Enhance your property by laying a new patio – part #4

Slate Tiles

With most of the below ground works finished it’s now time to start building the ground back up.
A green led laser level (more easily seen in daylight) was used to mark the highest point of the patio Then allowing for other factors like depth of service pipes below ground, slope of the lawn and distance of the slabs below the damp proof course (DPC) an amount of overall fall was calculated and then marked at the opposite end of the patio. In this case a fall of 40mm over 6 metres was achieved which is a little under the desirable gradient of 1 in 80.

Stakes were banged into the ground and string run between them to mark the top of the slabs from front to back. Allowing for the thickness of the slab, 40mm for the cement base and 80mm for the MoT type 1 subbase another string was run at the subbase level to show where the type 1 needed to be filled up to or ground shaved off to allow for the 80mm of type 1.

The ground was prepared with pickaxe and shovel to make it the right level for the Mot type 1. Excess spoil removed in the process was sieved through an automatic rotary soil sieve to create a pile of topsoil and another pile of stones which would be used as the first layer below the type 1 subbase. Any difficult areas of the old concrete patio base were broken up with a hex shank electric breaker using a wide flat chisel.

Once the ground was prepared the stones extracted from sieving the spoil were spread over the proposed patio area as far as they would go and then compacted using a petrol compactor plate (wacker plate). Then the rest of the required thickness was made up by the MoT type 1 and compacted using the plate.
The next step was to set the channel drain. This was installed 3mm below where the top of the patio slab would finish and laid in a bed of 4 to 1 sand and cement. End caps were put on at the highest ends using PVC pipe weld cement and the lengths were cut to clip into the 4 way corner unit which joins into the top of the soakaway pipe via the P trap through a double socket coupler joined to a piece of pipe. A gap of 10mm was left between the channel drain and the wall to allow gun injected patio mortar to be applied once the patio had been laid.

Now it was time to lay the first patio slab. The first slab required a cut to make it fit round the base of the concrete fence post. The cut was made with the combination of an angle grinder and an electric tile cutter using wet cut diamond blades. The electric tile cutter has a tray which you fill with water that the blade runs through to aid dust suppression. A facemask, face guard, protective goggles and ear defenders were used to protect the operators. Water was dribbled on to the slab while the slab was being cut to help the dust suppression process even more.

Type 1
Type 1 laid and pounded into flat surface.

Enhance your property by laying a new patio – part #3

New drainage pipe for channel drain

Round by the garage and the back door of the property the wall of the garage is built into the bank of the house next door. The gravel boards of the boundary fence also act as a retaining wall holding the earth back. Rainwater runoff from higher up the road runs into the patio area of the house and makes the external walls wet when it rains hard. There is a Damp Proof Course (DPC) which prevents water penetrating internally.

To alleviate the effects of the surface rainwater run off a channel drain will be installed against the kitchen wall and continued round at the bottom of the patio running parallel with a new retaining wall which will hold back the earth from the garden. The retaining wall is made of new sleepers of lengths 1.2 metres and 1.8 metres and widths 100mm x 150mm. A narrow trench was dug and filled with type 1 with a sand and cement base that the first lot of sleepers were laid on with haunching (cement support) applied to the back of the sleeper wall once the wall was finished.

Type 1 and cement base for sleeper wall
Type 1 and cement base for sleeper wall

The sleepers were staggered to match the height of the earth that would be retained behind the wall. They were cut and offered up dry to start with to make sure they fitted together properly. Holes were drilled in the sleepers to accept 1.2 metre long 20mm steel rods which were passed through the sleepers and hammered into the ground with 2 part polyester resin being used to glue the rods inside the sleepers. The sleepers were also glued in place with a quick setting Silyl Modified Polymer glue.

Sleeper wall partially built
Sleeper wall partially built

Once the wall was complete it was left for 24 hours to allow the adhesives to set properly.

Sleeper wall finished
Sleeper wall finished

The rainwater which comes off the garage roof is carried away by a gutter into a downpipe. An inspection pit was dug following the line of the downpipe from the gutter in order to trace where the water was draining to.

Inspection pit to reveal drainage pipe leading to soakaway
Inspection pit to reveal drainage pipe leading to soakaway. Main main foul water sewer pipe routed above.

The downpipe exited into a 110mm 90 degree bend by means of a flexible reducer pushed over the pvc pipe. The inspection pit revealed that the pipe went under the shared services foul water drainage pipe and continued into a soakaway. A trench was dug to run the pipe which would be teed off and run up to the channel drain.

Inspection pit to reveal drainage pipe leading to soakaway
Inspection pit to reveal drainage pipe leading to soakaway. Main main foul water sewer pipe routed above.

In order to carry away the water from the new channel drain it was proposed that the rainwater drainage pipe for the garage roof gutter would have a tee placed into it and a new trench would be dug for a pipe to be laid and run upto a P trap. The use of a P trap was just to stop any possible gases coming up from the soakaway and exiting into the atmosphere at ground level through the channel drain. The P trap would have a downpipe that joans the bottom of the corner joint of the channel drain. Here the pipe is cut to accept the slip coupling and double socket branch.

Pipe cut ready to fit slip coupling
Pipe cut ready to fit slip coupling

Then the slip coupling is inserted with pipe lubricant …

Fitting slip coupling
Fitting slip coupling with joint lubricant to aid movement of coupling up and down pipe.

… and the double socket branch is inserted into the pipe.

Double socket branch tee fitting
Double socket branch tee fitted to facilitate installation of drainage pipe to channel drain.

Then a piece of straight pipe was inserted into the double socket outlet and 90 degree adjustable double socket bend was inserted into that which allowed a long piece of pipe to be run upto a 15 degree bend and into the P trap. The P trap was placed on type 1 and then a piece of broken patio slab to give a firm base. Once the P trap outlet was judged to be in the correct place to accept the channel drain outlet 10mm pea shingle gravel was shovelled into the trench to backfill the space around the pipes.

Trench backfilled with 10mm gravel pea shingle
Trench backfilled with 10mm gravel pea shingle