For a while I've been more and more troubled by water flooding into the garage, every time it rains particularly hard.
Its a concrete sectional job, with a slab concrete floor. The reason it flows in, is that on one side the ground level rises from front towards the rear, to about 3" higher than the base slab. The 'ground' is actually where the drive continues past the side of the garage - 3x2 slabs, with the gap between slabs and garage filled in with concrete.
I dug the entire stretch of concrete alongside up, to a width of 6" to expose the garage slap, since when I have painted slab and garage wall to ground level with Tetraseal car body underseal applied liberally to waterproof the entire length - so there is no gap for water to gain entry.
I wasn't sure about using the Tetraseal, but I had plenty of it stored up and it seemed to be bitumen based, so should work. Having flooded the channel with water to test it, there was no sign of any ingress so it at least looks promising.
I just need to decide now, what to refill the channel with - more concrete, gravel with a thin topping of cement, or just loose gravel.