Why Are My Mastic Asphalt Steps Cracking and How to Fix Them?

If your mastic asphalt steps are cracking, you might worry about safety, looks, and future damage. At Elite Asphalt Services in London, we’re expert mastic asphalt contractors. We’ve fixed thousands of staircases and seen almost every kind of crack, blister, or failure. Many property owners ask us: “Why do my steps crack? Could I have prevented it? What’s the best way to fix it for good?” This guide provides answers to your questions. It uses real-life experiences and practical advice from the field.

Cracks are not just a cosmetic problem. They can let in water, lead to more serious damage, and even cause slips or trips. But with the right knowledge, you can understand what’s happening—and how to solve it properly. To make your steps last for decades, not just a few years, keep reading. Here’s what every homeowner and property manager needs to know.

What is mastic asphalt, and why is it used for steps?

Mastic asphalt is a unique, highly durable material made from bitumen, limestone, and fine aggregates. It’s heated to a liquid state then poured or trowelled onto surfaces, where it cools and sets hard. For steps, mastic asphalt is popular because:

• It creates a completely waterproof seal.

• It’s flexible enough to handle slight movement.

• It provides a smooth, anti-slip finish.

• With proper installation and care, it can last 30–50 years.

In London, many older buildings have mastic asphalt steps, especially those built from the Victorian period onward. But even new builds use it, as it’s considered a premium finish for both appearance and function.

Common Reasons Why Mastic Asphalt Steps Crack

To fix cracks, you must first know why they happen. Based on decades of repairs by Elite Asphalt Services, these are the main causes of mastic asphalt step cracking:

1. Poor Preparation Of The Base

If the concrete or brickwork under the mastic asphalt is not clean, dry, and sound, the asphalt can’t bond properly. Any movement or weakness in the base will eventually crack through to the surface.

2. Thermal Movement

Mastic asphalt expands in hot weather and contracts in cold. If there’s not enough room for movement (for example, no expansion joints), the material can split as it tries to stretch or shrink.

3. Overloading

Steps are often used to carry heavy items—furniture, deliveries, bins. If they were not designed to support this weight, or if the load is dropped hard, the asphalt can crack under the stress.

4. Age And Wear

Even the best-laid mastic asphalt will get brittle after many decades of use. UV rays, frost, and simple foot traffic all take their toll. Old asphalt loses flexibility and is more likely to crack.

5. Water Ingress

If water manages to get under the mastic asphalt, it can freeze and expand in winter. This lifts the asphalt and creates cracks, known as “blowing” in the trade.

6. Poor Installation

Sadly, many cracks are the result of rushed or unskilled work. If the asphalt was not heated to the right temperature, applied too thinly, or not finished with the proper tools, it won’t last.

7. Substrate Movement

If the building settles, or the ground shifts (especially after plumbing leaks), the underlying structure moves. The asphalt, being less flexible, can crack as a result.

8. Incompatible Repairs

Using cement, silicone, or poor-quality bitumen to “patch” mastic asphalt never works for long. These materials expand and contract differently, creating stress points.

9. Chemical Exposure

Some cleaning products, de-icers, or even animal urine can attack the surface, making it brittle and more likely to crack.

Non-obvious insight: In London, tree roots are a hidden cause of cracks. If a large tree is close to your steps, its roots may lift the structure very slowly, causing mysterious cracks that seem to appear overnight.

How To Identify The Type And Cause Of Cracks

Not all cracks are the same. How you fix them depends on their size, direction, and location. Here’s how to diagnose your problem like a pro:

Hairline Cracks

These are thin, surface-level cracks. Usually less than 1mm wide, they often appear due to age, minor movement, or temperature changes. Hairline cracks are not usually urgent but should be sealed to prevent water entry.

Wide Or Deep Cracks

Cracks more than 2–3mm wide or those you can feel with your finger are a bigger concern. They indicate movement or major stress and may mean the base is failing.

Blisters And Bubbles

If you see raised areas or “bubbles” under the surface, water is trapped below. This is called “blowing”. When these burst, they leave holes and cracks.

