Fasteners are one of the most important elements of any facade insulation system. A competent choice of dowels is the key to high quality and durability of the facade system.
This article discusses three main criteria that determine the correct choice of dowels for specific conditions.
Facade dowels are special fasteners that are used to install and fasten various structures and materials to the walls of buildings. There are many types of such elements, but the plate-shaped facade dowels are most in demand.
Attach with the help of a wall dowel front such elements as:
- facing of the building;
- thermal insulation;
- wooden structures;
- metal profile constructions;
- wall cabinets and more.
Most often, the facade dowel is used specifically for the installation of heat-insulating materials, since its use allows achieving maximum adhesion of the heat insulator to the wall surface. In this case, fixation occurs precisely due to the wide cap-plate of the fastener and the clamping effect of the screw core.
What are they made of?
The plate-shaped dowel got its name because of the non-standard shape of the hat, resembling a small plate or hat of a mushroom. Such fasteners are made either entirely from polymeric materials, or partially from metal, which allows you to securely attach the material or structure to the facade of the house.
The facade dowel consists of a retainer, anchor and spacer elements. The latch is made of plastic, the anchor element is made of polyamide, and the spacer is made of fiberglass, basalt plastic or metal.
A distinctive feature of the facade dowel is a longer rod in comparison with other types of dowels – this is what allows it to be used for fixing thick materials and structures with a large cross section.
Some types of dowels are even equipped with special antennae, which allows you to securely fix them in hollow and soft products.
Reviews: advantages and disadvantages
According to experienced builders, a wall dowel has a lot of advantages, including:
- maximum material fixation (increased wind load to constructions fixed in this way is not terrible);
- resistance to temperature fluctuations (the dowel can serve in the range from -40 to +80 degrees);
- resistance to corrosion processes and resistance to mechanical stress.
Moreover, the disadvantages of such fasteners include a rather high cost. However, high-quality products cannot be cheap, so properly selected dowels are a good investment in the future.
Types of facade dowels
Today, experts distinguish two types of facade fasteners:
The first, as a rule, are used for mounting brackets, and it is recommended to use plate-shaped dowels for cladding facades.
Depending on the material of manufacture, dowels are polymer and with a metal nail.
What sizes are there?
We suggest that you familiarize yourself with the table of the ratios of the dimensions of the dowel and the thickness of the heat-insulating layer:
|Length of facade dowel, millimeters||The maximum allowable thickness of the insulator, millimeters|
The bearing bases of buildings are divided into three types:
- solid solid foundation (concrete, ceramic and silicate solid brick);
- solid hollow base (alkaline brick, hollow concrete or expanded clay blocks);
- porous solid base (aerated concrete, gas silicate blocks).
In modern dowel technology, various anchoring principles can be implemented. For each type of support base, the optimal anchoring principle is selected. So, in strong substrates, friction anchoring is used, and in porous – anchoring with the shape of a dowel sleeve. Why is this necessary?
Porous bases (aerated concrete, gas silicate) have an increased ability to fracture at constant pressure. For this reason, for buildings with a porous base, it is impractical to use dowels, the anchoring of which is carried out by friction. It should be noted that when anchoring by friction in aerated concrete in the initial period (up to 3 thousand hours), acceptable force values are observed when testing the dowel “to break”, then the situation deteriorates noticeably, and after 10 thousand hours the maximum loads perceived by this dowel are much reduced. This fact is confirmed by numerous studies (this property of aerated concrete has been studied especially comprehensively in Germany).
Anchoring the shape of the dowel sleeve allows you to avoid pressure on the material or, more precisely, to make it non-determining during the operation of the dowel. The protrusions on the dowel sleeve form “pockets” in the aerated concrete, which do not work on the spacer, but on the shear of the BUT material. This fundamental difference made it possible to achieve the most reliable, and most importantly, durable anchoring in such a difficult material as aerated concrete.
Dowel head shape
This aspect is often, sometimes at the highest and most technically competent level, overlooked. In order to correctly assess the value of the shape of the head in the operation of the dowel, it is necessary to clearly understand how the dowel “works”: how it perceives and transfers the load to the supporting base. When considering the interaction of the dowel head and the bracket in the facade system with the air gap, special attention should be paid to the influence of the shape of the head on this interaction.
In order to reliably transfer the load from the bracket to the carrier base through the spacer element, it is very important that the head rests on the bracket along the plane.
Unfortunately, in practice, the use of so-called frame anchor dowels for mounting brackets is very common. Frame dowels have a “flush” conical head and are used to fasten window frames or a wooden beam; they fix elements having a conical landing nest or low compressive strength, which allows this nest to be formed during installation. When fixing steel or aluminum brackets with frame dowels with a hole for an anchor dowel, the dowel head and bracket contact in the best case along the line, and in the worst case (in the case of an oval hole) at two points. In this case, there is no need to talk about reliable and durable fastening, because the polymer material of the dowel sleeve separating the head of the spacer element and the bracket will simply be cut over time with the sharp edge of the bracket hole. This will lead to the appearance of backlash and the risk of destruction of the connection. In addition, there is a possibility of moisture penetration and corrosion of the spacer element.
Most system manufacturers recommend that the anchor dowel be positioned so that the dowel sleeve separates the bracket and the spacer. The implementation of this recommendation is very important, since its implementation eliminates the likelihood of electrochemical corrosion, which occurs in the presence of a pair of metals that are far from each other in the electrochemical series, and a conductive medium (water). For example, zinc and aluminum, steel and aluminum, corrosion-resistant steel and aluminum form pairs that are prone to electrochemical corrosion.
Electrochemical corrosion is dangerous by a significant decrease in the strength properties of the material, as a result of which destruction of the compound is possible. Electrochemical corrosion can be avoided if there is a polymer washer on the dowel sleeve that separates the material of the spacer element and the system bracket. In addition, the polymer washer contributes to a more even distribution of the load when twisting the spacer element and prevents mechanical damage to the bracket, for example, punching.