Basement bathroom floor - plywood subfloor vs self-leveling cement?

[zolotiyeruki]

I'm closing in on completing our basement, and we have carpet coming in a few weeks, before which I need to have the bathroom flooring installed. We'll be putting in sheet vinyl, but the concrete floor isn't smooth enough to put the vinyl directly on the floor.

My initial thought was to use 1/4" cement board, but it's nasty stuff to work with.  I've had recommendations both for a thin (1/4") plywood subfloor, and alternatively for applying self-leveling cement to get a nice smooth surface.  I've never used self-leveling cement, but I'm not afraid to try it.  I'm partial to the plywood for insulation reasons--I've experienced too many tile-on-slab bathroom floors--but potential water damage/rot/mildew is also a concern.

What should I do?

[lthenderson]

I have not used it either but it seems like a basement bathroom floor is the ideal place to use self-leveling cement. I would be hesitant to use either of the other two options unless you were mudding them into place. Just laying thin plywood or cement board over uneven concrete will cause all those imperfections to telegraph through to your sheet vinyl face over time.

Personally my basement bathroom is tile on slab. It has held up great over the years. Curious as to your bad experience doing it that way.

[zolotiyeruki]

Personally my basement bathroom is tile on slab. It has held up great over the years. Curious as to your bad experience doing it that way.

Very cold feet! :)

[lthenderson]

Personally my basement bathroom is tile on slab. It has held up great over the years. Curious as to your bad experience doing it that way.

Very cold feet! :)

I solved that by putting in one of the electric mesh floor heaters. It used about the same amount of electricity as an electric blanket but works really well. To save some on the electricity, I hooked my to a thermostat to only run about four hours a day when I'm most likely to use that bathroom.

[Jon Bon]

I dont really like any of your options....

Plywood might work? But you would need to use treated and then tapcon the crap out of it which sounds terrible. It might get out some imperfections but not the slope. I would also by using 3/4, not 1/4

Concrete board might be better as you could level it with thinset/concrete as you went, but would still need so many tapcons.....

Ive never done self leveling cement, but feels like one of those things that is easy to mess up..... You willing to pay to have it done correctly?

I would just do tile but that is me. You planning on being down there every day? If its a secondary bathroom I say cold feet every so often is NBD. 

[zolotiyeruki]

I can see the need to screw down plywood, but why would cement board need to be screwed to the floor if the flooring is sheet vinyl?

[lthenderson]

I think what Jon Bon was referring to when saying screws are necessary for cement board is for wood subfloors applications where there might be bounce in the subfloor that can crack the thinset and thus screwing is also needed. But to me, putting concrete boards on a concrete surface is redundant unless you are doing it to make it level and in which case, you would need thinset to fill in the low spots. Perhaps there is a different cement board than what I typically buy but the stuff I get is a lot rougher than most finished concrete surfaces and I think would be worse at telegraphing through to your sheet vinyl.

[former player]

Personally my basement bathroom is tile on slab. It has held up great over the years. Curious as to your bad experience doing it that way.

Very cold feet! :)

I solved that by putting in one of the electric mesh floor heaters. It used about the same amount of electricity as an electric blanket but works really well. To save some on the electricity, I hooked my to a thermostat to only run about four hours a day when I'm most likely to use that bathroom.

I've put electric underfloor heating in every bathroom I've renovated and wouldn't do anything else now.  For preference you want insulation underneath it, to direct the heat upwards (yes, it does rise anyway).  You need a smooth surface to put the wires on, though.

[Linea_Norway]

When we renovated the bathroom in our previous house, we put both central heating pipes in the floor, as well as electric floor heating for in the season that the central heating is not on. Both types of heating needed to be covered by concrete on all sides. Self-leveling heating is very good for this.

