Readers Ask ConSeal: Why Is My Concrete Tank Leaking?

Priming, Coating, and Sealing Concrete

While it is critical to seal concrete tanks to prevent leakage at the joint, a leak does not mean that the sealant is not working. Concrete is, by nature, a porous material. During hydration and curing, capillaries are formed that can and do allow water to seep or “wick” through the concrete. Higher water to cement ratios and shorter curing cycles make this worse.

Figure 1

In Figure 1, a bead of sealant was placed on concrete made in a lab. The sealant was compressed to adhere to the concrete and to create a dam for holding water. The sealant ring was then completely filled with water. After 15 minutes, considerable dampness was observed outside of the sealant ring. After 30 minutes, the water within the ring had completely absorbed into the concrete or evaporated.

Primers, sealers, and coatings eliminate absorption of water into concrete

  • Primers are applied to the surface of the concrete to improve the adhesion of sealant to the concrete.
  • Sealers typically penetrate the concrete several inches, and after reacting with compound in the cured concrete, form a crystalline structure which acts to block the pores within the concrete, keeping water from penetrating.
  • Coatings will also stop the absorption of water through the formation of a barrier on the surface of the concrete.
Figure 2

Occasionally, a leak is detected like the one shown in Figure 2. Water is seeping through the concrete at the seam through the capillaries. The sealant is not failing. A little additional effort in the assembly process can eliminate this problem.

Concrete is a durable product that will provide many years of service. But not all concrete is the same. The preparation of the concrete tank, as well as the proper application of the sealant, is the best assurance for a watertight system. Do it right the first time, so there will be no need to fix it later.



ConSeal develops and manufactures a complete line of concrete sealing products including precast concrete joint sealants, exterior butyl wraps, hydrophilic waterstops, concrete sealers, specialty admixtures, trowelable/caulk sealants, surface coatings, primers, and lubricants.

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