Why is there scaling or pitting at the end of a stamped, colored driveway?

The contractor is very capable and knowledgeable and does beautiful work. His routine consists of using 32 MPA concrete that contains quarry stone. Has customer wet cure the driveway once in the morning and once in the evening for 2-3 days. He waits 1-1 1/2 days for the driveway to dry and then sprays a coat of CS-309-25 on the driveway. Normally 10 days later he will return and apply a coat of CS-309-25. Has had great success and loves our products. Has noticed that so far three of the driveways that he did last year have scaling or pitting on the last three feet of the driveway against the road. Looks like the paste has let go.

Scaling and pitting is typically caused by repeated freeze thaw cycles in colder climates and/or improper finishing and placement techniques in all climates. In many cases you will see an application where a driveway and a patio have been done the same day and the driveway is experiencing problems and the patio isn’t. This happens since typically driveways are shoveled during the winter months, the sun comes out and the snow melts and is absorbed by the concrete. As the temperature lowers the water freezes and expands to occupy a space greater than when it is in its liquid state. If the air content is insufficient to allow these repeated freeze thaws or if workmanship or concrete quality have created a weakened surface scaling and/or pitting occurs. The patio on the other hand goes through far fewer freeze thaw cycles per year since the snow is typically left on the surface and acts as an insulator.

Scaling also happens when the top surface of the concrete is weaker than specified. This typically is caused by over finishing, adding water during the finishing operation or rapid surface drying of the concrete due to wind and or sun. This weak surface is susceptible to deterioration.

In this case the fact that the scaling only occurs near the road is definitely telling, did the sun come over the house in the afternoon and create rapid drying of the surface, were these the last loads placed as the concrete stiffened, was water added, was the concrete blessed with water to aid in finishing? All of these would have led to a weakened surface susceptible to scaling and pitting. The contractor in this case, although knowledgeable, didn’t understand the need for proper curing. Having the owner “water down” the concrete and again at night would not have provided proper curing; he should use a curing or curing and sealing compound. The contractor should also consider the use of wind breaks and Evapre to prevent premature drying of the surface.

By following these basic concreting procedures this contractor could have avoided this potentially costly problem.