Preparing Existing Screeds for Floor Refurbishment
Refurbishing existing floors is a very different challenge to screeding on a new build. The screed is already in place, and before you can apply new floor finishes — or even consider an overlay screed — there are several critical factors to assess. Getting this right saves considerable time and cost compared to discovering problems after work has begun.
Assessing the Existing Screed
The first step is always a thorough survey of what's already there. We'd recommend checking five key areas before committing to any refurbishment approach.
1. Screed Strength
An existing screed may look acceptable on the surface but be structurally weak underneath. The BRE screed tester (a calibrated drop hammer device) is the standard method for assessing in-situ screed strength. Results are categorised from Category A (strong, suitable for all finishes) to Category D (very weak, requiring remedial work or replacement).
If the screed tests at Category C or D, you have a decision to make: either remove and replace the screed entirely, or use a strengthening primer or consolidating solution to improve the surface before overlaying. We stock specialist primers from Ardex and Mapei that can upgrade a weak screed surface to accept new finishes — but only if the underlying structure is sound. A screed that's crumbling throughout its depth generally needs replacing.
2. Surface Flatness
Check the surface regularity using a 2-metre straightedge and feeler gauges. The tolerance required depends on the intended floor finish — ceramic tiles are more forgiving than thin vinyl, and vinyl is more forgiving than resin coatings. If the existing surface doesn't meet the required regularity standard, you'll need to apply a levelling compound to correct it.
Our Ardex and Mapei self-levelling compounds are specifically designed for this purpose. They can be applied from 2mm to 50mm+ in a single pass, flowing to achieve SR1 surface regularity and drying rapidly — often walkable within 2-4 hours.
3. Contamination
Years of use leave their mark on a screed. Oil, grease, adhesive residues, paint, sealers, and old floor finish remnants all need to be identified and addressed. Any contamination will prevent bonding of new materials above, so the surface must be mechanically cleaned — usually by shot blasting, diamond grinding, or scarifying — before any new treatment is applied.
Pay particular attention to adhesive residues from old vinyl or carpet tiles. Some older adhesives contain bitumen or other materials that are chemically incompatible with modern levelling compounds and adhesives. In these cases, a specialist barrier primer is essential.
4. Moisture Content
This is arguably the most critical factor in any refurbishment project, and it's the one most frequently overlooked. An existing screed that has been covered with an impermeable floor finish for years may appear dry, but removing that finish can reveal significant residual moisture — particularly if the original DPM was inadequate or damaged.
Always test moisture levels using a calibrated hygrometer or calcium carbide method before applying any new finish. Most floor finishes and adhesives require the screed to be below 75% relative humidity (approximately 0.5% moisture content for cement screeds, or 0.5% for anhydrite screeds when tested by the calcium carbide method).
If moisture levels are too high, consider a surface DPM product or moisture-suppressing primer. Alternatively, our fast-drying screed overlay products can provide a new, controlled-moisture surface ready for finishing within days rather than weeks.
5. Cracks and Structural Movement
Map any visible cracks in the existing screed and investigate their cause. Fine surface crazing is usually cosmetic and can be bridged with a flexible levelling compound. Wider cracks may indicate structural movement, drying shrinkage, or missing joints — and these underlying issues need addressing before any overlay, or the cracks will simply telegraph through to the new surface.
For structural cracks, we'd recommend consulting a structural engineer. For shrinkage cracks, filling with a flexible resin and incorporating crack-suppression matting beneath the new finish is often the most practical solution.
Refurbishment Options
Once you've assessed the existing screed, the main options are: apply the new finish directly (if the screed is in good condition), apply a levelling compound to correct flatness before finishing, apply a thin overlay screed for a completely new surface, or remove and replace the existing screed entirely. The right approach depends on the results of your survey and the requirements of the intended floor finish.
Expert Support
Related Reading
Refurbishment projects can be complex, and the consequences of getting it wrong are expensive. If you're unsure about the condition of your existing screed or which products to use, call us on 0118 370 2060. We can recommend the right preparation, priming, and finishing products from our Ardex, Mapei, and Weber ranges. Free delivery on orders over £600 ex-VAT.
