Where the final appearance of the article or the performance of the finished item is dependant on what lies below, it is true that the long-term performance of any liner system depends so much on the surface quality and of what lies below it.

To this end, Enviro Seal stipulates requirements for earthworks preparation and the surface finish of concrete structures which have been gained over many years of site –related experience and which contribute greatly to the efficacy and performance of the final liner system as installed .

Earthworks preparation and the finish details of any concrete structure must, therefore be considered as elements which are equally as important as those relating to the MQC and CQC of the liner material itself.

The following should be viewed as minimum criteria for subgrade preparation, namely that the earthworks or structure below the liner should be stable (during and subsequent to liner installation) , well compacted , smooth and dry.

The surface of the bottom and side slopes in contact with the membrane liner shall be free of broken stones and/or hard objects within 100mm of the surface. Stones larger than 20mm in diameter shall not be permitted within 100mm of the surface.

The surface must be well compacted and free of loose stones, protrusions , roots and vegetation. No stones that may be detrimental to the liner will be permitted on the surface and where vegetation or organic material is present which may have a tendency for the underlying formation of gas – then a slow release herbicide is also a useful recommendation.

Generally a maximum particle size of 3mm is required, regardless of liner thickness. If the prepared surface is found to be unsuitable then a protective non woven geotextile of nominally 300g/m2 MIN. is suggested or a stabilised sand blinding layer of no less than 75mm is to be applied.

Any slope gradient can be lined by the lining contractor , but it is necessary for the client to design and build a structure which is stable both during and after construction.

Please note: Linings are used only to fulfil watertightness requirements and should not be regarded as re-inforcing elements . They rely very much on the integrity of the underlying structure for their own –long term integrity.

To ensure that the liner remains in position for the long- term, a perimeter anchor trench is necessary to lock the liner in position. The type, size and position of this anchor trench will be determined by the in situ soil materials, liner thickness, slope length and gradient.

Other means of fixing such as perimeter beams and mechanical attachments can be used in certain circumstances and Enviro Seal can advise on what measures are the most appropriate for any particular situation.

The anchor trench detail should be filled only when the structure has been filled in order to evacuate any entrapped air and the client should ensure that suitable backfill material is used and that adequate compacted density is achieved.

Should there be any propensity whatsoever in the area below the liner system to accumulate and trap either groundwater or gas, then a suitable system of water drainage and gas evacuation should be considered as an essential design and construct element.

It is strongly recommended that any Earthworks are prepared with a maximum deviation for any finished surface in any orientation being no more than +/- 50mm from any 3,0m straight edge and any sudden deviation from this line will be limited to 5mm maximum.

All concrete bonding surfaces shall be:

• Cleaned ( all shutter nibs shall be ground flat ) ;
• Straight (maximum deviation for any finished surface in any orientation should be no more than +/- 10mm from any 3,0m straight edge and any sudden deviation from this line will be limited to 5mm maximum.
• Smooth (steel trowel floated smoothed prior to anchoring the liner and 90 degree edges to be chamfered).

The Site Supervisor will inspect all earthworks and substrate with the Client’s Representative for acceptance prior to start of any installation and on completion of the liner works.

Enviro Seal can advise and recommend on the most cost-effective, safe and appropriate lining solutions to meet clients specific requirements. Contact Enviro Seal now for a fully professional service relating to advice on product selection, capability profiling and quotations for the supply and /or installation of lining solutions for specific projects.

back to the top