How To Level A Floor
How to Level a Floor
With spring right around the corner, my wife and I are focused on getting the cabin porch into shape. We are starting with the floor.
The plan is to remove the old carpet, level the floor and resurface the floor with rustic tile. We were starting with very old carpet glued to a very out of level concrete slab.
Removing the carpet was fairly straight forward, it was several decades old and came up very easily. Unfortunately, the carpet glue residue left on the concrete slab was not so easy to remove.
After hours of scraping at the stuck carpet glue residue, I figured there must be an easier way, and headed to the rental center at the local Home Depot.
I rented a Clarke FM series commerical floor polisher. Using the brush attachment, I was able to remove most of the remaining glue residue in about 30 minutes.
Once the floor polisher did it job all I needed to do was vacuum up the dusty residual glue / carpet backing mess and finish by hand the portion of the floor to close to the wall and corners for the polisher.
Finally down to the bare slab, I was ready to proceed with leveling the concrete slab floor. If you look closely alone the inside wall and you will appreciate just how sloped the floor is — nearly 3″ low half way across this 12′ span! Prior to leveling the slab, you should check to be sure any structural / support issues are addressed prior to leveling the floor. Additionally, ensure that the floor to be leveled can handle the weight of the material to be added for the leveling process.
Knowing how expensive self-leveling floor products are and realizing I needed 3 inches of material in some areas, I need to find a way to complete the leveling process in an economically reasonable fashion and using a method that could fill in the deeper deficits I had.
The idea I came up with was to use both conventional concrete mix (and motor mix) as a base layer, to get the floor close to level and finished with the more expensive self-leveling underlayment mix.
It is true that some of the self-leveling floor mixes can be used by themselves to level floors with an inch or more out of level, but these products are typically five to ten times the cost of traditional concrete products, making them cost prohibitive for me to use for the entire project.
So to get started, I used premixed bags of high strength portand cement mix (fortified and fiber reinforced) for the first layer and to fill in most of the deficits. To feather the edges of the coarse rock aggregate, I used a sand motar mix fortified with latex. The final leveling layer used the more expensive self-leveling underlayment mix.
The results were fantastic. The less expensive concrete worked well to fill in the the majority of the low spots and allowed me to use much less of the more expensive self-leveling underlayment mix. I saved well over a thousand dollars by using this multiple material in layers technique. The trade off was time. The concrete needed 3 – 4 weeks to cure prior to applying the floor leveler, requiring over a month to complete the entire process.
How to Level a Floor
Preparation and Materials
- Level: Intermediate
- Time: Days to Weeks
- Cost: $300 – $500 +
Project Big Picture
- Prep floor.
- Determine deficit.
- Fill deficit with concrete.
- Level with floor lever.
Level a Floor – Materials and Cost
|Item||What I used||Cost|
|Self-Leveling Floor Mix||$36 / bag|
|Concrete Mix||$10 / 80 lb bag|
|Mortar Mix||$6 / 60 lb bag|
|Concrete Latex Primer||$30 / gal|
|Concrete Waterproofing Membrane||$45 / gal|
|Angle Iron Screed guide||$10 / 4′|
|Tapcon Concrete Screws||$25 / 75pc|
Level a Floor – Tools / Supplies
|Item||What I used||Cost|
|Floor Maintainer (Rented)||$35 / day|
|Cement Mixer (Rented)||$50 / day|
|Wheel Barrow or Mixing Tub||$15|
|Bull float or similar||$90|
|Hand tools, drill|
How to Level a Floor – Step by Step
- Clear and clean floor.
Prepare floor by clearing floor of all furniture and items. Floor must be clean and prepped according to the manufacturers recommendations of the concrete or fill product you are using. For this project I removed the old carpet and the carpet glue/capet backing residue with a rented commerical floor polisher (Clarke FM series). The floor was then scrubbed with a household detergent and water.
- Prime floor with latex additive.
To improve the bonding of the concrete patch to the existing concrete slab, prime the floor by applying a coat of latex concrete additive (Patching & Leveling Latex Additive from Custom Building Products). I used the latex additive straight from the bottle and rolled it on with a 1/2″ nap roller. Of note, you should delay the latex additive application until you just about ready to pour your concrete patch. Bonding of the new concrete to the primed surface is best before the latex is completely dry.
- Prepare the slab for the first layer of concrete fill.
