Concrete has been used for the construction of a whole area of manmade structures since ancient Roman times. Recently this has included the construction of fluid containing structures and tanks. Like steel tanks, concrete tanks can be attacked by the contents stored within them and may require a protective tank lining to guard against them. In addition to this cracking or dynamic movement may result in a leaking concrete tank which could again be resolved by using a suitable tank lining.
There are some important considerations to take in to account when lining a concrete tank that are different from steel tanks. From 30 years’ experience in lining and relining concrete tanks we know the key steps that are required to ensure a successful tank lining in a concrete structure.
As for all tank linings correct preparation is required to ensure optimum adhesion of the new tank lining. As concrete cures Laitance can form on its surface where cement and fine aggregates rise to the surface, creating a weak and friable layer. If the tank lining is applied to this surface it will certainly fail as any tank lining materials adhesion is only as good as what it is adhered to. This layer must be removed either mechanically, by abrasive blasting or by high pressure water jetting before the tank lining can be applied. Sufficient preparation will also remove mould release agents which are used when concrete tanks are made, which can be detrimental to the adhesion of the tank lining.
Another essential consideration when lining concrete tanks is the blow holes and porosity that are always present in the concretes surface. Blow holes are caused by air trapped in the concrete against the form/shutter wall and sometimes through insufficient vibration/pokering when the concrete is poured. IT IS NOT POSSIBLE TO FILL BLOW HOLES WITH PAINT as many less experienced contractors fail to understand when lining concrete tanks and structures. Blow holes must either be filled using a suitable material prior to tank lining application or bridged using a suitable material such a chopped strand matting. Failure to address the blow holes in concrete will mean that your lining is not seamless and the concrete beneath the tank lining will be attacked or serve to provide points where bacteria and aquatic microorganisms can harbour in water tank linings.
Concrete when new uses large amounts of water, some of which will always be present, typically less than 4%. When lining concrete tanks it is important that the moisture content of the concrete is correct for the lining being applied as a moisture content beyond what the tank lining can tolerate will result in poor adhesion, potential blistering and tank lining failure. This can be tested using appropriate gauges and testing equipment as per our standard practice to ensure that the tank lining will perform as required.
When relining old concrete tanks and structures the surveyor must look for evidence of cracking or dynamic movement. If present and occurring this will guide the specifier towards a tank lining material which is capable of accommodating such movement – typically using polyurethane or polyurea tank linings – although crack bridging epoxies and cementitious materials are available and effective.
As with all tank linings when applying the thickness of the material being applied must be checked and monitored to ensure that the tank lining is being applied as per specification in order to perform as required. For slow setting coatings this can be done using wet film combs or for fast setting materials such as polyurea tank linings using digital gauges.
Finally as with all tank linings we test for pin holing and porosity of the tank lining when cured using DC Holiday spark testers. As with blow holes pin holes will provide a point for aggressive agents to attack the concrete or harbour aquatic microorganisms.