Should I install the vessel in concrete or gravel?

A common question, when installing a sewage treatment system or septic tank, is which backfill material to select. The two backfill materials that we recommend for installation are concrete or pea gravel/pea shingle.

Benefits of backfilling with concrete

When concrete sets, it forms a natural solid shell around the tank without placing any undue pressure on the structure of the vessel. This means that the integrity of the tank won’t be compromised, and if there is any flooding or movement on site, the tank should be offered extra protection and stability. When we install sewage treatment systems or septic tanks, we always install the vessel on a concrete bed and backfill with concrete.

Benefits of backfilling with pea gravel/pea shingle

Some vessels specify that they are suitable for installation with pea gravel/pea shingle. This material is a lower cost than concrete, but as it doesn’t set to form a shell like a concrete backfill, the vessel must be able to withstand the pressure of the gravel against the structure of the tank.

Please note: Generally vessels manufactured from GRP (fibreglass) are unsuitable for installation with pea gravel as the material can be compromised or can implode when installed. Please always read the installation manual for suitable options.

If you are unsure whether the vessel you are interested in is suitable for the backfill material you want to use, check the brochure or give us a call on 01388 537050, email sales@direct-drainage.co.uk or click the Live Chat button on the bottom-right of the page and we’ll be happy to advise.