Concrete Levelling with a Truss Screed

Concrete levelling with a Truss Screed is a common method used to ensure that a fresh concrete slab is perfectly level and smooth. The Truss Screed is an essential tool for large concrete pours, particularly in industrial, commercial, and large residential applications. It is typically used for leveling concrete floors, pavements, and slabs, ensuring a uniform thickness and a smooth surface finish.

A Truss Screed is typically a motorized or manually operated tool with a long frame that spans the width of the pour. It uses vibration or mechanical movement to distribute and smooth the concrete, filling in low spots and ensuring a level surface.

Here’s a step-by-step guide to concrete levelling using a Truss Screed:

1. Preparation Before Levelling

Materials Needed:

• Truss Screed (manual or motorized version, depending on your project)

• Concrete mix (freshly mixed to the required consistency)

• Vibration or power tools (if your screed is motorized)

• Surveying tools (such as a laser level or string line to set elevation)

• Concrete finishing tools (such as trowels or bull floats for smoothing edges after levelling)

Prepare the Area:

• Check the Base: Ensure that the sub-base (the layer of material below the concrete slab) is properly compacted and level. A poor sub-base can affect the levelness of the concrete.

• Set Screed Guides or Rails: Install screed guides (also called screed rails or stakes) along the edges of the pour area. These guides will help the Truss Screed maintain a consistent height and ensure a uniform thickness of concrete. The rails should be level and positioned at the required finished height of the slab.

• Prepare the Concrete: Pour the concrete mixture into the area to be levelled. Ensure that the mix is consistent and has the right slump for screeding—neither too wet nor too dry. A slightly wetter mix is typically used to help with flow during levelling.

2. Setting Up the Truss Screed

Positioning the Screed:

• Place the Screed on the Rails: The Truss Screed is typically designed to run along rails or guides. Position it at one end of the pour area, with its frame sitting on the rails.

• Check for Proper Vibration (If Applicable): If you are using a motorized Truss Screed, ensure that the vibration function is working properly. Vibration helps the concrete settle and fill in low spots, creating a smoother finish.

• Ensure Proper Height: Check the height of the screed relative to the rails to ensure it’s set at the correct level for the finished surface. You can adjust this by adjusting the height of the screed frame or by using shims.

3. Levelling the Concrete

Start the Screeding Process:

• Start at One End: Position the Truss Screed at one end of the slab, with the screed frame touching the concrete surface. If your screed is powered, start the motor and let the vibration help level the concrete.

• Move the Screed Across the Concrete: Push or pull the Truss Screed across the concrete slab, allowing it to move along the guides or rails. For powered screeds, the motorized action will help move the screed while the vibration helps level the concrete. The goal is to keep the screed in constant motion to avoid creating dips or uneven areas.

• Use a Steady, Smooth Motion: Move the screed at a steady pace across the slab, keeping the frame level and following the contour of the concrete. The weight of the screed and the vibration will help smooth and level the slab.

• Work in Multiple Passes: For large pours, it’s common to make multiple passes with the Truss Screed, filling in low spots and ensuring that the concrete remains level across the entire area. If the screed doesn’t reach all areas on the first pass, continue moving it back and forth in overlapping passes.

Adjusting for Levelness:

• Check Level Consistency: After the initial passes, check the slab with a level to ensure the surface is even. Use a laser level or a string line to check the height of the slab at multiple points along the pour. Adjust the screed position as needed to fill any low spots.

• Fine-Tune: In areas where the screed didn’t quite level the concrete as needed, use a trowel or other hand tools to smooth over the surface after you finish screeding. You may need to make slight adjustments in thickness to ensure a perfect finish.

4. Finishing the Surface

• Use a Bull Float or Hand Trowel: After the initial levelling, use a bull float to smooth the surface further. The bull float helps to fill in any minor inconsistencies left after screeding and provides a uniform finish.

• Edge Finishing: Once the surface has been levelled, use an edging tool to smooth and finish the edges of the slab, ensuring a clean and uniform appearance.

• Wait for Initial Set: Allow the concrete to cure slightly before applying any further finishes like finishing trowels or texturing tools. This helps prevent over-working the surface.

5. Post-Levelling Steps

• Allow Concrete to Set: After levelling, let the concrete set for the required amount of time (depending on the type of mix and environmental conditions) before allowing foot or vehicle traffic. The slab should be left undisturbed during this curing phase to achieve maximum strength and stability.

• Curing: Curing is critical for the longevity and durability of the slab. Depending on weather conditions, you may need to use curing compounds or moisture-retaining covers to keep the concrete hydrated as it sets.
  

Key Tips for Concrete Levelling Using a Truss Screed:

• Timing is Important: Start the screeding process as soon as the concrete is placed, but before it sets too much. Concrete that’s too wet or too dry will not level properly. The ideal time is when the surface is still soft enough for the screed to move through easily but firm enough to support the weight of the tool.

• Monitor Concrete Slump: Ensure that the concrete mix has the right slump (consistency). If it’s too dry, the Truss Screed won’t move easily through the concrete. If it’s too wet, it may be difficult to control the levelling process.

• Work in Sections: For very large pours, it can be helpful to break the pour into smaller sections and screed one area at a time to ensure better control over the consistency of the slab.

• Check Consistently for Levelness: Use a laser level or spirit level to check the slab frequently as you work. Even small inconsistencies can lead to larger issues if left unaddressed.
  

Benefits of Using a Truss Screed for Concrete Levelling:

• Efficiency: The Truss Screed is faster and more efficient than manual screeding, especially for large pours. It can cover wide areas quickly and evenly.

• Precision: It provides a level and uniform finish that would be difficult to achieve by hand, especially on larger slabs.

• Reduced Labor: The motorized versions of the Truss Screed can reduce the amount of manual labor required and help avoid uneven spots that often result from hand tools.

• Improved Concrete Flow: The vibration function helps the concrete to flow more evenly and fill gaps, reducing the likelihood of air pockets or low spots.
  

Using a Truss Screed for concrete levelling results in a smooth, professional-grade finish that is essential for durable, high-quality concrete floors or slabs. By following the steps and tips outlined above, you can achieve a perfectly level and uniform surface.