Subfloor leveling ideas for shimming

Discussion in 'Floor Preparation' started by RetroJoe, Jun 25, 2018.

  1. RetroJoe

    RetroJoe Member

    I have an old home with some unlevel floors (3/4" cedar planks) that I have jacked as much as possible. Unfortunately, I had all of my insulation, electrical and plumbing done before realizing how much the floor wasn't 'flat." For example, two feet off the exterior walls the floor slopes about half of an inch. I've corrected what I can from underneath but sistering joists is not an option at this point. I am putting 4x8 sheets of OSB subfloor on top of the planks and want to fill the low spots under that to get it as flat as possible for the hardwood flooring. Can you recommend what would make good shims to level out the low areas? I've read asphalt shingles and felt paper work great, but I've also read that some people are sensitive to the smell that felt paper may give off, so I don't want any issues.

    Also curious what is the best technique to make sure you are getting the floor flat in both directions simultaneously? I tried using shims the first time around, but since they are angled it would level one way and throw the other off and I went crazy and ripped it all up. Not to mention I ended up 2" higher at doorways which is no good. I have an 8-foot, 6-foot and 4-foot level, plus a mason line. If anyone has done this before I would love some advice. Photos also would help. I'm a show and tell kinda guy. Thanks so much!

    Joe
     

    Attached Files:

  2. Barry Carlton

    Barry Carlton I Support TFP Senior Member Published

    For small areas and thicknesses I use vinyl scraps (paper backed or inlaid materials) much the same way one would use shingles or felt.
    I have also used cedar shakes.
     
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  3. RetroJoe

    RetroJoe Member

    Please excuse my ignorance, but what are the vinyl scraps from? Not familiar with that. Also, do they have any possibility of compressing over time. Aren't cedar shakes tapered? My concern is ending up where I started the last time with the cedar shims and be level in one direction but off in the other.
     
  4. Barry Carlton

    Barry Carlton I Support TFP Senior Member Published

    I install vinyl flooring. The scraps are from those jobs. I try to use commercial inlaid material as these will compress less than felt.
     
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  5. RetroJoe

    RetroJoe Member

    That makes sense. Aren't those scraps about 1/8" thick or so?
     
  6. Jim McClain

    Jim McClain Owner/Founder Administrator

    I hope you understand that flat is more important than level, unless you are using the room as a bowling alley or marbles tournaments. And please forget you ever heard of OSB. As the subfloor in new construction, we have learned to live with it, but when remodeling or at any time you have a choice of products to use, choose plywood, not OSB.

    From the photo, it looks like you have some serious flatness issue goin' on. I would consider using 2x4 lumber ripped on a table saw to conform to the highs and lows and fastened on 16" centers. Then install some 5/8 or 3/4" thick T&G subfloor plywood (CDX) on that. If you need a smooth surface, use 5/8" subflooring, then a layer of quarter or 3/8" underlayment panels on top.
     
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  7. kwfloors

    kwfloors Fuzz on the brain Charter Member I Support TFP Senior Member

    Knowing what I know now, that's a floor for Uzin 172. Seal the cracks and pour it on.
     
  8. RetroJoe

    RetroJoe Member

    I do know that flat is more important, but they are not flat or level. If it was a continuous slope over a length then no problem. But it dips then starts coming back up then starts to dip again in spots. I actually made a grid using a laser level on the wall and measured down. (pdf attached). Higher numbers obviously are low spots. The upper right corner is the highest spot in the house. I'm not sure how strict the 3/16" is over a 10' span but not sure I can meet that restriction.

    As for the OSB, it's too late. I already had purchased it months ago and have it ready to be installed. Can't return it as I had first purchased 1/4" luan and exchanged that for the 22/32 osb, so no more returns allowed. I hope that doesn't screw things up.
     

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  9. RetroJoe

    RetroJoe Member

    Ok, but how do I nail my hardwood into cement?
     
  10. Mark Brown

    Mark Brown On The Surface Flooring I Support TFP

    you glue it...
     
  11. Graeme

    Graeme Pro Member

    Good work mapping out the flatness requirements on that PDF. That is the tricky part over with.
    The way I would approach that is to use sheets of door skin (1/8" plywood) Common and inexpensive around here (hopefully in your area as well). It can usually be cut to size with a utility knife, and layered on the low spots as necessary. You will end up with what looks like a topographical map on your subfloor. Just keep going until you have eliminated the gaps under a 10' straightedge - check in each direction. You can staple or nail them in place as you go, or bond it all with a construction adhesive. Once you have flattened your subfloor, you are ready to install the new underlayment (really wish you had gone with a t&G plywood instead of OSB, but we can't win em all)

    As stated above, flat is more important than level for your application. Hope that helps. Let us know how you manage.

    Cheers,
    G
     
  12. RetroJoe

    RetroJoe Member

    Thanks for the input! Is the 1/8" door skin sort of like an mdf type material? I think I have some on hand. I will take your advice on layering the low spots. I am curious what are the disadvantages of OSB vs plywood subfloor? The OSB I purchased is 22/32 tongue and groove.
     
  13. Mark Brown

    Mark Brown On The Surface Flooring I Support TFP

    Doorskins are usually mahogony or other wood. They are a ply style panel. The disadvantages of OSB subfloor are only apparent when trying to nail into it. The OSB has poor holding strength compared to a plywood and in the long term does not hold up as well. That being said, many a million of square feet of hardwood is installed every year on the stuff and it is generally accepted however it is always preferred to use Ply. Do yourself a test, when the time comes, nail a test board into the osb, then find a scrap of 5/8 plywood and nail into that, then try and remove the two boards by prying on them from the tongue side up. You will understand.
     
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  14. Scott Horton

    Scott Horton Soundproofing Pro

    Where do you get doorskin material? I can't think of any place around me (Nashville TN) to even look. Millwork houses, what kind of places do you get it from?
     
  15. Mark Brown

    Mark Brown On The Surface Flooring I Support TFP

    Any lumber yard will have something in a 1/8 sheet. Here i buy "bintangor" or rotary mahogany as it is referred to for some reason... neither seems true... Really all you are looking for is something in 1/8 ply style, 3/16 will work in a pinch, but it is more work to sand
     
  16. Scott Horton

    Scott Horton Soundproofing Pro

    Ah, 1/8, I missed that clearly stated detail and went off searching for something thinner. It was the "cut it with a utility knife" that misdirected me brain. My 1/8 ply isn't that friendly LOL. Anyway 1/8 ply is pretty available I think. So your practice is to "topo" it then sand the skins? Not to derail the thread, but I had envisioned, in the case of a "bowl depression" for examples sake, a small disc at the bottom of the bowl, then a larger disc, then a larger one and so on. Trim the "bowl"'s last layer with patch around the edges depending on what's going on top. Presuming I got that wrong, can you elaborate on your method? Thanks for chiming in.
     
  17. Fishon2

    Fishon2 New Member

    Some great information! I have the same issue in a 16x28 room where I have a 2 1/2 inch drop among the front wall. I was thinking of building custom shims and then adding 1 1/8 T&G plywood. I will then be gluing 3/4 engineered hardwood. I'm thinking this is easier than ripping out 1x8 boards that make up the subfloor now and then adding new 2x12's to level the floor.
     
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