Rising damp occurs when moisture from the ground is drawn up through a concrete slab due to capillary action. If your slab lacks a proper damp proof membrane (DPM), or if the barrier has failed, you may experience surface dampness, discolouration, efflorescence, or failure of tiles, coatings, or flooring. In this guide, you’ll learn exactly how to stop rising damp in concrete — whether it’s for a small repair or full floor retrofit.
Rising damp is caused by moisture coming up through the slab, not from above. Check whether water appears even when the room is well ventilated and dry. Use a calcium chloride or RH probe test to confirm internal moisture, and inspect for missing or failed DPM. If you only see condensation on cold surfaces, the issue may be environmental, not structural.
Strip back any tiles, vinyl, carpet, or coatings over the slab. Moisture often accumulates beneath impermeable surfaces. Remove adhesives, underlays, and any contaminants with grinders or scrapers. You’ll need a clean, exposed slab surface for treatment and moisture mitigation to be effective.
Use a concrete grinder, shot blaster, or scarifier to remove the top layer of laitance and open the slab’s pores. Rising damp treatments rely on penetrating or adhering to the concrete — so proper surface prep is essential. Vacuum thoroughly after grinding to remove all dust.
If conditions allow, leave the slab open and ventilated for several days or even weeks to reduce moisture levels. Use fans, heaters, and dehumidifiers to assist. Drying the slab lowers internal pressure and improves the success of the treatment. For heavily saturated slabs, skip ahead to forced mitigation methods.
Use a two-part moisture-blocking membrane such as an epoxy DPM or polyurethane primer. These are designed to resist vapour transmission even on damp substrates. Apply in two coats with a roller, ensuring full coverage and no pinholes. Let each coat cure fully before applying flooring or screed. This acts as a new internal DPM over the concrete slab.
If the slab is uneven or damaged, follow the DPM with a self-levelling overlay made for damp substrates. Use cementitious smoothing compounds rated for high moisture and compatible with the membrane. This creates a new, flat surface ready for tile, resin, or other finish. Ensure your chosen product is suitable for your floor type and thickness requirements.
In extreme or persistent rising damp situations, consider installing a perimeter drainage channel, sump system, or internal cavity drain membrane. These are more common in basements and older buildings but may be required if the moisture source is severe or linked to groundwater pressure. Always evaluate long-term movement and cost before full systems are installed.
Once moisture is under control, choose floor coverings that are resistant to damp. These include polished concrete, sealed resin coatings, or moisture-tolerant adhesives for vinyl and tiles. Avoid floating floors or timber unless fully isolated from the slab using underlay and vapour barriers. Re-test the slab before installation to confirm moisture control has worked.
Rising damp issues can return, especially in older slabs. Regularly inspect corners and high-risk areas for moisture or efflorescence. Reseal your DPM or coating system as per the manufacturer’s lifespan — usually every 3–5 years. This is especially important in high-traffic areas or near external walls and doors.
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