Fixing Floor Screeding Issues
Troubleshooting Screed Floors – How to Fix Imperfections and Avoid Future Problems
Spotting an issue with your floor screed is what every screeder wants to avoid – take it from one who knows! It’s not uncommon, though and it can happen however much experience you have. The good news is that the solutions are often simpler than you think. This blog is packed with expert advice on how fixing floor screeding issues, so you can repair the problem and move on with the job.
At Buxton Flow Screeds, we’ve spent over 20 years supplying and installing floor screeds, so we’ve seen (and fixed!) it all. Our hands-on experience means we understand the practicalities and problems you’re dealing with. So, you can trust us to offer genuine advice that actually works. Ready to fix your floor?
How to Fix The Top Five Floor Screeding Issues
Most screed problems have solutions you can often tackle yourself. In this section, we look at the most common ones and give you clear, practical ways to get your floor back on track.
1. Cracking (Shrinkage Cracks, Crazing, or Larger Cracks)
Perhaps you’ve noticed fine, map-like cracks, straight shrinkage cracks often near corners or pipes, or perhaps some wider cracks. These can occur due to rapid drying, or a slightly incorrect mix.
The Fixes:
For Fine Hairline Cracks (Crazing or minor shrinkage):
1. Clean – Thoroughly vacuum the cracks to remove all dust and debris.
2. Option 1 (If covering with tiles/bonded flooring) – Often, these fine cracks don’t compromise the floor’s integrity for bonded coverings like tiles.
3. Option 2 (For a sealed or resin floor finish) – Use a low-viscosity epoxy resin crack repair product. These are very thin and will penetrate deep into the fine cracks. Mix the two-part resin and pour or inject it into the cracks. Allow it to cure fully.
For Wider Cracks (e.g., 2mm - 6mm):
1. Prepare the Crack – Use a diamond crack chaser (an angle grinder attachment) or a sharp Stanley knife and a straight edge to carefully open the crack slightly and create a clean, square-edged ‘channel’. This gives the repair material a good body to bond to.
2. Clean Thoroughly – Vacuum out all dust and debris carefully.
3. Prime (if recommended) – Some repair mortars or resins require a primer. Check the product instructions.
4. Fill:
• Epoxy Repair Mortar – For structural repairs, a two-part or three-part epoxy repair mortar is excellent. Mix as directed and trowel firmly into the prepared crack, ensuring it’s well-compacted.
• Cement-based Repair Mortar – Specialist polymer-modified cementitious repair mortars can also be used. Again, mix and apply as per instructions.
5. Cure – Allow the repair to cure fully as per the manufacturer’s guidelines before light foot traffic or applying finishes.
2. Debonding or Hollowness
When you tap the screed, it sounds hollow in places, or it feels loose underfoot, this indicates the screed hasn’t properly bonded to the substrate below. This could be due to poor preparation of the substrate, incorrect primer (or no primer), or screed dried too quickly before bonding.
The Fixes:
For Small, Localised Hollow Spots:
1. Identify Extent – Tap around the hollow spot to find its boundaries.
2. Drill Injection Holes – Carefully drill small (6-10mm) holes through the screed down to the substrate, spaced about 150-200mm apart over the hollow area.
3. Vacuum – Thoroughly vacuum the holes to remove dust.
4. Inject Low-Viscosity Epoxy Resin – Use a specialised low-viscosity epoxy resin designed for slab injection. Mix the resin and inject it slowly into the holes until it starts to exude from adjacent holes or the edges of the hollow spot. This shows the void beneath the surface is filling.
5. Cure – Allow the resin to cure fully. The screed should now sound solid.
For Large or Severely Debonded Areas:
1. Assess – If a large part of the floor is debonded, injection won’t work.
2. Removal – Carefully cut out the debonded section of screed using a floor saw or angle grinder down to the substrate. Remove the loose screed.
3. Prepare Substrate – Thoroughly clean the substrate. Remove all dust, debris, and any loose material. If the original primer failed, remove it.
4. Prime – Apply a bonding primer for the substrate and the new screed material. Allow it to become tacky or cure as suggested in instructions.
5. Re-screed – Mix and lay a new section of screed, ensuring it’s compatible with the existing screed and well-compacted, particularly around the edges where it meets the old screed.
6. Cure – Allow the new screed to cure properly.
Uneven or Unlevel Surface
You can see that your screed surface has high spots, low spots, or is generally not flat or level enough for the floor covering you want to use. This is generally down to poor installation, screed slumping before it set, or insufficient compaction.
