After winter, outdoor hardscaping materials such as stone, brick, and pavers often need some attention. Leaves, mildew, snow, and other debris can leave unsightly stains on these surfaces. Below, we explore effective methods for cleaning various hardscape materials, drawing on expert advice from mason Mark McCullough. As demonstrated, masonry cleaning can rejuvenate your stonework, restoring its natural beauty and extending its life.
About Hardscape Stains
Various stains can mar the appearance of your hardscape:
- Algae: This green growth is common on stone surfaces and, while harmless, can be unsightly and may indicate excessive moisture.
- Leaf stains: When leaves decompose on porous stone surfaces, they can leave behind stubborn brown or yellow marks that penetrate the stone’s surface.
- Masonry runoff: When minerals from mortar or concrete leach onto surrounding surfaces, they leave white or yellowish deposits, impacting the aesthetic appeal.
- Mildew: Often appearing as black spots, especially on bluestone, mildew thrives in damp, shaded areas and can cause slip hazards.
- Rust: Metal furniture or decorations can leave orange-brown stains on stone or concrete, sometimes requiring specialized treatments for removal.
Factors Affecting Stain Formation
Several factors contribute to stains on hardscape materials. Recognizing them can help in treatment and prevention.
- Porosity: More porous stones such as limestone absorb more moisture and contaminants.
- Moisture: Frequent rainfall or irrigation promotes algae and mildew.
- Shade and sunlight patterns: Areas in shade remain damp longer, fostering mildew.
- Proximity to trees and plants: Organic material and sap from plants can stain surfaces.
- Use of deicing salts in winter: Salts can penetrate the stone, leading to efflorescence and damage.
Hardscape Cleaning Supplies
To clean your hardscape effectively, you’ll need an assortment of supplies to tackle various stain types and materials.
- Clean water
- Garden hose
- Gloves
- Safety glasses
- Stiff bristle brushes
- Stone cleaner or masonry detergent
- Washing tubs (for smaller stones)
Choosing the right cleaner for your specific stone type preserves its integrity while removing stains.
Pro Tip: Mark, a This Old House masonry expert, breaks down the key cleaning agents homeowners should know: “First off is muriatic acid. It may not be a candidate. Why? Because it’s probably too strong. That’s why you see the gloves and the glasses and the long-handle brushes. Then we have vinegar. It’s really specific to one stain that is common with masonry. That’s called efflorescence. This is the bleach. This is the stuff that is most commonly used on the mold, the mildew, and the algaes.” He also recommends an all-purpose cleaner, which handles what all three specialty products do individually.
Safety Precautions
Safety is paramount when handling cleaning chemicals. Improper use can result in damage to the material or health risks.
- Always wear protective gloves and safety glasses to protect your skin and eyes from harsh chemicals.
- Keep cleaning products out of reach of children and pets, and store them safely when not in use.
- Never mix different cleaning products, as this can create toxic reactions.
- Read and follow all manufacturer instructions carefully for each product.
- Work in a well-ventilated area to avoid inhaling fumes.
Pro Tip: Certain cleaners can cause serious damage to specific stone types. According to This Old House Magazine, you should never use anything acidic—even seemingly harmless vinegar—to clean marble, as it can dissolve and etch the stone’s top layer. The same goes for granite: acidic cleaners can eat away at the surface. And avoid chlorides, like bleach, on metal-adjacent surfaces, as they can cause corrosion.
Cleaning Techniques for Hardscape Materials
Different hardscape materials require specific cleaning approaches. You must match the technique to the material to prevent damage.
Cleaning Limestone
Limestone is a soft, porous stone that requires gentle cleaning. Its sensitivity means it can easily be etched by harsh cleaners.
- Prewet the limestone surface thoroughly with water to prevent absorption of the cleaner.
- Apply a limestone-specific cleaner with a soft brush to avoid scratching.
- Allow the cleaner to sit for a minute but not too long to avoid damaging the stone.
- Rinse thoroughly with clean water to remove any residue.
- Repeat if necessary for stubborn stains, being careful not to over-scrub.
