Wall putty is a mixture of whitening powder and linseed oil (javas tel ),used to make wall surface smooth or plane.

Wall putty is typically available in either white or blue, with some products also available in grays or other colors. Putty of various colors is regularly marked as safe for walls and is unlikely to pull off paint during removal. When working with white or light-colored walls, however, it's advisable to use white or neutral-colored putty, as more colorful products are more likely to leave a stain on the back of the poster or even the wall.

After plastering wall was not too finish or smooth. Here you can use 12mm coat of 'plaster of paris', before painting. This makes wall surface gloosy and after painting it looks great. It cost's too much.Instead you can use wall putty,which is cheap and gives good looking ! You can use wall putty to fill cracks and holes also, for good result you can use 'crack seal' to fill gaps!