ET-T screw and impact driver

[jishi]

I'm screwing together a joist for decking with recessed screw beams and have used Essve ET-T to avoid joist hangers.

The instructions state that it must be screwed in a continuous pull and that you should not use an impact driver. No real explanation as to why.

I tried using a screwdriver, but it was a real nightmare to screw these, with a high risk of slipping the bit. Then I tried using the impact driver, which was a dream.

Does anyone have a good explanation for why these instructions exist and what you compromise on by using the impact driver anyway? And what are your experiences?

I'm also going to build a balcony and plan to use the same screws, where there's clearly a greater risk if the suspension fails...

 

[kniv]

The reason you shouldn't use an impact driver on construction screws is precisely because of the impact. There is a "risk" that the impact might cause the steel to break or crack, etc. How likely this is in practice, I do not know. However, you need a rather powerful driver if you're going to drive them in without impact; drivers that "ordinary" people have are often not powerful enough. I believe, however, that the risk is generally quite small and you can probably continue using the impact driver.