Gravel slabs are concrete slabs with rolled (round) gravels. Before the complete setting of the concrete, these slabs are washed with jet to make appear the gravels. To manufacture them yourself requires the preliminary preparation of a mold.
- Tabbed box
- Wide brush
- Bubble level
- Tasseau (30 x 30)
- Motor oil
- River gravel
- Concrete irons
- Formwork preparation
- Manufacture of concrete slabs
- Laying slabs
1. The first step in the manufacture of washed gravel slabs is the realization of the formwork intended for molding them. This formwork makes it possible to shape several slabs at a time (4 for example), which has the advantage of reducing the time spent in their manufacture. Saw a plywood board to make a 1m square. Use the square to form perfectly straight angles. Place the cut panel on the workbench, and cut 4 lengths of 1 m cleat. When sawing, use the miter box, to make the 45° cut, in order to correctly assemble the corner cleats. Nail the cleats, bevelled at their end, on the turn of the plywood panel.
2. It is necessary, at this stage of the work, to define the exact shape of the slabs in order to set up the crisscrosses delimiting each plate. A simple job of sawing and nailing makes square slabs with cut sides, more original in appearance than the square or the rectangle. Saw a length of battens equal to the inside of the formwork frame. Place this cleat cut on the bottom of the formwork, to divide it into two equal parts. Then cut two identical lengths of cleat: place them crosswise on both sides of the first cut piece. The formwork is now divided into four equal parts. To obtain slabs with cut sides, saw at 45° of the 10 cm cleats, then place them in the 4 corners of the formwork. Proceed in the same way for the angles formed by the cleats and the frame of the formwork. Put all the elements in place correctly and nail the pieces at an angle to the bottom of the formwork. Nail a cleat on the central cross: it strengthens it and will serve as a handle for demolding.
3. Once the formwork is complete, grease each location with drain oil. Prepare sufficient amount of concrete cover to fill the 4 cells.
Manufacture of concrete slabs
1. Lay the mold flat and pour the concrete with the shovel into the 4 cavities. Hammer the sides of the formwork to tamp the concrete.
2. Each slab must be scraped for strength. Cut pieces of concrete reinforcing bar with a length equal to the diagonal of a slab. Place two cross pieces in each one. Hammer the formwork again.
3. Do not let concrete take completely. Arrange river gravel evenly over the surface of the slabs.
4. Allow the concrete slabs to harden in the formwork for eight days. Place the formwork in a ventilated place, preferably outside, but sheltered from the rain. When the slabs are strong enough (check by feeling their surface), water them with a jet of strong pressure. The powerfully projected water facilitates the subsequent dismantling and washes the chippings of the cement laitance that may have been deposited during the pouring slabs. This jet gives the gravel its natural clear appearance, by cleaning them with the particles of mortar that dirty them. If concrete pieces come loose from the slab, stop sprinkling immediately and allow the slabs to dry longer.
5. Once the washing is complete, hammer the formwork one last time on all sides, on all its structures and cross wood. Remove the central cross section (which has not been nailed to the bottom of the mold), taking it by the handle of the middle elements. Take the opportunity to check, by raising the cross slightly, that there is no lack on the underside of the slabs. If this is the case, do not handle the elements anymore and wait before unmolding them; otherwise, completely remove the removable element. Gently remove each slab from its cell, without touching the fixed parts of the mold, nailed to the bottom. Use the trowel if the take-off of the bottom is difficult: but the greasing of the mold, allows easy stripping and several consecutive uses.
1. The laying of slabs in their final location in the garden requires a preliminary preparation of the ground. Delimit the area to be paved with a taut cord. With the spade, dig about 10 cm deep. Flatten the bottom of the cavity roughly by treading it with your foot.
2. Spread a layer of sand about 5 cm thick in the bottom of the excavated area. Equalize the sand with a rake, without mixing it with the ground, until the walls of the cavity. This bed of sand, constituting an incompressible sole, prevents slabs from becoming bogged down in the ground. It also plays the role of drain, facilitating the flow of rainwater and watering and avoiding the formation of mud under the sole plates.
3. Place the slabs on the sand in a regular layout and alignments. Use a bubble level to place them horizontally.
4. Place topsoil in the joints, without making it flush with the slabs. Sow seeds of grass, the slabs will harmonize with the surrounding lawn.
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