Experts in Concrete Patio installation

Does Your Patio Smell Damp or Musty? Causes & Fixes

A damp, musty smell around your patio isn’t just unpleasant, it could be a sign of deeper issues like poor drainage, waterlogging, or hidden algae and mould. If left untreated, these can damage the surface, affect indoor air quality, and reduce the lifespan of your patio.

In this guide, we explore the common reasons patios develop musty odours and what you can do to fix and prevent them, especially in the damp UK climate.

Free quote More topics

What Causes a Musty or Damp Smell on Patios?

Persistent smells outside your home are usually due to moisture retention, poor airflow, or organic growth. These are the most common reasons your patio may develop a musty odour.

Trapped Moisture Under Furniture or Planters

When garden furniture, plant pots, or rugs sit on the patio for long periods, they trap moisture underneath, especially if the concrete is unsealed or already damp. Over time, this creates a micro-environment perfect for mould and mildew to grow, resulting in a musty smell. Regularly moving furniture and elevating planters can help your surface breathe and stay dry.

Inadequate Drainage or Standing Water

A patio that doesn't drain properly will retain moisture, particularly along joints, edges, or low points. Pooled water seeps into the slab and sub-base, promoting bacteria and fungal growth below the surface. If this water isn’t given a way out, the damp smell will linger, even in dry weather. Drainage channels or gravel strips are essential to solve this long term.

Algae, Mould or Moss Growth

Damp, shaded patios, especially those facing north or surrounded by fencing, are perfect environments for algae and mould. These organisms not only cause slippery surfaces, but they also emit an earthy, stale smell. Algae thrives where water lingers, and if left untreated, can stain and degrade concrete over time.

Organic Debris Buildup

Leaves, bark, grass clippings, or soil left on the patio surface can decay when wet, producing strong musty or rotting smells. This is especially true in autumn when gardens are messier and patios aren’t cleaned as often. Organic buildup also feeds mould and algae, compounding the problem.

Lack of Airflow and Sunlight

Even with proper drainage, a patio that sits in constant shade and has little airflow will struggle to stay dry. Moisture lingers longer, giving moss, mould, and odours time to build up. Areas close to fences, outbuildings, or enclosed gardens are particularly at risk of remaining damp for long periods, especially during autumn and winter.

How to Remove Musty Patio Smells and Prevent Them

Clean Thoroughly and Regularly

Use a stiff brush and patio cleaner or mild bleach solution to scrub away any visible algae, dirt, or organic matter.
Pressure wash the surface if needed, focusing on joints, corners, and high-traffic areas where buildup occurs.
Rinse and allow the patio to fully dry before replacing furniture or planters.

Improve Drainage and Airflow

Add drainage channels or gravel borders to help water escape rather than pool near your walls or base.
Keep furniture slightly elevated and move it regularly to prevent water-trapping underneath.
Trim back bushes or fencing to allow sunlight and airflow to naturally dry the surface faster.

Seal the Patio Surface

Apply a breathable, weatherproof sealant to reduce how much water penetrates the surface.
Sealed patios dry faster, are easier to clean, and are far less likely to develop musty smells over time.
Reapply every 2–3 years for maximum effectiveness in UK weather conditions.

Frequently Asked Questions

This is usually caused by trapped moisture, algae, or decaying organic material like leaves or mulch. Poor drainage and shade can make this worse. A deep clean and seal can help eliminate the smell.

Yes. A sealed patio repels moisture and organic buildup, helping prevent mould and algae from growing. It also allows the surface to dry faster, which limits the conditions that cause odours.

Bleach can be used in diluted form to kill mould and algae, but it should be rinsed thoroughly and used carefully to avoid damaging surrounding plants. Eco-friendly patio cleaners are a safer alternative for regular use.

Persistent odours may indicate deeper moisture problems under the surface or within the sub-base. In such cases, drainage improvements or resurfacing might be necessary to permanently solve the issue.

In large amounts, mould and algae can affect air quality and become a slip hazard. While generally not dangerous outdoors, they should be cleaned regularly to keep your patio safe and fresh.