How to Clean Outdoor Plaster

Cleaning outdoor plaster effectively involves a combination of preparation, appropriate cleaning methods, and targeted stain removal to restore its appearance and prolong its life.

Preparing Your Plaster for Cleaning

Before you begin cleaning, proper preparation is crucial to ensure safety and protect your property.

Clear the Area: Move any furniture, plants, or decorative items away from the plaster wall to prevent damage and give you unobstructed access.
Protect Surroundings: Cover nearby windows, doors, electrical outlets, light fixtures, and delicate landscaping with plastic sheeting and painter's tape to shield them from water and cleaning solutions.
Inspect the Plaster: Check for any cracks, loose sections, or existing damage. Address these issues before cleaning, as water pressure can exacerbate them. For guidance on repairs, consult a plaster repair guide.
Gather Tools: Collect your chosen cleaning tools and solutions, ensuring you have everything readily available.

Effective Methods for Cleaning Outdoor Plaster

The most suitable cleaning method often depends on the type and severity of the dirt.

1. Pressure Washing: A Powerful Solution

High-pressure cleaners are an ideal and established standard for plaster facade cleaning, offering exceptional results, especially for persistent grime. They are particularly effective at removing dust and soot that has settled into the porous, rough surfaces characteristic of rendered walls.

Benefits of Pressure Washing:

Efficiency: Cleans large areas quickly.
Deep Cleaning: Penetrates porous surfaces to dislodge embedded dirt, dust, and soot.
Versatility: Effective against a wide range of pollutants, from general grime to heavy atmospheric deposits.

Tips for Pressure Washing Plaster:

Start Gentle: Always begin with the lowest pressure setting and a wide-angle nozzle (e.g., 25-degree or 40-degree) to avoid damaging the plaster. Gradually increase pressure if needed.
Maintain Distance: Hold the nozzle at least 12-18 inches away from the surface. Too close can strip paint, chip plaster, or force water into cracks.
Consistent Motion: Use smooth, overlapping strokes, working from top to bottom to prevent streaking.
Pre-Wet: Lightly spray the plaster with water before applying any cleaning solutions to help them spread evenly and prevent drying too quickly.
Rinse Thoroughly: After applying and allowing any cleaning solution to dwell, rinse the plaster meticulously from top to bottom until all residue is gone.

2. Manual Cleaning for Lighter Dirt

For lighter dirt, smaller areas, or delicate plaster, manual cleaning with a soft brush or sponge might be preferred.

Steps for Manual Cleaning:

Wet the Surface: Dampen the plaster with a garden hose.
Apply Cleaning Solution: Mix a mild, all-purpose cleaner or a solution of warm water and a few drops of dish soap. For tougher dirt, specialized outdoor plaster cleaners are available. Always follow product instructions.
Scrub Gently: Use a soft-bristled brush or a non-abrasive sponge to scrub the plaster in small sections. Avoid harsh scrubbing that could damage the surface.
Rinse: Thoroughly rinse the area with a garden hose, ensuring all soap residue is removed.

3. Specialized Treatments for Specific Stains

Different types of stains require specific approaches for optimal removal.

a. Mold, Mildew, and Algae

These biological growths thrive in damp, shaded areas.

Solution: A mixture of one part bleach to three parts water, or a commercial mold and mildew remover (e.g., bio-degradable mold cleaner).
Application: Apply the solution to the affected areas, allow it to sit for 10-15 minutes (or as per product instructions), and then scrub gently with a soft brush before rinsing thoroughly. For large areas, a pressure washer can be used with the appropriate cleaning solution.

b. Dirt and Grime

General atmospheric dirt, dust, and pollen are common issues.

Solution: Mild detergent and water, or an all-purpose exterior cleaner. Pressure washing is highly effective for these.
Application: Apply the solution, let it dwell, and then rinse or pressure wash.

c. Soot and Carbon Deposits

From fireplaces, grills, or air pollution, soot can deeply stain porous plaster.

Solution: Pressure washing, as highlighted, is exceptionally effective for removing soot that has settled into porous, rough plaster. For very stubborn spots, a specialized degreaser or alkaline cleaner might be needed.
Application: Use a pressure washer carefully with an appropriate cleaner.

Safety Precautions

Always prioritize safety when cleaning outdoor plaster:

Wear safety glasses to protect your eyes from splashes and debris.
Wear gloves to protect your hands from cleaning chemicals.
Wear appropriate clothing and non-slip footwear.
Ensure good ventilation if using strong chemicals.
Test any cleaning solution in an inconspicuous area first to ensure it doesn't discolor or damage the plaster.

Maintenance for Lasting Cleanliness

Regular maintenance can significantly extend the period between deep cleans:

Routine Rinsing: Periodically rinse your plaster walls with a garden hose to prevent dirt and dust buildup.
Trim Foliage: Keep plants and shrubs trimmed away from plaster walls to improve air circulation and reduce dampness, which discourages mold and algae growth.
Address Leaks: Fix any roof, gutter, or pipe leaks promptly to prevent water stains and biological growth.
Apply Sealant (Optional): Consider applying a breathable, clear sealant to your plaster after cleaning to help repel water and dirt, making future cleaning easier. Consult a building materials expert for suitable products.

By following these methods, you can effectively clean and maintain your outdoor plaster, preserving its aesthetic appeal and structural integrity for years to come.