How to Resurface Exposed Aggregate Concrete

Dull or weathered exposed aggregate can make your entire outdoor area seem worn out. You may wonder, how do you resurface exposed aggregate to bring back its aesthetic appeal? This guide breaks down how to resurface exposed aggregate concrete: preparing your surface, applying a new layer, and sealing for endurance.

Exposed aggregate concrete, with its unique blend of natural stones and aggregates, creates a visually appealing and textured surface that adds character to driveways, patios, and walkways. However, over time, exposure to the elements and regular use can cause wear and tear, resulting in cracks, stains, and a dull appearance. By resurfacing your exposed aggregate concrete, you can bring back its original charm without tearing the slab out.

What is Exposed Aggregate Resurfacing?

Exposed aggregate resurfacing is like a fountain of youth for your concrete surfaces. It involves applying a new surface layer to the existing concrete, not only enhancing its appearance but also giving it a fresh wearing surface. Think of it as a facelift, a rejuvenation that revives the aesthetic appeal of your concrete while retaining its unique texture.

Resurfacing isn’t just about beauty; it’s also practical. It eliminates the need for a complete replacement, which can be costly and time-consuming. It’s about giving your exposed aggregate surfaces a fresh wearing layer. Cracks and unsound areas still have to be repaired first.

Exposed aggregate resurfacing involves applying a new layer of material over the existing exposed aggregate surface to rejuvenate its look and functionality. The resurfacing material can be a specialized concrete overlay or a specifically formulated coating designed for this purpose. The new layer covers the existing aggregate, providing a fresh surface with improved aesthetics and durability.

The process typically begins with an assessment of the condition of the existing exposed aggregate concrete. This evaluation helps identify any cracks, stains, or areas in need of repair. Once identified, necessary repairs and cleaning are conducted to prepare the surface for resurfacing.

The resurfacing material is then applied to the prepared surface, often using trowels or specialized tools. The material is spread evenly to achieve a consistent thickness and texture. Depending on the desired outcome, additional techniques such as stamping or texturing may be employed to create unique patterns or finishes.

After the resurfacing material is applied, it undergoes a curing process. This allows the material to harden and strengthen, so it can be used as intended. The curing time can vary depending on the specific product used and environmental conditions.

Exposed aggregate resurfacing offers several benefits. It can transform weathered and worn-out surfaces into fresh, visually appealing areas. The new layer also gives the surface a fresh wearing course and can be sealed against stains. Additionally, resurfacing can help improve the overall functionality and safety of the surface.

Whether it’s a driveway, patio, or walkway, exposed aggregate resurfacing allows you to breathe new life into your existing concrete surfaces, improving their appearance.

A Second Option: Seeding New Stone

Resurfacing does not have to hide the stone. A decorative overlay is a mixture of cementitious materials installed over an existing concrete slab, as the ACI guide to decorative concrete defines it. For an exposed aggregate look, installers can seed decorative stone into the fresh overlay and then expose it. If your existing aggregate is worn or stained but the slab is sound, ask the installer which route fits it.

Benefits of Exposed Aggregate Concrete

Exposed aggregate concrete offers several benefits that make it a popular choice for various applications. Here are some advantages of exposed aggregate concrete:

1. Aesthetic Appeal

Exposed aggregate concrete showcases the natural beauty of aggregates and stones, creating a visually captivating surface. The exposed aggregates come in various colors, shapes, and sizes, allowing for customization and complementing the surrounding environment. The texture and depth of the exposed stones add depth and character to driveways, patios, and walkways, making them visually appealing and unique.

2. Slip Resistance

Exposed aggregate has a textured surface that gives shoes and tires more grip than smooth or polished concrete, which can help on wet driveways and pool decks. How much grip you get depends on the stone and on how smooth the surface is left, and a resurfacing layer that fills in the texture between the stones reduces it.

3. Durability

Exposed aggregate concrete is a hard-wearing surface because the stone is held in the concrete matrix. The aggregates act as a protective layer, reducing the visibility of surface scratches, scuffs, and signs of wear. That makes exposed aggregate concrete a common choice for high-use areas like driveways and commercial walkways.

4. Low Maintenance

Exposed aggregate concrete needs only routine upkeep, making it a practical choice for homeowners. The textured surface helps to hide dirt, dust, and stains, reducing the need for frequent cleaning. Regular sweeping and occasional pressure washing is usually sufficient to keep the surface looking fresh and well-maintained.

5. Heat Storage

Concrete absorbs heat during the day and releases it slowly after dark, so a sunny slab can stay warm underfoot into the evening.

How to Prepare for a Successful Resurface

Preparing exposed aggregate concrete for resurfacing is a crucial step toward achieving a durable and visually appealing result. Proper preparation gives the overlay the best chance of bonding well and lasting. Here’s a walkthrough of the essential steps to effectively prepare your exposed aggregate concrete for a successful resurfacing project.