Determine the floor deficit and desired amount of fill using a level, laser level or similar. An easy and inexpensive method is to use a string with an attached line level. Once you determine the desired floor level, create a method to mark this level and guide the concrete and self leveling mix pours.
I was able to mark the wall and build an on floor guide using angle iron mounted to the wall. The angle iron guide also served as screed guide and allowed easy leveling of the concrete pour. You can also mark the floor to indicate where fill should end if the entire floor will not be covered. For the angle iron screed guide, I arranged pre-drilled angle iron along the floor as a reference to the desired depth of the pour and eventual surface of the concrete fill. Along the foundation wall I bolted short pieces of the angle iron to support the longer guides extending onto the slab. Once I adjusted the guides to the desired level of the pour, I secured the guides in place with Tapcon® concrete screws.
- Mixing the first batch of concrete.
Rather than mix the concrete by hand, we rented a Kushlan electric wheel barrow style concrete mixer from Home Depot. The beauty of this mixer is the wheel barrow function that allows you to easily transport and dump each batch of mixed concrete.
If you have not used a concrete mixer before, the preferred method is to sequentially add the dry mix to the water in the mixer. A common method would be to first fill the mixer with most of the water required for the batch you intend to mix. Most small mixers can easily a batch consisting of 2 bags of dry mix.
Once the water is added to the mixer, start the mixer and add one half of the concrete mix for the entire batch (example; 1 bag if total batch is 2 bags) and allow it to mix fully. Next, slowly add the remaining concrete mix (the second bag). Once all the dry mix has been added and is fully mixed, add water to adjust the thickness of the final mix.
- Pour mixed concrete onto slab.
Starting with the section of floor furthest from your access, dump fresh concrete and continue until the level was just at the top of the previously installed angle iron guides and comes just short of your on floor mark (if any). Then settle, level and screed the concrete using a length of straight 2×4 or similar. Finishing the concrete pour surface with a fine broom or textured finish to promote bonding to the to-be-applied self-leveling underlayment layer.
- Mix latex fortified mortar mix to finish the slab edges.
Because the concrete mix used for the initial pour contains large aggregate (gravel, rock) it cannot be spread thin and feathered at the edges. Mortar mix, however contains only sand as an aggregate and therefore can be applied much thinner. Thin applications of mortar can be brittle, so I added a Latex to the mortar mix by substituting 50% of the required water with a latex additive when mixing the mortar. Once mixed, I applied the mortar to the edges of the concrete pour and used a float to feather the edges to the slab.
- Allow concrete to cure for at least 28 days.
Allow the concrete to completely dry. This generally takes at least 28 days depending on the conditions and materials used. Remember to finish the concrete pour with a fine broom or textured finish to help with bonding to the self-leveling underlayment mixture we will apply after the concrete has cured.
- Mix and apply the self-leveling floor underlayment mix.
For the final layer of the floor, use a commercial self-leveling underlayment floor mix. I used LevelQuik RS® from Custom Building Products. These products are specially blended portland cement and gypsum mixtures that pour on, self level and are stable even when applied very thin. These mixtures set quickly and therefore need to be applied and leveled in an efficient manner. For this project, one of us mixed a batch in a 5 gallon bucket with a heavy duty 1/2 inch drill and mixing attachment, while the other poured and leveled the batch. Even though these self-leveling products are mixed thin and designed to their own level, I found the use of a bull float very helpful to spread the product just after the pour. Once spread with the bull float, the product is good at self leveling. I apologize, but at the time of this writing I was not able to find the images of the self-leveler application. I will add them if found.
- Allow self-leveling product to dry and then seal floor.
Once the self-leveling layer was dry, typically 4 hours for this Rapid Setting product, I sealed the entire surface with a brush-on waterproof membrane. This waterproof barrier is optional, but it is easy to apply and will impede the movement of water through the slab into the porch living area. It will also improve the performance of the eventual tile finish surface for this floor. Read the directions from the manufacturer for application recommendations for the specific product you plan to use. I used RedGard® waterproofing and crack prevention membrane by Custom Building Products. With the Redgard product, the recommended techique is to apply a water diluted primer coat (1 part Redgard : 4 parts water) to the self-leveling underlayment before applying the full strength product.
After the primer coat is dry, apply at least one coat of full strength Redgard membrane with brush, roller or sprayer. I used a roller.
- Finish floor.
Once the waterproof membrane is fully dry, up to 12 hours, the surface is ready for finishing. To finish this porch floor, we plan to add electric radiant floor heat and tile. Check back for a summary of the finish work!