The flooring industry has always placed a strong emphasis on smooth and level concrete surfaces upon which to install resilient flooring. With today’s large amount of commercial remodeling/renovation projects, the attempts to reduce costs in the new construction market and the declining availability of competent cement finishers, you need a product that help to solve most problems related to floor leveling and repair. Fortunately, modern self-leveling cements provide you with solutions that are technically sound and cost effective.
Cementitious Self-leveling flooring is polymer-modified cement that has high flow characteristics and, in contrast to traditional concrete, does not require the addition of excessive amounts of water for placement. Self-leveling product also called self leveling concrete, is typically used to create a flat and smooth surface with a compressive strength similar to or higher than that of traditional concrete prior to installing interior floor coverings. Self-leveling concrete has increased in popularity as the degree of flatness and smoothness required for floor covering products has increased, with vinyl goods getting thinner and floor tiles getting larger, for example.
The term self-leveling was coined in the United States by one manufacturer in year 1978 in reference to their first self-leveling product. The term was used to differentiate it from traditional concrete, which is typically stiffer and requires more labor to get it into place and finish with a trowel.
Area of Application
Cementitious Self Leveling floorings are classified into two main groups of materials: underlayments and toppings. Underlayments are installed over an existing subfloor to smooth it out and correct any surface irregularities prior to the installation of all types of floor coverings, including sheet vinyl, vinyl composition tile (VCT), wood, ceramic tile and carpet. Toppings perform a similar function but act as the actual finished floor without the need for a floor covering. Some typical applications for concrete toppings include warehouse floors, light industrial applications, retail stores and institutional facilities. Concrete toppings can also receive pigmented color dyes, stains, saw cuts or mechanical polishing to produce a decorative concrete finished wear surface. These floorings can also be coated with advanced coatings based on epoxy, acrylic and polyurethane resins.
When self-leveling concrete is poured, it has a viscosity similar to pancake batter. A gauge rake is used to move it into place without spreading it too thin. The finishing is then done by lightly breaking the surface tension of the product using a tool called a smoother. The polymers in the self-leveling mix keep the viscosity of the product such that it remains uniform in composition from top to bottom without the sand aggregates sinking to the bottom of the installed layer. The typical installation thickness of these products is about 0.25 inches to ensure there is enough mass present for the material to flow, although some self-leveling products now exist that can be installed at an average thickness of only 0.125 inches extending up to 3 inches for highly undulated subfloors.
What is Self-Leveling?
Many think “self-leveling” means that you pour a mixed batch in the centre of the room and it will take care of itself. But it is not so. It means that mixture of powder and water has a low viscosity to allow material to seek its own level before setting. Material need to be taken to other place with gage rake and smoother.
Traditional methods of leveling and repairing concrete floors are both labor intensive and require the use of screeds, trowels and sanders that are less than desirable because of site mixing, waves, cracks, etc.
Self leveling prodicts have a variety of advantages over trowelable underlayments:
1. Application is about eight times faster than trowelable underlayments.
2. They do not require the same high degree of expertise as hand troweling.
3. They can be used to repair a variety of substrates.
4. They are fast setting and can be walked on in a few hours.
5. Floors can usually be installed the next day.
6. They can be installed from a feather edge to several inches in one pour with little to no shrinkage.
7. They develop high compressive strengths (4,000 psi or greater).
8. They are water resistant and do not promote the growth of microbial contaminates.
The key to success when installing self-leveling products is to achieve a good bond between the substrate and the self-leveling underlayment. Proper preparation of the concrete surface is the most important factor. The surface must be sound, clean and free of such residuals as oil, grease, wax, dirt, sealers, curing compounds and adhesives. Most self-leveling substrates are shot blasted to insure that the substrate is clean and free of contaminants. Remember, taking a shortcut in substrate preparation is an open invitation to failure.