1. Assessing the Current Condition

Before you embark on resurfacing, it’s vital to assess the current condition of your concrete. Look for visible damage such as cracks, blisters, or flaking. These indicate the presence of unsound concrete that needs attention before resurfacing can proceed.

It’s not enough to depend on visual inspection alone. Tapping the surface with a hammer and observing the bounce back can help assess the concrete’s soundness. For cracks, a depth evaluation using a crack width ruler is essential to measure their severity. Damaged areas and cracks need to be repaired and allowed to set before the resurfacing can commence.

2. Cleaning the Surface

Once you’ve assessed the condition and addressed any damage, the next step is to clean the surface. A clean surface is crucial for effective adhesion of the resurfacing material. A power washer, particularly one with heating elements and higher pressure settings, is ideal for this task.

Pretreating stains with specific cleaning agents is essential for heavily contaminated areas before conducting pressure washing. Stubborn oil stains and tire marks can be addressed using a combination of high-pressure hot water and a commercial-grade degreaser. For smaller, stubborn stains, a poultice made with a powerful solvent can be effective. A methodical, section-by-section cleaning approach gives a thorough clean, which helps the overlay bond.

3. Ensuring a Dry Workspace

Now, onto the third preparation step: ensuring a completely dry workspace. It might appear trivial, yet it’s critical to the success of your resurfacing project. Overlay products set their own temperature limits, so check the data sheet of the product you are using. One common resurfacer's data sheet, for example, says not to apply unless the dampened surface will stay above 50°F for 8 hours after placement and will not drop below freezing for 24 hours after placement. High humidity can prevent proper drying and should be avoided.

How do you confirm if your concrete surface is sufficiently dry? Moisture meters or plastic sheet tests can help you determine this. Additionally, ensuring that water freely drains from the slab’s surface can prevent potential issues such as vapor pressure expansion. Covering the resurfacing area also aids in keeping the workspace dry, protecting it from environmental moisture.

How to Resurface Exposed Aggregate Concrete

With the preparation out of the way, it’s time to learn the resurfacing process itself. This is a multi-step process that requires careful attention to detail, but when done right, the results are nothing short of transformative.

Let’s walk through these steps on the floor.

1. Applying the Overlay Mix

The first step in the resurfacing process is applying the overlay mix. The mix includes a combination of:

• Cement
• Sand
• Special polymers
• The right proportion of aggregate

These special polymers act like glue, ensuring the mixture binds effectively to the existing smooth surface for a durable, abrasion-resistant texture.

The overlay mix is applied as a thin skim coat, filling in the areas between stones in the exposed aggregate surface to achieve a smoother finish. After the first coat dries completely, which depends on the product, the temperature and the humidity (the data sheet above, for example, says to let the first coat sit undisturbed for 2 to 3 hours, and 1 to 2 hours longer if the surface still dents under foot pressure), a second coat may be applied for floors with significant damage.

2. Smoothing It Out

With the overlay mix applied, it’s time to smooth it out. A squeegee can be employed to apply the overlay mix evenly across the concrete, providing consistent coverage and aiding in smoothness.

Proper smoothing of the overlay mix immediately after application is crucial for reducing the later necessity for extensive sanding. For areas that require additional smoothing after the overlay mix has dried, a rub brick can be utilized to sand the surface for a smoother final finish.

3. Curing Time Is Key

Curing is where the overlay gains strength and durability. Strength keeps building for weeks, but the data sheet sets earlier milestones for when the surface can take traffic.

Keep the curing overlay within the temperature range on the data sheet and protect it from rain and direct sun, which can change how it cures, especially in hot weather. The same data sheet asks for moist curing for 24 to 48 hours, protection from rain for at least 8 hours, and special procedures when temperatures will exceed 90°F. Be aware that environmental conditions can significantly affect the curing time of the overlay mix.

Wait for the time on the data sheet before the surface takes foot or vehicle traffic. One common resurfacer's data sheet, for example, says to wait 6 hours for foot traffic and 24 hours for vehicles.

4. Grinding for Perfection

Next up is grinding. An angle grinder equipped with a diamond cup wheel is used to precisely grind down the surface for the final smoothing of exposed aggregate concrete.

Consistent movement with the angle grinder is necessary to avoid surface gouging and to maintain a uniform finish throughout the exposed aggregate. The same angle grinder, when used gently, can expose the decorative stones within the new surface layer. Grinding concrete releases respirable crystalline silica dust, so control the dust at the tool. For handheld grinders, OSHA's silica standard for construction requires employers to use integrated water delivery (outdoors only) or a shroud with a dust collector, and to add respiratory protection when the work is indoors. The same controls make sense for homeowners.

5. Sealing the Surface

The final step in the resurfacing process is sealing. Sealing can deepen colors and helps keep water and oil out of the surface.

When selecting a sealant, consider silicone, urethane, or acrylic-based options that resist yellowing, dry to a thick coat, and are suitable for future reapplications. Always test a small area before the full application of the sealant to ensure the desired protection and appearance are achieved. After sealing, allow the area to cure for the time on the sealer label.

