Preparing a not very flat or level OSB subfloor

Discussion in 'Floor Preparation' started by Bee509, Jul 9, 2019.

  1. Bee509

    Bee509 Member

    Just started a remodel of my home and doing a 2400sf luxury vinyl plank project in my home. I’ll be doing upstairs and below grade basement. I purchased cortec pro plus flooring.

    I’m currently setting up to battle a not very flat or level OSB subfloor in a 2008 era spec home. I’m playing with the idea of using triton backer board as an underlayment. An idea given to me from a concrete polishing contractor. He’s also tested a few panels with an epoxy application that we may try out in my laundry room.
  2. Commercial Floor Rep

    Commercial Floor Rep I Support TFP Published

    First off welcome to TFP!!! We're very glad you're here.:welcome:

    Can I ask why you're considering that specific product? Not that it's bad, just trying to understand if there is a reason to use this specific underlayment.
  3. Bee509

    Bee509 Member

    My friends words were that it might be less expensive to use this triton backer board as a underlayment and fill low spots, rather than trying trowel something like planipatch or some other product. And then that maybe a bit more user friendly. But this specific product in has done well in some tests he’s completed when it’s submerged in water in epoxy applications.
  4. kwfloors

    kwfloors Fuzz on the brain Charter Member Senior Member

    What is not level? I use an edger to hit the joints as they are always peaked but other than it getting rained on a swelling, what is your situation?
  5. Bee509

    Bee509 Member

    There’s a slight sag and the joists weren’t crowned
  6. Chris 45

    Chris 45 Director of P.R. on some deserted island. I Support TFP

    Is there an outside reason your subfloor is sagging? Something like excessive moisture underneath your house? What is your joist spacing? Subfloor thickness? If you have sagging subfloor panels, there is a reason.
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  7. Mike Antonetti

    Mike Antonetti I Support TFP Senior Member

    There’s no height adjustment with panels of underlayment. You’re just mimicking exactly what’s underneath.
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  8. Chris 45

    Chris 45 Director of P.R. on some deserted island. I Support TFP

    Exactly. There is no structural integrity to backer board so it’s not the same as adding a second layer of plywood down to beef up your subfloor.
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  9. Commercial Floor Rep

    Commercial Floor Rep I Support TFP Published

    Thanks for the feedback. The reason I was asking is because this product isn't designed to be used under resilient flooring. It also requires, per the manufacturers instructions that you thinset and then mechanically fasten (proper screws or nails) these panels down. That's an awful lot of work to go through for something that's really not made for what you're trying to do. It's also adding a considerable amount of weight as Chris mentioned to an already "compromised" floor.

    With regards to cost, I don't know what that specific product runs in your area but I handle a very similar product from James Hardi called Hardibacker. a 3'x5'x1/4" (15sf) panel runs $12.89 from me and a 4'x4'x1/4" (16 sf) sheet of warranted wood underlayment runs $12.69. I'm sure your friend has experience with epoxy coatings but that isn't really the same as someone who installs resilient flooring day in and day out. Maybe he does both, I don't know, but it sounds like he's maybe a little out of touch with the flooring side. Might not be his area of expertise.

    If it's just minor sagging, like say 1/8' - 3/16" between joists then that can be addressed as Chris said with "beefing up the subfloor" by adding an additional layer of plywood and some minor patching with a trowelable cement based patch to fill in your low spots or by sanding down the high spots depending on what's needed. We typically want a minimum total thickness of 7/8" - 1" thickness of subfloor and underlayment to properly support a resilient, laminate or wood floor. Often times spec homes don't have anywhere close to that because no ones checking on them to make sure they did it properly.

    If it's out more than that then you really need to make sure the subfloor is supported correctly and if possible correct the underlying structural problems first before you install. You may need to contact a structural engineer depending on how severe the problem is and get their input so that you don't create a bigger problem than you already have.
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  10. Chris 45

    Chris 45 Director of P.R. on some deserted island. I Support TFP

    I see 5/8” as code for subfloor all the time. The reality is that while you won’t fall through the floor, 5/8” is the bare minimum and often times is insufficient in limiting deflection perpendicular to the joists. I had a tile job I had to decline because the plywood subfloor wasn’t T&G, in addition to the joists not meeting L/360. Too much movement between the subfloor panels.

    Do you have something you can use as a straight edge that you can use to measure the flatness of your subfloor. Post a picture of it. Minimal sag can be corrected easy enough by sanding down the high spots and using up to 6 layers of roofing felt to fill in the bellies. The roofing felt will look like a topographical map. If your floor needs more than that, I’d recommend going with an additional layer of plywood to help things out.

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  11. Bee509

    Bee509 Member

    Thanks for all the input. I meant to get some photos posted earlier today. It’s not moisture, I think it’s just shoddy building, the builder has a reputation for taking corners. Now that I’m finishing the basement and doing flooring upstairs I’m just sifting through the gremlins while keeping a hold of my wallet.

    The header there in the basement has been pushed up a bit, as much as possible w/o a jack, and reinforced. And no my friend doesn’t do anything other flooring than concrete grinding, polishing and other coatings like epoxy. He’s doing this as a favor and we were just brainstorming cost effective strategies. I think he mention the triton stuff was $6 a 5x3 sheet or in that range. But we didn’t account for the extras as pointed out. I’m still just gathering information.

    Attached Files:

    Last edited: Jul 11, 2019
  12. Commercial Floor Rep

    Commercial Floor Rep I Support TFP Published

    I don't really see anything in the photos that's alarming too with regards to structural integrity. I think you will definitely want to address the uneveness and get it into spec for flatness.

