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Paver sealants protect surfaces but can release harmful chemicals into soil and water through leaching, especially in areas like Maryland with its freeze-thaw cycles and heavy rainfall. This article compares four types of sealants – coal tar-based, asphalt-based, acrylic/water-based, and silane/siloxane – focusing on their durability, chemical risks, and environmental impact. Here’s a quick breakdown:
- Coal Tar-Based Sealants: Durable but highly toxic, releasing PAHs that harm soil, water, and wildlife.
- Asphalt-Based Sealants: Safer than coal tar but still leach petroleum compounds over time.
- Acrylic/Water-Based Sealants: Low toxicity and minimal leaching but need frequent reapplication.
- Silane/Siloxane Sealants: Long-lasting, low-impact, and ideal for Maryland’s climate, though more expensive upfront.
For Maryland property owners, selecting the right sealant is crucial for balancing surface protection and minimizing ecological damage. Silane/siloxane options stand out for their durability and reduced chemical risks, making them a strong choice despite higher costs.
1. Coal Tar-Based Sealants
Coal tar-based sealants have raised alarms due to their environmental and health risks, spurring tighter regulations and a growing preference for safer options within the industry.
Chemical Composition
These sealants are packed with polycyclic aromatic hydrocarbons (PAHs) like benzo[a]pyrene, chrysene, and phenanthrene, along with coal tar pitch, refined tar, clay fillers, sand, and additives. Research has shown that coal tar sealants contain much higher levels of PAHs compared to asphalt-based alternatives. The U.S. Environmental Protection Agency (EPA) has labeled many PAHs as probable human carcinogens.
As the sealant deteriorates, these harmful chemicals can become mobile and enter the surrounding environment.
Leaching Risks
Coal tar sealants are known to leach chemicals over time. While PAHs don’t dissolve easily in water, the breakdown of the sealant – caused by freeze-thaw cycles and UV exposure – can release these compounds. According to the U.S. Geological Survey (USGS), runoff from coal tar-sealed surfaces often contains high levels of PAHs.
In areas like Maryland, freeze-thaw cycles lead to small cracks in the sealant, which allow water to seep in during heavy rain. This process carries the released chemicals into storm drains and eventually into larger waterways like the Chesapeake Bay watershed. Additionally, summer heat (with temperatures above 85°F) can increase the sealant’s porosity, further encouraging chemical migration.
This leaching doesn’t just pollute water – it can have far-reaching effects on ecosystems.
Impact on Environment
The release of these chemicals creates a ripple effect of environmental damage. PAHs are bioaccumulative, meaning they build up in the tissues of plants and animals over time. They’ve been found in urban streams, sediments, and aquatic organisms near coal tar-sealed surfaces.
Soil microorganisms, which play a critical role in nutrient cycling, are particularly affected. Studies indicate that soils exposed to coal tar runoff see a decline in beneficial bacteria, potentially disrupting soil health and fertility.
Wildlife, including birds, small mammals, and aquatic species, can ingest or absorb these toxins. Amphibians are especially at risk, as they absorb contaminants directly through their skin, making them highly vulnerable to PAH exposure.
Soil and Stormwater Effects
Coal tar sealants leave a lasting mark on soil, where PAHs bind to organic matter and slowly leach into groundwater. This long-term contamination poses challenges for both soil health and water quality.
Stormwater management systems also struggle to handle runoff from coal tar-sealed surfaces. Elevated PAH levels in runoff can hinder the effectiveness of treatment methods like retention ponds and bioswales. For areas like the Chesapeake Bay, where strict Total Maximum Daily Load (TMDL) limits for PAHs are in place, meeting regulatory standards becomes increasingly difficult. These issues can lead to higher treatment costs for municipalities.
In light of these challenges, many hardscaping professionals in Maryland, including teams from Pro Landscapes MD, are moving away from coal tar-based sealants. Instead, they’re opting for products that are less harmful to the environment and public health.
2. Asphalt-Based Sealants
Asphalt-based sealants are becoming a popular alternative to coal tar products, offering similar protective benefits but with a smaller environmental impact, particularly when it comes to soil and water quality.
Chemical Composition
These sealants rely on a refined asphalt emulsion combined with water, mineral fillers like silica sand or limestone, clay additives, and polymer modifiers to enhance durability. Unlike coal tar-based options, asphalt-based sealants contain significantly lower levels of polycyclic aromatic hydrocarbons (PAHs), which are known for their environmental and health risks. The refining process eliminates many volatile compounds found in raw materials, making the final product safer. To further increase their longevity, most formulations include UV stabilizers and antioxidants, which protect the sealant from sun damage and reduce the frequency of reapplication. This refined composition ensures a safer and more durable product.