However, the Norwegian rules for bathrooms require to have a 1/100 fall in the bathroom floor towards the drain in the floor, as well as a 1/50 fall directly around the drain. My DH used solid concrete to make the 1/50 fall around the drain (a small area without floor heating). But he was swearing and cursing about the self leveling concrete to make the rest of the floor. Self leveling stuff is indeed very fluid and crawls nicely under the heating cables. If you want your floor to have an amount of fall, this is not the ideal stuff to use. DH ended up by making temporary wooden compartments in the floor and working at one compartment at the time. He made the fluid concrete a little less fluid and kept pushing it into the right fall with a plank until it started to stiffen a bit. It is all very stressful as fast-drying concrete starts drying very fast, like after half an hour or so, before you might be done with your floor. Therefore the compartments worked well, as they gave him one piece to handle within reach.

If you want a normal, level floor, then self leveling concrete is great stuff and you don't need to worry about the paragraph above. If helps if you are 2 people, where one mixes the concrete and the other one walks it into the house and spreads it out. As mentioned, it dries fast and you need to work fast.

[zolotiyeruki]

Thanks all for the replies!

@Jon Bon :  I'll be using sheet vinyl, so I'm not worried about cracks in grout

I'd love to put in some sort of heat, but the walls are closed up already.  Since I'm using vinyl, there's less of a need for insulation, but I'd still like to have something between it and the cold concrete floor.

What about this idea: put down a layer of 1/4" foam insulation (to smooth out the bumps, and provide insulation), topped by 1/4" plywood subfloor (for stiffness)?

[Jon Bon]

What I was asking about with the cement board. Are you going to thinset it into place? If not you gotta be able to secure it to something. You will inevitably get some sort of bounce in your subfloor without property securing it. Any bounce will eventually destroy whatever material you use (tile, lvt, or sheets)

or maybe im just not understanding the project.

But I also tend to overdo my subfloors for the reason above.

[zolotiyeruki]

This will be on top of our basement slab, so I'm not particularly concerned about bounce in the floor :)

[big_owl]

We used dricore when we did our basement in order to isolate the slab from the flooring (in our case either tile or engineered hardwood or carpet depending on location in the basement.  We also installed heated mat in the bathroom in order to heat the travertine tile floor.

THe order went:

1. Slab
2. Dricore (secured with tapcons only in the areas that were to be tiled)
3. Cement board (only for tiled areas)
4. Ditra (only for tiled areas)
5. electric heat matting (only for tiled areas)
6. Tile/wood/carpet (depending on application)

It's been almost five years and not a single grout/tile crack so clearly our method of installation was plenty adequate. Using both cement board and ditra was prob a bit overkill but I didn't want to rick any tile cracks.  The same would no doubt work with vinyl tile and would also provide a moisture separation barrier in your case (vs. plywood lying on the slab).  The tapcons were a bit of a PITA but went pretty quick with a rotary hammer (not hammerdrill!) and impact wrench for the screws.  The primary reason we used dricore under the tiled areas as well is that I wanted the thermal isolation for the heated tile.

[jpdx]

Can you frame out the floor with 2x4 sleepers, with ridged foam insulation in between and plywood on top? That will give you a level, solid, well-insulated subfloor.

[Fru-Gal]

Even though we have both worked in construction and husband is very good carpenter and we tiled the upstairs bathroom ourselves, for the basement bathroom we paid a really good tile guy. He mudded everything with self-leveling cement. There are a lot of complicated curves too so he made all that look really beautiful. The tile was inexpensive white mosaic from Lowes. I love how it turned out. Water is a major concern since there has been leakage over the years on occasion. Always good to remember that a basement is a hole in the ground.

[CowboyAndIndian]

Always good to remember that a basement is a hole in the ground.

A hole that can fill with water, aka a well :-( I hope you have a sump pump and a back-up for it?

I would not put plywood on a basement bathroom floor. Basement are damp. A bathroom in a basement is even damper. Perfect for mold to grow.

Self-levelling cement looks quite easy. Fills in the low spots. Never done it but I would go this way.

