I and getting ready to install 3/4″ Oak Hardwood in my master bedroom, over a 3/4″ plywood subfloor. Attached is a partial mapping of the current subfloor flatness in a corner of the room (the closet area). It shows a localized 5/8 to 3/4″ max low point when checking with an 8 foot level in the E/W direction. When checked in the N/S direction, there is only a 1/4″ sag at the same point. I would appreciate FHB members’ input on how best to flatten this local closet area sag.
I was planning on using thin plywood sheets of differing thicknesses to buildup and feather back to main flooring. However, if I base my fill on the E/W measurements, I will end up with a hump (high point) when going in the N/S direction. Since I am laying my hardwood in the N/S direction (parallel to joists), I am guessing that it would be better to make the N/S direction flat and live with some but less dip in the E/W direction?
I haven’t seen this discussed, but I imagine it must be common for the depth of sag to be different depending on which direction you are measuring it (parallel to joists, perpendicular to joists, diagonal to joists, etc.). Basically, my question is “How do you deal with such situations?”
Thank you
Dan
Replies
I'm having a little trouble following. The way the diagram displays, are the joists running from left to right? Are the dips just between the joists or do they include the area over the joists?
Yes, the joists are running left to right in the sketch. The dips (basically one dip) is lowest between joists, but is out of spec (>1/4") over about a 6 feet distance in the top to bottom (E/W) direction. In the N/S direction it is not much out of spec at all and only for a couple of feet.
Dan
A good method is to use some vapor retarder or roofing asphalt and make a topographical map type of build-up that will feather out as you work away from the low spots. The lowest spot will have the most layers and the number of layers will decrease and 'feather' as they run toward 'high ground'. Wood shingles which taper could also be used to accomplish this.
Have you looked into leveling compounds? Here’s one of many: https://www.homedepot.com/p/Henry-555-Level-Pro-40-lb-Self-Leveling-Underlayment-12165/100549588?=&irgwc=1&cm_mmc=afl-ir-29332-456723-1083244&clickid=zgo2Tk2U-xyIU-LSYLyQdQ62UkBVZyVFwU8bXE0#overlay
Well, I am hesitant to use leveling compounds because I am nailing down my 3/4" x 3.25" hardwood planks. My understanding is that there are no leveling compounds designed for application under nailed down hardwood planks.??
If that is the case, I figured my best choice is to sand high points and fill low points. My remaining challenge is to understand, or confirm my hunch, that the most important direction for flatness is along the run of the hardwood planks.
Dan
You can nail hardwood over leveler if you use cementious types. Here’s one common version: https://cdnmedia.mapei.com/docs/librariesprovider10/products-documents/1_3000231-self-leveler-plus-en_dc197939dacc488fa2ad99ce45c44243.pdf?sfvrsn=506c1dde_0
Don't know if this applies to your situation. Can you go under the house to repair, replace, support the underfloor joist, girders or posts?
My floor is over. an attached garage with textured and insulated ceiling. At this point I am leaning toward filling low point with plywood panels and layers of vapor barrier, but be careful to not put too much fill so that the gaps are minimized in all directions, especially minimize the gaps in the direction parallel with the 3 1/4" planks.
First off would be screwing down the subfloor to your joists.
Any shim type filler should glued as well as fasteners. Each layer.
Or
Cut out and remove the bad spot, shim the joists and replace the sheeting.
Thanks Calvin, I will glue and fasten my wood shims as you recommend.
I just did this with some 8 in. wide flooring. Filled the low spots with various thicknesses of plywood ranging from 5/8 to 1/4, and faired the transitions with shims. I used 2 cases of PL Premium in the process. Squeak free and as flat as one can expect where two sections of an old house meet.
Andy, this is good feedback, thank you! Thats alot of glue :). How many low spots did you end up adding plywood to? I would imagine that for wide (8") flooring, flatness is even more important. Did you have situations where you could not get the same flatness in all directions (without adding plywood fill wall to wall)? If so, did you prioritize to make it flattest in the direction of the flooring, just keep extending the plywood to the walls as needed?
Regards,
Dan
It was an old house so perfection wasn't in the cards. I did the most work in areas of greatest variation regardless of orientation. With 8 in. wide flooring, the wood tended to span small gaps anyway. And did I mention I used a lot of PL? The one area where it was noticeable was where the floor in the butler's pantry joined the main kitchen floor at a right angle. There was a bit of lippage there which the floor finisher was able to sand out.
Got it, thanks!
As usual Andy has a good suggestion. Another option is to remove the subfloor plywood and shim from below or sister up the exisitng joists before replacing the sub.
Yes, I have considered that, but I'm more comfortable with the fill option :)
Thanks
Dan