How to build a manhole cover
Introduction
If there's a manhole (also known as a drain inspection chamber) in an area you're paving, you can disguise it by creating a recessed cover for it. Or if your finished paving is higher than the original ground level, you might have to raise the existing manhole cover.
How to build a recessed manhole cover
A recessed manhole cover is an open tray that disguises a manhole in a line of paving. The paving is laid right up to the rim of the cover, then more is added in the tray on a bed of mortar, which keeps the paving pattern. You could also choose to fill a manhole cover with gravel, or buy one in which you can lay turf. And if you need to inspect the drain, you can lift the tray out using special manhole keys.
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Top tip - Skeleton manhole
If you're making a concrete path or drive, use a skeleton type of manhole cover. You install it in the same way as a recessed cover, but the tray is filled with concrete that's reinforced by a metal grid.
Step 1
Bed the manhole cover on concrete, making sure that the lip is 2mm to 3mm below the level of the finished paved surface. Smooth the concrete around the edges with a trowel, taking care to leave enough room for the depth of the paving and its mortar bed.
Step 3
Lift out the tray and cut the paving to fit inside it. Then remove the paving, spread a bed of mortar over the whole of the tray and set the paving in the mortar. Cover the keyholes with masking tape while you fill in the paving joints.
How to raise the height of a manhole cover
If you've built a new patio or drive, the surface will often be higher than the previous ground level. That means you'll need to raise the cover of any manholes to the same level.
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Step 1
Start by lifting off the manhole cover and laying a polythene sheet or plastic bag in the bottom, so debris doesn't clog the drain up. Then chip the old mortar away from the edge of the manhole frame with a club hammer and a sharp chisel. Take care not to hit the frame - if it's old it might be made of cast-iron, which can crack easily. Lift the frame off and clean away any mortar that's covering the top surface of the brick walls of the manhole.
Step 2
Build up the manhole with engineering bricks bedded in mortar, made with three parts soft sand to one part cement. If you want to raise the height less than the depth of one brick, use brick slips (which are narrow sections of brick that you've cut to size).
Step 3
Spread more mortar onto the new bricks, then place the frame on top and tap it into position using a timber off-cut and club hammer. Then check with a spirit level to make sure it's level across its length and width.
Step 4
If you're gravelling the area, slope the mortar around the frame to direct rainwater away. If you're laying slabs or blocks, then cut the mortar in line with the bricks so you can pave right up to the frame. After this, remove the polythene and any debris from the bottom of the manhole. You'll need to cover the frame with a board weighted down with bricks while the mortar dries.
