Do's and Don'ts of Installing Concrete Underlayments and Overlays

What is concrete underlayment?

Concrete underlayment is a thin coating material that is poured over a concrete substrate. The material smooths out imperfections, creating a flat base that is ready to accept a variety of other floor coverings, such as carpet, tile, vinyl, etc.

Underlayment can provide a quick and affordable fix to floors that are heavily cracked, pitted, or uneven. Rather than ripping out and replacing the concrete subfloor, underlayment covers imperfections, provides a seal to prevent moisture damage, and is more cost-effective.

Underlayments can be installed in a variety of thicknesses, ranging from featheredge to 1.5 inches in depth.

What is a concrete overlay?

Like underlayments, concrete or cementitious overlays also help to cover concrete flooring imperfections; however, overlays are more customizable and offer a range of decorative options, such as dyes, polishing, aggregate, and inlays.

These self-leveling toppings can be applied over any hard surface, including concrete, terrazzo, and tile. Because the previous flooring system does not need to be fully removed, overlays reduce material waste, reducing environmental and disposal costs, as well as labor and installation time.

Overlays create an attractive and seamless covering that cures quickly, usually within 24 hours, which keeps production schedules on track.

Tips for Installing Concrete Underlayment or Overlays

Both underlayments and overlays require the same basic installation care and precision. Experts from the Jon-Don Concrete Team have prepared a helpful list of do's and don'ts for contractors looking to install either system.

THE DO'S:

1. Do Perform Proper Surface Preparation: Properly prepare the surface by cleaning it thoroughly, removing any dirt, debris, oil, grease, or existing coatings. The surface should also be roughened or etched to Concrete Surface Profile (CSP) 3 to promote better adhesion and ensure success.

2. Do Follow the Manufacturer's Instructions: Always follow the manufacturer's instructions and recommendations regarding mixing ratios, application methods, curing times, and environmental conditions.

3. Do Use the Right Tools: Use appropriate tools for the job, such as trowels, mixers, sprayers, gauge rakes, spike rollers, etc. to ensure proper application and finish. To apply RapidSet Tru PC, the Portamix® MEGA HIPPO Mixing Station is required. Depending on the size of the job, multiple mixers may be necessary to ensure each batch is blended properly and applied to the floor. If a wet edge is not maintained and each batch is curing at a different ratio, the results may be catastrophic.

4. Do Apply Primer if Required: Some overlays and underlayments may require the application of a primer to improve adhesion and ensure the moisture is not removed prematurely from the material. This can be an epoxy and sand broadcast or an acrylic primer/sealer. Follow the manufacturer's recommendations regarding primer application.

5. Do Work in Sections and Plan Accordingly for Large Areas: When applying overlays or underlayments over large areas, work in manageable sections to ensure consistency and avoid drying or setting before you can finish. BONUS TIP: If utilizing an overlay, make sure to get a written sign-off for approval of your terminations plan.

6. Do Control Joint Placement: Incorporate control joints as necessary to prevent cracking, especially in large areas or where movement is expected. Saw cuts with joint filler or the incorporation of Schluter strips are common.

7. Do Consider Temperature Variances: Consider installing a thin, flexible foam around the perimeter to allow the overlay or underlayment room to expand and contract with varying temperatures.

8. Do Allow Sufficient Curing Time: Ensure that the overlayment or underlayment has adequate time to cure properly before subjecting it to foot traffic or applying finished flooring systems.

THE DON'TS

1. Don't Rush the Surface Preparation: Proper surface preparation is crucial for the success of the overlayment or underlayment. Skipping or inadequately preparing the surface can lead to poor adhesion and premature failure.

2. Don't Ignore the Sand Broadcast into the Epoxy Primer. Typically, these epoxy primers are tinted white, as in the Rapid Set TXP Fast primer. The purpose of this is to ensure a full broadcast of sand is applied to hide all the white. The material will not adhere to bare epoxy-even if there is a small area that has been skipped by the broadcast. The potential for failure is high. The cementitious overlayment must adhere directly to a complete broadcast of sand.

3. Don't Neglect Mixing Ratios: Always follow the recommended mixing ratios provided by the manufacturer. Deviating from these ratios can result in a mixture that is too thick or too thin, compromising performance. Consider performing a slump test to dial in the amount of liquid added to each batch. This can vary depending on your geographical location or environmental conditions. It is critical to have consistency for each batch, especially when dealing with a polishable overlay system. Overwatering can drive the aggregate to the bottom, making it impossible to expose while grinding. Inconsistent liquid can result in a variation of color across the finished surfaces.

4. Don't Apply in Poor Weather Conditions: Avoid applying overlays or underlayments in extreme temperatures, high humidity, or rainy conditions, as these can affect curing and adhesion. Ice buckets with a long length of wound hose can help ensure the water is cold. Keep the materials under a tent or in a controlled temperature environment to help offset extreme temperatures.

5. Don't Overwork the Material: Avoid overworking the material once it has been applied. Overworking can trap air bubbles, weaken the mixture, and compromise the finish.

6. Don't Ignore Safety Precautions: Always prioritize safety when working with concrete overlays and underlayments. Use appropriate personal protective equipment (PPE), such as gloves and goggles, and follow safety guidelines for handling and application.

Find Concrete Overlays and Underlayment from Top Brands at Jon-Don!

Jon-Don is a one-stop shop for concrete contractors, construction professionals, and general contractors. Find concrete underlayment and cementitious overlays from top brands, plus all the application supplies and equipment you need for your next project.

Plus, with equipment service and repair centers across the country, a robust training calendar with learning opportunities for your team, and experts on call, Jon-Don has everything your business needs all under one roof.

Have a technical question or need help with a job specification? Our team of experts is ready to help. Call 800-556-6366 to speak with a member of our Concrete Team today!