What made these zig-zag marks on pressure treated timber

[OldKettle]

Hi,
I am currently working with some 6 metre long 2x6 timbers.

I have bought a number from the same supplier, but I have noticed that latest batch all have a zig-zag marking on them, and I would like to understand what it is.

It almost looks as if the timbers have been joined at that point.

I initially thought that it was just the marks from strapping but, on closer inspection it looks as if the two sides of the timber don't exactly match. In one location there is even a knothole on one side of the zig-zag that doesn't seem to continue on the other side.

I can't picture what process would have created this pattern, but wonder if it is part of the pressure treating process.

Can anybody please advise on what these marks are, and whether they in any way compromise the strength. I am currently using them to make rafters across a span of almost 5 metres.

Any thoughts would be much appreciated.

 

[Nozzle]

It's where the timber is machined to join two lengths together.

Nozzle

 

[OldKettle]

OK. So it looks like it is finger joined timber.

This is the stuff that I bought.

https://www.bradfords.co.uk/treated-sawn-timber-47mm-x-150mm-ttl136

Is it OK to use it for rafters on a pergola? I've been having a quick read online and it seems that opinions are mixed on the use for rafters. In my case the load should be fairly low (worst case snow on the pergola polycarbonate roof).

 

[Nozzle]

What you've linked is C24/C16, which is structural timber - and I'm not convinced that the timbers you've been supplied (with those joints) is actually suitable to be graded C24/C16... builders on the forum could confirm.

It should have C24/C16 stamped on it, if so.

https://thecraftsmanblog.com/is-finger-joint-lumber-worth-it/

But then you ordered 6.0 metres, and that is perhaps too long for decently priced non-jointed equivalent

Nozzle

 

[Nozzle]

.

 

[Deleted member 174758]

But then you ordered 6.0 metres, and that is perhaps too long for decently priced non-jointed equivalent

Almost all the C24 200 x 75 and 220 x 75 we were using last year was finger jointed lengths over about 5 metres (we even had a few 6.7 metre monsters). The grading is done after the finger jointing and 4/s machining and as modern glues are stronger than the wood it shouldn't be an issue

 

[OldKettle]

What you've linked is C24/C16, which is structural timber - and I'm not convinced that the timbers you've been supplied (with those joints) is actually suitable to be graded C24/C16... builders on the forum could confirm.

It should have C24/C16 stamped on it, if so.

https://thecraftsmanblog.com/is-finger-joint-lumber-worth-it/

But then you ordered 6.0 metres, and that is perhaps too long for decently priced non-jointed equivalent

Nozzle

Thanks. Other timber that I have bought from them do have stamps, but I cannot find any stamps on these 6m lengths that I bought recently.

 

[OldKettle]

Almost all the C24 200 x 75 and 220 x 75 we were using last year was finger jointed lengths over about 5 metres (we even had a few 6.7 metre monsters). The grading is done after the finger jointing and 4/s machining and as modern glues are stronger than the wood it shouldn't be an issue

Thanks @JobAndKnock. If it is C16/C24 as advertised, should it definitely have stamps on it?

All of the previous 4.8 metre timbers I have bought from the supplier have had stamps (a couple of examples below), but there is definitely nothing like it on the 6 metre ones I have bought recently.

 

[Deleted member 174758]

It needs to be marked "CE Dry Graded" or the like and have the grading clearly marked, together with an identifier for the supplier. I've never seen structural stuff which wasn't marked (including the last big job I was on where we installed over 10k of C24 joists)

 

[johnny2007]

I would not use them for a pergola.
If you can't get full lengths, use two full joists joined by the side with connector bolts.

 

[^woody^]

I would not use that crap for structural work - stud work and vertical maybe, but not for the likes of rafters or joists.

 

[Deleted member 174758]

I would not use that crap for structural work - stud work and vertical maybe, but not for the likes of rafters or joists.

C24 8 x 3s are not really carcassing. Believe it or not thay are rated for it

 

[John D v2.0]

Carcassing: Going to great lengths - Timber Trade Federation

The trend towards more open-plan housing is fuelling demand for longer lengths in carcassing. Certain TTF members already specialise in this area, such as Wardell Long Lengths, who serve length demands going up to special order items of 7.8m in dimensions of up to 300...

ttf.co.uk

 

[^woody^]

Carcassing: Going to great lengths - Timber Trade Federation

The trend towards more open-plan housing is fuelling demand for longer lengths in carcassing. Certain TTF members already specialise in this area, such as Wardell Long Lengths, who serve length demands going up to special order items of 7.8m in dimensions of up to 300...

ttf.co.uk

I wonder if the glue really will last as long as the timber would do, or how it performs in a fire - timber will char and not necessarily fail, but if glue in a structural timber softens ....

Or should I just get with the 21st century.

 

[Deleted member 174758]

Yes