Quick Answer
The direct answer is good, but specifying that the 'black stuff' can also be black algae (which is more common on patios than black mold) would be a minor improvement. The cost, while a good starting point, might be a little low for more extensive professional cleaning. Suggesting a range for the 'afternoon of scrubbing' cost to account for cleaner concentration and tool needs might be helpful too.
Common Symptoms
Possible Causes
Step-by-Step Diagnosis
Step 1
Visually identify the type of growth. Is it slimy green (algae), fuzzy green (moss), or black spots (mold)?
Step 2
Assess the environment. Note any large trees, buildings causing shade, or nearby downspouts dumping water onto the area.
Step 3
Perform a water test. Pour a bucket of water on the hardscape and see if it runs off or pools in low spots, which indicates a drainage problem.
Step 4
Identify the hardscape material. Is it concrete pavers, natural stone like flagstone or limestone, or dense porcelain? This dictates the safe cleaning method.
Step 5
Perform a gentle scratch test with a fingernail or plastic scraper. If the growth comes off easily, it's superficial. If discoloration remains, it's a deeper stain.
DIY vs Professional Costs
| Repair Type | DIY Cost | Professional Cost | Time Required |
|---|---|---|---|
Basic Scrub with Commercial Cleaner | $30 - $60 | N/A | 2-4 hours |
DIY Pressure Washing | $75 - $150 (for rental) | N/A | 3-6 hours |
Professional Cleaning (Pressure Wash & Treatment) | N/A | $250 - $800+ | 4-8 hours |
Professional Clean, Re-Sand & Seal | N/A | $750 - $3,000+ | 1-3 days |
When to Call a Professional Concrete
- When the growth is extensive, covering a very large area that would be overwhelming to a DIYer.
- If your hardscape is made of expensive or delicate natural stone like travertine, limestone, or slate that can be easily damaged.
- When the problem returns quickly after you've already cleaned it yourself, indicating a more serious underlying issue like poor drainage.
- If you don't own or feel comfortable using a pressure washer, and the job requires more power than just a hose and brush.
- When the surface is dangerously slippery and you need the problem solved quickly and effectively for safety reasons.
Prevention Tips
- Regularly use a leaf blower to clear off leaves, dirt, and other organic debris before it can decompose.
- Trim overhanging tree limbs and shrubs to allow more direct sunlight and air circulation to dry the surface.
- Apply a quality penetrating sealer every 3-5 years (for concrete/natural stone) to reduce water absorption.
- Address any drainage issues. This might mean re-grading the area or installing a channel drain to carry water away.
- Apply a preventative 'spray and forget' cleaner like Wet & Forget once or twice a year to keep growth from starting.
Frequently Asked Questions
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