- Differences between stamped concrete technology and conventional
- Preparatory part
- Preparation, pouring and painting of concrete mix
- Stamping and surface finishing
Stamped concrete is not inferior to paving slabs in terms of decorative qualities, and surpasses it in durability. It has a higher resistance to mechanical and climatic influences than conventional concrete. And most importantly, it is great for making garden paths and playgrounds with your own hands..
Differences between stamped concrete technology and conventional
Initially, the technology appeared in the middle of the last century in the construction of defense facilities, namely, for the construction of runways for army aviation. It differed from the manufacture of standard monolithic concrete by double reinforcement (traditional metal reinforcement and mineral microfiber), as well as the use of chemicals to accelerate the process of hydration of the concrete stone and increase the surface strength. All this made it possible to quickly and at relatively low cost create a monolithic coating that can withstand extreme loads. This technology is called “top concrete”.
For “peaceful purposes” the technology was improved – painting and the creation of a three-dimensional surface texture were added. Thanks to such innovations, nondescript gray monolithic concrete is able to imitate artistic masonry made of paving stones or bricks, a path made of chipped or tumbling stone, and the texture of a terrace board. Moreover, in each case, the palette and transitions of shades of the surface are not repeated and have an artistic personality. Such decorative features gave two more variants of the name of this type of concrete: “stamped” or “art-concrete”. And it is used not only in the construction of sidewalks, platforms or blind areas, but also in the finishing of vertical surfaces (walls, fences, parapets), and in the manufacture of small architectural forms.
Arrangement work begins with marking. It is carried out in the traditional way using pegs and twine..
When planning, it is necessary to take into account that for carrying out monolithic work on the ground, the “trough” under the track should be slightly wider than the canvas itself. Firstly, you need a place for the formwork, which means that you need to add the thickness of the board plus the section of the supporting pegs on each side. Secondly, if it is planned to install a curb or lay along the path of storm sewer trays, then their width must also be taken into account.
On the entire planned site, the fertile soil layer is completely removed. Construction organizations SNiP III-10–75 (clause 1.6) prescribe this soil to be stored in a specially designated place, protected from weathering and leaching, so that it does not lose its properties. A private person, of course, can not fulfill this norm, but if the soil is of good quality, then it can be used to level the plot or arrange a flower bed.
The depth of the trough depends on the thickness of the humus layer, the type of the underlying soil layer and its bearing capacity. Taking into account the minimum height of the cushion (10 cm of compacted sand) and the “underground part” of the monolithic tape, it starts from 15 cm. For central Russia, the thickness of the fertile layer in most regions is about 20 cm, for “fat” soils – up to 30 cm. practice, you have to deepen more than 15 cm, which means that the pillow under the concrete must be made thicker.
After the end of the excavation, the bottom of the trough is well compacted until the rammer stops leaving depressions. They check the evenness of the base with a rail, and with a difference in height of more than 15 mm by 2 m along the longitudinal axis, add soil and ram it again.
The thickness of the crushed stone preparation depends on the depth of the trough. The main purpose of crushed stone is to improve the bearing capacity of soft soils. But if the fertile layer is small, and the underlying layer has a high design resistance (for example, coarse sand or clastic soil), then crushed stone preparation is not needed.
In principle, the crushed stone layer should compensate for the depth below the minimum 15 cm, but physically it cannot be small either, at least based on the size of the main fraction (40–70 mm). Plus to these 70 mm it is necessary to add a wedging layer from a fraction of 5-10 mm. And although the “wedge” will go mainly to fill the voids between the large fraction of rubble, but it will take some volume. The thickness of the crushed stone bedding will not be less than 8–10 cm. The crushed stone is compacted by pouring water in three steps. Do this until the mobility of the rubble under the roller or rammer disappears. The evenness of the crushed stone preparation should be no worse than at the base.
Then a layer of sand is poured and rammed, on top of which a plastic wrap is laid as a spacer.
