Before we get started
Before we get started with the floor leveling, there are a few tools you will see that I use in this step. Most of these tools you probably already own and if you don’t, then you will need to get these tools to be able to do this yourself. They are tools that you will need to install the tile anyway, so you should be covered. More on what you need later.
I am going to simplify floor leveling as much as possible. Just be sure to follow these simple steps that I will layout for you and all will be good.
Tools and supplies that you will need for floor leveling-
- 4ft level or straight edge(if you don’t have one that is okay)
- Chalk line
- trowel with a flat side(you can use the back side of your tile trowel)
- modified thin set
- carpenters pencil(the rectangle pencil you can get at the lumber yard)
- bucket and water
Tip 1- Stretch out a chalk Line to find dips and humps
Whether the room is 20 x 20 or 4 x 5 the methods are the same for floor leveling. Have someone help you with this by holding one end of the chalk line. Stretch the chalk line out across the room, both ends should be held on the floor. Now check to see where there are any dips and humps in the floor and continue to move the chalk line around the entire room. The chalk line never lies and it will reveal all the problem areas to you.
Once you see where the problem areas are, you can then concentrate on those areas alone. So what I mean is, if you see a dip when looking down the chalk line(and you might need to get your head down to the floor to really get a good look down the chalk line) then move to that area and shrink up the chalk line. Now you need to mark where the dip begins or where the hump begins. Just keep moving the chalk line around and mark the floor where these areas begin and end.
If it’s a hump, then write that on the floor and the same goes for a dip.
Humps can be ground down with a grinder(concrete) or belt sander(wood sub floor). If you do not have one, it can be rented for a reasonable price.
Dips can be filled with thin set and I have a super simple method for this.
Tip 2- Use at least a 4ft Level or Straight edge to find dips and humps
This is really going to be the same exact floor leveling strategy that we talked about above. The only difference is, it will take longer to cover a bigger area. I usually use the chalk line to find the bad areas and then use the straight edge to pin point the exact locations of where they begin and end.
Once you find a bad area, it is a little easier to just slide the straight edge or level around and mark these areas out. This is my preferred method .
You might not be able to use a 4 ft level or straight edge if the area is too small for these to fit into.
Tip 3 – Find out how deep the dip is
Once you have marked out the dip, you will need to find out how deep it is. I do this by resting either the chalk line or straight edge over the the area.
Then I measure it with a tape measure. You could also hold you tile trowel with notches next to the straight edge or chalk line. This is a quick guide to see if the dip is deeper than the notch in your trowel.
If the dip is deeper than your notch, you would either need to get a trowel with a bigger notch or we will have to do the floor leveling in a couple of steps. That would be okay, so no worries! If the notch is too big, that is even better and I’ll explain in a moment.
Tile trowels come in many sizes – click here to see chart
Most of the time when using a 12 x 12 or 13 x 13 tile, I use a 1/4 x 3 /8 square notch trowel.
Tip 4 – Fill the dip
Now that we know what trowel we need to use let’s start the floor leveling process and fill this dip. Mix up some thin set. I usually only mix about 1/2 of the bag at a time. Mainly so I don’t mix too much and it’s just easier to mix up in smaller batches. You could mix smaller or larger batches.
Once the thin set is mixed, I then use my tile trowel(the notched side) to spread the thin set over the dip in the floor. I will stay within the lines that we drew on the floor in Tips 1 and 2. I will then pull my trowel across the floor trying to leave nice even tracks.
Now you are ready to rake the dip. I use my straight edge and pull it across the dip collecting any thin set that will not be needed. This will eliminate the dip and all that should be left is the thin set that is needed to fill the dip. You might need to scrape the dip more than once, but be careful not to pull out too much. Always try to hold the straight edge the same way each time to avoid taking out too much.
Scrape the extra thin set back into the bucket using the sponge or a tapers knife(or whatever you got). Be sure to clean off your straight edge or level. Thin set is very hard to get off if you let it dry on these tools.
Tip 5 – Grinding a hump-
I would recommend renting a grinder that has a vacuum attachment on it. This will minimize dust. Never run your vacuum without a filter and when I say vacuum, I mean a wet dry vac!! Don’t use your household vacuum.
When floor leveling a hump, grind from the middle to the edges. Try to make even passes. Then stop and check the hump with your straight edge frequently. This will stop you from taking too much off. This is usually a pretty easy process and I know you can do it.
