Expert: Dan Griffin - 2/2/2008

Question
QUESTION: I plan on installing a  solid hardwood floor in a room 10 by 10. When I put a 7 ft straight edge on the floor I have a gap about the thickness of a nickel under the staight edge on one joist. This joist must be a eight inch lower. Is this a problem, should I try to build this up with rosin paper since I'm laying paper first? What do you think?

ANSWER: Bob,

Yes, I would level the floor.  It can be hard enough to get the tongues and grooves together and the gaps driven up tight without fighting a dip in the floor.  It also provides a great place to develop squeaks.

You don't say what you have for a subfloor, but I think I would use floor leveler.  I prefer the cement based products like Planipatch by Mapei - sets very fast, do not make too much at a time.  There are some excellent vinyl based ones also.

---------- FOLLOW-UP ----------

QUESTION: I have a plywood sub floor. Can I use this on wood?

Answer
yes.


There are gypsum based floor levelers and cement based floor levelers, either can be quite satisfactory in your circumstance, though I would recommend using the latex "milk" to increase workability and bond.  If you have a small area to do, you can use Durham's Rock Hard Water Putty.