How to level a sub floor

Fixing a floor that has settled over time.

1. First you will need to determine the structural integraty of your sub floor.

There are several methods you may use to decide whether or not your floor is stable and whether it can handle additional weight of the repair materials. L/360 is desired


a). If you don’t feel that it is safe to walk on the subfloor then immediately contact a structural engineer or inspector to assist in repairing the structure.
b). Assuming that it is now safe to walk and work on you will first want to know will this support the addition of leveling materials. If the floor seems stiff with little or No deflection then you will most likely be able to put 14 pounds per square foot on it without worry of over load. You must have a qualified licensed professional determine this in writing for you to be sure.


2. Next determine the best method to level your sub floor. There are 4 general methods used to level a floor.

a). Some will level the floors by lifting the entire structure if it is a sinking issue.
b). While others will level floors by jacking the floor up from the floor below and setting spin jacks to hold it in place.
c). A Carpenter will most commonly repair from the top of the sub floor by using wood, sleepers and shims. this method is labor intensive but it can save weight when leveling very deep sections by creating a level platform over the original subfloor.
d). A Tile or Masonary installer will want to level the floor using wire lathe for structure and then blending a damp mixture of Portland Cement and Fine Sand. The reason for the wire is that the mud set as it is reffered to does not have enough moisture to create a bond to the sub floor. So the wire holds the portland and sand mix together.
e). Floor leveling professionals will not use any of the above methods though they will occasionally suggest this for people in certain situations to save them money when there is a job that is to small to warrant the cost of floor leveling crews on site.
Instead Floor Leveling professionals preffer using pourable materials that will bond to the subfloor and not require additional reinforcement in most cases. Also because they are installed in a liquid state they will have a smooth flat finish with typically 3 to 10 times the strength of other methods.


3. Determine the High Point in a room. There are three devices you may use to find the highest point in a room.

a). First you can use a long water bubble type level and set nails or shims under it to record the differance. This method can be time consuming but it does not require a major investment for a laser or altimeter.
b). Your second option would be to use leveling or self leveling laser. First level the laser then take a ruler and go around the area looking for the lowest number on the ruler when set on the ground. Once you find the lowest numerical value mark the spot as your highest point in the area.
c). The Third tool you can use to is made by Nivicomp and Ziplevel. Both are good but the zip level has more function and is made in the US. These are both altimeters with digital readout the ziplevel may be purchased at, for Nivicomp contact for distributors.


4. Setting pins or pegs to the height to level the floor.

Now that you found and marked your high point, you will now mark the rest of the floor with a marker so you can see what you’re dealing with.

a). First set your leveling devise to lock in on the height you found so that when it is even it will represent 0 point.
b). Now if your going to pour a leveling compound or any other method you will need to account for the minimum thickness the product can be. If your going over concrete you will most likely use a cement type option including mud job or pourable leveling compound. If your going over wood you can include the carpenter option as well. When going over wood with leveling compound you will need to allow for 3/4″ of material over the high point. If going over concrete some materials will allow you to start at a feather edge for short distances and 1/2″ minimum over the remaining areas. Mud job will require 1.5″ minimum.
c). Now that you have decided on which material to use you will add the minmum thickness to the top of your high point.
d). Next lock in your leveling device to your new high point.
e). Then with your marker write the measurement or differance from the high point in a three foot grid pattern. You can now read all your measurements and decide if you need to change your leveling strategy due to the deep sections. If you need to drop down sections, you can drop the floor a maximum of 1/8″ every 3 feet in each direction without noticing the change.
f). Since you have decided whether to make the floor dead level or to to pitch it down, you will now start setting leveling pegs. Note: If you are installing sleepers your carpenter will shim the floor under the sleepers instead of setting pegs. Note: If you are installing a damp mud install you will need to install felt paper and wire lathe prior to this step.
g). There are three types of leveling pegs you can use. Nivicomp pre made plastic tabs/LEVELROCK plastic tabs with two sided tape. You may use nails or screws. The third option is to use wood, if you use wood you will take round wood closet rod and cut it to the height you marked down in each three foot section then glue it down with liquid nails. If you use nails or screws you will set them into the wood sub floor to the finished height of you marks. Over concrete you will have to drill first and set tapcons if you wish to use screws. If you know where to purchase Nivicomp Leveling Pegs you will need to convert your inch’s into mm’s using the formula 1″ = 25.4 mm. Then take a pair of wire cuters an cut the tabs at the correct number then stick them to the surface in your three foot grid pattern.


5. Once your floor has been pinned you may now make any necessary changes. If you have no more changes needed then you may now begin leveling your floor following the directions from the manufacturer on any additional required prep, Such as Cleaning, Priming, Reinforcing or with some store bought products you may need to install blue stone over a certain depth. Next you will need to bring all these products into the area you will be mixing in. You will also need a water supply, so run a hose and use a new garbage can to hold the water temporarily. Then you will need a mixing device such as a batch mixer or another garbage can with a 1/2″ drill and mortar mixing wond. Finally you will need a finishing device. We make our own so ask the manufacturer of the product. A word of caution be prepared to finish what you start, most pourable leveling products don’t respond well to slow installation and can flash or prematurely harden causing you to repair all your hard work.


If this is something that is right up your alley then enjoy yourself and have fun!


If you would prefer to have a professional install the work for you please call or email David Melnick