Hi All,

I have a question about pressure-treated decking joists:

Our house has a decked cantilever balcony around 2 sides on the 1st
floor, where the balcony joists protrude about 1 metre from the outside
wall, and go right through the cavity wall and bolt to the floor joists
on the inside. (Hope you can understand this description!)

Anyway, it's all rotten and I have now removed most of the old joists,
leaving just slots in the brickwork ready to accept some new joists.
Obviously I want to replace with pressure treated decking joists, as I
don't fancy doing this job again for a while! However, I'm having
problems sourcing joists that will fit into my existing slots...

I've determined that the joist sizes I need are 2.4m long, 43mm thick,
and 170mm tall, i.e. not a standard size. (This is about 1 or 2 mm
undersized so I can be sure they'll fit - don't know whether I need to
take shrinkage/expansion into account here?)
However ringing round the local timber merchants, one has said that you
can't plane pressure treated joists as you'll lose the weather
resistance, and one has said they can saw it but not plane it (for the
same reason)!!??

Now some things I've read tell me the pressure treatment penetrates
right to the middle of the wood, but is this the case? Is it a waste of
time to plane pressure treated joists? Surely sawing would give the same
problem if it is an issue?

Thanks,
Ben.