Leaching Risks
One of the key benefits of asphalt-based sealants is their lower potential for chemical leaching. Their limited water solubility and slower breakdown process result in fewer harmful substances being released into the environment. In Maryland, where freeze-thaw cycles are common, these sealants perform well by resisting cracking and preventing water infiltration. During the warmer months, they also emit fewer airborne contaminants, as elevated temperatures do not lead to significant chemical volatilization. This means less migration of harmful substances into surrounding soils and air.
Impact on Environment
In Maryland’s diverse climate, the reduced hazardous content of asphalt-based sealants plays a critical role in protecting delicate ecosystems. By lowering PAH levels, these sealants help prevent bioaccumulation in plants and wildlife, reducing disruptions to local ecosystems. Soil microorganisms, essential for nutrient cycling and overall soil health, are less affected by runoff from asphalt-sealed surfaces. Aquatic environments also benefit significantly, as the lower chemical load minimizes risks to fish, amphibians, and other water-dependent species. This is particularly vital in areas like Maryland, where waterways feed into sensitive ecosystems such as the Chesapeake Bay.
Soil and Stormwater Effects
Runoff from asphalt-based sealants carries fewer contaminants, which makes it easier for stormwater systems to manage and reduces long-term impacts on soil and groundwater. Green infrastructure solutions, like bioswales and retention ponds, can handle this runoff more effectively without becoming overloaded with toxic compounds. For municipalities striving to meet the Chesapeake Bay Total Maximum Daily Load requirements, the lower PAH levels in stormwater translate to reduced treatment costs and better compliance with environmental regulations.
Professional hardscaping companies, such as Pro Landscapes MD, frequently recommend asphalt-based sealants to clients who want durable surface protection without the environmental drawbacks of coal tar products. Their combination of reliable performance and reduced ecological impact makes them an excellent choice for both residential and commercial use across central Maryland.
3. Acrylic and Water-Based Sealants
Acrylic and water-based sealants are a go-to option for those looking to balance effective paver protection with environmentally-conscious choices. These sealants have gained traction among homeowners and professionals alike due to their performance and reduced environmental footprint.
Chemical Composition
Water-based acrylic sealants are crafted using synthetic acrylic polymers dissolved in water rather than petroleum-based solvents. The key ingredients include acrylic resins, water as the carrier, and coalescing agents that help the sealant form a durable film quickly. Unlike solvent-based alternatives, these sealants emit fewer volatile organic compounds (VOCs) and hazardous air pollutants. The resulting polymer film is flexible and breathable, allowing moisture vapor to escape while keeping liquid water out. Many formulations also include UV-resistant additives and anti-foaming agents, ensuring a smooth application and long-lasting color stability. This design not only reduces harmful emissions but also minimizes the risk of chemical leaching.
Leaching Risks
Thanks to their water-based composition, these sealants significantly reduce the chances of chemical leaching. Since water serves as the primary medium, there’s minimal migration of residual solvents during application or the product’s lifespan. In areas with heavy rainfall, such as Maryland, these sealants have shown excellent stability, ensuring that stormwater runoff remains largely free of harmful contaminants. Their pH-neutral cured films also help maintain soil chemistry and safeguard plant root systems, even in regions that experience fluctuating temperatures.
Impact on Environment
Water-based acrylic sealants offer several environmental advantages, particularly for soil health. The breathable film they create allows natural gas exchange between the soil and the atmosphere, which helps maintain conditions favorable for beneficial microorganisms. Additionally, their water-based formulation makes them safer to apply, requiring fewer ventilation precautions compared to solvent-based products. This reduced risk benefits not only humans but also local wildlife, plants, and areas where children play or gardens thrive.
Soil and Stormwater Effects
Surfaces treated with acrylic sealants contribute to cleaner stormwater runoff, aligning with stormwater management goals. The inert, breathable film ensures rainwater remains uncontaminated, which is especially important for properties with bioswales or rain gardens. These sealants are well-suited for sensitive watersheds, such as those that feed into the Chesapeake Bay, as they maintain the natural pH and nutrient balance of the soil. By preventing the buildup of salts or other harmful compounds, they support plant health and allow captured stormwater to remain suitable for irrigation.
Many professionals, including the team at Pro Landscapes MD, recommend water-based acrylic sealants for sustainable hardscaping projects. Their ability to provide strong protection, low maintenance, and a reduced ecological impact makes them a popular choice across central Maryland’s varied communities.
