How to Install Self-Leveling Cement over Plywood Subfloors?

If you’re remodeling a home or business and want to upgrade to an elegant, polished concrete floor, it’s probably easier and more affordable than you think. If you’ve got a plywood subfloor, like many buildings do, you can leave it in place and apply self-leveling concrete directly on top of it. Once the plywood subfloor is covered, just apply the finish you want to achieve the desired look. You can also use self-leveling concrete on plywood as an underlayment for other types of floor coverings, such as carpet or tile.

Whether you’re a homeowner, contractor, or property manager, self-leveling concrete is a cost-effective, durable option for replacing floors that are cracked, uneven, or worn.

What Is Self-Leveling Concrete?

Self-leveling concrete has been modified with a polymer to make it flow more easily. When it’s poured, it can be easily spread to the surrounding areas with the help of a gauge rake or another smoothing tool.

The polymer also helps keep the mixture homogeneous so that larger, heavier particles don’t settle at the bottom as the floor cures. This means that the thickness of the concrete can vary over the floor’s surface without changing the appearance, ensuring a uniform, level look across the entire floor.

Self-leveling concrete applied over plywood is effective for various surfaces. It is suitable for use under flexible coverings or wooden flooring, enhancing cement and concrete surfaces. Additionally, it can be applied to gypsum substrates and is ideal for renovating old floors like terrazzo and ceramic tiles. This type of concrete is also compatible with rubber and resilient floor coverings, and it works well on OSB board and plywood surfaces.

One of the main advantages of self-leveling concrete over plywood is its ease of application. This concrete can be applied directly without the need for priming, making it a quick solution for leveling and smoothing uneven surfaces. It is designed specifically for interior applications, and when used, it significantly reduces dust during installation.

The properties of self-leveling concrete include rapid hardening capabilities, which allow it to be ready for floor covering installations within 12 to 16 hours for a half-inch thickness and 48 hours for a two-inch thickness. It supports various flooring coverings such as flexible and wood flooring, cement and concrete surfaces, gypsum, terrazzo, ceramic tiles, rubber, and other resilient coverings.

Furthermore, self-leveling concrete over plywood exhibits very low shrinkage, preventing cracks and ensuring durability. It is also compatible with underfloor heating systems, enhancing its utility in modern construction settings. The layer thickness of the applied concrete can vary from 1/8 inch to 3 inches, depending on the requirement.

In terms of strength, self-leveling concrete demonstrates formidable compressive strength, achieving up to 6300 psi after 28 days and 2400 psi after the first day, according to ASTM C109 standards. This high strength makes it suitable for areas with heavy foot traffic and even wheel loadings from casters.

Overall, self-leveling concrete provides a robust, efficient, and versatile solution for smoothing and leveling plywood substrates, ensuring they are suitable for a wide range of applications and achieving a professional finish in any construction or renovation project.

Benefits of Using Self-Leveling Concrete on Plywood

In addition to the aesthetics, there are plenty of reasons you might want to use self-leveling concrete to replace an existing floor. Some of the benefits of this approach include the following:

Use the existing subfloor

Once you remove the existing flooring to reveal the plywood subfloor, you don’t have to remove any additional layers. Simply prepare the plywood, following the installation instructions, and pour the self-leveling concrete on top.

Apply with ease 

Because self-leveling concrete has a lower viscosity than regular concrete, installation and leveling do not require vibration or compaction, making it easier to install, especially for the DIYer. There is no need to rent any special equipment, and the installation steps are easy to follow.

Get a new floor faster

Compared to regular concrete, self-leveling concrete requires less time to install. The curing time is also generally shorter, so once the concrete is poured, your new floor can be ready in hours instead of days.

Save money

Self-leveling concrete can be applied in a thin layer, with a typical thickness around half an inch. This reduces the amount of material required compared to regular concrete, making it a cost-effective solution. For businesses, a new floor can be poured overnight and be ready to use in the morning, reducing downtime and having a minimal impact on customers.

Get the look you want

A range of sealants, colors, and finishes allow you to get the look you desire. Whether it’s a utilitarian shop floor or a modern concrete tile look in the kitchen, self-leveling concrete lets you do it without the need for a professional installation.

Enjoy a lifetime of durability

With its high compressive strength, the new floor can be sealed as a wear surface. Whether you’re using it as an underlayment or the finished floor, you can count on it to last a long time.

How to Install Self-Leveling Concrete

Although a professional certainly can install your new floor if it’s not a task you want to undertake, installing self-leveling concrete can also be a DIY project.

Requirements for installation

The plywood subfloor must be firm in order for the concrete surface to be installed correctly. It must not have any bending or deflection more than L/480. If it does, it needs to be strengthened first. You can do this by applying another layer of plywood that is screwed down on six-inch centers.

