Types of dowels for foam blocks: how to choose, install

Foam concrete blocks have long been used for low-rise construction.Owners of apartments and houses only note difficulties in selecting fasteners for walls made of foam blocks. Choosing the right dowel for a foam block is quite difficult; the material is durable, but too fragile. Therefore, hammering a cork into a wall or ceiling in the same way as is customary for brick or concrete will obviously not work.

Requirements for fasteners to foam blocks

We must immediately make a reservation, we are talking about walls made of foam concrete. It has fairly large pores filled with air. The material is quite soft and fragile, but if necessary, it can be drilled with an ordinary feather drill, even of a large diameter, 15-20 mm. Foam blocks are easily recognized by their characteristic gray color, since the basis of the material is cement.

The properties of the foam block determine the requirements for the fastening method. You can screw a self-tapping screw with a large spiral winding directly into the foam block, use a dowel with a plastic plug, or choose a fastener with a special configuration.

What you need to pay attention to when choosing a method:

1. The pressure on the walls of the hole must be distributed in depth, so the holes for the plug are made deep. If you try to install a short dowel in foam concrete, then when tightening the self-tapping screw or screw, the plastic will destroy the upper layers of the block.
2. The dowel plug must not be hammered into the hole in the foam block with a strong tension on the surface.Any friction between the outer surface of the plastic or metal and the walls of the hole breaks it into crumbs. Such fasteners will not hold in foam concrete, even if the self-tapping screw is screwed in with a slight interference fit.
3. For fastening in foam concrete, you cannot use screws, self-tapping blocks with a helical spiral whose vertices are rounded or too sharp (small pitch). They also destroy the foam block material without forming adhesion.

All of the above fastening options, as a rule, use dowels with a plastic plug and a long steel self-tapping screw. But foam concrete has a rather fragile structure. A plastic or metal insert can withstand static loads well when pulled away from the wall. But most often you have to look for a way to secure objects, furniture, door frames, brackets that create a dynamic load with a dowel on a foam block wall.

For example, if you need to hang a wall cabinet on a foam block wall in the kitchen, you can use the classic version of a dowel with a plastic plug, but it will not last long. Due to the swinging of the cabinet body (when the doors are opened), the dowel will “come out” of the foam concrete in a matter of weeks, so for dynamic loads you have to use metal dowels or fasten the cabinet the old fashioned way.

Varieties

Dowels are divided into metal “breakable”, wedging with a reverse cone, and plastic - with a bursting plug or twisting insert. There are also chemical dowels. But this is a completely different type of fastening and can only be used in limited conditions.

Usage options:

1. Light fasteners, for example, hooks, clamps, loops for fixing cables, wiring, small objects weighing up to 200 g, can be secured using a regular carpentry (black) self-tapping screw with a large screw winding. The length must be at least 60 mm, then it will hold.
2. Heavier objects, up to 2 kg, can be fixed into foam concrete using a classic dowel - a 6x60 mm nylon plug and a carpentry screw. For more complex loads, the plastic dowel must be selected individually.

For heavy objects, a chemical or metal frame dowel can be used. Usually these are ceiling mounts or the option of installing brackets with complex bending loads on the foam block.

Plastic dowel

For fastening into foam concrete, you can use any type of dowels with nylon or polypropylene plugs. There are many different options on the market with a fir-tree notch, screw, toothed (point) surface. All of them adhere quite well to the wall material, so they can withstand static pull-out loads relatively easily.

To attach furniture, such as shelves or cabinets, to the walls of an apartment or private house, use dowels with a plug with a diameter of at least 8 mm. The main condition is that the length of the plug and screw must be at least 60 mm. In practice, for fastening to a foam block, they try to use dowels with a diameter of at least 10 mm.

Another type of dowels for foam concrete is with a twisting plastic plug. There are longitudinal cuts on the surface, so during the process of screwing in the self-tapping screw, the back part is crushed and folded into a thickening.

In theory, pulling out such a dowel is much more difficult than a regular herringbone plug for brick.But in reality, the strength and reliability of fasteners with a breakable dowel depend on how correctly the diameter is selected and how the hole is drilled into the foam concrete.

For reinforced fastening, dowels with additional radial flanges are used. If you follow the installation rules, the strength of the dowel can be up to 20 kg, and when using adhesive mass - up to 30 kg.

Also, plastic dowels and self-tapping screws are often used for foam blocks. Essentially, it is a short, large-diameter screw with a large helical knurl. The design of the fasteners was developed for laying insulation on walls made of aerated concrete, but the dowels that “loved” began to be used for foam concrete.

Read this useful article: How and with what to tap walls for wiring

Metal dowel

For small fasteners on foam block walls, you can use split plugs. Essentially, it is a sleeve or tubular insert with a slight taper and longitudinal cuts. On the surface of the metal plug there is a toothed notch, thanks to which the dowel enters into a fairly strong adhesion to the material of the hole walls.

Of all the metal dowels, the split dowel is considered to be the easiest to install; in addition, the diameter of the hole for the sleeve is chosen slightly smaller than the size of the plug at the head. Therefore, even if the installation of fasteners fails, there will be no cracks or damage on the surface of the foam block. You can always try a different type of dowel.

The most reliable fastening is a frame dowel. It has a special design. The embedded element is made in the form of a split sleeve with two nuts at the ends. After installing the sleeve, tighten the threaded screw.At the same time, the distant nut begins to move towards the surface, squeezing and crushing the sleeve.

Thanks to the cuts on the sleeve, the material is easily deformed and rests against the walls of the hole. The pressure force is simply enormous, which allows the frame dowel to easily support a weight of several tens of kilograms.

