Preparing old wood surface to paint

[Greenhorn]

I am getting ready to paint a 50 year old house. The paint on the wood siding is scaling really bad in places, especially where exposed to the sun. I intend to use an oil based primer (Kilz) and a latex based finish coat. I know that I will be unable to get all of the old latex paint off to the bare wood in most places. I have been told that you cannot use oil based paint on latex. Is that true? The preparation directions on the Kilz does not mention this.

Thanks in advance.

[Bumblerazz]

Typically you can not put latex on oil or oil on latex, though oil on latex has been done before with reduced quality of finish.

I am surprised that a 50yr old house has latex paint on it, unless the previous owner has repainted recently.

The issue is that without proper preparation neither will last very long when exposed to the elements. When switching types one MUST remove all remnants of the previous type to have any long lasting quality finish, or you will have cracking and peeling same as you described. And to be honest with you, I am surprised that you would consider switching back to oil after the house has been redone with latex. Do not under any circumstances try and mix an oil base coat with a latex top coat, at least not without adding a binder coat in between. I have only used a binder coat once and though the finish was as expected, the cost and time involved in the "extra" coat (not to mention hazardous) was a pain in the ***.

Latex exterior paints have significantly improved over the past few decades to the point that the longevity, quality and finish (not to mention the environmental impact) is, in most cases, considered to be better than oils. I always choose latex over oil, unless I am staining and even then it will depend on the application.