In almost all self-leveling products they recommend the use of a primer to work as a bonding agent. There are two types of primers used. One is for porous and absorbent substrates, while the other type is used when going over a non-porous substrates, such as ceramic, quarry, terrazzo, marble, steel, lead, and cutback adhesive residues.
On special types of substrates an additive may be recommended for special types of substrates such as metal substrates and or cutback adhesive residue. The additive will add additional bonding strength and will allow a little bit of deflection into the mix.
Temperature control is vital to the success of using self-levelers. With self-levelers heat is your worst enemy. When you are dealing with a self-leveling product, you must monitor four temperatures.
1. Ambient temperature
2. Slab temperature
3. Powder temperature
4. Mix water temperature
If any of these temperatures exceed 28.0°C it will prove to be detrimental to the application. In warm weather conditions the pour may have to be done early in the morning or late in the evening when temperatures are cooler. Powders can be stored in a cool place and the mix water container can be filled with several blocks of ice to cool the mix water. Heat causes the self-leveling mix to stop flowing prematurely, usually less than five minutes, making it difficult to get it placed on time.
In cold conditions the self-leveler will slow its set time down, but beware of any temperatures below 10.0OC, as it will also have an adverse effect on the mix.
Mixing: When mixing, it is critical to use the correct water-to-powder mixture. Mixing is done by adding the correct amount of powder to a premeasured amount of water. Once the powder is added to the water it is necessary to power mix with a heavy duty drill at about a 650 rpm for approximately two minutes. Power mixing will break the surface tension in the water, allowing for a smooth mix that will flow easily for about six to eight minutes. Once the mixing is complete, get the mix out of the container and on to the floor without delay. The approximate time from the time the powder hits the water to the stop of the flow time is about 10 minutes at room temperature, and you still need time for the spreading and smoothing process.
Spreading: Immediately after the mixing process is completed, pour the mix onto the floor and move the mix with a spreader to obtain a uniform thickness. The spreader is a stand-up, hand held device that can be set to apply a desired even thickness of underlayment over the substrate.
Smoothing: The smoother is a second hand held-device to place the final smoothing by removing the spreader marks, footprints and all irregularities.
The working time varies eight to ten minutes depending upon temperature. While this doesn’t seem like much time it is more than adequate to spread and smooth the area. For example, a crew of three can cover about 1,500 square feet per hour without any difficulty.
Pumping: For large installations self-leveling underlayments can be pumped. The pump will control the critical water-to-powder mixture and allow for a faster installation. For example, a three-man crew can easily do 7,000 sq. ft. per hour.
The usual drying takes about two hours before you can walk on the newly installed surface, and resilient flooring can be installed the next day. Care must be taken to not allow the under-layment to dry too fast.
Specifications of SLU Flooring
Appropriate floor flatness requirements for the slab, based on conditions, intended usage, and service requirements, can be found in ACI 302 section – Guide for concrete Floor and Slab Construction. Although there is no exact method of comparing f-numbers to conventional straightedge testing results, the following chart can be used as a guideline to approximate values between the two:
F-Number Results of Self-Leveling Applications
Installing a self-leveling under-layment makes it easy to exceed the requirements of the floor covering. Using the testing procedures outlined in ASTM E-1155, floor surfaces covered with a cementitious SLU have rendered f-numbers in the mid to upper 80’s. Other guidelines for SLU may be seen in ANSI sections A108.01 and A108.02
Condition Requirements Prior to Application of Self-Leveling Under-layment
It is typically recommended that SLU be applied in conditions where ambient temperature is above 10° C, and not more than 28° C. To ensure the integrity of the primer, the moisture vapor transmissions rate (MVTR) from the substrate should not be in excess of 2.2 kg of water/day/1000 sq. ft., based on a standard ASTM F-1869 (Calcium Chloride) test, or 80% rh, based on ASTM F-2170. A moisture content that is too high will also slow the cure of the SLU and can affect the subsequent floor finish. Most floor covering manufacturers will have acceptable limits for MVTR and their recommendations must be followed. Consult with Multichem’s technical representatives for specific recommendations regarding Multichem’s SLU and your particular installation.cal White Paper
Compatibility of Self-Leveling Applications as Part of a Complete System Assembly.