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4. Silane/Siloxane and Penetrating Sealants
Silane and siloxane sealants are a greener choice for protecting pavers. Unlike surface coatings, these sealants work from the inside out, offering protection without altering the natural look or breathability of the surface. They dive deep into the paver material, ensuring long-lasting defense while preserving its original appearance.
Chemical Composition
Silane and siloxane sealants rely on silicon-based compounds that bond chemically with the minerals in concrete and natural stone pavers. Silane molecules, being smaller, penetrate deeper into the material, while siloxane molecules provide more surface-level coverage. Many professional-grade products combine both, creating a balance of deep and surface protection.
These sealants are typically formulated with active silicone compounds suspended in water or a mild solvent. As the carrier evaporates, the compounds chemically bond with the paver’s minerals. Unlike surface-forming sealants, they leave no synthetic film behind, which means there’s no risk of peeling or degradation over time.
When exposed to moisture, the silane and siloxane molecules react to form silicone resin networks within the paver’s pores. This creates a water-repellent barrier while still allowing the surface to "breathe", letting vapor escape naturally.
Leaching Risks
One of the standout benefits of penetrating sealants is their minimal risk of leaching. Because they chemically integrate into the paver material, they become a permanent part of the structure within 24–48 hours of application. Once cured, the compounds are immobile, effectively eliminating the chance of leaching.
Even in climates with significant temperature swings, like Maryland’s, these treatments remain stable. The bonds formed between the silicon compounds and the paver substrate hold strong through freeze-thaw cycles, unlike some surface sealants that might release compounds under similar conditions.
Environmental Considerations
These sealants are a solid choice for eco-conscious applications. Their ability to preserve the natural porosity of pavers supports gas exchange between the soil and the atmosphere, which is important for healthy microbial activity. By avoiding the creation of a surface barrier, they also reduce the risk of moisture entrapment, which can lead to issues like efflorescence or material degradation.
This effective moisture management means less frequent reapplication, which further reduces their environmental footprint. Once cured, these treatments are safe for birds, beneficial insects, pets, and nearby plants. They don’t alter soil pH or introduce harmful salts, making them a responsible choice for landscapes.
Soil and Stormwater Benefits
Pavers treated with silane and siloxane sealants can improve stormwater management by reducing surface wear. Untreated pavers often produce dust and chalk that can contaminate runoff, but the water-repellent properties of these treatments help rainwater flow off quickly while maintaining the paver’s breathability. This is especially beneficial for permeable paving systems.
In Maryland’s freeze-thaw climate, these sealants help protect pavers from damage and minimize particulate runoff, all while keeping stormwater pH-neutral. This combination of durability and environmental care makes silane/siloxane treatments an excellent option for sustainable hardscaping projects.
Pro Landscapes MD frequently recommends silane/siloxane sealants for clients who want long-term protection with minimal impact on the environment. These treatments align with their mission to provide sustainable and effective landscaping solutions throughout central Maryland.
Pros and Cons
This section breaks down the practical advantages and disadvantages of each sealant type, helping property owners weigh performance, cost, and environmental considerations.
Coal tar-based sealants are known for their exceptional durability and resistance to weather, offering strong protection against wear and UV damage. However, they come with a significant downside: the presence of PAHs (polycyclic aromatic hydrocarbons), which can leach into the soil and groundwater, posing serious environmental concerns.
Asphalt-based sealants strike a balance between affordability and performance. They provide dependable protection with lower toxicity compared to coal tar products, making them a safer choice. That said, they still carry moderate leaching risks due to their petroleum-based composition, which can gradually seep into surrounding soil.
Acrylic and water-based sealants stand out for being environmentally friendly and easy to apply. They emit minimal odors and reduce health risks for both applicators and nearby residents. The trade-off? These sealants typically require reapplication every 2–3 years, which can lead to higher long-term maintenance costs.
Silane and siloxane penetrating sealants are highly regarded for their eco-conscious design. Once applied, they chemically bond to the paver, reducing leaching while allowing the surface to breathe. Their primary drawback is a higher upfront cost. However, their long lifespan and reduced need for maintenance often justify the initial investment.
| Sealant Type | Durability | Leaching Risk | Environmental Impact | Cost | Reapplication Frequency |
|---|---|---|---|---|---|
| Coal Tar-Based | Excellent (5–7 years) | High | Very High | Low | Every 5–7 years |
| Asphalt-Based | Good (4–5 years) | Moderate | Manageable | Low–Medium | Every 4–5 years |
| Acrylic/Water-Based | Fair (2–3 years) | Low | Low | Medium | Every 2–3 years |
| Silane/Siloxane | Excellent (8–12 years) | Minimal | Very Low | High | Every 8–12 years |
This comparison equips Maryland property owners with the information they need to choose sealants that align with their budget, maintenance preferences, and environmental priorities.