The Fixes:
For High Spots:
1. Identify – Use a long straight edge or level to find the high points.
2. Grind – Carefully grind down the high spots using a concrete/masonry grinding disc on an angle grinder or a dedicated floor grinder for larger areas. Wear a dust mask (P3 rated), goggles, and gloves to do this.
3. Check – Keep checking with your straight edge until the area is level.
For Low Spots or Generally Uneven Screed:
1. Clean & Prime – Clean the screed surface, removing all dust, laitance, and contaminants. Apply a suitable primer recommended for the chosen levelling compound and allow it to dry/cure.
2. Apply Self-Levelling Compound – Mix a good quality cement-based self-levelling compound. Pour it onto the primed screed and spread it using a smoothing trowel or a spiked roller (which helps release trapped air). Work quickly as these products have a limited working life.
a. Feather Edges – Make sure the compound is feathered neatly to zero at the edges of the area if not covering the entire floor.
b. Cure – Allow it to cure fully (check drying times – usually 24-72 hours before foot traffic or tiling, longer for sensitive finishes like vinyl).
4. Dusting or Friable (Powdery/Weak) Surface
This is when the screed surface is soft, powdery, and easily scuffed or scratched. When you rub it with your hand it leaves dust and sand. Dusting occurs when screed dried too quickly, there’s too much water in the mix, or the surface is overworked during finishing.
The Fixes:
1. Thorough Cleaning – Sweep and vacuum the surface carefully to remove all loose dust. Repeat until no more dust can be removed.
2. Apply a Surface Hardener & Sealer:
• Choose a good quality liquid surface hardener and dust-proofer (often silicate-based or acrylic). These penetrate the screed, bind the loose particles, and densify the surface.
• Apply using a watering can with a rose, a soft broom, or a sprayer, as per the manufacturer’s instructions. Ensure even coverage and work it into the surface if recommended.
• You may need one or two coats. Allow the first coat to soak in and dry (or follow specific product instructions for re-coating times).
3. Test – Once fully cured, the surface should be harder and less dusty. Try scratching it with a coin – it should be more resistant.
4. Prime (if needed) – If you’re applying a floor covering, you may still need to prime after the hardener has cured, depending on the hardener type and the adhesive/finish requirements. Check all product data sheets.
5. In Severe Cases – If the screed is very weak throughout its depth (not just the surface), a hardener won’t work. It might need a bonded topping screed (after suitable preparation and priming) or, in worst-case scenarios, removal and replacement.
5. Slow Drying or Retained Moisture
If you find your screed is taking longer to dry than expected, or moisture tests show it’s still too wet to lay your chosen floor covering, the problem could be to do with the drying conditions. Alternatively, your screed may have been laid too thick, or perhaps there was too much water in the original mix.
The Fixes & Management:
1. Improve Drying Conditions (Crucial!):
• Ventilation – Create good airflow across the screed surface. Open windows on opposite sides of the room for cross-ventilation. Use fans to circulate air.
• Heating – Gently raise the ambient temperature to around 15-20°C. Avoid fan heaters blasting onto one spot as this can cause cracking or curling. Underfloor heating, if installed, can be commissioned on a low setting and gradually increased (follow UFH and screed manufacturer guidance).
• Dehumidify – Use industrial dehumidifiers. These are effective at drawing moisture out of the air, which in turn helps draw it from the screed. When using them, make sure the room is sealed as much as possible. Empty them regularly.
2. Patience & Testing – Screed dries from the top down, typically at a rate of around 1mm per day up to 40mm thickness, and then much slower for thicknesses beyond that (e.g., 0.5mm per day or less).
• Regular Moisture Testing – Don’t guess! Use a reliable method to test moisture.
3. Consider a Damp Proof Membrane (DPM) – This is often a last resort. If residual moisture is a persistent issue and you cannot wait longer for it to dry naturally, a liquid-applied surface DPM might be an option before installing floor coverings. This creates a barrier. It also traps the moisture in the screed, which is not ideal for all situations or screed types (anhydrite screeds are very sensitive to trapped moisture).
While these DIY fixes can tackle many common screed issues, sometimes you just want the peace of mind that comes with a professional job! For over 20 years, Buxton Flow Screeds has been ensuring flawless floors.
If you’d rather we handled your screed repair, or you’re planning a new floor and want it done right first time, we’re here to help every step of the way. Contact us to discuss your needs – 020 3369 3396/ 07590 625100
