Shuttering - The Hempcrete Topic: Designing and Building with Hemp-lime - page 285

Keep screws and spacers organized as you move around
the building.
The screws used need to be available in a range of sizes from 150mm to 300mm (the usual
length needed is 200-250mm, to take into account the width of the shuttering board and the
proportion of the screw that should sit in the frame to support the boards), and should be
strong enough to hold the boards in place without moving. The head of the screw needs to
be heavy duty, and up to the job of being repeatedly driven in and out, time and time again.
The best we have found are extra-long decking screws, which come in a range of sizes and
are very heavy duty (which is lucky because they are not cheap!).
The length of screw required can be calculated by combining the thickness of the shutter-
ing board + length of the spacer + 30mm (minimum) sunk into the frame. The optimum
length sunk into the frame is probably about 40mm; anything over 50mm is too long, as
it risks splitting the timber. It also makes the job harder, as you have to sink more of the
screw than necessary into the timber frame - and get it out again when you strike the shut-
tering. This means that the job takes more time (and battery power) than it would do oth-
erwise, so ideally the shortest possible screw should be used, while meeting the minimum
length as outlined above. Don't forget that some screws include the head (which stays out-
side the shuttering) in the length of the screw.