How to Maintain Your New Surface

Here’s how to maintain your newly resurfaced concrete surface to ensure that it keeps looking its best:

1. Sweeping

Regularly sweeping the surface with a broom or brush with stiff bristles is essential for keeping your concrete surface clean. This removes loose dirt, leaves, and debris that can accumulate on the surface over time. By sweeping regularly, you prevent these particles from scratching or wearing down the concrete. Start from one end of the surface and work your way across, ensuring that you cover the entire area.

2. Washing

Periodically washing the surface with water helps remove dirt, grime, and other substances that may dull its appearance. Using a garden hose or a pressure washer set to a low setting, spray water evenly across the surface. Start from one end and work your way across, allowing the water to effectively rinse away the dirt. Pay special attention to areas with stains or heavy soiling. Avoid using high-pressure washing as it may damage the surface or dislodge the aggregates.

3. Brush thoroughly

For tough stains, gently brush the wet surface with a hard brush: If you encounter stubborn stains on your concrete surface, it’s important to address them carefully. Start by wetting the stained area with water. Then, using a hard-bristle brush, gently scrub the surface in a circular motion.

The goal is to lift the stain without causing damage to the exposed aggregate. Avoid using harsh chemicals or abrasive cleaners, as these can harm the aggregate or the surface. If the stain persists, consider using a specialized concrete cleaner recommended for the specific stain type.

Taking preventative steps can help preserve the appearance and quality of your concrete surface. For example, ensure that vehicles parked on the surface are not leaking oils or other fluids. These substances can stain the concrete and deteriorate the sealant over time. Promptly address any spills or leaks by cleaning them immediately to minimize the chances of staining. Regularly inspect the surface for any signs of damage or wear and address them promptly to prevent further deterioration.

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Should I consider resurfacing my exposed aggregate concrete or replacing it altogether?

If your exposed aggregate concrete has significant damage or structural issues, it may be more practical and cost-effective to replace it altogether. However, if the damage is minor and the concrete is still structurally sound, resurfacing can be a viable option to restore its appearance and functionality. It’s recommended to consult with a professional to assess the condition of your concrete and determine the best course of action.

What can I put over exposed aggregate?

You can put a concrete overlay, stamped concrete, tile or pavers, decorative coatings, or outdoor carpeting over an exposed aggregate concrete surface to achieve a different look or cover the existing surface. These options provide various aesthetics and can be chosen based on your preferences and the desired outcome. It’s recommended to consult with a professional to determine the most suitable option for your specific needs.

What materials do I need to resurface exposed aggregate concrete?

To resurface exposed aggregate concrete, you will need concrete resurfacer/overlay, bonding agent/primer, water, mixing tools (such as a mixing paddle or drill), a trowel or squeegee for application, and any desired tools for texturing or finishing the surface (such as a broom or stamping tools).

Can I change the color or texture of my exposed aggregate concrete during the resurfacing process?

Yes, it is possible to change the color or texture of your exposed aggregate concrete during the resurfacing process. There are various techniques and products available that allow you to achieve different colors and textures for your concrete surface.

For changing the color, you can use concrete stains or dyes that penetrate the surface and provide a new color. These stains or dyes come in a wide range of shades and can be applied during the concrete resurfacing process to achieve the desired color.

How much should I budget for concrete resurfacing?

The cost of concrete resurfacing can vary widely depending on the size of the area, the type of resurfacing product used, and whether you hire a professional or do it yourself. On average, expect to pay between $3 to $10 per square foot.

How can concrete resurfacing transform your space?

Concrete resurfacing can transform your space, that involves applying a new layer of concrete or a concrete-like material over existing surfaces to restore their appearance and functionality. It can dramatically improve the look of driveways, patios, and walkways, making them look new again.

Can I resurface only certain areas of my exposed aggregate concrete, or does it need to be done on the entire surface?

Yes, it is possible to resurface only certain areas of your exposed aggregate concrete instead of the entire surface. This flexibility allows you to address specific areas of concern or make targeted improvements while preserving the existing areas that are in good condition.

Resurfacing specific areas can be cost-effective, especially if the damage or wear is localized. It allows you to focus your efforts and resources on the areas that require attention, rather than resurfacing the entire surface.

However, it’s important to note that the appearance and texture of the newly resurfaced areas may differ slightly from the existing exposed aggregate. Achieving a perfect match can be challenging, particularly if there has been significant color variation or aggregate exposure over time.

To ensure a cohesive look, it’s recommended to consult with a professional who can assess the condition of your concrete, guide you on the best approach, and help you determine the most suitable resurfacing options for the specific areas you wish to address.

National Concrete Polishing resurfaces outdoor slabs such as driveways and pool decks, including the repair and prep work under the new surface. Contact National Concrete Polishing to talk through your slab.