Yonsai muttley's Avatar
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    Looks good. Any plans for the shading material?

  31. #19
    Not really, I’m having to ease she who must be obeyed into this slowly, I think polycarbonate might be a step too far right now. It’s probably too of my list as ultimately I want to add heating and a full enclosure for winter.
    As it happens, that corner of the garden doesn’t get too much direct sunlight and there’s a Goat Willow (weed?) right next to the pond which provides a food amount of shade...and Catkins!
    Luckily they don’t appear to fall in that direction when they come down but now I’ve put the kiss of death on that, next year the pond will be covered in them no doubt. Still, it’ll give the skimmer a good workout


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