Help I have a old 1900's house with plaster walls. The original paint was an oil base. And was never repainted till 3 or 4 years ago. They used a latex paint from what I was told. Now the paint is flaking off the walls and ceilings my question is do I need to remove all the paint and start over or just the flaking and prime with oil base? Thaks for any help I can get!

There could be several reasons why the paint is failing. To remedy what you will want to do is scrape the paint that is flaking off. You may want to give the paint underneath a lead test (very cheap and available at home depot). If it tests positive then you will want to wear a mask when scraping and to be sure to vacuum/clean all the chips. Always wear safety glasses while scraping. The reason for caution is that while scraping you may scrap the underlying paint which may have lead. Once the area of flaking paint is scraped I would recommend a light sanding to the the walls. Just to scuff up the surface a bit. Use a good primer - it doesn't have to be oil but you could certainly go that route. Some excellent primers are available from Pittsburgh paints, Zinsser, and Kilz is pretty good too. You will want to use a quality top coat like Pittsburgh, Benjamin Moore or Sherwin Williams. Be sure to allow the primer and each coat of paint to dry completely before the next coat. Follow the dry time on the labels. This should take care of the problem. Also be sure that the humidity is not over 85% when you are painting so that the primer/paint can dry properly. If you have air conditioning this shouldn't be an issue at all.

Good luck!