Understanding Laitance Removal
If you’ve noticed a weak, dusty film on the surface of your recently laid screed, you’re looking at laitance. It’s nothing to worry about, this is a natural result of the curing process and appears on most jobs within 24-48 hours. If you want your final flooring to adhere properly, though, this layer needs to go. This blog will explain how to remove laitance from screed.
Here at Capital Screeding, we do more than just supply and install screed across Essex, the South East and London – we provide the expertise that guarantees a successful project from the ground up. We’ve built our reputation on high standards and expert knowledge, so you can trust our techniques for laitance removal as they’re the result of our years of practical experience.
Understanding the ‘What’ and ‘Why’ of Laitance
Laitance is a weak surface layer created during the screed’s hydration process. As the screed settles and cures, water naturally bleeds to the surface. This bleed water carries with it the finest, lowest-density particles from the cement and sand. After this water evaporates, a deposit of these weak, powdery particles remains. The amount can vary depending on the water content of the initial mix, but its presence is a given.
Now, why is removing it so important? Simply because laitance is a bond-breaker. Floor adhesives are designed to create a powerful, permanent bond with the screed. If laitance is in the way, the adhesive sticks to this unstable, crumbly surface instead. This creates a critical point of failure right below the floor covering, guaranteeing that the finish will lift or become unstable over time. Careful removal of laitance is the only way to guarantee that your adhesive bonds directly to the solid substrate.
How to Remove Laitance From Screed – The Step-by-Step Guide
Now for the practical part. Removing laitance isn’t complicated, but you do need the right tools and a methodical approach to get it right. The process is known as mechanical abrasion, and it’s the most effective way to prepare your substrate for the final floor covering.
What You’ll Need:
- Floor Grinding Machine With Diamond Cup Discs – A rotary machine is essential for an even finish.
- Abrasive Pads – A coarse, 60-grit pad is usually the best starting point.
- Industrial Vacuum – A powerful, M-Class or H-Class vacuum is needed for dust control.
- Hand Grinder – For edges and tight corners.
- Full PPE – Don’t skip this. You’ll need an FFP3-rated dust mask, safety goggles, gloves, and ear defenders.
When to Remove Laitance:
Timing is important. Start too early, and the screed will be too soft. Leave it too late, and the job gets much harder. For liquid screed, the ideal window is between 5 and 14 days after it has been laid.
The Step-by-Step Guide:
Get Set – Before you start, put on all your PPE. The dust created is extremely fine which makes it dangerous to inhale.
Prepare your Machine – Attach the 60-grit abrasive pad to your grinding machine.
Work Methodically – Start in a corner and work across the floor in overlapping parallel lines, like mowing a lawn. Keep the machine moving constantly to avoid gouging the surface. The goal is to grind off the weak top layer.
Tackle the Edges – Use a hand-held grinder for any areas the main machine can’t reach.
Vacuum Thoroughly – This is the most important final step. Go over the entire surface with your industrial vacuum until every trace of dust is gone. Vacuum in two directions just to be certain.
Your Finished Surface
Once complete, the screed should have a uniform, slightly rough texture, similar to fine sandpaper. You will see the darker, solid screed and small particles of exposed aggregate. It should feel solid underfoot, with no dusty or crumbly patches. This surface provides the perfect mechanical key for adhesives to form a permanent bond.
Common Laitance Removal Queries
Here are some quick solutions to common problems and questions that pop up during floor preparation.
This happens for one of two reasons. Either the machine wasn’t kept moving at a steady pace, or your passes didn’t overlap enough, so some areas have been missed. It’s easy to put right. Go over the floor again, focusing on blending the patchy areas together. Use a methodical, overlapping pattern until the floor has a single, uniform texture and colour.
No, that fine dust has to be removed. Any dust left behind will act as a “bond breaker” for your adhesive. This is why an industrial-grade vacuum is so important. You need to vacuum until the surface is completely clear of all signs of dust. Your final check should be to wipe the surface with a dark, damp cloth—it should come away clean.
Hand-sanding with a block is not effective enough to remove the hardened laitance layer. You won’t be able to apply enough consistent pressure to abrade the surface properly. The result will be a weak perimeter around the room that’s likely to fail. Using a mechanical hand-held grinder is the only way to make sure the edges are prepared to the same standard as the rest of the floor.
Guarantee a Perfect Finish with the Experts
As you can see, removing laitance is an essential process where close attention to detail matters. For over two decades, Capital Screeding has not only supplied and installed screed across the South East but has also provided the final preparation that guarantees success. For complete peace of mind, let our professional screeders remove the laitance for you, ensuring a perfectly bonded, long-lasting floor every time.
Talk to us About Your Liquid Screed Flooring Today. Get a Free Quote or Expert Advice on 020 3369 3396
