- How the concrete substrate behaves
- Rules for the device and preparation of the concrete base
- Laying tiles on glue
- When is it better to lay on bedding
- Masonry and lining technique
Sometimes, instead of a bulk substrate for paving slabs, a precast or monolithic reinforced concrete slab is prepared. We offer you to get acquainted with the specifics of laying in such conditions and study the rules for arranging pavement pavement so as not to deprive it of its strong qualities..
How the concrete substrate behaves
A concrete base for pavement looks the most preferable. A massive and ideally flat slab, it would seem, excludes any possible subsidence and other irregularities, even under very serious operating loads.
Since the reinforced concrete is hidden under a sufficiently thick face layer, it is less affected by overheating by direct sunlight. Therefore, thermal expansion can be neglected for the sake of high strength and solidity. However, such a road surface arrangement will inevitably hinder the free drainage of moisture, which means that the forces associated with water and frost erosion will manifest themselves to a large extent..
1 – compacted soil; 2 – sand cushion 100-150 mm; 3 – crushed stone 100-150 mm; 4 – reinforcing mesh; 5 – concrete 120 mm; 6 – sand-cement mixture; 7 – paving slabs; 8 – border
In general, the concrete base plays the role of backfilling with road rubble, but due to the initial integrity it has a higher service life. Much less effort is required to maintain and re-lay the paving stone on this basis, and the permissible load increases in proportion to the strength of the concrete slab. Of course, over the decades, concrete will become more and more fragmented and from a certain point will turn into ordinary gravel bed.
Rules for the device and preparation of the concrete base
There are no significant requirements for the structural strength of concrete on the base for the tiles. Often, the decision on the construction of a concrete base is made for economic reasons: a washed construction battle is used as a filler, the remains of cement are used after long-term storage. If a prefabricated concrete mass is purchased, preparatory concrete grade 100-150 will be sufficient.
Frost resistance is much more important. This is the main reason why the brand is specifically raised to 200-250, although from the point of view of the actual loads, this is not justified. The problem, however, can be solved by frost-resistant modifiers for plasticizing or air-entraining concrete. The most modest concrete reinforcement will not be superfluous, often polymer meshes are used for it with a cell pitch of 100 or 120 mm..
It should be borne in mind that the pavement covering on a concrete base should be arranged in the presence of a system of storm drains of surface or hidden types. This requirement is all the more important, the larger the area of the covered area. A strict slope of the concrete slab of at least 1000: 1 is required, mandatory framing with curb stones, as well as a system of storm channels. However, when casting a slab, they can be arranged directly in it, having laid foam cutting as recoverable templates.
For small areas without the prospect of constructing a stormwater system, it is allowed to do with drainage perforations. Before pouring in the plane of the slab, pieces of plastic pipes are immersed in the gravel bed, the excess length of which is cut off after the concrete has set. The ingress of moisture under the concrete base or high groundwater level enhance the effect of frost heaving, in such cases it is recommended to install a damper substrate from PSB slabs up to 50 mm thick.
Laying tiles on glue
The simplest and most common way of laying paving slabs on a concrete base is to plant it on an adhesive mixture or cement-sand mortar. This method is most popular in the improvement of the concrete blind area of the foundation, but you must remember that you should only move from such a site to an adjacent one, where bedding is used, with a curbstone and height separation. First of all, it is worth clarifying the disadvantages of laying on a solution or glue:
- the coating remains absolutely not subject to re-laying and fragmentary repair;
- the glued coating is extremely sensitive to improper drainage of water: the slightest accumulation of water (for example, during the melting of snow) can lead to the fact that the tiles will simply be torn by frost;
- laying small-sized tiles on glue is very laborious and most often leads to the appearance of differences between adjacent stones;
- with significant temperature differences and low frost resistance of the adhesive, it may peel off after several seasons.
Often the tiles are laid directly on raw concrete, carrying out a residual leveling with a mixture of sand and cement 1: 2. The seams between the tiles are left on the eye from 1 to 3 mm to compensate for thermal expansions and preserve the order of the masonry, then they are filled with the same composition. After preliminary setting of the solution, it must be immediately washed off with water, and dried residues wiped off with a wire brush.
Laying can also be carried out on tile adhesive, which is especially effective when installing floors in indoor spaces. On terraces and under sheds, to compensate for frost shrinkage, the preliminary wiping of the concrete base is carried out by rolling out the fiberglass mesh. After the glue dries, the seams are wiped with a liquid cement-sand mortar.
When is it better to lay on bedding
Laying small-sized paving stones (more than 20 pcs / m2) it is better to carry out over a layer of filling from a mixture of sands or screenings of different fractions (up to 4 mm) with the addition of cement grade 400. Its content can vary from 3: 1 to 10: 1, depending on the desired resistance of the coating to traffic loads. However, you should be aware that the formation of a knurled track with a depth of several millimeters over time is a completely normal phenomenon, which is eliminated by partial shifting..
The thickness of the concrete fill should be about 60–70% of the thickness of the tiles used. It is very important to prevent erosion, therefore all gaps in the base and curb stones are sealed with cement mortar. If the coating must maintain hygroscopicity, before filling the mixture, the base is covered with needle-punched geotextile or synthetic burlap.
You need to ram the bedding with an effort commensurate with the future load. To maintain even high pedestrian cross-country ability, a hand roller and rammer will suffice. Under the collision of transport, the bedding should be prepared only by a mechanized method. Please note that the backfill must remain dry until the moment the tiles are laid, otherwise it may be difficult to level the coating.
Masonry and lining technique
Paving slabs on a concrete base can be laid using the same technology as for filling from sand and gravel. It is allowed to pour the mixture under each element and additionally seat it with a mallet in order to level the difference in the thickness of the tile and the unevenness of its shrinkage.
And yet, the presence of a concrete base is an excellent reason to prepare a flat, tamped area, and then lay tiles on it without additional impact. This method is especially recommended when there is a chamfer or a convex front surface, as well as when working with tiles of high decorative qualities..
When the tile is laid in a sufficiently large area, a mixture of dry washed fine sand with cement in a ratio of 1: 4 is poured over it, and all the seams are thoroughly swept with the resulting composition. It is better to use not an ordinary broom, but brushes with a long synthetic bristle: you need to achieve the most dense and complete filling of all the cracks, otherwise the germination of seeds brought by the wind cannot be ruled out in them. After that, rinse the tiles with water or wait for rain – it’s entirely your choice..