Anchoring 2x4 into slightly uneven concrete flooring

[Martina]

Hello! I am constructing a shower build-out wall to accommodate a niche, requiring me to anchor a 3ft. piece of treated 2x4 to concrete flooring. The floor in that area is slightly uneven (small humps along the path). What is the proper way to level the base? I saw a YouTube video where someone simply used wood shims to level out the stud over plywood flooring, however, since we have concrete, can regular wood shims be used? I was under the assumption that you need treated lumber. With this structure being in a shower area, what would be the best way to level out my base piece? Thanks in advance for any forthcoming responses.

 

[Jadnashua]

Pressure treated wood, unless KDAT (kiln dried after treatment) is not a great choice where tile is involved as it tends to warp, twist, shrink, and check when it dries out. Finding KDAT stuff may take some searching as it adds time and an extra step which adds to the cost. Some plastic underneath should help to keep moisture from the slab keeping even regular studs safe.

It sort of depends on how out of whack the floor is. Shims could solve your problem...they do make them in plastic that shouldn't be affected by moisture. A diamond cup wheel on a grinder might make quick work of a peak if you wanted to go that way. Depending on what you're planning for the shower, you might consider using some self-leveling concrete mix (SLC), but be aware, it won't level itself without some help! If you're planning on tiling the whole area, this should be maybe your first step.

If it's now flat, you could use either something like Tapcon screws or lead anchors to attach the bottom of your wall to the floor without worrying about gaps, since it should now be flat. FWIW, tile wants flat, it doesn't care about level, but things like a shower base DO need level. You can overcome discrepancies with that by setting the pan in a mortar bed, and smushing it until it's level when setting the pan. Depends on what method of shower construction you're planning, what would work out best there.

www.johnbridge.com is a good resource for building a shower.

 

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[LLigetfa]

AFAIK pressure treated sill plate over concrete is a code requirement. It is also best practice (and might be code) to use sill plate gasket which is a closed cell foam which should compress where the uneven high spots are.

 

[Martina]

Pressure treated wood, unless KDAT (kiln dried after treatment) is not a great choice where tile is involved as it tends to warp, twist, shrink, and check when it dries out. Finding KDAT stuff may take some searching as it adds time and an extra step which adds to the cost. Some plastic underneath should help to keep moisture from the slab keeping even regular studs safe.

It sort of depends on how out of whack the floor is. Shims could solve your problem...they do make them in plastic that shouldn't be affected by moisture. A diamond cup wheel on a grinder might make quick work of a peak if you wanted to go that way. Depending on what you're planning for the shower, you might consider using some self-leveling concrete mix (SLC), but be aware, it won't level itself without some help! If you're planning on tiling the whole area, this should be maybe your first step.

If it's now flat, you could use either something like Tapcon screws or lead anchors to attach the bottom of your wall to the floor without worrying about gaps, since it should now be flat. FWIW, tile wants flat, it doesn't care about level, but things like a shower base DO need level. You can overcome discrepancies with that by setting the pan in a mortar bed, and smushing it until it's level when setting the pan. Depends on what method of shower construction you're planning, what would work out best there.

www.johnbridge.com is a good resource for building a shower.

Hello, Jim! Thank you for your response and detailed advice. Unfortunately, I didn't see your reply until now. I actually constructed the niche build-out a couple of days ago. I ended up cutting two pieces of treated lumber to surround the uneven floor surface (see picture) and then placed a full length 2x4 on top. I felt comfortable with that solution as the entire structure is only 3 feet wide and solely intended for the accommodation of a shower niche, so it won't hold much weight.

Also, thank you so much for your additional advice on the shower pan. I am using the Schluter prefab shower base. In the past, I used self-leveler before installing it, but this time around I wondered if I should simply put down some additional thinset to smush and level the pan. I think I will take your advice as it eliminates the use for self-leveler. Thanks again for all your help. Much appreciated!

 

[Martina]

AFAIK pressure treated sill plate over concrete is a code requirement. It is also best practice (and might be code) to use sill plate gasket which is a closed cell foam which should compress where the uneven high spots are.

Your post prompted me to do some more research on treated lumber. I never knew there were so many different types. With regards to your comment about sill plate gaskets- I don't 'think' those are required in our area. We recently removed an interior wall which required us to take up the base plates. We did not find any evidence of sill plate gaskets. Our house was build about 20 years ago.

 

[Jadnashua]

Thinset tends to shrink and crack if it is applied too thick. Generally, 1/4" is max, but some will allow more. If you want to fill in depressions with thinset, and it's more than that, do it in layers and let it cure in between. SLC may end up faster, as it can handle a thicker layer. So, it really depends on how far out of whack your floor is whether more thinset will work. Thinset is not designed to be used to flatten a floor prior to tiling, but you can get away with it if you keep it thin.

Keep in mind that until the foam pan is fully embedded, the foam pan WILL bend some, so it might just end up with a divot or two in it. FWIW, some people put the Kerdi on the wall, tile it all except for the last row on the bottom, then install the pan and tile on it and the remainder of the wall. That can also allow you to place a ledger into the wall, and cover those holes when you then install the Kerdiband and pan. Regardless, you want to protect the foam with something like a thin sheet of ply while you're walking over it. To embed it, shuffle your feet, do not walk normally,otherwise, you'll end up with the potential for compressing it. That type of foam is quite robust if you treat it properly and once you've added the fabric and tile. In fact, it's used in some places when building bridge approaches as part of the ramp up and down from the span as it doesn't compress as easily as fill, and there are fewer potential errors than if you did that with gravel and stone. Plus, it's much cheaper to ship than rock and gravel in some places.

 

[Martina]

Thinset tends to shrink and crack if it is applied too thick. Generally, 1/4" is max, but some will allow more. If you want to fill in depressions with thinset, and it's more than that, do it in layers and let it cure in between. SLC may end up faster, as it can handle a thicker layer. So, it really depends on how far out of whack your floor is whether more thinset will work. Thinset is not designed to be used to flatten a floor prior to tiling, but you can get away with it if you keep it thin.

Keep in mind that until the foam pan is fully embedded, the foam pan WILL bend some, so it might just end up with a divot or two in it. FWIW, some people put the Kerdi on the wall, tile it all except for the last row on the bottom, then install the pan and tile on it and the remainder of the wall. That can also allow you to place a ledger into the wall, and cover those holes when you then install the Kerdiband and pan. Regardless, you want to protect the foam with something like a thin sheet of ply while you're walking over it. To embed it, shuffle your feet, do not walk normally,otherwise, you'll end up with the potential for compressing it. That type of foam is quite robust if you treat it properly and once you've added the fabric and tile. In fact, it's used in some places when building bridge approaches as part of the ramp up and down from the span as it doesn't compress as easily as fill, and there are fewer potential errors than if you did that with gravel and stone. Plus, it's much cheaper to ship than rock and gravel in some places.

Once again, great advice- thank you, Jim! Based on your statement about, I will proceed to use self-leveler first, as I don't want the thinset to shrink or crack. I did a shower remodel about six years ago using the Schluter prefab shower pan and followed the same steps: self-leveler followed by embedding the shower pan in thinset. It turned out great and based on our recent demolition, it held up incredibly well. You are absolutely correct- that shower pan is very robust. It took quite an effort to rip it out. I was initially apprehensive about it, because it reminded me of simple Styrofoam, but it turned out to be a great product and easy to install. I will be sure to protect it with some cardboard when installing the wall tile. Thanks again, Jim!