Learn how to use boiled linseed oil to treat cedar siding. Find out why you should used boiled linseed oil but not raw linseed oil for sealing cedar siding.
LESLIE: Charles in Maryland, welcome to The Money Pit. What can we do for you today?
CHARLES: I have a question about linseed oil. I have a cypress board on the outside of my house and my mother-in-law has been putting linseed oil on it. However, she’s passed away now and I don’t know what she was using. Was she using boiled or was she using raw linseed oil?
TOM: Interesting question. Do you know what the difference is between boiled linseed oil and raw? The difference is that the boiled linseed oil  is the only one that dries. The raw one does not dry. And so, for a siding sealing material, for an exterior finish, you use boiled linseed oil.
LESLIE: When would you ever want it to not dry?
TOM: You know, that’s a good question. I don’t know. I think if you were doing a finish technique called a French polish, which is something that’s used in furniture making …
TOM: … where you mix wax and linseed oil together and you do it like on a lathe when something’s spinning around very fast. That’s one time I think I’ve used it, but for the most part, in terms of sealing anything outside the house, always use boiled linseed oil.
CHARLES: Thanks a lot.
TOM: You’re welcome. Thanks so much for calling us at 888-MONEY-PIT. One other useless fact that I’ve trapped in my brain.