Best stain or oil for softwood Pergola made with C24 Pressure treated timber

[chazzyB]

I'm in the middle of building a pergola and noticed most of the regularised C24 Pressure Treated timber was bent or twisted. I assume this is from incorrect storage. The bloke at the timber yard let me cherry pick some replacements but with rain and hot sun it is probably going to bend up again as it dries unevenly.
I want to get some protection on as soon as possible, to keep the moisture out but don't know what to go for. It rained the other day and the grain colours really came out nice and would like to do the same with a protective oil or something. Keep finding products labelled decking oil that are water based.

Also any advice for removing the C24 grading stamps down each length of 6x2? Do I need to be sanding those out?

 

[Blokky27]

Hello

I'm certainly no expert, but I'll give you my thoughts having built my own pergola last year.

I used 100x100 treated for the verticals and then I think 6x2 for the side horizontals and 4x2 for the ones across the top - all pressure treated. So to get the grading stamps yes it was just a case of sanding these off.

In terms of colour I was going to do some sort of treatment like you especially as the verticals were much darker than the rest. As it turns out I never got round to it and they've ended up looking the same with a bit of sun and don't need doing.

That said if you do find or try something I'd be interested to see the before and after photos?

In terms of twisting etc, none of mine was perfect, but I haven't had any problems with the C24. However, the 100x100 timber treated posts I bought (sorry I can't find any records of what I bought exactly, but they were definitely treated in some way to be destined for this type of job) have split quite badly. It's quite likely because I cut a notch out of the top for the horizontals to sit on and the water has got in from the top. I did get some treatment specifically for sealing cut ends but it perhaps wasn't up to the task. Possibly the splits are nothing to do with that at all, who knows. They split very early after I'd set them in the concrete post-mix, but they don't seem any worse since (a year on) so I'm actually not bothered now.

Hope that helps.

 

[chazzyB]

Thanks for sharing the details of you build.
Progress has been slow because of weather, the notched posts got rained on and was a few days before it was dry enough to use the cut end treatment, nasty stuff...
I had a plan to do some fancy rail ends but my jigsaw wasn't up to cutting curves straight through 2" so went for simple diagonal cuts with the circular saw on the bearer rails. I got one of these replaced because the original was twisted and bent in 2 directions and got 3 of the worst top rails replaced.
I decided to put a 7degree slope on this by putting the front posts lower. This was a dumb move in hindsight because it made notching the top rails accurately a lot more difficult.

Currently it's all been up for over a week, still need to treat the notch cuts and decide on how I'm going to fix them down. the slope means I can't just go straight down and not keen to recess the screw head on the top as it would let water in. I'll either drive some >200mm screws straight up, through the 150mm bearer rail into the top rail, or maybe go diagonally.
What fixings did you use?
I haven't fixed the bearer rails to the posts yet but was looking into to using a couple of coach bolts through each one. and use some steel bracing either side
I wish timber was as regularised and precise and as easy to move around as in my design software