900 Kilograms of MOT Type 1 Compacted by a Wacker Neuson Plate on a 15-Square-Metre Base

Ordering 3.4 Tonnes When the Bag Says 900kg

A 15-square-metre area finished with 150mm of settled MOT Type 1 needs 2.25 cubic metres of compacted material. Once a Wacker Neuson DPU or a lighter Bomag plate has locked the stone together, bulked density sits near 2.0 tonnes per cubic metre. Loose aggregate arrives nearer 1.5t/m3, then loses volume under vibration, so the delivered quantity climbs above 3.4 tonnes. The 900kg figure is only a single loose spread of about 40mm across the area, which is the depth a plate can consolidate in one pass without leaving an unsettled layer below.

Dumping the full 150mm and compacting from the top causes many patio failures. A 90kg plate sends useful vibration perhaps 100mm into loose stone; beneath that depth, the surface can bridge over voids that later show up as dips. Two 75mm lifts, lightly wetted and passed three to four times in overlapping lanes, produce a tighter matrix than one 150mm layer hit repeatedly from above. MOT Type 1 crushed limestone or granite works well because repeated impact fractures and interlocks the angular material, while uncrushed gravel mainly shifts position.

MOT Type 1 Depth Against the Load It Carries

Sub-base depth is set by the load and the ground below it. A pedestrian porcelain patio over stable clay subgrade commonly sits on 100mm to 150mm of MOT Type 1. A driveway for a 1.8-tonne saloon moves into the 150mm to 250mm range. Soft ground or previously cultivated garden soil pushes the depth upward and needs a geotextile separation layer beneath the stone, so the sub-base does not punch down into the clay.

Reactive clay shrinks in drought and swells in winter, and that movement can lift or drop a shallow base even after careful plate compaction. A Terram or similar non-woven geotextile placed at formation level keeps fines from migrating up into the stone and keeps the stone from sinking into the subgrade. Free-draining sand or chalk subgrade is usually suitable for the lower end of the depth range. Excavation to formation, membrane on doubtful ground, then aggregate placed in lifts gives the base its best chance of a long service life.

For 15m2 at 150mm final depth, 15 multiplied by 0.15 gives 2.25m3 compacted. Loose supply at 1.5t/m3, spread as two 75mm lifts, means ordering closer to 3.4 to 3.5 tonnes once compaction loss and edge waste are allowed for. Bulk bags of MOT Type 1 are commonly sold as 850kg to 900kg, so four bags cover the job with a margin for spillage around the digger.

The numbers also explain why a site can look overstocked before compaction starts. Four bulk bags across 15m2 can seem excessive when the area is still open formation. After the first lift is levelled, damped and vibrated, the loose depth drops, the edges need topping, and the second lift takes the surface to a finished platform able to receive the bedding layer.

Falls, Channels and Where the Water Actually Goes

Porcelain needs a working fall of at least 1:80, equal to 12.5mm of drop per metre. Across a 4-metre run away from the house wall, that is 50mm difference between the threshold side and the garden edge. Sandstone and riven surfaces hold more surface water in their texture, so 1:60 gives them a better shed. A fall can be almost invisible and still drain; if the slope is obvious from normal standing height, the patio often begins to read like a ramp.

Where water is directed toward a boundary or wall, an ACO or Aquadrain linear channel catches the sheet flow before it reaches the building. The channel is connected to a soakaway or to the surface water drain, never to the foul drain. On impermeable porcelain, almost all the rainfall leaves the surface, so the channel must cope with close to the full load from 15m2. In a heavy British downpour of 30mm per hour, that means several hundred litres passing through the drainage run in an hour. If the channel or outfall is undersized, water collects at the low corner even when the falls are set accurately.

A soakaway has to be sized and built as part of the drainage system. The usual construction is a pit backfilled with clean 40mm shingle, wrapped in geotextile to prevent silting, and positioned at least five metres from the house foundation. That gives intercepted water somewhere to disperse. On clay with poor percolation, a soakaway contributes very little, and the run may need to reach an adopted surface water sewer, changing the drainage plan before excavation is set out.

Permeable Block Paving as a Different Base Entirely

Permeable block paving works as a reservoir system. Rain enters through 5mm to 10mm jointing grit between the blocks, drops into an open-graded angular aggregate such as 4/20 or 2/6.3, and is stored in the voids before slowly releasing. MOT Type 1 is unsuitable in this build-up because its fines clog the system. Clean, single-sized stone with about 30 percent void space forms the storage layer below the surface.

In England, replacing a front garden with an impermeable surface over five square metres that drains to the highway can require planning permission. A permeable construction that manages its own water on site generally avoids that requirement. Marshalls Drivesys and Tobermore both make permeable ranges designed to fit sustainable drainage expectations. The construction is deeper than a bound patio, often 350mm or more once the storage layer is included, so excavation and aggregate quantities increase. Plate compaction is carried out on the clean stone, and a rubber mat is used over the blocks to avoid chipping.

Jointing Porcelain Without the Compound Failing

Porcelain slabs have near-zero absorption, so ordinary sand-cement mortar joints have very little grip on the tile edges. A two-part epoxy or resin jointing compound such as GftK vdw 850 or Marshalls Weatherpoint 365 is brushed into 5mm joints while the surface is damp. The installer works it in with a jointing float and cleans the slab face before curing, because cured epoxy haze on porcelain is extremely difficult to remove.

Most resin compounds cure too fast above 25C and fail to set properly below 5C, so jointing is done on a mild overcast day when the slab surface is not baking. The bedding below matters as much as the joint. Porcelain laid on five dabs of mortar leaves voids, and those voids can crack the slab under point load. A full mortar bed with a slurry primer coat on the underside of each slab is the durable specification. The primer is often an SBR bonding slurry painted onto the back of the slab, and it is the step that helps stop frost from lifting corners.

Efflorescence and Sealing on Natural Stone

Efflorescence appears as a white bloom on Indian sandstone and limestone when soluble salts are carried to the surface while bedding mortar dries. It is not a stone defect. Scrubbing with water can make the bloom worse by dissolving more salt and allowing it to redeposit later. A proprietary efflorescence remover based on dilute acid clears the surface when applied to a pre-wetted slab and rinsed thoroughly; pre-wetting limits acid draw into the stone and reduces etching risk.

Sealer is applied only after the bloom has stopped recurring and the stone is fully dry, which can mean waiting several weeks after laying. A breathable impregnating product such as Marshalls Fairstone sealer sits in the pores without creating a surface film, allowing vapour to escape and preventing salts from being trapped behind a blistering glaze. If sealer goes over damp mortar too early, moisture is locked in and a cosmetic bloom can become a permanent cloudy patch.

The Gravel Path Nobody Weeds Twice

A gravel path depends on the geotextile membrane beneath it. A non-woven separation membrane laid over compacted formation keeps decorative 10mm to 20mm gravel from migrating into the soil, helps block weed roots from below, and still allows water to drain through. Without it, two seasons can be enough for gravel to disappear into mud at the edges while couch grass threads up through the stone. The membrane stays buried, while the first visible failure usually appears along the gravel edge.