Pro Tip: Fred M. Hueston, director of the National Training Center for Stone and Masonry Trades, explains why limestone is so vulnerable to staining: “Granite, marble, and limestone consist of interlocking mineral crystals with pores between them. So spills soak into unprotected stone in just 15 to 20 minutes for granite, and 30 minutes to an hour for marble and limestone.” This is why prewetting the surface before cleaning is so critical—it fills those pores with clean water first.
Cleaning Bluestone
Bluestone is more resistant to harsh chemicals but still requires care to avoid damage to its finish.
- Wet the bluestone surface with water to prepare it for the cleaner.
- Apply a suitable stone cleaner or masonry detergent formulated for bluestone.
- Scrub gently with a stiff brush, letting the cleaner do most of the work.
- Rinse thoroughly with clean water to avoid buildup.
- For mildew stains, you may need to repeat the process to fully eradicate them.
Pro Tip: Mark, a This Old House masonry expert, advises always doing a test area first: “We’re always going to want to do a test area. That way we can make sure the cleaner doesn’t discolor the bluestone, ruining the entire patio.” Apply a small amount of your cleaning solution to an inconspicuous spot and let it dwell for 30 seconds to a minute before evaluating the results.
Cleaning Brick
Brick’s durability allows for more rigorous cleaning than softer stones such as limestone.
- Wet the brick surface thoroughly before applying any cleaner.
- Apply a masonry cleaner suitable for brick, ensuring it penetrates the grooves.
- Scrub with a stiff brush, focusing on stained areas to lift embedded dirt.
- Rinse completely with clean water, ensuring no cleaner residue remains.
- For tough stains, a second application may be necessary to fully remove discoloration.
Advanced Hardscape Cleaning Techniques
For particularly stubborn stains or large areas, more advanced cleaning methods may be necessary. These techniques are typically effective when traditional methods don’t work.
Pressure Washing
Pressure washing can be effective for cleaning large hardscape areas, but it must be done carefully to avoid damaging the surfaces.
- Use a pressure washer with the appropriate pounds per square inch (PSI) for your hardscape material, typically starting low and adjusting as needed.
- Begin with a wide nozzle and test in an inconspicuous area to ensure it won’t damage the surface.
- Keep the nozzle moving to avoid etching patterns into the stone or concrete.
- Use a detergent attachment for stubborn stains, ensuring the detergent is compatible with your material.
Pro Tip: Pro refinisher Erich Specht cautions that even at a low setting, pressure washers “expel water at a velocity that can not only splinter wood but shatter glass.” He suggests you “set the washer at no higher than 3,000 pounds per square inch with a 40-degree tip, or follow the manufacturer’s recommendations.” Keep the head moving, use long, smooth strokes when working over a surface, and stay away from electrical fixtures and windows.
Chemical Treatments
For certain stains, specialized chemical treatments may be necessary. Always ensure compatibility with your material before applying these treatments.
- You can use efflorescence cleaners for white, powdery deposits that can detract from your stone’s finish.
- Try organic stain removers for leaf and algae marks, allowing the natural color of the stone to show through.
- Rust removers are made for metal stains that penetrate the surface and require deeper cleaning.
Always test these products in a small, hidden area before applying them to the entire surface to prevent unintended damage.
Maintaining Clean Hardscape
Once you’ve cleaned your hardscape, regular maintenance helps your stones last longer and look good.
Regular Maintenance Tips
A few simple steps can help preserve your hardscape’s appearance, making cleaning less frequent and burdensome.
- Apply a sealer to protect porous stones and enhance their natural beauty.
- Address spills and stains promptly to prevent them from setting in.
- Rinse surfaces periodically with a garden hose to remove surface contaminants.
- Sweep or blow leaves and debris regularly, especially after storms.
- Trim nearby vegetation to reduce organic debris falling onto your hardscape.
Preventative Measures
Taking proactive measures can minimize future staining and make cleaning easier, preserving your hardscape investment.
- Consider using mats or rugs in high-traffic areas to protect against wear and tear.
- Install proper drainage to reduce standing water, which can lead to mold and mildew growth.
- Use furniture pads under metal objects to prevent rust stains from forming.