For Maryland properties, the local climate – with its frequent freeze-thaw cycles – adds another layer to consider. Penetrating sealants like silane and siloxane are particularly well-suited to this environment because they allow surfaces to breathe, preventing moisture from becoming trapped. Surface-forming sealants, on the other hand, can trap water, which may expand during freezing and lead to premature damage.
Pro Landscapes MD has noted that clients who initially opt for more budget-friendly options often switch to silane/siloxane products after experiencing the benefits of reduced maintenance and improved environmental safety. For Maryland property owners, where stormwater regulations and freeze-thaw cycles are common challenges, selecting the right sealant is essential for long-term durability and environmental care.
Conclusion
Choosing the right paver sealant means weighing performance, cost, and environmental impact. Sealants vary significantly in how they protect Maryland’s soil and water, making the selection process an important decision for property owners.
Coal tar-based sealants are known for their durability, but their high levels of polycyclic aromatic hydrocarbons (PAHs) make them a poor choice for the environment. With growing concerns about groundwater contamination, these sealants are increasingly seen as unsuitable for responsible property care.
Asphalt-based sealants strike a balance by offering moderate performance with lower toxicity compared to coal tar-based options. However, they still pose risks of petroleum-related leaching over time, which can impact environmental safety.
Water-based sealants are a more eco-conscious choice, offering minimal leaching and immediate benefits for long-term environmental health. That said, they may require more frequent reapplication. On the other hand, silane/siloxane sealants provide longer-lasting, low-impact protection, making them a strong option for those seeking durability and environmental care.
Penetrating sealants stand out for Maryland properties, as they allow pavers to "breathe" while effectively protecting against moisture damage. This feature makes them especially useful in managing the challenges of the local climate.
Investing in environmentally safe sealants not only reduces maintenance costs but also contributes to protecting natural resources. Silane/siloxane products, in particular, offer extended protection cycles compared to water-based alternatives, making them a worthwhile consideration.
Pro Landscapes MD is dedicated to providing sustainable hardscaping solutions tailored to Maryland’s unique climate, helping ensure your pavers remain protected while supporting environmental health.
FAQs
What makes coal tar-based sealants harmful to the environment?
Coal tar-based sealants are dangerous because they carry high levels of polycyclic aromatic hydrocarbons (PAHs) – toxic chemicals that threaten both the environment and human health. When these sealants break down, PAHs can seep into the soil and water, polluting lakes, streams, and groundwater. This contamination puts aquatic life at risk and disrupts delicate ecosystems.
Over time, PAHs from these sealants settle in sediments, creating long-term hazards for wildlife. For humans, exposure to these chemicals can increase the risk of cancer. To avoid such risks, look for sealants specifically designed to reduce chemical runoff and help preserve soil and water quality.
What makes silane and siloxane sealants different from other types in terms of environmental impact and durability?
Silane and siloxane sealants are known for their durability and eco-conscious design. Silane sealants, with their small molecular structure, penetrate deep into surfaces, creating a strong defense against water damage and wear from the elements. This deep penetration helps protect surfaces from cracking and ensures they can withstand tough conditions over time.
Siloxane sealants, in contrast, work by forming a water-repellent layer on the surface. This barrier keeps water out while still allowing the material underneath to breathe, which helps maintain its structural integrity. Both options are made with biodegradable ingredients, which reduce their impact on the environment. These qualities make them a smart, long-lasting solution for safeguarding pavers and other surfaces.
Why do many Maryland property owners choose water-based acrylic sealants even though they require more frequent reapplication?
Many property owners in Maryland lean toward water-based acrylic sealants, largely because they produce lower VOC emissions compared to solvent-based alternatives. This makes them a more environmentally considerate option. Beyond that, these sealants are simple to apply, dry faster, and are less prone to cracking or shrinking. This results in a finish that lasts longer and maintains a consistent look.
Another advantage is their ability to retain their finish with minimal gloss loss, which is especially valuable for outdoor surfaces exposed to Maryland’s unpredictable weather. While they might require reapplication more often, the combination of ease of use and environmental perks makes them a popular choice for homeowners.
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