Edge Cracking

Cracks at the edge of steps often mean the asphalt has separated from the upstand or wall. This is a common water entry point.

Pattern Cracking

A “crazed” or patterned network of fine cracks usually points to old, brittle asphalt. This is common on steps over 25 years old.

Crack Location Table

To help you work out what’s happening, here’s a comparison of common crack locations and what they suggest:

Crack Location	Likely Cause	Urgency
Centre of tread	Thermal movement, overloading	Medium
Edge of step	Poor bonding, water ingress	High
At upstand or wall	Substrate movement	High
Across several steps	Structural movement	Very High
Random hairlines	Age, UV exposure	Low

If you’re unsure, a professional survey from a company like Elite Asphalt Services can pinpoint the problem and prevent costly mistakes.

The Risks Of Ignoring Cracked Mastic Asphalt Steps

It might be tempting to “leave it for now”, especially if the crack looks small. But as specialists, we’ve seen minor cracks turn into major problems, such as:

• Water damage: Water will always find a way through a crack. This can lead to rot, rusting metal, or even internal leaks inside the property.

• Frost damage: When water freezes in a crack, it expands and makes the crack much worse. This is a common cause of rapid failure after winter.

• Trip hazards: Uneven, broken steps are a real safety risk, especially for children or elderly people.

• Accelerated wear: Cracks let in dirt, seeds, and roots. Over time, this breaks down the asphalt faster.

• Costly repairs: Fixing a small crack is quick and cheap. Fixing a collapsed set of steps or underlying structure is far more expensive.

Non-obvious insight: Insurance companies may refuse claims for water or slip damage if your steps are known to be in poor repair. Regular maintenance can protect you legally as well as physically.

How To Fix Cracked Mastic Asphalt Steps: The Right Way

The repair method depends on the type of crack, its cause, and the age of the steps. As a London contractor, Elite Asphalt Services follows these industry best practices:

Step 1: Assess The Damage

Before any repair, check the full length of every step. Look for:

• All cracks, not just the visible ones

• Loose or hollow-sounding areas (tap with a hammer handle)

• Blisters, bubbles, or soft spots

• Damage at joints or edges

Take photos and measure the cracks. This helps track if they are getting worse over time.

Step 2: Clean The Area Thoroughly

All repairs start with a clean, dry surface. Remove:

• Dirt, moss, and debris (use a stiff brush or pressure washer)

• Loose, flaking asphalt (scrape with a chisel if needed)

• Old repair materials (silicone, cement, etc.)

Let the steps dry fully before repair. Moisture under a patch will make it fail.

Step 3: Choose The Right Repair Method

For Hairline Cracks

• Warm the area with a hot air gun (not a blowtorch) to encourage bonding.

• Apply a thin layer of hot mastic asphalt using a small trowel.

• Feather out the edges for a smooth finish.

• Sprinkle with fine sand for grip.

For Wide Or Deep Cracks

• Cut out the crack to create a neat, square-edged slot (10–20mm wide).

• Heat the area to help bonding.

• Pour in new hot mastic asphalt, ensuring it fills the depth.

• Smooth and finish as above.

For Blisters Or Blown Areas

• Cut out the entire blistered area, back to solid material.

• Check the underlying base for wetness or damage.

• If the base is wet, let it dry completely. If it’s broken, repair with new concrete.

• Prime the area with bitumen primer.

• Lay new hot mastic asphalt in layers.

• Finish and sand for slip resistance.

For Edge Or Upstand Cracks

• Carefully remove loose asphalt at the edge.

• If the upstand has moved, repair or rebuild it first.

• Prime both step and upstand.

• Install a special angle fillet (a sloped strip) for waterproofing.

• Apply new mastic asphalt, making sure it laps up the upstand by at least 50mm.

For Patterned/crazed Cracking

If the whole surface is “crazed” or brittle, patching won’t work. The best solution is to overlay with a new 20mm layer of mastic asphalt, after repairing any base defects.