Generally a cement-based self-leveling underlayment is a suitable surface for most bonding mortars and adhesives. To assure compatibility, all installation products should come from the same manufacturer. All Multichem Products cement- or epoxy based thin-set mortar and grouting material are 100% compatible with MUTICHEM SLU products. So are MULTICHEM’s waterproofing and crack isolation membranes, such as PrimeGuard, Multiguard Flex, CrackBuster, or Fibrecon GMat. Multichem’s ability to provide a complete system inclusive of SLU (LevelTop, LevelQuik, LevelFast or LevelLite), crack isolation and waterproofing, uncoupling membrane (PrimeGuard, Multiguard Flex, CrackBuster, setting mortar (PrimePatch, SuperPatch or FeatherPatch) and grout (SureColour or SurSilk Commercial Epoxy Grout) makes single sourcing from one manufacturer a simple process.
Custom Building Products Answers the Challenges of the Enhanced Floor Flatness Standards with LevelTop, LevelQuik, LevelFast AND LevelCrete
LevelCrete products are engineered to meet a wide range of job requirements and address a variety of existing floor conditions. Formulated with Multichem Controlled Cure Technology (MCCT), LevelFast is Fast Setting Self- Leveling Underlayment seeks its own level within minutes, and provides a high early compressive strength that can accept thin-set bonded tile applications in 4 hours or less after application. LevelQuick will maintain a compressive value of 4400 psi after a complete 28-day cure, and can be applied up to 1″ in thickness in a single pour. LevelTop Plus can also be feather-edged for smooth transitions to adjacent floor conditions and finishes. With a 30-minute working time, LevelTop ThicknThin Extended Set Self-Leveling Underlayment is ideal for large applications that require longer cure rates to allow for additional tooling and working after pour. As a result, LevelTop Thickn Thin is ideal for large single or multi floor projects that require the self-leveler to be pumped with mechanical pumping equipment. LevelTop ThicknThin is formulated for application in conditions that require as much as a 2″ thick leveling agent and that can be tooled down to a feather edge. This provides for smooth transitions to other floor finishes and project conditions.
LevelTop Latex Primer is recommended as a preparation for all surfaces prior to treatment with any cementitious self-leveling material. LevelTop Latex Primer dries within 30 to 60 minutes, depending upon the project conditions (including temperature and humidity), and it dramatically improves the adhesion of the SLU to the substrate while controlling subsurface porosity. For high-rise buildings, where structural load is critical, LevelLite self leveling product is most suited, with very light weight.
Contributions of SLUs to LEED® and Green Building
One recent trend in the formulation of self-leveling underlayments is the addition of post consumer recycled aggregates to enhance the materials’ contribution to LEED certification and green building. Multichem has also identified the benefits of using post-consumer recycled raw materials to achieve a lighter weight formula. In some cases, the selection of a so-called “lightweight” SLU can reduce the per square foot (psf) weight of the floor by as much as two pounds per square foot. Exactly how much an SLU can contribute to minimizing floor psf weights will depend on the thickness requirements of the self-leveling agent as a floor leveler. The thickness of the SLU will vary based on the existing conditions and thickness of the substrate, as well as transitions to other floor finishes. Multichem Responds to LEED and Green Building Requirements with LevelLite Lightweight SLU. Engineered with over 20% Post-Consumer recycled content, LevelLite from Multichem provides the highest level of Green contribution under LEED 4.1 compared to any other material in the cementitious self-leveling product category. Formulated with a unique blend of high quality cements and aggregates, Level Lite provides a subsurface that is up to 2 lbs. per square foot lighter than standard mortar bed installations. LevelLite can accept a thin-set / tile application in as few as 4 hours after pour, and can be applied up to 2″ in thickness in a single pour, down to a feather-edge for smooth transitions to other floor surfaces.