- Varieties of permanent formwork systems
- Constructive variety of permanent formwork
- Types of permanent formwork according to the characteristics of the insulation
- Permanent formwork types by materials and cladding arrangement
- Fixed formwork: prices
In the second part of the article, we will talk about various structures of permanent formwork and the materials that are used to create such systems. We will also talk about how economical this construction method is..
There are dozens of companies on the market that produce fixed formwork. The overwhelming majority of manufacturers are our domestic companies, many of which are improving the well-known technology in every possible way. Interestingly, they manage to create not just marketing options, but systems with new performance characteristics and more affordable prices..
Varieties of permanent formwork systems
Constructive variety of permanent formwork
According to this criterion, we highlight the following options, which differ significantly in terms of construction technology and performance:
- Reinforced flat panels.
- Frame systems:
- cast blocks from expanded polystyrene;
- prefabricated blocks of various sheet materials.
The fixed system, made in the form of a frame, consists of two formwork contours, inside which steel reinforcement is laid and concrete is poured. The sectional wall has a formwork-reinforced concrete-formwork structure.
These structures are in the form of blocks, which are separated by vertical seams in a checkerboard pattern and lean against each other during exposure (without the use of adhesives and solutions). In some cases, formwork elements of different rows and at the ends can be connected by means of locks – grooves or selected quarters, which greatly facilitates installation and eliminates the outflow of mass. Blocks are solid cast or collapsible.
Cast permanent formwork is popularly called “thermoblock”. Everything here is made of gas-filled polystyrene foam or its derivatives (density from 25 to 40 kg / m3), and both sheets are already at the manufacturing stage are connected by rigid bridges of the same material. The dimensions of cast blocks from different manufacturers may differ, but on average it is about 1000x250x250 mm (weight is about 1 kg). The thickness of the insulation is around 5 centimeters, the thickness of the concrete is 150 mm (about 0.13 cubic meters per square meter of the wall). It is interesting that no more than 3 rows can be concreted, ideally two and a half so that the seam is located in the middle of the blocks. Low-power vibrators are used, often the concrete mass is compacted by bayonet.
From the unpleasant:
- Inside the room, a layer of foam is formed, which must be protected from damage (glue gypsum board, assemble frames and install cladding …).
- Connoisseurs of sustainable materials have concerns about the emission of harmful substances.
- The dew point inside the outer wall behaves unpredictably. Due to the presence of insulation on the inside, we cannot properly warm up the concrete core. Therefore, at minus “outboard” temperature, the dew point is somewhere in the array, near the foam of the room (this means that if there is excess moisture and poor heating, then condensation may fall out).
- Since the blocks are ready-made and quite bulky, it can be difficult to organize their delivery and storage..
Prefabricated blocks are two sheets of different materials (wood concrete, polystyrene, gypsum, cement …), which, before being installed in the design position, are assembled into a three-dimensional spatial structure using special accessories. The distance is maintained by using several spacers made of polymers (so as not to form cold bridges). Spacers can also tighten the panels, but sometimes removable ties are used for these purposes, including made of metal.
Compared to cast systems, a wall cake can contain more than three layers, and in any combination of materials. For example, two rigid sheet claddings are often used, and polystyrene foam is placed near the outer sheet as a heater. The sectional wall looks like this: “outer rigid sheet-foam plastic-reinforced concrete-inner rigid sheet”.
The main advantage of a collapsible block is the ability to change the width of its internal cavity, for example, in order to use a thicker insulation. It is only necessary to order a different size of ties / spacers.
Here, too, the issue of the dew point wandering in the wall is easily solved. Styrofoam is not placed on the inside, and the wall heats up well.
Collapsible blocks can be made independently, they are convenient for transportation and storage.
“Formwork 3D” or reinforced self-supporting panels is a rather exotic method of construction, but already time-tested and gaining popularity in the post-Soviet space. Here, a polystyrene foam plate with a thickness of 100-270 mm and a density of 15 kg / m 2 acts as a form-building element.3, which is reinforced on both sides with a 4 mm black welded mesh with a cell of 50×50 (the one used when pouring screeds). The grid maps are connected by a W-shaped wire track running through the foam board. The panels reinforced in this way have a size of about 1200×3000 mm, therefore they are exposed to the height of the entire floor and propped up. Then, on both sides, they are covered with several layers of strong concrete (B30 and higher), ideally, torqueting installations (spray of a solution under pressure) are used to apply the mass, but manufacturers also approve of manual technologies – such as throwing a “fur coat”. The concrete layer on each side should be about 5 cm, it will clamp the insulating core and perform load-bearing functions. Although it seems unlikely, the bearing capacity is very high, as well as the impact strength – on the basis of these panels, floors and roofs are even assembled.