Step 4: Finishing And Curing

• Sprinkle the final surface with sand or decorative grit while still hot.

• Avoid walking on new repairs for 2–4 hours, or longer in cold weather.

• Keep heavy objects off the steps for at least 24 hours.

Step 5: Check For Recurrence

Monitor the repaired area over the next few weeks. If cracks reappear quickly, the underlying problem may not be fixed (such as ongoing movement or leaks).

Repair Method Comparison Table

Here’s a summary comparing the methods for each crack type:

Crack Type	Repair Method	Longevity	Typical Cost (£)
Hairline	Surface patch	5–10 years	£100–£175
Wide/Deep	Cut out & replace	10–20 years	£175–£350
Blisters	Full area replacement	20+ years	£300–£900
Edge/Upstand	Fillet & overlay	15–25 years	£200–£500
Crazed	Full overlay	30+ years	£600–£2,000

Note: Costs are rough estimates for domestic steps in London (2026), and may vary.

Materials And Tools Needed For DIY Repairs

If you’re confident with basic building work, small cracks can be tackled by a skilled DIYer. You will need:

• Mastic asphalt (available in blocks, must be heated to 210–230°C)

• Bitumen primer

• Small trowel and bucket

• Hot air gun or industrial heat gun

• Sand or fine grit for finishing

• Safety gloves, goggles, and mask

Warning: Melting asphalt is very hot and can cause severe burns. Always wear PPE and never use gas torches indoors or near flammable materials. For anything larger than a hairline crack, or if you’re unsure, it’s safer to call a professional like Elite Asphalt Services.

When To Call A Professional Contractor

For many repairs, experience matters. Call a specialist if:

• The crack is wider than 5mm or runs across several steps

• There’s evidence of water under the asphalt

• The steps move when stepped on

• You see blisters, bulges, or sinking

• The surface is over 25 years old and looks brittle

• The steps are used for public access (legal safety requirements apply)

Professional contractors have access to high-grade materials, industrial heaters, and can guarantee a seamless, long-lasting finish. At Elite Asphalt Services, we also provide free surveys and written guarantees on repairs.

Tips To Prevent Future Cracks In Mastic Asphalt Steps

Prevention is always better than cure. Here’s how to keep your steps crack-free for decades:

• Clean regularly: Remove moss, leaves, and dirt. Organic debris holds water and speeds up deterioration.

• Inspect after winter: Freeze-thaw cycles are harshest in London. Check every spring for new cracks.

• Repair promptly: Small cracks can be sealed cheaply. Delaying allows water in and makes repairs more costly.

• Avoid harsh chemicals: Do not use de-icing salts or acidic cleaners. They break down the binder in asphalt.

• Control heavy loads: If you must move furniture or bins, use boards to spread the load and prevent point impact.

• Maintain upstands: The vertical sides should always be well-bonded. If you see gaps, call for repair.

• Check drainage: Make sure water runs off steps and doesn’t pool. Blocked drains or gutters can cause hidden leaks.

• Trim nearby trees: Roots and falling branches can cause or accelerate damage.

• Consider sealing: On older steps, a professional surface sealer can add extra protection from water and UV.

Non-obvious insight: Many London homes were built with “cold” steps—uninsulated and exposed on all sides. Adding insulation under new mastic asphalt not only prevents cracking from temperature swings but also makes the entrance warmer and drier.

How To Choose The Right Contractor For Mastic Asphalt Repairs

Not all companies are equal. Here’s what to look for when hiring:

• Experience: Ask how many similar repairs they’ve done and for references or case studies.

• Accreditation: Look for membership in the Mastic Asphalt Council or similar trade bodies.

• Guarantee: Good contractors offer at least a 5–10 year guarantee on step repairs.

• Materials: Insist on high-quality, UK-sourced mastic asphalt.

• Insurance: Make sure they carry public liability insurance.

• Aftercare: Will they return for follow-up checks or if problems recur?

Elite Asphalt Services, for example, has over 30+ years’ experience in London, uses only top-grade materials, and stands behind every repair with a written warranty.

