preping the ground

There should be 4 layers to all residential flexible block or
brick paving installations, whether on a drive, patio or for
a path. There are complicated assessment methods used
in the paving industry to determine 'ideal' dimensions and
specifications for each application. We find that the following
specification is adequate for 90% of residential applications.

he surface needs to be dug off to a depth of approx. 200mm. average depth of paviors 40mm bedding 100mm sub-base Remove all weeds and other unwanted organic matter. Excavate any soft spots and fill with compacted sub-base material. If the area of the paving is troubled with weeds, you may treat the excavated sub-grade with a general weedkiller such as Sodium Chlorate, but it is unlikely any normal weed will be able to penetrate the upper layers.

If the excavated sub-grade is suspect, clayey, riddled with Mares Tails or other pernicious, deep-rooted weeds, an appropriate geo-textile can be laid over the sub-grade. These geo-textiles can act as root barriers, and help to keep the overlying sub-base material from sinking into a clayey or softish sub-grade. If you require a kerb, this is a good point to construct it. Road kerbs, plain or decorative edgings, small unit kerbs, or setts laid lengthways are all suitable. The kerbs must be laid on and haunched with concrete in order for it to restrain the body of the paving and prevent it from disappearing into the garden. If you do not use a concrete bedded kerb unit at the free edges of the pavement, you MUST lay the edging courses on concrete and haunch them as you would a kerb unit. Note: Kerbs for flexible block pavements are normally laid on a concrete bed directly over the sub-grade layer or in a shallow channel excavated into the sub-base to ensure a full 100mm depth of bedding material. Bedding the kerbs over the un-altered sub-base results in too shallow a bed and haunch. The sub-base is the load-bearing layer of a block or brick pavement , and should never be omitted. Having said that, existing sub-bases that are sound and competent can be re-utilised. The sub-base should be a minimum 100mm thick, but can be reduced to 75mm for paths or patios on good ground. Following completion of the sub-base, the edging courses of the paving should be constructed before placing the bedding layer and the blocks /bricks. The perimeter edges of the paving can be laid in a different colour, or even a different block/brick, which should be laid on a concrete bed and haunched to prevent lateral (sideways) movement of the paving. These edges 'frame' the body of the paving and must be strong enough to withstand the lateral forces generated on a pavement by traffic. Note: Edging restraints for flexible block pavements are normally laid on a concrete bed directly over the sub-grade layer or in a shallow channel excavated into the sub-base to ensure a full 100mm depth of bedding material. Bedding the blocks over the un-altered sub-base results in too shallow a bed and haunch. There is an exception to the above recommendation, and that is when an edging course is laid against an existing solid object, such as a wall, in a position where it can not be overrun by a vehicle, as shown in the diagram opposite. In a situation such as this, it is acceptable to lay the soldier edging on a 50mm concrete bed, solely to ensure that the blocks will not move or settle when used as a level guide for subsequent screeding of the bedding layer. SAND There seems to be more confusion regarding Grading of Fine Aggregate Percentage by mass passing B.S sieve Sieve Size Overall Limits Additional Limits for Grading C M F 10.00 mm 100 - - - 5.00 mm 89 -100 - - - 2.36 mm 60 -100 60 - 100 65 - 100 80 -100 1.18 mm 30 -100 30 - 90 45 - 100 70 -100 600 µm 15 -100 15 - 54 25 - 80 55 -100 300 µm 5 -70 5 - 40 5 - 48 5 - 70 150 µm 0 - 15 - - - Sand grading limits - from For general on-site construction purposes, there are two main working categories of sand, namely building sand (aka soft sand) which is primarily used in the preparation of mortars, and grit sand (aka sharp sand), which is used as a bedding material for paving. Naturally there are intermediate sands and applications thereof, such as jointing sand, but these are the two most regularly encountered categori Building sand tends to be a fine sand, often with a clay content of 10% or more while a grit sand will have a low clay content and a greater proportion of larger grain sizes. Finally, two specialist sands; jointing sand, as mentioned above, is used to fill the joints of block paving and is specially selected to have a very low clay content and have grain sizes that will generate a high degree of friction, thereby giving stability and resistance to loading in a block pavement. Page 3