OK, finally found a source for Soiltac in the Netherlands.
We made 2 test sections to see what it does.
( see: Soiltac - MAC Vlijmen (3) - proefdeel 1.JPG )
The 1st section was done as it was explained by the guy who sold it to us. Mix with water ( about 1 to 8 ) and put out a few coats. The grip on this section is very high, but because it was to thick to be taken in by the clay there is still a thin coat of Soiltac on the surface. So far this section hasn't been damaged at all. Downside is, that because of the thin layer on the clay, the ground will not take any water. So if it rains there are immediate puddles, and the grip is gone. Because of the thin coat on top of the clay there is also the discussion on "is it still a natural off-road surface ?"
( see: Soiltac - MAC Vlijmen (2) - proefdeel 2.JPG )
2nd section is on the main straight, its just got one layer mix 1/20. This section doesn't have the thin coat on top of the clay surface, but the Soiltac is now part of the clay. The grip is good and there is no more dust. We threw a couple of buckets of water on it to see what would happen. the clay did take in the water now, and the grip was still "race able". But well have to see and wait what happens if it rains for real.
In the end, we'll probably end up with 2 coats of 1/20.
( see: Soiltac - MAC Vlijmen (5) - reparatie.JPG )
Eitherway its works very good for making small track repaires