Waterproofing a concrete floor is an important process that helps prevent moisture from seeping up through the concrete and into the flooring above. This prevents a variety of problems such as mold growth, warped or buckled floors, and moisture stains. There are several methods for waterproofing concrete, but the most common and effective way is to apply a concrete sealer or membrane. This article will provide a step-by-step guide to properly waterproof a concrete floor using sealer.
Page Contents
Why Waterproof a Concrete Floor?
Concrete is naturally porous and allows moisture to pass through. Over time, moisture can accumulate under flooring and cause damage. Here are some of the main reasons you may want to waterproof a concrete floor:
- Prevent moisture from seeping up through the concrete into flooring materials like wood, tile, vinyl, and carpet.
- Avoid warped, buckled, or rotting floors due to excess moisture.
- Prevent growth of mold, mildew and other fungi.
- Reduce damp or musty odors.
- Limit efflorescence deposits on the concrete surface.
- Reduce humidity levels and prevent condensation buildup.
Waterproofing creates a moisture barrier between the porous concrete and the flooring above. This barrier blocks liquid water and moisture vapor from passing through the concrete slab. Properly waterproofing a concrete floor provides long-lasting protection and prevents thousands of dollars in damage over time. It’s almost always worth the small upfront investment.
Choosing the Right Concrete Sealer
There are many concrete sealers on the market, but not all are ideal for waterproofing. Here are the best options:
Epoxy
Epoxy is the most durable and moisture-resistant option for concrete sealing. It provides a thick, plastic-like coating that fully seals the concrete from moisture. Epoxy sealers come in two parts that must be mixed prior to application. They require more skill to apply than other sealers.
Polyurethane
Polyurethane concrete sealers provide protection comparable to epoxy with easier application. Like epoxy, polyurethane cures into a hard, plastic-like finish. Polyurethane is nearly as durable as epoxy, while allowing for a little more flexibility.
Acrylic
Acrylic sealers offer an affordable and user-friendly option. They penetrate the surface and binds the concrete to provide a moisture barrier. Acrylics are easier to apply than epoxy or polyurethane, but do not offer the same level of protection. They require reapplication every few years.
When selecting a concrete sealer, consider the amount of moisture exposure the concrete will get, as well as how frequently you wish to reapply the sealer. Epoxy and polyurethane provide long-lasting protection, while acrylics must be reapplied more often.
How to Apply a Concrete Sealer
Follow these steps to properly apply a concrete sealer for waterproofing:
1. Clean and Prepare the Concrete
The surface must be completely clean and dry before applying sealer. Sweep away dirt and debris. Use a concrete degreaser to remove oil and grease spots. Wash the floor with a high-pressure washer or stiff scrub brush and let it fully dry for at least 24 hours. Vacuum up any remaining dust.
2. Repair Any Cracks and Holes
Look for cracks, chips, spalls or holes in the concrete and fill them with a concrete patch compound. This provides a smooth surface for the sealer to adhere to. Fully cure patches for the recommended time before sealing.
3. Tape and Mask Surrounding Areas
Apply painters tape along the edges where the floor meets walls, drains, or other fixtures. This prevents the sealer from getting onto adjacent surfaces. Place drop cloths down to protect nearby surfaces.
4. Apply Primer if Necessary
For bare concrete that has never been sealed, apply a thin primer coat first. Consult the sealer manufacturer’s recommendations to see if a primer is required. Priming improves adhesion and evens out surface absorbency.
5. Pour Sealer into Paint Tray and Apply
Carefully follow the product instructions for mixing and preparing the sealer, if required. Pour a small amount of sealer into a paint tray and apply using a nap roller with a long handle. Start at the back corner furthest from the exit and work your way out of the area systematically. Maintain a wet edge and work in thin, even coats.
6. Allow Proper Dry Time Between Coats
Let the floor dry fully according to the manufacturer’s recommendation before adding additional coats. This is usually a minimum of 24 hours. Adding another coat before the previous one has dried will cause problems with curing. Repeat for the recommended number of coats.
7. Remove Tape and Reinstall Flooring
Once the final coat has dried for the recommended time, carefully remove all painters tape. Clean up any drips or spills with the appropriate solvent. The concrete is now waterproofed and ready for installation of new flooring.
Tips for Successful Waterproofing
Follow these tips for best results from your concrete sealer application:
- Test a small hidden area first to ensure compatibility with the concrete.
- Thoroughly mix two-part epoxy or polyurethane sealers as directed.
- Maintain proper dry times between coats for full curing.
- Apply thin, even coats according to manufacturer spread rate recommendations.
- Plan the application route so you don’t get trapped in corners.
- Use a paint sprayer for large floor areas to ensure consistent coverage.
- Keep the sealed floor clean and dry to maximize durability.
- Spot mop up spills immediately to prevent moisture penetration.
- Reapply acrylic sealers every 2-4 years for ongoing protection.
Taking care to properly clean, prepare, apply, and maintain the sealer provides the best waterproofing results. Test areas allow you to ensure compatibility and appearance before committing to the entire project.
Considerations for Various Concrete Floor Locations
Certain areas may require additional preparations or specialized application methods depending on the type of use, exposure to moisture, and traffic.
Garage Floors
Garage floors need maximum protection from road salts, chemicals, and vehicle fluids. Use an epoxy or high-quality polyurethane sealer. Apply a slip-resistant additive for safety. Install expansion joints to allow movement.
Basement Floors
Since basements are prone to humidity and occasional flooding, use a hydrostatic pressure relief system under the slab along with a thick epoxy or polyurethane sealer on top. Seal any cracks thoroughly.
Shower Floors
Frequent direct water exposure makes showers especially vulnerable to moisture damage. Use a two-part epoxy sealer and coat the walls as well as the floor. Apply caulk at all joints and corners.
Outdoor Concrete
For driveways, patios, and walkways apply solvent-based instead of water-based sealers. Acrylics work well outdoors but require more frequent reapplication. Add anti-skid particles to high traffic areas.
FAQs About Waterproofing Concrete Floors
Here are answers to some of the most frequently asked questions about waterproofing concrete floors:
How long does concrete sealer last?
Epoxy and polyurethane sealers can last 5-10 years or longer before needing reapplication. Acrylic sealers last 2-4 years on average. Durability depends on the quality of product used and following the manufacturer’s application instructions.
Can you apply sealers over existing sealers?
Yes, it is usually fine to apply a fresh coat of sealer over an older application, provided the previous coat is fully cured and still in good condition. Always test first.
What is the best sealer for indoor concrete?
Epoxy sealers provide the greatest durability and moisture protection for indoor use. Polyurethane is also an excellent option for indoor concrete. Acrylic works well for indoor applications needing less frequent re-coating.
Can you use sealers on polished concrete?
Yes, polished or decorative concrete can be sealed for protection. Use an acrylic sealer or wax to avoid diminishing the shine. Test first on a small area to ensure compatibility.
How long do I have to wait to walk on the sealed floor?
Cure times range from 24-72 hours before foot traffic, depending on the sealer used. Always observe the manufacturer’s recommended curing times before walking on the sealed floor or replacing heavy furniture.
Conclusion
Waterproofing a concrete floor provides long-term moisture protection for your flooring investment. While the process requires careful preparation and application, it yields great benefits by preventing costly damage from excess moisture. Be sure to select the right sealer for your needs, apply it correctly, and maintain it properly over time. With the right waterproofing approach, your concrete floors will stay dry, stable, and mold-free for many years to come.