How Does Mudjacking Work? Vital Factors to Understand

How Does Mudjacking Work?
Mudjacking can be done at half the cost of replacing a concrete slab. For those who are wondering what is mudjacking and how does it work, this Buzzle post is a must-read. It answers important questions about mudjacking, along with telling you about its cost, applications, advantages, and much more.
Did You Know?
Mudjacking an existing slab is beneficial, as aged concrete is tougher than a newly-laid slab.
Mudjacking is a cost-effective and convenient alternative to tearing out and replacing an entire concrete slab. When a concrete slab 'settles' down as air spaces are created below it due to compacting of soil, it undermines the stability of the entire structure, besides creating a trip hazard for people.

Concrete slabs affected by this problem of settling are all 'free-floating' slabs, which means that they have been poured separately from the foundation. When these slabs settle, the walls of the house stay where they are. This is the reason why mudjacking can be carried out on them, because raising these slabs does not affect the foundation of the house. Also, mudjacking free-floating concrete slabs like driveways, patios, or even steps, is easier, because they lack foundations.

Mudjacking differs from slab replacement in various ways. To replace a slab, it has to be torn down completely, after which a new slab has to be poured. This new slab takes around 24 to 28 days to cure completely, until which it cannot be subjected to loads. On the other hand, mudjacking can be easily accomplished within a day, and used without delay.
What is Mudjacking?
Mudjacking is a technique used to raise a sunken concrete slab by pumping a concrete slurry below the slab, under hydraulic pressure. The slurry lifts up the slab to the desired level. This process is also known by several other names, like slabjacking, concrete lifting, concrete raising, pressure grouting, and concrete leveling.
The slurry used is a low-strength mixture of cement, sand, and a structural fill, commonly known as 'mud' by professionals, and hence, the name 'mudjacking'. Polyurethane foam can also be used in place of the slurry; the foam on curing expands, releasing gas bubbles which provide the pressure to lift the slab up. Mudjacking with foam is expensive, though more precise.
How Does Mudjacking Work?
Mudjacking
Drilling
First, the operators drill holes which are about 2" in diameter, in the concrete slab to be raised. The spacing and number of these depends on the size of the slab, though they may be between 3 to 8 feet apart.
Pumping
A semi-liquid cement grout is hydraulically-pumped into the holes using a portable pump and flexible hoses. First, the slurry occupies the empty spaces between the slab and the ground, and then, as more is pumped in, it becomes pressurized, causing the slab to be raised. Until the slab reaches the desired height, the pumping continues. For best results, it is advisable to vary the amount of grout injected at different places.
Plugging
After the slab has been raised to the desired height, the hose is removed and the holes are thoroughly cleaned. A shrink-proof cement mixture is used to plug the holes shut.
Mudjacking Cost
The cost of raising a concrete slab by mudjacking is usually between half to one-fourth of that of replacing the entire slab after removing it. This is because, tearing out a slab requires more labor and equipment, and is messier. The exact cost of mudjacking depends on the size of the concrete slab that has sunk, its age and condition. The volume of empty space to be filled affects the amount of the grout mixture required, and hence, affects the cost. In fact, mudjacking some patios costs only about 1/12 the total expense required to replace them.
How Long Does Mudjacking Last?
A concrete slab can remain stable for many years after mudjacking. This process is very durable, and in some cases, it has lasted for more than 30 years. However, the process is based on the stability of the surrounding soil, so a slab can sink even after mudjacking if the soil settles lower.
Factors to Consider
Reasons for Concrete Slab Settling
● Increase in slab age
● Poorly compacted soil around foundation
● Poor drainage design
● Soil erosion by water
● Heavy loads placed on slab for a long duration
● Misplaced downspouts
● Sprinkler heads close to slab
● Burrowing animals
Applications of Mudjacking
● Sidewalks
● Steps
● Concrete patios
● Concrete indoor floors
● Driveways
● Pool decks
● Preventive void filling
● Factory floors
● Aprons
● Grain bins
● Roads
● Curb and gutter
● Basement floors
● Ramps
● Grouting cement blocks
● Stoops
● Parking lots
Advantages
● Removes trip hazards
● It is cost-effective
● More convenient, as landscaping alterations are unnecessary
● Load removal from slab is unnecessary
● More aesthetic, as concrete retains color
● Less time required, between few hours to a day
● Municipal building permits are not necessary
● Repaired concrete can be used immediately
● Environment-friendly, as non-toxic slurry used and less waste produced
● Suitable for hard-to-access areas
● Less equipment utilized, minimizes surrounding damage
● All-weather process
Disadvantages
● It is suitable for slabs thicker than 4"
● Uneconomical if slab is in poor condition
● Settling subsoil renders the process useless
● Slab settles with time if slurry is deposited in pyramidal form
● Can clog sewer lines if not done properly
While mudjacking is a much easier alternative to slab replacement, it should not be done by an amateur. Certain situations call for a slab replacement, such as when large sections of the slab have deteriorated, or when it is heavily sloping. A sunken slab, however, should never be ignored, as that is when it starts affecting the other components of a structure.