A Guide to Micro Cementing Over Your New Screed
You’ve poured the screed, the hard work is done, and you are ready for that stunning micro cement finish. But can you micro cement over newly laid screed? Not if you want that seamless, showroom look. To achieve that, your new screed needs to breathe and cure first.
Skipping the drying phase can trap moisture, ruining the bond and wasting the money you’ve already spent. In this blog we describe how long you’ll need to wait, and exactly how to prep your new floor so your micro cement looks incredible for years to come.
Capital Screeding is a supplier and installer serving Essex, London, and the South East. We have poured thousands of square metres of screed and hand-applied just as much micro cement. We know the pitfalls and challenges. Our advice isn’t just theoretical – it’s built on years of on-site experience.
The “Before You Pour” Checklist – Preparing Your Screed for Micro Cement
Micro cement is a decorative coating, rather than a structural fix. Which means it will reflect any imperfections or problems happening underneath it. If your screed is damp or shifting, your micro cement will be too.
To get that professional, showroom-quality bond, you need to pay attention to humidity, laitance, and surface texture. To help you out, we have broken it down into a simple step-by-step process:
1. Check the Moisture Content
Never guess. Your screed needs to have a relative humidity of below 4%. As a general rule, screed dries at a rate of 1mm per day. If in doubt, use a moisture meter. Check out our article: Why Floors Fail – The Vital Screed Moisture Test
2. Identify Your Screed Type
Are you using anhydrite screed (calcium sulphate)? If so, it will have a layer of “laitance” (a weak, powdery surface) that must be sanded to prevent chemical reactions with the cement. Check out our article: How to Remove Laitance From Screed
3. Commission Underfloor Heating
If you have UFH, it must be fully commissioned before application (see below).
4. Inspect Surface Flatness
Micro cement is thin (usually 3-4mm). If your screed has divots or rough patches, use a self-levelling compound first. Micro cement won’t hide an uneven floor – it will highlight it.
The 3-Week Protocol – How to Commission Your Underfloor Heating
Don’t assume that once the screed looks dry, it is ready for heat. And turning your heating on fully without a “commissioning” phase is the fastest way to shock the floor and cause fractures. You need to simulate the thermal expansion and contraction of the screed before the micro cement is applied, not after.
Follow this protocol to ensure your substrate is stable:
Wait for the Initial Cure – Make sure that your screed has had its standard drying time (usually 7 days for cementitious screeds, varying for anhydrite) before turning the system on. For a guide to screed drying times, click here.
Start Low and Slow – Turn the UFH on at the lowest setting. Increase the water temperature by exactly 5°C per day.
Hit the Peak – Continue increasing until the water temperature reaches a maximum of 26°C. Do not exceed this.
Hold the Heat – Maintain this 26°C temperature for two full weeks. This forces out deep-seated moisture and settles the screed.
Cool Down Gradually – Decrease the temperature by 5°C per day until the system is off or at room temperature.
Final Check – Check the substrate humidity is below 4% before applying your primer.
Troubleshooting Your Micro Cement Install – Frequently Asked Questions
Even after you’ve followed the checklist, every build has its quirks. Here are the answers to the tech questions we get asked most regularly at Capital Screeding.
No. You must respect the structural movement joints in the screed. If you bridge over them with micro cement, the movement of the floor will eventually snap the surface. Instead, use a neat metal profile or a colour-matched flexible sealant to mirror the joint through to the surface.
No. PVA is water-soluble and will re-emulsify when the wet micro cement is applied, causing the bond to fail. You should use a specialist acrylic or epoxy primer designed for porous substrates. This creates a non-soluble barrier that regulates absorption and guarantees adhesion.
Probably not. Minor shrinkage cracks are common in new screeds, but they must be treated before you start. We recommend opening the cracks slightly with a grinder, filling them with an epoxy resin, and using a fibreglass mesh across the repair zone to prevent them from telegraphing through your final finish.
Very little. A standard micro cement system (including mesh and base coats) adds around 3-4mm. This makes it ideal for renovations where door clearances or meeting existing floor levels is tight.
The Foundation of a Flawless Finish
Micro cement is an incredible material, but it is very unforgiving of shortcuts. By following the steps in this guide – checking humidity, sanding laitance, and respecting thermal movement – you are setting your project up for success.
Whether you are managing a self-build in Essex or a renovation in South London, the rules of the substrate remain the same. Get the foundation right, and the finish will follow.
Need an installation team that understands the science behind the style? Call Capital Screeding on 020 3369 3396 to discuss your project with an expert.