    Everything I see there I would probably deal with using a trowleable cement based patch and some sanding of high spots. If you wanted to add some rigidity to the subfloor you can add a layer of 3/8" plywood and away you go.

    That would give you a nice consistent substrate to work from to install your new floor.
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  13. Bee509

    Bee509 Member

    Any products that you would or wouldn’t recommend for use with osb specifically?
  14. Commercial Floor Rep

    Commercial Floor Rep I Support TFP Published

    Both Ardex & Mapei make great products that work well for the application. Uzin & Schonox also make good products but they aren't as widely available. In my market (Indiana, Michigan, & Ohio) Ardex Feather Finish and Mapei Planipatch are the 2 "go-to" products. I think I'm safe in saying that Ardex Feather Finish is widely regarded as the "Cadillac" of trowelable cement patches available on the market.

    I would avoid getting product from the box stores (Lowe's and HD). The products sold in the boxes are not the same formulation that professionals use and are actually much harder and more unforgiving to work with. It's a price thing for them. Try to find a local flooring supply house or distributor and get your installation supplies there.

    By the way, this is also true of tile installation products such as grouts and mortars. The products that the boxes carry are not the same formulations as what the professional installers use. Again, many times they are skinny'd down versions to hit a price point.

    With regard to an underlayment or plywood:
    • Use something that's rated for use as an underlayment for resilient flooring.
    • You want something that's dimensionally stable.
    • You want something that's constructed with an exterior grade adhesive. (No pressure treated or walmonized products though those are not suitable and can cost a whole host of other issues.)
    • If your looking at actual plywood try and find something with an APA A-C grade or better but it should also meet all of the other criteria here.
    • It should be sanded on at least one side and filled (free of any voids)
    • Minimum 1/4" thickness. (For your application you may want to strongly consider 3/8" if it won't cause any height issues for you as it will help with any subfloor deflection and add some rigidity)
    • It should have a specific warranty to be used as underlayment or subfloor from the panel manufacturer
    • Not required but I would avoid "composite" underlayments as the can often prove to be problematic with regard to dimensional stability and they are often not consistent in thickness
    • Again, not required but I would try and find something with a birch or poplar face veneer and a poplar core. (Birch faced underlayments can be pricey as they are often times used in cabinetry and furniture making but they are generally of high quality.
    • DO NOT USE LUANN - it is not an acceptable underlayment and it does not meet the requirements for dimensional stability, it can and often does have voids in it, it often times is dyed for color consistency and this can bleed through many types of flooring, especially if the flooring is directly adhered to it.
    • Make sure whatever you purchase you follow the panel manufacturers fastening schedule and instructions with regards to abutting to adjacent panels. Some manufacturers want their panels tightly butted while others want a gap left between panels.
    I would again advise against purchasing the plywood or underlayment from the box stores and either try and find it where you get your patch or try and choose a "local" lumber yard as they tend to carry better quality products than the boxes.

    Many of these criteria aren't as critical when installing a floating floor but if you stick to them it will give you a good substrate to work from and they will hopefully help you address some of the "sins" that your builder left you to deal with. And, should you ever choose to replace this floor and install a directly adhered flooring, you'll be able remove the Coretec and with some minor prep install the new floor without much hassle.

    I hope that helps and I wish you well with your project and your new floor. Coretec makes a very nice product and if installed correctly it should last you many years.
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  15. Mike Antonetti

    Mike Antonetti I Support TFP Senior Member

    I was gonna say all that!
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  16. Bee509

    Bee509 Member

    I’ve been brushing up on Uzin, I was able to find a place where I can find the nc 150 & PE 260 for reasonable prices but may be overkill? The NC 886 is probably more affordable and practical. Finding information that’s not in German or Polish seems a little difficult though :D Slowly making progress.
    Last edited: Aug 18, 2019
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  17. kwfloors

    kwfloors Fuzz on the brain Charter Member Senior Member

    Is that beam underneath bowed? You can see the gapping on both ends where there is open space. How does that corelate to the top?
  18. Bee509

    Bee509 Member

    The floor sags a little. 9’ beam with sitting on pocket walls Wasn’t supported well when they built and finished the home in 08. We reinforced the beam and framing the best we could with out tearing it all out, jacking it up, popping drywall and putting a glue lam in.

    image.jpg image.jpg E047BCDF-AF84-4E96-86F1-229CF571B20B.jpeg 13C581B4-CA20-4240-95D4-90B4CBA97BB5.jpeg 4DFCD4AE-C8C9-4CD5-9381-0E38352E733A.jpeg 9B6B113E-35EE-4F36-B267-B9E77E85D108.jpeg C5A0788B-8EF8-483B-BF09-5791EE769D10.jpeg image.jpg 8F294E3F-D3D6-4093-BCDD-999DCF0FF836.jpeg 73310952-52B3-4636-9A37-2D7E4CEDB3B0.jpeg
  19. Jim McClain

    Jim McClain TFP Owner/Founder Administrator

    Unless you plan to play marbles on that floor, you should focus on flatness, not level.
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  20. Bee509

    Bee509 Member

    That was my attempt to show KWfloors how the sag below translates to the floor above, in that section of the house. Some of jargon escapes me but That section has its own joists that span longer than the the rest of the house. The floor plans mirrored from those images big but gives you the bigger picture. The Sag is between the stairway banister and outside kitchen wall. That section splits between the living room/kitchen - sag is of course on both sides.

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