Recessed Covers
Recessed manhole or inspection covers are available in a wide range of sizes, and are intended to be filled with whatever product is being used for the main areas of the paving project. These may include concrete, tarmac, resin-bonded aggregates, paving in variety including block or cuboid units. They are formed in two sections; a ridged frame with a metal flange to enable mortar to secure it in place, and a ‘tray’ of between 50mm and 100mm (deeper for commercial use) to match the depth of the chosen product which fits inside the frame.
Some are suitable for use on driveways and car parks, and are rated to support different weights, whilst others are suited to pedestrian use. Always check the stated load-bearing rating shown on the product. This will be shown as a Gross Plated Weight (in tonnes).
They are usually constructed in galvanised metal, with integral lifting keys or handles, with or without a double seal to suppress any unpleasant smells from drains. Some may be simple lift on and off, whilst others will be screwed to secure the lids.
‘Filling’ the empty tray is usually carried out by laying a suitable bed of mortar to secure the paving product to the tray, ensuring the units are not mobile within the confines. This method may be supplemented using a suitable adhesive, depending on the material.
If possible, the laying pattern of the remainder of the work should not be interrupted by the presence and location of the tray, with lines and pattern translated across the recessed cover. Often, this may include more than one product, dependent on where the drain is situated within the work, and the tray depth will have to suit the deepest/thickest of the products.
Great care must be taken when removing and fixing inspection covers, to ensure that no debris is allowed to fall into the gulley, as it may easily cause a severe blockage of one or more drainage systems, requiring an expensive rodding operation to clear the pipes. A useful suggestion for preventing this from becoming a problem is shown in the cross sectional drawing below. Using two bicycle inner tubes, inflated to fit the chamber, one below a suitable sized piece of plywood, and one above to seal the space, can be used multiple times.
