Bruce wrote:

MOT Type 1 is a fully graded material, with everything from 3" (75mm)
down to dust, and all intermediate sizes present. Â*It must be made of
crushed limestone.

I've got the spec somewhere but MOT type one is just a strength and size
assortment, quite a loose one at that, plus the material needs to be
angular, not round. It does not specify limestone and many quarry
waste "crusher runs" will fit the spec.

I know this because I had to find and inert (pH 7 or lower) sub base for a
car park on a sensitive acid heath and it's actually quite difficult to
find an alternative to limestone scalpings for type 1, but they are
available. In fact a granite type one is available but this too has a pH
7.

In my searching I very nearly decided to have some local pebbles (rejects)
crushed to mix my own type one.

The very fact that the spec is the correct assortment for no voids suggests
it shouldn't compact much.

AJH