When floor joints go wrong

Floor joints are a necessary but problematic part of a warehouse floor. Without them, the large expanse of concrete would soon crack after the floor was first poured. Yet with them, warehouse owners and operators face the issues of joint maintenance, damage and replacement. Steve Swan of Permaban explains why floor joints are needed and what to do when damage occurs.

Construction joints in the floor are used to control the shrinkage of the concrete while it cures, caused by the evaporation of water in the concrete. When a large expanse of concrete shrinks, the forces in the concrete literally pull the slab in different directions, causing cracks. Adding floor joints in strategic places controls those forces by creating planned artificial breaks.

The different types of floor joint

Typically in a warehouse floor there will be metal armoured joints, laid in a grid pattern on the ground before the concrete is poured. These joints have two sides which are pulled apart as the concrete shrinks. The two sides are connected by dowels, to ensure stability and good load transfer across the whole slab. These joints stay in the floor permanently, and defend the edges of the concrete from damage once the building is in use.

In between the armoured joints are often ‘saw-cut’ joints – narrow joints a few millimetres wide in the surface to provide extra points of control. These are usually filled with a sealant to support the edges.

Why straight joints fail

Where MHE crosses a straight joint at 90?, the impact on the joint, vehicle and driver can be severe, and this is exacerbated where small hard vehicle wheels are used.

It has been traditionally thought that the thick steel top strips on straight armoured joints would defend the joint. However, in practice the impact energy actually passes unabated through the steel, and thus the concrete behind the joint can still often suffer damage. Once damage has occurred, it will only get worse until it is repaired.

The cost of a failing joint

A damaged floor joint is ‘costly’ to a warehouse owner or operator in several ways:

• the cost of the joint repair itself

• the cost of disruption to smooth operations while the floor is being repaired

• the cost of damage to the vehicle, which can be caused by jolting across a damaged joint

• the cost of health and safety and staff absenteeism if MHE operatives suffer from back problems caused by repeatedly jolting across a damaged joint

Focusing solely on the repair cost ignores these other three very significant costs. Repairing a joint more than once risks multiplying the costs in these other areas too.

Repair options

When a straight joint has failed there is no choice but to remove it and repair the area. Traditional approaches include:

a) a DIY repair – chipping out damaged concrete from behind the joint and filling the gap with a repair mortar or screed. This is often the first approach, undertaken by in-house maintenance staff. While initially quick and easy, this type of repair deals with the symptoms, but not the cause. Once the area is brought back into use, the damage will soon be repeated.

b) replacing a straight joint with another straight joint. When a DIY repair has failed, a more serious repair is often needed, which involves cutting out the damaged joint and the surrounding concrete, and making the area good. In this case it’s likely that a straight joint will be replaced with another straight joint – either a metal repair joint, or a saw-cut joint in the new concrete. Although the area will now be ‘as new,’ the new straight joint will still be prone to damage in the future. If a saw-cut joint has been cut into the repair mortar (to control concrete movement, which can still occur many months after the building was first constructed), it will still need to be maintained with joint sealant.

Solving the joint problem once and for all

Permaban’s Signature joint has been designed to counter the problems of straight floor joints once and for all.

Signature’s solution is not to create a stronger defence against impact damage, but to solve the core problem by preventing the impact from happening at all. The product’s unique half-hexagon shape means that vehicle wheels pass smoothly across the floor’s surface, as if the joint wasn’t there, regardless of the angle of approach. Thousands of metres of Signature have now been successfully installed in new buildings worldwide.

The next step for Permaban has been to create a repair system for damaged straight joints, based on the principles of Signature.

Permaban Signature AR (arris repair) is installed by cutting a shallow trench in the floor to remove the damaged straight joint and the damaged concrete surrounding it. Then the product is placed in the trench, and embedded with a specialist repair mortar. The whole repair area is then ground to a flat and seamless finish. The Signature joint cannot be damaged by MHE impact, and will remain completely maintenance free for the life of the building.

www.permaban.com