Some surface cracks do appear on walls in new construction. These cracks are due to poor quality of sand in Pune, wide daily difference in city temperatures. Wall cracks also do appear, when high grade cements are used in construction, or if mixed mortar is applied little too late, when mortar has already started drying or setting. Hammering nails also produces cracks.

Surface cracks or shrinkage cracks, as these are some times called, develop and remain for 2 full seasons (years). These normally do not develop or widen afterwards. Filling Putty and repainting surfaces after 2 seasons, will solve this problem. Instead of hammering a nail, drilling a hole is more sensible, while drilling in a wall, or floor, please ensure that no services (concealed electric Conduits, water/hot water/gas pipes etc) are passing or likely concealed in the wall, you may damage these services, and create some other problems.

You should get worried, if the cracks are quite wide, and are seen further widening, that you can see through, call to Builder/Structural Engineer will help in ascertaining the true cause, and possible remedy.