drying out new floorboards (not kiln dried)

You need to stack them with spacers to allow free air circulation. You also need to put quite a bit of weight on them to minimise warping. Turn up the heat in that room, and leave them for a couple of weeks.

How have they been stored? It may help a bit to store them, but if they do cup, then you've had it. Depending on what has happened to them recently, I might be tempted to nail them down straight away. What are you putting over them?

not sure about previous storage, think they saw and t/g them to order from old boards - will be simply adding a varnish or similar finish

I relaid both my downstairs rooms with (redwood) pine. Left them for four weeks - stacked with one inch spacers.

I had some terrible warping/cupping.

Next time I'm paing someone to do it....

One thing I can really recommend if you are going to stain them is Dulux Diamond Glaze - it's expensive. But impressive stuff.

You really need 6 months or more for new wood even though it is all kiln dried to at most 20% (I think) . One solution is to lay the boards un nailed and then finish off 6 months or so later. You could lay them upside down so that they are all new and clean when you turn them and do the second fix. Drying stuff under weights is pointless - it will spring to the warped shape as soon as released.

cheers

Jacob

New stuff is dried to 17% moisture content (the point at which mould doesn't develop). Good quality redwood shrinks across the grain but shouldn't distort unduly. Whitewood is more reliable in this respect.

Reclaimed pitch pine from commercial premises is usually pretty dry, but a lot of it is taken from docks and other outdoor locations. Being a resinous timber, it takes a long time to dry. You still get a whiff of disinfectant when you cut it.