Important health and safety note: This is archived text from 2018. year, and not an assessment of a concrete wall, load bearing calculation or instructions for self-drilling and fastening. Before work, the material, condition and thickness of the substrate, the location of hidden electrical, gas, plumbing and other installations, as well as the appropriate fastening system and permissible load according to the manufacturer’s current documentation, should be reliably determined. Construction dust may contain respirable crystalline silicon, and old paints, plasters, coatings and insulation and other hazardous materials; proper dust extraction, eye, hearing and respiratory protection and professional judgment are required before disturbing unknown layers. Powder and other professional tools for direct fastening may only be used by qualified persons according to the rules for the specific tool and substrate. Heavy, hanging, dynamic, safety-critical and overhead items should be sized and installed by a qualified professional.
Attaching objects to the wall is not part of the new public offer of Savo Kusić. Current focus is wood windows, wood-aluminum windows, custom windows and doors. For a window or door project, you can send request for quote.
Fastening nails and hooks into walls
We can drive nails into concrete walls only with a gun. It is quite complicated to drive nails into brick walls as well. In most cases, knocking in is accompanied by the mortar falling off.
If we want to fasten strong nails in the wall, with a high load capacity, then dowels should be used. This not very convenient, but already domesticated name comes from the German word Dübel. Its original meaning is - a wooden insert that is placed in the wall with plaster. We can make this kind of insert from fir in the shape of a trimmed pyramid, whose bottom base is 10 x 10 cm. If we have cut out the insert, it should be placed on the wall with the lower base, mark the place with a pencil and then hollow out the wall about 10 cm so that the opening widens towards the inside. After this, the insole should be well wetted, the opening should be sprayed with water and plaster should be placed in it. We have to put some plaster on the bottom base and on the sides of the insert and then place it in the opening so that we fill enough plaster around it. Finally, the wall should be leveled. We have to work quickly with plaster, because it sets immediately. Only when the plaster is completely dry, we can attach the objects to the insole (fig. 1).
Image 1 — Historical representation of the installation of a wooden insert in the wall
In recent times, insoles made of artificial material are used. These liners are made of thermoplastic polyethylene that softens with heat, so heated screws must not be placed in them.
The length of the dowel is 45 mm, but can be shortened if desired by cutting off the end with the hole. The shape of the dowel is cylindrical, with a diameter of 6,8 and 10 mm. The outer surface is provided with ribs up to about three-quarters of its length. On the second rib, counting from the top, a tensioner is placed in the form of two small extensions. It prevents slipping out of the opening. Wood screws of 3-5 mm diameter can be placed in these inserts (for lighter objects, possibly also screws with normal grain), fig. 2.
Image 2 — Wooden insert and plastic dowel
For inserts made of artificial material, the corresponding holes should be drilled in the wall. Hand-held wall drills are best for this. If we want to place a screw with a smaller diameter in the insert (eg 3 mm), then the diameter of the drill should be slightly smaller than the outer diameter of the insert. For 4 and 5 mm screws, the diameter of the drill should be the same as the diameter of the insert. A wall drill is a three-bladed tool. It is drilled by hitting it with a hammer and at the same time turning it slowly by hand. Once we have drilled the hole, the insert is driven into the hole with light hammer blows so as not to damage the wall. It is recommended to put a glossy or painted pad on the screw to cover the hole in the wall, or end of insert.
Driving nails into a concrete wall — impact drilling
For drilling a concrete wall, we recommend several solutions, depending on who has what tools and who is willing to sacrifice for this purpose.
Apartment owners with greater pretensions usually also count on the fact that they will remodel the apartment premises later. If they still lack a manual electric drill in their tool kit, it pays to get one that drills with impact (eg types VV-110A1, VV-113A1 »lskra«).
Only carbide-tipped twist drills (vide) are used for drilling into concrete wall, as a normal twist drill would give out in no time.
For hanging lighter objects, it is enough to get drill bits with a hard metal insert with a diameter of 4-6 mm, and for heavier objects with a diameter of 8-10 mm. For hanging very heavy objects (above 100 kg) larger openings of 14-20 mm are needed, but it is more advisable to entrust this work to an expert.
The diameters, depths, angles, number of fasteners and loads listed in this historical text are not today’s anchor specifications. The bearing capacity depends on the specific wall, the condition and position of the substrate, the distance from the edges, the type of load and the exact fixing system; for heavy and safety-important objects, expert calculation and installation according to the manufacturer’s current documentation is required.