Essentially, the developers have combined panel and monolithic technology. The section of the wall looks like this: “sand concrete-reinforcement-heat insulator-reinforcement-sand concrete”. What’s great about 3D panels is:
- the ability to install insulation of various thicknesses;
- the ability to pour inclined planes and volumetric elements (concrete does not flow down due to mesh reinforcement);
- no foam inside the room (ecology, dew point, the need for additional cladding);
- external concrete perfectly protects structures from water and corrosion (if you use concrete for shipbuilding purposes, waterproofing is not needed at all).
Types of permanent formwork according to the characteristics of the insulation
Insulation in a permanent formwork system can play the role of a form-building element (thermoblocks, reinforced panels), or it can go as an additional insulating layer. In the second case, you can “play” with heaters and get some additional technological and economic bonuses. For example, if we do not want to have foam inside the room, we choose a prefabricated block and lay the foam only near the outer panel. We can completely abandon the use of insulation, for example, if we pour partitions, and there are no special requirements for sound insulation, or maybe we are building columns, a fence or walls of an unheated room. There is also a formwork, to the outer panel of which high density basalt wool is attached from the outside, suitable for finishing the facade with a wet method.
By the way, if you do not take into account the purely foam thermoblocks, the insulation material can be not only expanded polystyrene, but also polyurethanes, expanded perlites, foam glass, mineral wool, mats of plant origin. The main thing is that the density and design resistance to heat transfer of these materials allow them to be used in a permanent formwork system..
Permanent formwork types by materials and cladding arrangement
This point more refers to collapsible blocks, since shaping panels can be made from a variety of materials, often in combination. In any case, these are durable sheets that calmly resist moisture.
The classic of the genre is expanded polystyrene with a thickness of 50 mm, applied, as a rule, only outside (we have already spoken about the reasons).
Mineral sheets are also used to create the block. Decorative sheet concrete with a thickness of 30 mm is often used as the finishing of the facade, and gypsum panels can be used inside the building (they can be putty immediately).
An intermediate option between foam and mineral is polymer concrete. These are panels made of cement mortar filled with large expanded polystyrene granules. The advantage of this material is reduced weight with increased resistance to heat transfer.
Particularly noteworthy are eco-friendly slabs created on the basis of cement binder and plant fibers – wood concrete. The filler can make up to 80% of the volume of the product, for these purposes wood chips, agricultural waste (straw, cotton, crushed hemp and flax …) are used. Fiberboard material is also used in formwork – a mixture of softwood shavings and caustic magnesite.
Increasingly, permanent glass-magnesite formwork can be seen on sites. By the field of application, this material is an analogue of GVL, dense (about 1000 kg / m3) and moisture resistant, with good adhesion to concrete. It is made from caustic magnesite, reinforced with fiberglass.
It should also be borne in mind that collapsible blocks after pouring can be partially dismantled, which can significantly save money. For example, if you are building a non-residential heated building, such as a warehouse or a farm, then interior decoration is not needed. Such formwork is also purchased for the construction of cottages. Insulation is laid outside, it stays and works there, and the inner panels are removed and used to assemble the blocks of the next two rows. In such a configuration of a partially fixed formwork, moisture-resistant plywood or OSB with a thickness of 20 mm or more is used. After the walls are erected, expensive material remains on the farm.
Fixed formwork: prices
The main concern of the average private developer is cost savings. Manufacturers of permanent formwork claim the fantastic cost-effectiveness of construction using this technology, which is several times cheaper than traditional options. Is it so? Many people who are far from construction see the high price of components for permanent formwork and do not represent the benefits of this technology, but meanwhile, here it is necessary to take into account the savings on subsequent operations and materials for them, as well as on organizational issues. Others fully believe in super-cheap miracle technology. It is not correct to sum up the cost of panels and add cubes of concrete. In any case, in order to compare something, you will have to calculate the object completely, deduce the cost per square meter of the building by the floor (such estimates are freely available, they are quite adequately drawn up). Of course, the cost indicators are 3-4 times less compared to, for example, a house from a foam block is not obtained. Especially if you comply with all building codes in terms of organizing efficient ventilation, observing the correct percentage of reinforcement of monoliths or making the required grade of concrete. But to save a third of the budget is quite real. Availability is always relevant, but fixed formwork pleases novice builders and other delights.
Still, prices: the approximate cost of one square meter of a private house (construction of one and a half floors; rough work, taking into account stairs, windows, roof …), which was built using block permanent formwork, is located in the region of 225 cu. e. A similar picture emerges when using 3D reinforced panels. To be more specific, note that a square meter of a wall will cost about $ 65-100, depending on its design characteristics. Let’s compare: to build a square meter (by floor) of a similar foam block house, you need to pay more than $ 300. e. Please note that these figures are based on the use of proprietary formwork and construction fees. But if there is a desire, then collapsible formwork blocks can be made independently without problems, you just need to find high-quality material and buy suitable components from official suppliers – spacers, ties, fasteners.