Wood Sub floor-
If you have a hump in a wood sub floor then a belt sander will be the best tool to use. You Don’t want to take too much of the sub floor away, this will weaken the floor. Unless you add another layer on top to give it it’s strength back. For example, you could add a 1/2 inch layer of plywood or OSB after you sand the hump down.
This will add additional height to the floor, which can also cause problems with door clearance and other things like that. So think it out first.
Tip 6- Final Filling
Go around the areas that were filled and clean them up a little. Scrape off any excess thin set that was not needed and give it a quick vacuum.
Wait for the thin set to completely dry before moving to this step.(usually over night). You can speed this up by using a rapid set thin set It will dry within a few hours, however it is a little more expensive. You can find this at Lowes, Home Depot and Menards.
Once dried, you now need double check with your straight edge to see if you filled the dip completely. Don’t worry about the tracks from the trowel, we will be dealing with that shortly. If it wasn’t filled completely and the dip is still deeper than an 1/8 of an inch than you can repeat tip 4. Otherwise we will catch the rest in a moment.
Now we need to fill in the tracks that were left from the trowel. So mix up a little more thin set and apply it over the dip. This time we want to use that flat side of the trowel. If the dip needs a little extra thin set, than you can scrape over the dip with the straight edge once more. If all you needed to do is fill in the tracks then you don’t need to scrape it, just make it smooth.
It really does not need to be perfect, just get flat and when you spread the thin set while installing the tile, it will take care of the rest.
Thanks for your time,
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Can you do this after you put down backer board?
Yes. I have videos that will show you that inside my members area along with many other videos to walk you through your entire installation. I am also there for any help you need. Check out Tile University. Here is a link. Click here
I am so pleased to have found your website and videos. I am starting a project of tiling our bathroom floor for the first time and after doing research and talking with store reps, your videos answered and clarified many questions I had and I feel much more confident about the project. I have a question on leveling the floor. When you mix the thin set for filling the wholes, do you mix it with the same consistency as you mentioned in your video on laying cement backing? I saw a video from Home Depot on leveling and the quick set seemed to be much more of a liquid consistency when it was poured on the floor for leveling.
Yes I would mix it the same as you saw in my video. What you seen in the home Depot video was a different product.
Thanks a lot for your information. I have a quick question. There is hump around the top of the stairs to the 2nd floor, on the plywood. Now the hardibacker has been removed because of the bump.
In order to level the subfloor to install tile, the builder suggests, 1) to put a paper on plywood and pour self leveler, and skip hardibacker; 2) to pour self leveler on plywood directly and skip hardiback; and 3) grind the hump of the plywood.
Could I have your professional opinion? Thanks a lot.
Do you have facebook? You can also send me an email at firstname.lastname@example.org but if I could see a picture that would be great! But are you saying that it’s just that spot you won’t be using hardibacker? Anyway a wire mesh needs to be stapled to the floor not paper!!!! It will fail if it’s paper. Tar paper is used when it’s a sand mix (mud pack) but if it’s over a wood subfloor it will still need a wire mesh stapled to the floor.
After the floor is leveled as you describe, you then need to screw the back board on top. I think that is what Kathy is asking. Would the thinset crumble when screwing the backboard on?
It will not be a problem Andy, because the thin set that you spread under the cement board before screwing it down will secure and crumble areas. That is another reason(other than giving strength to the cement board) why you should always thin set your cement board down. The same thing happens to the cement board when you put a screw into it. The back crumbles. Anyway, no worries when the thin set underneath dries it will have strength and there will not be any noises from crumbling thin set.
Excellent description of each step and the explanation why it’s done that way.
Darn sad that I didn’t see your instructions before laying my bathroom tile, which is pathetic in parts. Suggestion: include when/why using thinset vs SLC.
And Thank you.
Patrick, Thanks for the comment. I will take your suggestion and work on some more content towards that. Glad you enjoyed it!!
Very informative. We have osb subfloor that’s very uneven and were wondering how to address it. I sanded what I could but the low areas needed to be corrected. Appreciate the information.
Thanks very glad to help!!!
hubbie’s worried that screwing the backer board into the dried thinset will cause the thinset to break up.
Don’t worry Kathy, when you screw into the dried thin set the wet thin set that you spread before installing the cement board will stop it from affecting anything! No worries, trust me I have been doing this a long time.
Very informative post. Thank you for sharing these tips.