The positions of the holes should be marked exactly for better control of the drill, the surface of the concrete should be roughened with a chisel, or a three-flute chisel for drilling walls (so the tip of the drill will not walk). Then, with the impact mechanism on, we can start drilling the hole. The longitudinal axis of the drill bit should be normal to the plane of the wall, but for safer load bearing, it is better if the hole goes a little downwards, or if it subtends an angle of 95-100° with the floor plane. In this way and in case of overloading, the insert, screw or hook is avoided from slipping out of the wall.
The depth of the hole is determined by the weight of the object to be hung. For the nail, on which the picture will be placed, it is enough to drill a hole with a diameter of 4 mm, a depth of 20-25 mm and place a dowel (insert) made of artificial material or hard wood in this hole. If the insert is a little loose in the opening, we can glue it. After drying, the part of the insert that protrudes from the wall should be cut off so that it is flush with the wall and then we can hammer in a nail for the picture. For hanging heavier objects, four or more holes with a diameter of 8-10 mm should be drilled, because the load is distributed depending on the number of supporting elements (wood screws, nails, hooks). It is best to place artificial material inserts with a diameter of 4, 6, 8 and 10 mm, which can be purchased in stores, in the openings.
Drilling with an electric drill
With a simple electric hand drill, we can also drill holes in a concrete wall. But this kind of drilling requires more care and patience. We must have a twist drill bit with a carbide insert. With a bit of ingenuity, we can make our own drill bit that will fit the purpose just fine, instead of using standard twist drill bits. On top of a piece of steel with a circular section and a diameter of 1-2 mm smaller than the diameter of the hole, which is to be drilled, a hard metal plate should be welded (see). The appearance of the shape of the drill bit is shown in picture no. 3. Sharpening according to pictures a) and b) has the disadvantage that the diameter of the drill bit decreases after each re-sharpening, while when sharpening according to sketch c) the diameter does not decrease even after several sharpenings.
The previous historical statement about self-welding a hard metal plate to an improvised drill should not be applied. Improper material, fitment, geometry or balance may result in breakage and ejection of parts at high speed; use only an undamaged, factory-declared drill bit compatible with the tool and substrate.
Image 3 — Historical representation of the drill bit and blade geometry
Drilling with simple electric hand drills should be done gradually. Since the number of revolutions of the drill is high (1400 rpm), after drilling for 10-15 min, the drill should be turned off, cooled and turned on again. Namely, due to the high number of revolutions of the drill blades, they wear out quickly during continuous drilling, and the drill heats up to such an extent that the solder melts and the hard metal insert can fall off. Therefore, it is necessary gradually, or intermittently, drill.
Since this drill does not “impact”, the small pieces of pebbles that are in the concrete wall are not broken, so when drilling, you hear a grinding sound when the blade encounters these pebbles. In such cases, drilling should not be continued, as this would only ruin the drill bit, but the pebbles should be broken with a kirner or a three-flute chisel. After this we can continue drilling again.
This kind of periodic drilling is only apparently complicated, but in fact it requires a little more attention and patience.
Example of electric impact drill
Manual drilling
A manual drill (Americaner) can be found in most houses. Working with this drill is quite tiring. Namely, drilling requires a large pressure force, and at the same time you need to turn the drill and maintain the correct drilling direction. True, drilling individual holes takes a bit more time, but since the drill does not heat up too much, it can be drilled continuously. If the drill bit encounters a pebble, it should be broken, as with a manual electric drill, and then continue drilling.
In none of the described cases of drilling, the drill must not be cooled with water, because the hard metal can crack due to sudden cooling. Likewise, cooling and lubricating agents should not be used during drilling, as this would only ruin the drill blade (fine concrete dust mixed with cooling and lubricating agents will create a mushy paste, which acts on the blade as a grinding paste).
Drilling with a chisel
Drilling concrete with a three-slot dowel drill is the fourth and also the cheapest method of drilling. These drills are available in four dimensions (4, 6, 8 and 10 mm). The position of the chisel - drill should be normal to the plane of the wall, or at an angle of 95-100 degrees in relation to the floor. Drilling should be done with frequent blows of the hammer and in the meantime turn the chisel gently and continuously (fig. 3). We have to pull the concrete dust out of the opening through the grooves. (Once we reach a certain depth, the dust should be periodically blown out with a ball pump). The diameter of the hole drilled with this type of drill bit is always slightly larger than the diameter of the drill bit (chisel) and because of this, dowels of the same size will always wobble in the hole, so it is recommended to install dowels made of artificial material or wood with a larger diameter.
The historical statement about the blowing of concrete dust should not be applied. Do not blow the dust into the room with your mouth, compressed air or pump; use a suitable system for extracting and vacuuming dust according to the instructions for the tool and material.
We have already mentioned that we can glue the dowel in the air conditioner opening with concrete glue. Neither cement nor plaster should be used for this purpose, as neither is suitable.