Dowel and anchor technology

An anchor is used when the screw that is to be screwed in cannot be fixed in the building material on its own. Dowels also have the advantage that they guarantee the stability and security of the connection.

A distinction is made between plastic dowels, cavity dowels, panel dowels, tilt dowels, sound insulation dowels, metal dowels and long-shaft dowels. All these anchors are available in our eShop.

One option is to fill the drilled hole with plaster or a repair compound. This does not have to dry, but the plug is inserted directly into the hole and thus into the compound. Once the compound has dried, work can continue. Another option is to insert a toothpick between the plug and the wall to provide additional support for the plug. This allows the screw to be screwed in without the wall plug spinning.

Nylon plugs are not suitable for safety-relevant applications with constant tensile loads. They must therefore not be used for ceiling suspensions (suspended ceilings, pendant lights).

Metal anchors such as ceiling nail FDN II, nail anchor FNA II or drive-in anchor EA II with reduced anchoring depth should be used for fastening substructures made of aluminium or steel profiles.

In the case of wooden battens as a substructure for ceiling suspension, the long shank anchor SXR with safety screw can be used in the concrete ceilings. Single fixings should be used with the FAZ II M6 or M8 bolt anchor for use in cracked concrete.

Which drill bit to use with which anchor depends on the diameter of the anchor, but also on the material. Before the plug can go into the wall, it is therefore important to determine the right drill bit for the job. To test the wall material, we recommend drilling a test hole with a small drill bit. A masonry drill bit is best suited for this. You can also use a masonry drill bit to drill the dowel hole for most wall materials. A metal drill bit is suitable for plaster walls.

As a general rule, the diameter of the dowel should be the same as the diameter of the drill bit. You will find the diameter size for the correct drill bit both on the drill bit and on the plug packaging (as part of the instructions on how to fit the plug). The diameter of a plug is also always indicated on the packaging. If you are not sure what diameter the drill bit has, you can read it off the drill bit itself.

If the wall material is soft, such as aerated concrete, choose a smaller diameter for the drill bit than that of the plug. So if the plug is 5 mm wide, a 4 mm drill bit is recommended to drill the hole. This allows you to secure the plug, it sits correctly in the wall and does not tend to turn so easily when the screw is screwed in. It also increases the load-bearing capacity.

Depending on the masonry or condition of the wall, different drilling methods are available:

For pre-drilling and determining the wall material: simple rotary drilling.

Soft walls made of masonry, perforated brick and aerated concrete: standard rotary drill.

Very stable and resistant walls made of solid building materials (concrete): Impact drilling and hammer drilling make drilling easier, but are not essential. An impact drill smashes the concrete with fast rotation and a high impact rate with low single impact energy, while hammer drilling does this with slow rotation and a low impact rate with high single impact energy.

Place the dowel at the tip of the drill bit and mark the drill bit at the end of the dowel length with coloured adhesive tape. This allows you to see when the hole is deep enough when drilling. The drill hole should be at least as deep as the length of the plug. If a layer of plaster has been applied to the wall, you must add this to the drilling depth so that the plug sits in the solid wall material rather than in the plaster. If the hole is too deep, the plug will sink into it.

Hold the drill at a vertical angle to the wall at the point where you want to fit the plug. Always hold the drill at the same angle when drilling. Changing the angle will widen the front part of the hole and jeopardise the hold of the plug. A so-called drilling aid can help you to drill a straight and clean hole. Professional drilling aids can be adjusted to the drilling depth.

In most cases, the drill hole should be the same size as the diameter of the plug. However, this does not apply to soft materials. For these, you should drill slightly smaller holes than the diameter of the plug. This can contribute to a better hold of the plug.

If you shorten a plug, you should be aware that this will reduce the load-bearing capacity. If shortening is unavoidable, only shorten the rear part, i.e. the part that protrudes from the wall, using a carpet knife or pliers. It is best to insert the plug into the appropriate drill hole first and then cut off the protruding part of the plug. If the plug is made of metal, you should shorten it with a hacksaw.

Important! As always, the screw must be longer than the plug.

Most wall plugs can be used with chipboard screws and wood screws, i.e. the most common screws. However, some special anchors are designed for screws with metric threads. Screws with pre-cutters/milling ribs are not suitable for plastic plugs.

The screw must drill through the entire length of the plug to ensure a secure hold. As a rule of thumb, the tip of the screw must protrude beyond the tip of the plug by the length of one screw diameter. In this way, the maximum load-bearing capacity can be achieved.

As a rough guide, we recommend screws that are 2 cm longer than the plugs used for classic and universal plugs.

How do you get wall plugs out of the wall?

Flat-nose pliers are suitable for gripping the wall plug. Alternatively, you can also try screwing a corkscrew into the wall plug. In any case, you should proceed carefully and slowly so as not to injure yourself or break the plug.

Removing the expansion plug

The expansion plug, the most common type of plug, expands when the screw is screwed in and thus anchors itself in the wall. With this type of plug, it is important to unscrew or pull out the screw first before removing the plug from the wall.

Removing metal plugs

Removing metal plugs can be a little more difficult in some cases. Use flat nose pliers for this. In some cases, it is possible to lightly screw a screw into the plug and then pull the plug out. Make sure that the screwed-in screw is not too deep and that the plug is spread open. If you pull an expanded plug out of the wall, this can damage the wall.

Removing cavity wall plugs

There are different ways of removing cavity wall plugs. Some can simply be unscrewed in the same way they were screwed in. This is the case with various plasterboard plugs, for example. Tilted cavity plugs fall into the cavity as soon as the screw and holding device are removed.

Removing fanned cavity plugs

Cavity plugs that have been fanned out with installation pliers can be folded back together again by hitting the screw. To do this, unscrew the screw a little from the plug so that it just engages in the thread at the back of the plug. You stretch it out again by giving the head of the screw a short tap and can then easily remove the plug.

Remove the plug from the wall by drilling out:

A somewhat crude variant if you want to get a plug out of the wall is to drill out the plug. The drill bit should be just big enough to fit into the plug and grip easily into the plastic. The thread of the drill bit eats into the plug and drills it out. If you pull the plug out of the wall in this way, residue may remain in the drill hole, which is best removed with a hoover.

Can't get the plug out of the wall?

If you cannot remove the plug completely, it is best to cut it off with a carpet knife and seal the hole with a filler.

Dowel tensile force: The tensile force acts on the dowel in the longitudinal direction when it is used for suspensions on the ceiling.

Dowel shear force: The shear force acts in the transverse direction. It is the force that acts vertically on the anchor when it holds very flat objects on vertical surfaces, for example. The inclined force acts on objects with greater depth.

Dowel inclined force: The inclined force is a combination of tensile force and shear force that acts on the dowel when heavy objects that protrude into the room are attached to the wall. These can be wall units, for example. This force then not only acts vertically downwards (shear force) on the anchor, but also pulls it out of the wall (tensile force). How strong the inclined force is depends largely on the dimensions of the respective load.

These forces are specified in Newtons, whereby 10 Newtons (N) correspond approximately to one kilogramme. When calculating the dowel load capacity of wall units, the additional weight of crockery and similar items must always be taken into account. With a large plate, a weight of up to 1 kg can certainly be expected.