Fixing Moisture Problems in Concrete slab

Fixing Moisture Problems in Concrete slab
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Concrete slabs on grade and basement slabs are weak to detrimental effect of moisture which lead to various problems. For instance, lifting tile off the floor, rotting hardwood, damping carpet, and coatings delamination.

Added to that, beneath
continuous flooring, moisture can also cause floor darkening or discoloration, efflorescence
deposits, and other deterioration. It can even damage the concrete itself and
corrode steel reinforcements within the concrete.

Free water in
concrete and rising moisture from below concrete are the source of moisture. Factors
that lead to moisture accumulation in concrete and subsequent related problems
include fast track construction schedule which does not allow free water to
evaporate naturally, inadequate moisture protection, and wet construction site.

Regarding fixing moisture problem, it can be divided into two groups namely, protective measures to avoid the moisture related problems and suitable procedure to tackle the issue after it is occurred.

Sources
of Moisture in Concrete

1. Free Water
in Concrete

It is from
within the Concrete itself which in excess of water required to hydrate the
cement particles and brings a concrete mixture to a workable consistency for
placement

Free Water in Concrete
Fig. 1: Free Water in Concrete

2. Moisture Rising
from Below the Slab

Concrete
slab is exposed to a perpetual source of moisture rising from below provided
that suitable moisture barrier or any other suitable technique is not installed
to prevent moisture migration form below the slab.

Moisture Movement from below the Slab
Fig. 2: Moisture Movement from below the Slab

Causes of
Moisture Accumulation in Concrete

  1. Wet Building Sites
  2. Fast-Track Construction
    Schedules
  3. Inaccurate, Insufficient or
    Misinterpreted Moisture Tests
  4. Inadequate Sub-Slab
    Moisture Protection
  5. Changing materials
  6. Inadequate water drains off from the building.
Wet Construction Site
Fig. 3: Wet Construction Site

Preventive
Measures

  1. A Low-Permeance Vapor Barrier / Retarder can Effectively keep Below-Slab Moisture from Reaching the Flooring System.
  2. Sometimes, providing adequate time for natural drying of concrete slab would solve the problem. In this case the concrete slab shall be tested prior to the installation of tiles, coatings, or paints.
  3. Sometimes, accelerated slab drying techniques can be used or a number of topical moisture and pH suppression systems can be applied as a preventive measure.
  4. Use a low water/cement ratio.
  5. Keep below grade excavations free of water to prevent potential reservoirs of moisture that can migrate upward through slabs. Excessive moisture below concrete slabs can cause structural degradation of soil bearing strengths, and swelling and shrinkage of soil. These can adversely affect a concrete slab on grade.
Vapor Barrier
Fig. 4: Vapor Barrier

Rehabilitation of Deteriorated
Concrete Slabs

If the concrete is experienced moisture
related problems, then certain measures shall be taken to halt further
deterioration, after that repair the damage.

  1. Installing
    subdrains at the building perimeter to carry water away from a building. this technique
    is costly but most effective solution at the same time to tackle further detrimental
    effect of the moisture on concrete slab.
  2. Remove,
    clean, and dry damaged area of the floor and place vapor retarders to restrict
    moisture movement
  3. Place
    a vapor retardant underneath the new floor finish.
  4. Making
    the floor finish vapor permeable. 
Wet Concrete Floor
Fig. 5: Wet Concrete Floor
Concrete slab suffered from moisture problems
Fig. 6: Concrete slab suffered from moisture problems



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