Scaffolding Base Jack Explanation And Use

What is a Scaffolding Base Jack?

A base jack, also commonly known as a base plate or adjustable base jack, is the load-bearing component that forms the foundation of a scaffolding standard (vertical pole). Its primary purposes are to:

1. Distribute the Load: Spread the concentrated weight of the scaffold and its load over a larger area of the ground or supporting surface to prevent sinking or shifting.

2. Provide Height Adjustment: Allow for fine-tuning the level of the scaffold on uneven ground.

3. Provide a Stable Base: Offer a solid connection point between the scaffold standard and the ground.

Key Parts of a Base Jack

A typical screw-type base jack consists of three main parts:

1. Base Plate: A flat, square (or sometimes circular) steel plate, typically 150mm x 150mm (6" x 6") or larger. This is the part that sits directly on the ground.

2. Threaded Leg / Outer Pipe: A fixed vertical post with a standard scaffold fitting (a spigot or socket) on top to receive the scaffold standard tube. This outer pipe has internal threads.

3. Adjusting Screw / Inner Threaded Rod: A steel rod with external threads that mates with the outer pipe. It can be turned to raise or lower the height. The bottom of this screw often has a small foot or plate to improve contact with the ground.

Types of Base Jacks

There are a few common variations:

• Standard Screw Jack: The most common type, as described above.

• Fixed Base Plate: A non-adjustable version where the base plate is welded directly to a short stub of tube. It's cheaper but offers no leveling capability. Used on perfectly flat and stable surfaces.

• Swivel Base Jack: Features a base plate that can pivot or swivel to accommodate angled standards or for use on sloped surfaces, providing full contact with the ground.

• Heavy-Duty Base Jack: A larger, more robust version with a thicker plate (e.g., 200mm x 200mm) and a higher load rating for heavier scaffolds or softer ground conditions.

Proper Use and Safety Considerations

Correct use of base jacks is critical for scaffold stability.

1. Use on a Firm, Level Surface: The ground must be capable of supporting the load. Compacted soil, concrete, or asphalt is ideal.

2. Sole Boards / Mud Sills: On soft or unstable ground (e.g., soil, gravel, asphalt), you must use sole boards (also called mud sills or scaffold planks). These are thick, rectangular timber or LVL planks placed under the base plates to further distribute the load. Never place a base plate directly on loose soil or uneven ground.

3. Minimum Extension: The adjusting screw should never be extended more than two-thirds of its total length. Over-extending it creates a dangerous leverage point and can cause the jack to fail.

4. Maximum Extension: Always follow the manufacturer's specifications, but a common rule is a maximum extension of 300mm (12 inches).

5. Adequate Contact: The entire base plate (or the foot of the screw when extended) must be in full contact with the sole board or ground.

6. Leveling: Use a spirit level to ensure the scaffold standards are perfectly vertical after adjusting the base jacks.

Installation Steps

1. Prepare the Ground: Ensure the surface is stable. Place sole boards if necessary.

2. Position Base Jacks: Place the jacks at the correct locations according to the scaffold design.

3. Adjust Height: Turn the adjusting screw to achieve the rough desired height. The screw should be mostly retracted into the outer pipe to start.

4. Erect Standards: Place the scaffold standard (vertical tube) onto the spigot of the base jack.

5. Fine-Tune Level: Once the first lift of the scaffold is built, use a level on the standards and fine-tune each base jack to make the entire structure perfectly plumb (vertical).