The Soviet normative documents do not indicate the mandatory separation layer. For example, in clause 3.16 of SNiP III-10-75 it is indicated that monolithic concrete coatings are arranged on a sandy base, and the obligatory waterproofing layer is present only for permafrost conditions as a gasket between the base and bulk soil. In another standard (SNiP 3.06.03–85), the waterproofing layer is laid on the main compacted soil, on top of which layers of “road pavement” are laid (clause 5.4).
The obligatory separation layer before the monolithic concrete pavement appeared later, in STO NOSTROY 2.25.41–2011 (section 18.104.22.168). The main purpose of the film is that moisture from the mixture does not go into the sand, that is, to create conditions for the correct hydration of concrete.
1. Ground. 2. Crushed stone. 3. Sand pillow. 4. Border. 5. Reinforcing mesh. 6. Concrete. 7. Waterproofing layer
After that, the formwork is exposed and reinforcement is carried out. The distance from the polyethylene film to the reinforcing road mesh is at least 3 cm (this is the minimum layer for fixing the reinforcement in concrete).
Preparation, pouring and painting of concrete mix
The path is not a road surface, therefore the requirements for the concrete grade are somewhat lower. And if M400 concrete is required for highways, M250 is sufficient for stamped concrete..
This is explained not only by lower loads, but also by the addition of mineral microfiber to the mixture, as well as the use of a colored hardener for grouting the surface. Each of these two additional ingredients increases the concrete stone’s strength, abrasion resistance and frost resistance.
Which concrete is better: ready-made or home-made? If there is a reliable concrete plant nearby, then it is easier to order a ready-made mortar of the desired brand and frost resistance (preferably F200). Otherwise, you can rent a concrete mixer and make a mortar on your own..
In any case, after the delivery or preparation of the solution into the concrete mixer, add mineral microfiber and mix for 7-10 minutes. Microfiber consumption for ready mix – 1 kg per 1 m3, in case of self-preparation of mortar – 200 g per 50 kg of cement.
Then the solution is poured into the formwork and compacted with a special roller, precipitating large fractions of the filler to the “bottom”. They do this carefully so as not to affect the reinforcing mesh and formwork..
After that, proceed to leveling the surface using the “float”. Processing is carried out until concrete milk appears on the surface..
The next step is to rub the colored hardener into the surface. Spread it in an even layer at the rate of 2-4 kg per 1 m2, and then rubbed into the surface with a trowel or trowel. It is the color of the hardener that will be the basic tone of the concrete. There are manufacturers who offer up to thirty basic tones to choose from, but if you wish, you can order any other color..
When the surface becomes elastic, it is the turn of the release powder. Most often it is black, but there are proposals for other shades (brown, gray, blue). This powder has several tasks:
- create a barrier between the stamp and the painted concrete;
- slow down the process of evaporation of moisture from the concrete stone;
- add “heterogeneity” to the main range;
- imitate the veins and blotches characteristic of natural stone.
The powder must be dispersed in two steps, carefully (especially in windy weather), use respiratory and eye protection. Consumption – about 100 g per m22.
Stamping and surface finishing
At the final stage, the top layer of concrete is stamped with special polyurethane molds. And you don’t have to buy them, you can rent them. There are dozens of form options, the choice depends on the tasks of landscape design.
Then, after a daily exposure, the powder is washed off. During this time, the hardener and powder “react” with the concrete stone. You can give a longer exposure – in this case, the effect of the color of the powder on the main tone will be more noticeable..
The wash is done with a stiff brush and detergents – the harder and longer you rub with the brush, the lighter the area will be. This creates an additional “play of halftones”.
The next step is cutting expansion joints. They are cut to a quarter of the thickness (reinforcement may already lie in half). It is recommended to maintain the distance between the joints in multiples of 25 dimensions of the thickness of the concrete coating. For stamped concrete, the cut of the seam can be aligned with the transverse lines of the drawing. The seams are filled with a sealant, and after three days the surface is covered with a sealant varnish.
After another three days, you can walk along the path.