Fixation items for construction

For over 16 years now, we at VIDIRA continue with our efforts to improve the quality of the products that we offer you and invest in the development of new items that you will find on the market.

We express our gratitude to all of you who prefer our products and invite those of you who are not familiar with them yet to convince yourselves that you can improve the profitability of your installation works through appropriate solutions for quick and qualitative installation and therefore, the quality of your product as well.

The high quality of the fixation products by VIDIRA is acknowledged by the authorized and accredited laboratories at the scientific research and design centres of the University of Architecture, Civil Engineering and Geodesy and the Higher School for Construction Liuben Karavelov in Sofia by issuing Bulgarian Technology Approval and certificate for compliance with the EU requirements.

Major principles

Major principles in the fixation technology

During the processes of design, fixation and sale of each product it is important to know the main determinants influencing the selection and application of the fixation product. That is why it is essential to provide brief technical information.

The various construction materials provide different conditions for dowel fixation. Hardly does a foundation exist without allowing fixation. On the contrary, it is the foundation quality that conditions to the highest extent the selection of the proper type of fixation and preliminary forces.

The most important foundations for dowel fixation:


Under concrete is generally meant concrete produced from cement, filler (sand, gravel) and water. Through hydration process the mixture of cement hardens, cement stone being obtained as a result, which is crucial for the concrete’s hardiness. The duration of the process of hardening is also influenced by the type of the used cement, the filler content, the water – cement ratio, as well as by temperature and humidity.

The concrete strength is expressed usually as stability under pressure that is examined by certain test samples like cubes and cylinders.

Caution! Dowel fixation is not recommended before the expiry of a seven-day period of hardening.

Concrete also demonstrates relatively high pressure strength, but insignificant snatch strength. For this reason, in order to absorb the tension forces in concrete shuttering is usually included. In the tension zone of the concrete and steel structures under operating load, the following is taken into account: Cracks in the concrete

These cracks can be hardly established, but they can reach up to 0.2 mm, in extreme cases even up to 0.4 mm on the surface. The cracks continue under bending loading in a wedge form through the depth of the structure element and end close to the natural fibres (threads).

Therefore, the application of dowels with additional unfold and force control action is recommended in the tension zone. Another solution in this particular case may be the application of dowels that can penetrate so deeply that their area of fixation lies in the pressure zone.

Caution! Cutting of shuttering steel for holes and dowels must be always and in all occasions approved by the respective engineer in charge of the measuring.


Masonry is a kind of inhomogeneous foundation. The dowel hole may come across construction mixture joints and hollow spaces. Because of the relative low masonry strength too high loads cannot be accepted.

On the market in Bulgaria one can still find various types and shapes of bricks:

  • Baked thick clay bricks, without pore formation additives, with minimal low scope strength from 12 to 20 N/mm2 N/mm2 Thick bricks
  • Bricks with pore formation additives, with minimal low scope strength from 6 N/mm2 Hollow bricks
  • Lime – sand (silicate bricks) – produced from quartz, lime and water, by means of thermal processing. The minimum pressure strength amounts to 6 N/mm2Lime–sand (silicate bricks)
  • Aerated concrete – fine pore concrete consisting of fine grain additives, binding substances (cement, lime), gas forming additives and water. The pore content is crucial for the minimal pressure strength, the bulk weight and the heat conductivity index. The product is delivered with various types of minimal strength of 2.5; 5.0 or 7.5 N/mm2 Aerated concrete
  • Light concrete – the most commonly used construction light concrete consists of sand, ceramist balls and cement. It is applied when good heat insulation must be achieved or for carrier components with low load from the own mass. Respectively, pressure strength of 15 to 35 N/mm2 can be provided for.Лек бетон
  • Gypsum- Gypsum hardens upon water absorption. It is used mainly for carrier components like wall and floor panes. The gypsum solubility in water restricts its application mainly to almost exclusive indoor use.Gypsum
  • Wood fibres, bound with cement – the wood fibres are bound with a mixture of cement and water. These light materials serve mainly for insulation and they can conduct small forces only.Wood fibres, bound with cement

Dowel fixation

The fixation or the installation of the dowels is performed as follows:

  • The hole is bored mainly by means of hard alloy drill and percussion rotation machine. If during drilling a reinforcement is encountered, this is established from the lowered progress deceleration and vibration intensification. The process must be terminated immediately so as to spare the drill and avoid any detrimental consequences.
  • The hole depth for each dowel can be obtained from the fixation data included in the technical specifications of the Vidira products. It must be complied with on a mandatory basis, especially for anchors with low fixation depth, as for example VND dowels. For dowels that position automatically with hammering through the screw head or the nut the hole can be a bit deeper without resulting in change of the bearing capacity.
  • Thorough cleaning of the drilled hole from any dust, for example by means of scavenge with a specially adapted appliance for this purpose, will lead to the optimal dowel function.
  • Setting of the dowel:
    1. With preliminary assembly – before the tem is fixed;
    2. Together with assembly – through the preliminary bored and correctly situated detail, holes are made into the foundation. Then the dowels are put into the detail to the foundation and fixed.
  • Normally through tightening of the dowel, the dowel fixation process is completed.

Errors made in dowel application that lead to reduced bearing capacity.

Here are some of these:

Error chart
  • Application of a drill that is too big;
  • Wrong boring approach: percussion boring when only rotation boring is required – for example in masonry;
  • Drilling NOT at right angle to the surface;
  • Holes that are not cleaned;
  • Insufficient fixation depth into the bearing foundation, for example in case of plaster or layers of insulation materials.