How do I adjust the asphalt emulsion rate for various surfaces when placing a chip seal?
The more coarse and porous the surface, the more asphalt emulsion that is needed to get the 60%-80% embedment of the stone which is recomended. Look at the adjustment table in our Pavement Maintenance workshop manual (available to download for free in the resources section below) which is a good place to see the effects on application rates.
For instance, a smooth blacktop road would need a smaller amount of emulsion than an old highly porous one as less emulsion will be absorbed by the surface. Chip sealing a gravel road would absorb more asphalt. In fact it is usually recommended to shoot a primer emulsion application before paving or placing a chip seal on a gravel road. Also, be sure the gravel is ready for the chip seal.
Pavement Maintenance Manual