Crooked terrace wooden planks - usable?

Hello,

my wife wants a wooden terrace for barefoot use, so we decided on Yellow Balau.

Yesterday the delivery arrived: out of 29 boards each 3.97 meters long, 2 are quite strongly curved in the middle, they are practically bow-shaped. The deviation is about 4-5 cm. A few others are also not completely straight, but tolerable for my layman's taste. 5% defects are allowed, the supplier insists on that and also says "wood is a natural product."

Question: Can this warped wood be straightened for decking? I once read something about spacers plus a ratchet strap and screwing. Or are these two boards unusable?

Addition: The floorboards are not warped upwards, but curved sideways

With "5% defects," the supplier is not in the green zone for 2 out of 29, which is almost 7%. Talk to him. I would not use the boards on the terrace; they are "defect."

The 5% does not refer to the quantity, but to the deviation per meter. That is 5cm per meter. We had something similar with our Garapa terrace. They were then about 10cm warped over 4.5m. With tension straps etc., it still worked.

OK, and how do you do it with the ratchet straps? Place one end on a straight, already screwed board and screw it in with the correct distance, then tighten piece by piece plus screw it in?

Is there an instruction manual for that?

I complained to the supplier, but nothing came of it. Then I brought up the right of return, you can return it within a week. Would you do that or is something like this standard?

OK, and how do you do it with the tension straps?

Since I’ve just gone through this with several terrace boards:
The whole installation goes faster, easier, and lasts longer if plastic spacers are used between the substructure beams and the boards. They cost only a few euros and are worth the money. Depending on the wood, 4 or 7 mm wide and about 6 mm high. This way, the distance is always the same and no wood lies directly on wood anywhere, so water can neither penetrate nor remain permanently damp.

Start with several as straight boards as possible. Even with seemingly straight boards, pull the one to be screwed straight with tension clamps or screw clamps (not too tight) to the already screwed ones, pre-drill holes, and screw tight. Move the clamps along while doing so. Start at one end, screw, reposition the clamp, screw again, etc. The straighter the board, the less often you have to reposition the clamp. Usually repositioning every 3-4 substructure timbers is enough. Even if it’s not visible at first glance by eye, most boards are warped a few millimeters. This is also hard to avoid.

If you don’t have a pre-drill guide, it’s easy to make a drilling template so that the holes always sit centered on the wood and have the same spacing: Build a "sled" from about a 30 cm scrap board or another piece of wood and two 10-15 cm pieces of construction timber. Mount the timbers lengthwise on the left and right bottom of the board piece so that the substructure fits exactly in between, and the timbers should stand parallel and end flush. Place the sled on the substructure so that the rest of the board piece lies on the board to be drilled, which is already aligned. Drill two holes exactly where the screws will later go through in the board piece. That is, centered between the timbers and about 2 cm from the board edge. Now you can always comfortably place the sled, pre-drill through the holes, and all screws will end up nicely lined up in a row and never too far inside or outside.

For warped/bent boards, like your two problematic ones, proceed as usual and align at the beginning so that it bends away from the already fixed boards. Then attach the tension/screw clamps (you actually never need more than two clamps), tighten until the next screw hole has the correct distance to the fixed boards, and then move along to the end. It’s best to always place the clamps as close as possible to the construction timbers; otherwise, the fixed boards temporarily bend at the clamp’s gripping point.
This process doesn’t harm the wood much, and the tension gradually releases over time.

If the board is twisted like a screw, proceed exactly the same way and make sure it lies so that the twist side facing the fixed boards points downward. This way, the board always rests on the spacer and is not pulled down first by the screw. Otherwise, the spacer can splinter.

Good luck