We are trying desperately to clean up, update and make some repairs to my grandmother's house. The house is about 80 years old and has some cracks in interior bedroom walls under the windows, which appear to be made of some sort of concrete-type material (it most definitely isn't drywall or wood and there is a dull thud when I tap on it...nails are very hard to pound in).

I am sure there has been some settling of the house due to its age and there probably are some foundation issues, but we are painting and would like to fill in these cracks. Down the road we will look at the foundation issues when we have saved up some money.

Are there any suggestions on how to fill these cracks?

Thank you!