Improper perimeter drainage can cause excessive subsoil expansion that results in greater damage to the surface from freeze/thaw action and can, in turn, cause the surface to heave and create "birdbaths." Also, this condition can cause loss of colour and permit dirt and silt to wash onto the surface. By lowering the elevation of perimeter drainage swales,and consequently lowering the water table, this condition is improved or corrected. If wet conditions are encountered, a subsurface perimeter drainage system such as a perforated pipe in stone aggregate is advisable.


Puddling or "birdbaths" can be corrected or greatly improved by patching or overlay but only if the original surface was installed to essentially the correct recommended slope of .833% to 1% on a true plane from side to side, end to end or corner to corner. (Side to side is recommended if site conditions allow.) If the existing asphalt has lost its life and a complete asphalt overlay is dictated, depressed areas of 3/8" or less are generally corrected by the overlay. Depressed areas in excess of 3/8" should be patched prior to the overlay. On the other hand, if the existing surface is essentially sound and relatively free of expansive cracking, simple filling and leveling of depressed areas would correct or greatly improve major "birdbaths".