Surface dressing involves spraying bitumen binder (a sticky tar-like substance) on a clean, dry road surface, over which stone chippings are spread (small, consistently-sized aggregate). ... The weight of vehicles passing over these loose stones will force them in to the bitumen to finish the new road surface.
The thing is, you have to control erosion to maintain integrity of the bitumen and tarmac. The bitumen itself will not allow water to seep through, lakini rain water on the side will erode the soil and then bitumen will crumble with weight.
The edges of the road should never be soil like it is here. At the wvery least, it should be a small trench design leading to a water run off area or kitu kama hii
1.you start with the first level(formation level)this is where drainages levels are
2.you put a sub base here you mix cement and soil.preferably red soil mixed with murram
3.you put a base(amix of murram and red soil plus cement.otherwise known as coarse and fine grained soils) while compacting each layer using asheep hoof roller, drum roller a double drum etc.
4.you pour k1_60(abinding substance)over aclean base surface.you have to ensure you use mechanical broom to sweep the road.then another layer of k_170 when you are about to put surface course(tarmac in lay man language)then you put chippings(small kokoto) as wearing course to stop the tarmac from being worn out by the tire friction coz its cheaper to do awearing course than surface course.nimechoka kutype ningelezea about shoulders zenye zinawekangwa rumble strips sometimes to discourage overlapping.but the shoulders should be constructed to the same standard as carriage way.