How to Use Self Leveling Cement to Level a Large Concrete Slab
Last weekend we finished pouring the fourth and final quadrant of self leveling underlayment over the radiant heating wires in the basement gameroom. The total floorspace in the area is about 1000 sq. ft. This pour constituted the last 250 sq. ft., and the second largest pour of the four we’ve made. When finished, we plan to install a ceramic or natural stone tile (e.g. slate) in the area.
For those of you considering pouring self leveling underlayment over large areas (75 sq. ft. or more), here’s an overview of the project and some tips to help you tackle this relatively easy-2-DIY job.
Why Large Areas Present a Challenge
- Most self-leveling underlayments are designed to dry quickly, especially the brands most commonly found in the big box home improvement stores. This is by far the most difficult challenge to surmount.
- Larger areas make it more difficult to get to the center, or wall-bound sections of the pour after the pour is underway. As you can see in the picture above, the studs on the back end of the basement are inaccessible during the pour.
- Despite the products’ names, most self-levelers are only partially self-leveling. They are most effective when a minimum thickness is maintained across the whole plain of the surface (about 1/2″). This problem is exacerbated over larger areas which tend to have more variations in surface height. Since self-leveler is expensive, you want to avoid pouring any more than necessary.
How to Prepare for Pouring a Large Area
Purchase a Self Leveler with a longer drying time. We used Custom Building Product’s Levelquik ES (extended setting) for the job. Levelquik ES boasts a 15 minute free flow time with an additional 15 minutes of “work” time. Note that Home Depot carries Levelquik RS (rapid setting), which only gives you 5 minutes of free flow and 5 minutes of work time — definitely not long enough for a large pour. You’ll likely need to get this product from a distributor.
Invite Friends to Help with the Job. For 225 square feet, we recommend 5 people for those who haven’t done this job before. With some practice, it can be done with 4, but no less. For very large areas, we recommend breaking up the job into multiple pours over several days.
Plan out the Pour in Advance and Prep all Materials. The key to a successful pour over a large area is planning as much as possible before you start mixing the leveler. Once mixing is underway, you have a finite amount of time to finish before part of the floor starts to dry.
Tools and Materials Needed
Besides the self leveler, you’ll need:
- At least four 5-gallon buckets. The job will be easier with more buckets, and since we had 9, we used all of them in our recent pour.
- Two heavy duty drills and two heavy-duty 18″ drywall mixing blades. Do not use cordless drills or smaller mixing blades. You run the risk of not getting the SLU mixed properly or burning out a drill.
- A painter’s extension pole and a squeegee that mounts on the end. Modify the squeegee by cutting out slots for spreading over the underlayment.
Prep Work At Least 24 Hours in Advance of the Pour
- Ensure that the area to be poured has good, reasonably tight borders all the way around. You may need to lay temporary barriers for the pour, especially if you are breaking a very large room into smaller areas to make the pour easier.
- Prime the slab for the self leveler. Most SLUs will come with their own instructions. Levelquik ES recommends using their Levelquik Primer.
Prep Work on the Day of the Pour
- Fill each bucket with the amount of water specified for one bag of leveler. The easiest way to do this is to mark a bucket with the amount of water needed, and use that as your measuring device for the rest. If you’re working with a small number of buckets, find other containers that can be used to hold “preset” amounts of water. As you empty SLU on to the floor, you’ll refill the bucket with the water from your preset containers.
- Open all of the bags of self leveler prior to starting the pour. This way, during the fast-paced action of the pour you won’t be struggling to open the bags.
- Setup your drills and mixing blades and ensure they’re working properly and the cords do not obstruct the area to be poured.
Start Mixing, Pouring and Spreading
In this step, it can get a little chaotic. The key is to ensure everyone is working together to get the floor poured. Usually, there’s one person spreading, two mixing, and two people with two roles: pouring dry powder into buckets, and pouring mixed compound onto the floor for the spreader.
The spreader’s job is crucial to achieving level floors with self-leveling underlayments, since the name is somewhat misleading.
A Video to Help Out
The first video we made focuses on working with self-leveling underlayment. Take a look at that for some encouragement that you definitely can do this job.
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