Experts in Concrete Patio structural solutions

Why Concrete Patios Crack Around Drain Covers or Manholes

If you’ve noticed cracks forming around a manhole or drain cover in your patio, you’re not alone. These access points are among the most common areas for concrete failure, and they often worsen with time if ignored.

In this article, we’ll explain why these areas are so vulnerable, what typically causes cracking, and how to fix or prevent structural issues around drain chambers in domestic patios.

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Why Cracks Form Around Drain Covers in Concrete Patios

Manholes and drain access points are built-in weak spots, and if they’re not properly installed or reinforced, the surrounding patio concrete often pays the price.

Inadequate Structural Support

Drain covers are usually inserted into the concrete after the chamber is installed below. If the area around the frame isn’t reinforced or properly supported, pressure from foot traffic, weather, or soil movement can cause the surrounding concrete to flex and eventually crack. This is especially true if the patio is laid directly over loose ground or poorly compacted backfill around the chamber.

Thermal Expansion and Movement

Concrete expands and contracts with changes in temperature. Metal drain covers expand at different rates than concrete, and without an expansion gap or flexible seal, the rigid contact between materials causes stress points. These small, repeated shifts can lead to cracking around the frame, especially in colder climates or patios that get full sun exposure during the day.

Poor Joint Detailing

A drain cover should always be integrated with the concrete using proper control joints or flexible filler to allow movement. If concrete is poured tightly up to the edge of a plastic or metal chamber without this buffer, the rigid boundary can fracture under pressure. Joint failure or missing sealant allows moisture in, freezes it in winter, and expands the cracks even further.

How to Repair and Reinforce Drain Cover Cracks

Cut and Patch the Damaged Area

Use a concrete saw or angle grinder to cut out a neat square around the crack or failed edge.
Clean the sub-base and refill with compacted aggregate or fresh bedding material.
Pour new concrete with proper edge bonding, ensuring the patch is flush with surrounding areas.

Install an Access Frame with Reinforcement

If the original drain frame is unstable, install a new recessed or decorative access frame with reinforced concrete surround.
Use steel mesh or fibre-reinforced concrete to provide added strength at the weak point.
Allow for a 10mm expansion joint between the cover and patio surface, filled with flexible sealant or compressible filler.

Prevent Future Movement

Ensure the sub-base beneath the manhole area is fully compacted and not loose from previous excavation.
Improve drainage or runoff if water is collecting near the area, this prevents washout and frost movement.
Check annually for signs of movement or hairline cracks to treat early with joint sealant.

Frequently Asked Questions

It’s possible, but not ideal without an expansion gap. Pouring concrete directly up to a metal or plastic frame can lead to cracking unless joints or sealant are used to manage movement.

This often happens if the chamber or bedding beneath has settled or wasn’t compacted correctly. Rebuilding the support base and resetting the cover flush is often required.

You can replace the lid or insert if it's a standard size, but for cracked concrete around the frame, it's best to hire a professional to ensure structural integrity is maintained.

Yes, applying a flexible outdoor sealant helps prevent moisture ingress and allows for expansion. This can extend the life of both the patio and the frame itself.

Yes, recessed covers allow for a neater, flatter finish and let you inset paving or concrete inside the lid, making it more visually cohesive and less prone to cracking at the edges.