I would also never put carpet in a basement.  I would use vinyl plank flooring or cork or even a pergo laminated floors.

My basement has tile on concrete for the bathroom and Pergo-like laminate on the rest. This basement was completed about 15 years ago, so I did not have the choice of vinyl plank floor. Both floors in the basement have done well over the years.

Also, check out the pictures of the basement built by @big_owl. Very nicely done!

[zolotiyeruki]

Yes, we have a sump pump, and our basement is quite dry (as long as the sump pump works!).  Once I complete the job, a sump pump backup (either a battery-backed pump, or just another pump altogether) is likely in the cards. 

I decided to just go with self-leveling concrete.  I've done a small amount of regular concrete before, and I've done tile before, but never self-leveling concrete.  It turned out ok, although not perfect.  Fortunately, the imperfections (some variation in height) are around the toilet flange, i.e. not where you'll be walking, so I'm not too concerned.

I know it's not the most safe, but we will lay carpet in the basement bedroom and living area.  It's super nice carpet (65 oz!), and we're getting a good deal on it, so a battery-backed sump pump is probably a wise choice.

[salty_monk]

Henry's Feather Finish Would seem to be exactly what you need... https://www.homedepot.com/p/Henry-549-7-lbs-Feather-Finish-Patch-and-Skimcoat-12163/100551687

It's easy to work with. A mixing paddle on a drill in one of the Home Depot buckets was the best way I found for mixing. You can spot patch with it. You can level up with a straight piece of wood. It can also be sanded.

I made a kitchen countertop with it a couple of years ago (laid up over two layers of rough ply).

The vinyl will help a bit with the cold feet and maybe get a large bathmat or two..

:)

[zolotiyeruki]

Yeah, the walked-on area is only about 3.5 x 7 feet, and DW reminded me that bath mats in front of the shower and sink will cover much of it.  We picked up vinyl today (did you know that Menard's sells 6x9 rolls for $25? I didn't!), and I'll try to get it in tonight.

[lthenderson]

I'm glad you had a good experience with the self leveling concrete. I have always wanted to try it but have never had the opportunity.

[cooking]

Henry's Feather Finish Would seem to be exactly what you need... https://www.homedepot.com/p/Henry-549-7-lbs-Feather-Finish-Patch-and-Skimcoat-12163/100551687

It's easy to work with. A mixing paddle on a drill in one of the Home Depot buckets was the best way I found for mixing. You can spot patch with it. You can level up with a straight piece of wood. It can also be sanded.

I made a kitchen countertop with it a couple of years ago (laid up over two layers of rough ply).

The vinyl will help a bit with the cold feet and maybe get a large bathmat or two..

:)

Could you please post a picture of the countertop if you're able to @ salty_monk?  I've been wondering what they end up looking like.  How has it held up since installation?

[Kevin_T87]

Plywood isn't a bad idea necessarily either, but only if you have a sump pump and preferably a dehumidifier as back-up to make sure moisture doesn't cause mold to appear. Size the dehumidifier to your basement and the wood won't suffer any alteration with the passing of time as there won't be any excess humidity ever. If you have trouble with sizing or want to compare some models, you can get help here bestdehumidifier.reviews

[MrSal]

question regarding this. I am also finishing my basement and tile is probably going to be used.

Do i need a decoupling membrane? This house/basement is 50 years old so i am thinking i can thinset directly? I doubt the house will settle more than what it already has?

[lthenderson]

I tiled a basement bathroom about seven years ago in a 50 year old house without a decoupling membrane and there hasn't been any cracking yet. There weren't any cracks running through the area and hadn't been any signs of settling so I felt it was safe to do.

[zolotiyeruki]

Tile on concrete, especially old concrete, is just fine without a membrane.  A membrane is there to soak up movement in the subfloor from temperature and humidity changes, and that's not an issue with a concrete basement slab.