Sinking floors, uneven slabs, or dropped sections don’t always require full demolition and replacement. In many cases, you can successfully build up the surface to correct levels using bonded screeds, resurfacing products, or slab lifting techniques. In this guide, we’ll show you exactly how to raise concrete floors without tearing everything out — saving time, money, and disruption on your project.
Before building up, inspect the slab carefully. If the base slab is cracked, hollow, moving, or structurally compromised, building up won’t solve the problem — replacement may still be needed. However, if the slab is largely sound but just low or uneven, you can successfully build up with the right techniques. Map out low zones using a laser level, and mark any serious structural issues to address before proceeding.
Depending on how much height you need to add, different methods apply. Thin build-ups (5–20mm) can often be handled with polymer-modified resurfacing products. Moderate build-ups (20–100mm) typically require bonded screeds. Major lifting (100mm+) might involve slabjacking (foam or grout injection under the slab) or topping slabs. Match the method to the amount of lift required and the slab's usage after correction.
Surface prep is crucial for adhesion. Grind or shot blast the slab to remove laitance, sealers, and contamination. Create a CSP 3–5 profile (medium-to-heavy roughness) for strong mechanical bonding. Vacuum dust thoroughly. Some overlays and screeds also require priming or applying a slurry bond coat before placement to further improve adhesion to the old concrete.
Many resurfacing and screed systems require either a chemical primer, a cementitious bond coat, or both. Follow manufacturer instructions closely — skipping primer reduces adhesion drastically and can cause de-bonding. Apply primer uniformly and allow it to cure properly (or work wet-on-wet if instructed). Ensure complete primer coverage over the prepped concrete before building up.
Pour, screed, or trowel the build-up material in place according to level marks or laser measurements. For bonded screeds, apply and compact material firmly into the surface. Maintain consistent thickness and slope to avoid dips or pooling. Use straightedges, screed rails, or finishing floats to level accurately. Avoid leaving thin feather edges — most overlays have minimum thickness specifications for durability.
Protect the fresh build-up from rapid drying, wind, foot traffic, and rain during curing. Use curing membranes, wet hessian coverings, or light misting if needed to retain moisture. Follow manufacturer cure schedules exactly. Rushing or drying too fast leads to shrinkage cracks, curling, and surface dusting. Only after full curing should grinding, sealing, polishing, or top-finishing be carried out.
Once cured and stable, you can proceed with your final finish. Build-up layers can be polished, sealed, resurfaced with decorative coatings, or even used as the finished wear surface depending on the system. Confirm moisture levels are appropriate before any sealing or coating. Properly built-up slabs provide a solid, smooth, and long-lasting platform for any future floor finishes.
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