Substrate Preparation for Microcement
The most critical step in any microcement project. A complete guide to surface assessment, moisture testing, priming and preparation for professional applicators.
Why Substrate Preparation is the Most Critical Step
More microcement failures in Ireland are caused by inadequate substrate preparation than by any other factor. Applicators — particularly those new to the material — are sometimes tempted to move quickly through preparation stages in order to get to the more visible application work. This approach consistently leads to problems: adhesion failures, cracking that mirrors substrate joints, bubbling caused by trapped moisture, and delamination. None of these defects can be repaired without full removal and reapplication of the entire system.
The key substrate checks are: structural soundness (the surface must not flex, hollow or move under load), moisture content (below 4% measured with a calibrated moisture meter), surface level (microcement does not self-level; irregularities above 3mm must be filled), surface contamination (oils, waxes, curing compounds, paint and adhesive residue must all be fully removed), and surface porosity (the substrate must accept primer correctly).
Suitable Substrates
Microcement can be applied over concrete floors, sand/cement screeds, anhydrite/calcium sulphate screeds (with appropriate primer), ceramic and porcelain tiles (bonded, no hollow areas, grout joints under 3mm), plasterboard walls (correctly fixed and jointed), render and plaster (fully cured and dried), and marine plywood (minimum 18mm, rigidly fixed).
Preparation Steps
Step 1 - Structural check: tap the entire surface and mark hollow areas. These must be repaired before proceeding. Step 2 - Moisture test: use a calibrated moisture meter. Readings above 4% require investigation and remediation. Step 3 - Surface cleaning: remove all contamination. Sand or grind if necessary. Step 4 - Level correction: fill any irregularities above 3mm with a compatible filler or self-levelling compound. Step 5 - Priming: apply the correct Cementec primer for the substrate type using a roller. Allow to dry fully before proceeding.
Substrate Suitability at a Glance
Concrete Floors
Suitable with correct primer. Moisture content must be below 4%. New concrete screeds require 4-6 weeks curing before application.
Existing Ceramic Tiles
Suitable if fully bonded, not cracked, grout joints under 3mm. Degrease thoroughly and use tile-specific primer.
Sand/Cement Screed
Suitable once fully cured and moisture content below 4%. Lightweight screeds may require additional assessment.
Plaster and Render
Suitable once fully cured and dried. New plaster should cure for a minimum of 4 weeks before application.
Marine Plywood
Suitable at 18mm minimum, rigidly fixed with no flex. Use plywood-specific primer. All fixings must be countersunk.
Flexible Vinyl and Carpet
NOT suitable. These substrates must be removed before microcement can be applied. The subfloor then requires assessment.
Frequently Asked Questions
Need Technical Advice on Your Substrate?
Contact the Cementec Ireland technical team for substrate assessment guidance before you start your next project.
Based in Kinsale, Co. Cork · Serving all of Ireland