The thickness of the plywood subfloor must be a minimum of 3/4″ of an inch, and it should be tongue-and-groove, untreated, APA-rated, Type 1, exterior-grade, plywood, OSB, or equivalent.

Prepare the surface

The surface of the wood must be clean and free of oil, grease, wax, coatings, and any contaminants that might prevent the materials from creating a strong bond. Follow these steps to prepare the surface:

• Sand the surface to bare wood to remove any visible sheen.
• Replace any weak or water-damaged areas with new plywood.
• Secure loose boards with deck screws.
• Ensure that no screwheads are showing.
• Seam the joints with structural mesh and structural urethane.

Create a perimeter around the area where you will be pouring the self-leveling concrete so it’s not allowed to spread beyond the edge. This will also help you get a clean edge for a professional look. You can use foam that is adhered with double-sided tape, or any other method that creates a temporary rim around the floor. If there are any penetrations through the floor for wiring, plumbing, or mechanical systems, these should also be surrounded by a perimeter lined with duct tape so that the concrete does not adhere to them. Once all of these steps have been performed, it’s time to prime the wood.

Prime the surface

Primer helps seal the wood so that none of the moisture from the concrete will be absorbed into the subfloor. Apply one thin coat of undiluted Paramol primer using a 3/8″ nap roller and a brush on the corners and edges. Ensure that all areas are covered and that there is no puddling anywhere on the subfloor. Brush off any puddles and excess primer and allow the primer to dry for 6-8 hours, but no more than 24 hours. If it has dried for more than 24 hours, another primer coat will be necessary.

If you’re applying the concrete topping to a wood floor where you have moisture concerns, a flexible waterproofing membrane over the plywood is all that is needed to provide protection.

Apply the lathe

Metal lath goes on top of the prepared wood and must be adhered firmly and cleanly. Once the primer is dry and tack-free, install galvanized, expanded diamond metal lath, using lath screws approximately every six inches, and overlap adjacent pieces approximately every six inches. Remember that the concrete overlay may be as thin as 3/8″, which is another reason the surface preparation is so important. After the lath is placed, allow the Paramol to dry thoroughly.

Apply the concrete

Wear dust masks and gloves to prevent both inhalation and skin contact as you mix and apply the self-leveling concrete. Using a 650 rpm drill, mix the concrete at the recommended proportions for three full minutes in large drums that have been pre-wetted to prevent them from absorbing water from the mixture.

Use a gauge rake with the ears set to the thickness at which you are laying the concrete to spread it in an even layer. Then use a smoothing paddle to help spread the material over the entire area. For larger areas that require walking on uncured concrete, wear cleats to avoid leaving large footprints behind. The new floor will be set within a few hours.

Common Challenges with Self-Leveling Concrete

Although installing a new floor with self-leveling concrete is an appropriate DIY job, there are some problems to avoid so you can get a flawless finish.

Visible screwheads

If screwheads are visible in the subfloor before you pour the self-leveling concrete, it could impact the quality of the floor. When the concrete cures, you might see the screwheads ghosting through the surface, which would make it look uneven and less uniform. Over time, if the screwheads rust, it could impact the bond between the concrete and the subfloor, making the new floor less durable.

Poorly applied primer

Although it might be tempting to skip this step or to rush through it, primer is essential for proper adhesion between the concrete and the wood. Not using primer or missing spots could also allow outgassing bubbles from the wood to rise through the concrete, affecting the smoothness of the surface.

Incorrectly applied lathe

If the edges of the lath are allowed to curl up or if there are any floating areas, the mesh could come through the concrete and affect the quality of the surface. Overlapping the edges and ensuring that the entire surface is firmly secured will help you avoid this problem. If you notice the lath coming through after the concrete has been poured, secure it with screws and smooth it out again.

Incorrect water-to-concrete proportions

Having too little water in the mixture will reduce its ability to spread and level out, whereas adding too much water will impact the strength of the cured concrete and could also result in visible smoothing lines.

Plywood Porosity

Plywood is challenging for pouring concrete due to its porous nature, which prevents the concrete from settling evenly. A viable workaround the porous nature of plywood involves using cementitious mixes designed to replicate the surface and durability of concrete, which can effectively address the issues caused by plywood’s porosity.

Use Duraamen for Your Concrete Floor

Replacing or fixing a floor can be a daunting task, but using self-leveling concrete makes it easier to get a flawless, even floor. Duraamen’s industrial and polished concrete flooring products are designed to provide long-lasting, labor-saving flooring solutions. Talk to an expert about your flooring challenges or to learn more about Param 5500 or any of our other self-leveling concrete products.

For complete Installation Instructions, please watch the videos on this page – How to Install Self-Leveling Concrete over Plywood Substrate (duraamen.com)

If you are DIY Enthusiast, you may want to consider our self-leveling concrete packages – DIY Self-Leveling Polished Concrete for Commercial & Residential (duraamen.com)