How should I deal with curves in new deck boards during installation?

Question

My son is making a backyard deck of about 6 x 6 metres for my daughter. I am too old and doddery to help much, but am advising. Now we find that some of the planks (400 x 23 cm composite) are curved by up to 2mm, that is like a banana lying on its side.

The standard plank spacing is 5mm, and we have invisible clips for this. But if two adjacent planks happen to be curved the wrong way the gap could be up to 9mm at the centre of the planks, which will look horrible.

It seems that we must select planks as we lay them to minimise this effect, but it's not trivial to sort and reverse 4 metre planks, weighing 10+ kilos, to find the best fit. Most of the time my son will be working alone.

Does anyone have any tricks or advice to make life easier?

Update 14 July: It turned out that we can (un)bend the planks with just a few kilos of force, applied with the knee. Thanks everyone for thinking along.

Answer 1

Put them down, wedge them over with a pry bar, and screw them in.

Decks don't need gap tolerances like Japanese automobile panel fits.

Answer 2

2mm (~1/8") isn't a bend in the carpentry world. I'll be surprised if you find any that aren't curved at least that much just due to milling (manufacturing) tolerances. It's your job as the carpenter to straighten them to your satisfaction.

Tiger Guy's right. Here are some tips to make that easier:

• Fasten one end using multiple screws (on the first two joists or whatever).

• Skip 2-3 joists and set the board there. It's easier to bend a board over a slightly longer distance, and you won't see any remaining curve in that span.

• Fasten the far end before you get too close to it. End positions are more critical than the middle, so leave enough free length so you can move it to the correct position without a struggle and so it doesn't affect the next board.

• Don't use spacers. They simply transfer error from board to board. Instead, eyeball from one end or use a string line to verify straight every couple runs.

Answer 3

Get a board bender. You tack one end of the board down and the move down the board bending it into place with the tool and tacking it at each joist.

Answer 4

Rotate them all 90 degrees about their long axis so they are on edge. Line them up. Order them from the highest to the lowest center deviation. Install in that order, spaced evenly at the ends. You’ll see minor deviations at about the 1/4 and 3/4 lengths, but the ends and centers should be near perfect, and the deviations will have a nice symmetry about the center, with some aesthetic randomness evident. (If you really want to be neurotic, tweak the results by flipping them about any of their three axes and reorder as needed so the the 1/4 and 3/4 deviations are as minimal as possible. But you may find that you get it so good that the few places where gaps are off are noticeable and distracting. Perfect can translate to no character.)