Can you scan through screed?

Yes, GPR can scan through typical floor screed to image the structural slab below. The signal passes through the screed, and a competent surveyor distinguishes the screed-to-slab interface from the targets within the slab.

How it works

A typical floor build-up might include:

• Tile or floor finish.
• A screed layer (sand-cement, anhydrite, or similar).
• A separating layer or insulation.
• Possibly underfloor heating pipes embedded in the screed.
• The structural slab.

GPR can see through the upper layers and pick up features above and within the slab, such as:

• The screed-slab interface.
• Any reinforcement in the slab.
• Embedded conduits, post-tension cables, or services.
• Voids or anomalies within the slab.
• The bottom of the slab where penetration allows.

A trained surveyor identifies each layer in the data and presents the findings clearly in the deliverable.

What may complicate scanning

A few situations make screed-and-slab scanning more demanding:

• Thick screeds. Add depth that the antenna has to penetrate before reaching the slab.
• Heated screeds with underfloor heating pipes. Pipes show as additional reflectors that need to be distinguished from slab targets.
• Wet or saturated screeds. Increase signal attenuation and may shift apparent depths.
• Screed-bonded finishes with metallic mesh. Add reflectors above the slab.
• Tiles with metallic content. Some specialist tiles affect the signal.

In each of these cases, a competent surveyor adapts the method, sometimes choosing a higher antenna frequency for clearer separation, sometimes pairing GPR with ferro scanning where shallow cover detail is needed, sometimes scoping additional scan density.

What the surveyor needs to know

Before attendance, supply:

• The expected floor build-up, finish, screed thickness, insulation, slab thickness if known.
• The presence of underfloor heating, if relevant.
• The brief, pre-drill clearance, reinforcement mapping, void detection.
• Any drawings of the build-up.

A surveyor with this information can configure the equipment appropriately and produce a cleaner deliverable.

When ferro is added

Where accurate cover depths are needed on bars in the slab below the screed, GPR alone may give the position and approximate depth, but ferro scanning can give more accurate cover figures where the bars are within its range. The combined deliverable (GPR for layout, ferro for cover) is a common approach for engineering work where the screed has not been removed.

If the slab cover-depth requires the highest accuracy and the screed thickness is significant, scoping the work to coincide with screed removal, if practical, gives the cleanest result.

Practical advice

For routine pre-drill work through screed: GPR alone is usually sufficient. For engineering-grade cover or bar-diameter estimates: combine GPR and ferro. For unusual build-ups: brief the surveyor with as much detail as possible before attendance.

For more on GPR’s capabilities, see How does ground penetrating radar work.