I've just taken delivery of a load of 135x19mm T&G oak floor planks for the
two downstairs reception rooms, and whilst I finish some other jobs and wait
for it to acclimatise I'm going through the detailed planning for it's
installation.

It's a Victorian terrace, so the floor downstairs is traditional joists over
a ventilated cavity, and of course all the services (gas, heating, electric)
are routed under the joists. A couple of the joists are knackered -
previous damp problems caused mild rot and a subsequent infestation of
wood-boring weavils - so they will be replaced with new, treated joists, so
I'll need to get most of the existing boards up to carry out that repair.

The people that delivered it expressed surprise that I wasn't going to
install it straight over the old boards, but I really don't want to raise
the existing floor level by another 19mm, and on top of that I'm really
concerned about access to the underfloor should the necessity arise in the
future.

My plan, therefore, has been modified from my original intention of screwing
& plugging the new floor straight onto the joists (this seems like a
ridiculous amount of work and complete overkill) and instead installing a
WBP ply subfloor & secret nailing to that, but creating a couple of
removable sections with the boards secret nailed to the ply, but screwing
and plugging those sections through to the joists instead of fixing them
permanently.

This seems to have a couple of advantages, namely

1) it creates a nice, flat subfloor for easy laying of the new floor;
2) it means that the boards will be somewhat protected from the humidity
variations in the ventilated cavity and hopefully prevent cupping and
warping;
3) the boards aren;t end matched (t&g each end) as I'd expected, so I won't
have to ensure that joins are above the joists.

However, there are a couple of questions about this...

- is 9mm ply thick enough to nail into, and is it enough to provide strength
for any joins that occur between joists (they're 14" centres)
- which ply to use? Champion stock Far Eastern WBP, Shuttering Ply WBP, BBA
Approved Construction Ply WBP, Marine WBP, at widely varying cost
- when secret nailing, is it necessary to pre-drill? I'm concerned about
nails splitting the tongue. Or will a (hired) nailer prevent this?

If 9mm isn't up to it, then I could just about accomodate 12mm, but 18mm
would be way too thick & I'd have to rethink (again).

Oh, whilst I think about it, I'll want a finish to darken the floor. Wax?
Oil? Any suggestions welcomed...


cheers
Richard


--
Richard Sampson

email me at
richard at olifant d-ot co do-t uk