Treating external 3x2

4 Jul 2004
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United Kingdom

I've ordered some 3x2 from a timber yard local to ours and unfortunately it's not pre-treated. It's going to be used for decking joists and noggins.

I'm just wondering what the best sort of treatment is for this? Standard wood preservative or alternative. Looking for cheapest solution cheers.
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Unlikely to last long, you need pressure treated timber, diy job will not penetrate timber, but rot will.
I told the guy what I'd be using it for and he said it would be fine

Then he shouldn't be selling timber if he is that ignorant or dishonest.

It should be a copper organic pressure treatment, preferably pine and not white wood (white wood being difficult to treat).

Even with pressure treatment, there are different levels of treatment (amount of penetration and retention), most "off the shelf" treated timber is only done to low levels.

the issue with brush applied treatments is lack of penetration and less predictive service life. If you go nuts, specially on the end grain, you might get 5 years reliable. You might get triple that, but you won't know until it happens. *Properly* pressure treated timber to a lowish spec will last min 15 years.
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I used CLS for my front fence, and treated it with Cuprinol Clear (brushed, but the ends dipped) followed by a water-repellent stain

It rotted quite badly at an upward-facing knot which had (I presume) allowed rain to penetrate past the surface layer of preservative. The other rail without an upward-facing knot seems fine.

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