12/30/2023 0 Comments Stamped concrete overlay problems![]() ![]() When concrete is placed on an impervious subbase, bleed water must rise to the top because it can't exit out of the slab bottom. There is less potential for delamination if you give the surface a light steel-troweled finish or a broom finish in exterior areas where slip resistance is a concern.ĭon't finish slabs placed on impervious surfaces too early. At air contents greater than 3%, a dense, hard-troweled surface isn't necessary. Be aware that sticky mixes with higher cementitious or sand contents tend to bleed more slowly.ĭo take precautions when finishing if the concrete is air entrained. Bleeding must be completed before starting finishing operations that close the surface (Photo 4). Here are a few dos and don'ts to follow to help you avoid delaminations:ĭon't seal or close the slab surface too early. Photo 4- Postpone final finishing operations until the bleed water sheen has evaporated. Here the depth of delamination is about 1/8 to 1/4 inch. Photo 3 - The thickness or depth of a delamination can vary, depending on the mix and the timing of final finishing. Stickier mixes, thicker slabs, different types of subgrades, initial concrete temperatures, different cementitious contents, and changes in ambient temperatures all affect the bleeding process and impact when finishing should begin. However, a finisher's job to properly time final finishing can be an art because job-specific influences impact this timing on each project. Following consolidation, and once bleeding is complete, there is nothing left to be trapped to cause voids. But this may not be as easy as it sounds. The simplest way to prevent delamination is to start final finishing of the slab after the bleeding process has run its course. When finishing operations occur too early, uniformly over the slab, a delamination problem can be quite widespread and affect larger zones of a slab surface (Photos 2 and 3). They occur in areas subject to moderate to high rates of evaporation and that are finished too soon. Blisters frequently happen when relatively sticky mixes with higher percentages of fines are placed. Blisters are small, isolated delaminations usually 1 to 3 inches in diameter (Photo 1). But if it's widespread, then you have a more serious problem that should be addressed.ĭelaminations come in various forms and degrees of severity. If the delamination is isolated to just one spot, it might not affect the performance of a concrete slab. Premature finishing resulted in widespread delamination. Photo 2 - Slab placed on waterproofing membrane on roof slab. (Photo courtesy of the Portland Cement Association) ![]() Photo 1 - Side view of slab surface containing a blister. Very thin mortar layers over delaminations may even detach when struck with a hammer, as you try to sound out the extent of the delaminated area. These voids create weakened zones right below the surface that can eventually detach during slab use. As concrete hardens, subsurface voids develop where the water or air is trapped. If finishing operations start prematurely and close or seal the surface before bleeding is completed, air and/or water are trapped under the densified surface mortar. This natural settlement causes excess mix water and entrapped air to be displaced (called bleeding), and the lighter materials migrate toward the surface. When fresh concrete is placed and compacted, the solids (cement and aggregate) settle. What's been discovered is a surface delamination in the concrete floor.įind concrete contractors near me How do delaminations happen? Using the hammer to tap around this spot, you identify more hollow-sounding areas. Instead of the clear ringing sound you would expect when metal hits solid concrete, a drummy sound or loud clack draws your attention. As work from other trades continues in the area, someone drops a hammer from a ladder onto the floor, and an unexpected sound is heard. A concrete floor slab placed days ago has hardened and cured. What is Concrete Delamination and How to Prevent & Fix It Learn what causes the paste layer to separate or flake at the surface By George Seegebrecht | Updated October 6, 2021ĭelaminations in concrete slabs can be a serious problem, but often they are "heard" before they are seen.
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