Case Study: Repairing Victorian Mastic Asphalt Steps In Central London.

A recent project in Bloomsbury involved a set of Victorian-era steps serving four flats. The owners noticed hairline cracks, which quickly turned into wide splits after a cold winter. Our survey found:

• Poor repairs with cement had failed, letting water in

• The concrete base had broken down in two places

• The upstand had separated from the wall

Our solution:

• Cut out all failed areas, including old patches.

• Repair the base with new, reinforced concrete.

• Prime and lay a new 20mm mastic asphalt overlay, including fillets at all edges.

• Sand-finish for slip resistance.

The result: a seamless, watertight set of steps, guaranteed for 20 years. The owners commented on the improved appearance and no more damp problems inside their basement flat.

Real-world Data: Average Lifespan And Repair Frequency

Mastic asphalt is famous for its durability. Here’s what we see as contractors:

Step Age (Years)	Typical Condition	Repair Needed
0–10	Like new	None/cleaning
10–20	Minor hairline cracks	Surface sealing
20–30	Some wider cracks, edge wear	Cut-out repairs
30–50	Crazing, blisters, leaks	Overlay or full renewal

With good care, mastic asphalt steps outlast most alternatives, including concrete, stone, and tiles.

Should You Overlay Or Replace Your Steps?

If cracks are localised, repairs are usually enough. But if the whole surface is old, brittle, or leaking, an overlay or complete renewal may be better value. Here’s what we advise:

• Overlay: If the base is sound and the steps are not moving, a 15–20mm mastic asphalt overlay seals all cracks and gives a fresh finish. Costs less than full replacement.

• Full replacement: If the base is broken, the steps are sinking, or there are repeated leaks, it’s best to strip everything back to the base and rebuild.

Pro tip: A proper overlay can add another 20–30 years of life to your steps, with less disruption and cost than a rebuild.

Legal And Safety Considerations For Public Access Steps

If your steps are used by the public (for shops, offices, or communal entrances), you have extra responsibilities:

• Slip resistance: Surfaces must meet British Standard slip ratings. Sanded mastic asphalt easily achieves this.

• Trip hazards: Cracks or unevenness over 4mm can be considered a “dangerous defect”.

• Accessibility: Steps should be uniform in height and depth.

• Maintenance records: Keep notes of inspections and repairs for legal protection.

Always use a professional, insured contractor for public access steps to avoid liability.

Reach out to our team for support or inquiries about Why Are My Mastic Asphalt Steps Cracking and How to Fix Them?

If you’re in the London area and want advice or a free survey, Elite Asphalt Services is ready to help. Don’t let a small crack become a big headache—invest in quality repairs now, and your steps will look great and stay safe for years to come.

All You Need to Know

What’s The Difference Between Mastic Asphalt And Regular Asphalt?

Mastic asphalt is much denser and contains more bitumen, making it waterproof and very durable. Regular asphalt (used for roads) is more porous and not suitable for steps or waterproofing.

Can I Use A Cold-applied Patch For Mastic Asphalt Cracks?

Cold-applied bitumen or repair tapes are only a short-term fix. They rarely last more than a year on steps. For a permanent repair, hot-laid mastic asphalt is needed.

How Long Does A Professional Mastic Asphalt Repair Take?

Most small repairs can be done in a single day. Larger overlays or full renewals may take 2–3 days, plus drying time. The area can usually be walked on after 4–6 hours.

Is It Worth Overlaying Old Asphalt Steps, Or Should I Always Replace Them?

If the base is sound and there’s no major movement, overlaying with new mastic asphalt is an excellent solution—adding decades of life at a lower cost than full replacement.

Where Can I Find Official Guidance On Mastic Asphalt Standards?

For technical standards, visit the Mastic Asphalt Council’s technical guidance. This resource provides in-depth details on installation, maintenance, and repair.

Cracked mastic asphalt steps are a common issue, but with the right knowledge and approach, they’re also one of the most straightforward to fix. Acting early, using correct materials, and getting expert help when needed can save you money and stress.