The frame dowel can withstand static, alternating and bending loads. The mount is held on the foam concrete wall until the end, until the bracket is broken or the petals of the sleeve are deformed.

Article for you: How to choose good dowels for aerated concrete

Chemical anchors

This type of fastener cannot be completely attributed to dowels, although its design also contains an embedded part - a capsule and a load-bearing element - a threaded rod. Unlike other types of fastenings, a chemical anchor is glued rather than screwed into the mounting hole.

The essence of the installation is as follows:

• a cylindrical capsule with an adhesive composition is placed inside the hole in the foam concrete;
• when screwing the pin, the capsule squeezes out glue, which fills all the free space between the metal and the wall of the hole;
• after hardening, the anchor is firmly fixed inside the hole without any additional settlement or crimping.

Chemical anchors are used for heavy loads. In the description you can find values ​​up to 600 kg. But under ideal conditions, in practice for this type of fastener the limit is limited to 200 kg. Installing a chemical anchor requires careful preparation of the hole in the foam block and compliance with the sequence of procedures.

This is not a dismountable connection; if it doesn’t work out, then the pin will have to be cut off from the surface of the foam block with a grinder.In addition, a chemical anchor “does not like” vibrating loads, so it is used for fastening heavy but statically stationary objects.

But there are cases when a chemical anchor becomes simply irreplaceable. For example, when building a house from foam blocks, you always need to solve the problem of how to attach the Mauerlat beam to the upper edge of the walls. On brick walls, the mauerlat is secured with ordinary pins driven into the top row of bricks. This method is unsuitable for foam blocks, so chemical anchors are used to fix the beams.

How to install correctly - step-by-step instructions

Before installing the dowel into the foam block, you need to choose the right tool. You can tighten the self-tapping screw with a Phillips screwdriver, a screwdriver, or in some cases you will have to hammer it in with a hammer.

The rule is quite simple:

1. To screw the self-tapping screw into the body of the foam block, only a screwdriver is used. This is the only way to tighten the fastener without breaking the engagement of the spiral winding with the wall material.
2. In the case of dowels (the hole inside the foam block is 6-8 mm) with short “breakable” petals (up to 40 mm), a regular screwdriver is used. It is difficult to twist by hand, but this is the only way to correctly deform the petals and not turn the fasteners inside the foam block. But with some practice and skill, after a couple of hundred screws wrapped, you can get used to working with a screwdriver.
3. All dowels larger than 8 mm are screwed in with a screwdriver, including chemical anchors.
4. Large-diameter plugs with additional screw flanges on the surface, as well as all “folk” versions of dowels, are driven into the foam block with a carpenter’s wooden hammer. Wooden, because this is the only way not to break the hole inside the foam block.A carpenter's hammer (mallet) forgives slight inaccuracy when hitting a cork. If you use a regular 300-400 g hammer, then one wrong movement can lead to the surface of the foam block being punctured. It is recommended to use a regular plumber's hammer to hammer in steel cases - frame and split sleeve ones.

Installing conventional plastic dowels on a foam block wall

After marking the attachment point, you need to make a hole for the plug. For all types of plastic plugs, the depth of the hole is selected 10 mm greater than the length of the dowel. The diameter of the drill is 0.5 mm less than the size of the plug at its thinnest point.

Then everything is simple, a plug is inserted into the hole and pressed down by hand to the cut level. It is clear that the settlement must occur with force. This means that the plastic adheres reliably to the foam concrete. You don’t have to blow out the hole in the foam block; remaining dust will only improve adhesion. And everything that is unnecessary will be squeezed out into the depths. All that remains is to tighten the screw with a screwdriver, but without excessive force.

Advice! If the drill size was chosen incorrectly and a hole in the foam block is 1-1.5 mm larger than required, then before inserting the dowel, you need to dip it with PVA or office glue (liquid glass). Such a dowel will stay inside the foam block even better than a regular one.

Plastic dowels with screw or “wings”

Self-tapping screws with ordinary plastic plugs hold normally on foam blocks only if the load is directed horizontally or vertically. Any alternating loads knock out ordinary dowel plugs in a couple of days.

Therefore, to fasten heavy objects, plastic bushings with “wings” or “blades” are used.They are called differently, but the essence is that additional elements on a plastic plug increase the load-bearing capacity of fasteners on foam concrete by almost five times. Today this is the best dowel for foam blocks.

How to correctly install a model with “blades”:

1. The plastic case is marked, for example, “RD10”. This means that for fastening you need to drill a hole with a diameter of 10 mm in the foam concrete.
2. You need to drill with a regular drill and an electric drill with a collet chuck. A hammer drill with a quick-release chuck and a drill with a carbide insert breaks a hole in foam concrete up to 11-12 mm, and this is already a defect.
3. Now you need to insert the insert into the hole and hammer the plug completely with gentle blows.

You need to hit it carefully so that the dust from the foam block, cut off from the walls by the blades, has time to fall out and does not interfere with the progress of the plug. The blades fit into aerated concrete very easily; they can be driven in in 3-4 hits. For a foam block, the number of blows doubles or triples.

Advice! If the edge of the hole fell apart due to impacts, a piece of the foam block fell out, no big deal. You need to expand the size to 20 mm with a feather drill and glue the dowel onto the alabaster.

In addition to models with wings on foam blocks, plastic dowel screws are used. The plug looks like a large self-tapping screw with a head and a spiral winding on the body, similar to a thread.

Such a dowel is wrapped in a foam block like a regular self-tapping screw. But first you need to drill a hole to a depth equal to the length of the plug, plus 10 mm. The diameter is determined by the head of the “screw”. To screw it into the foam block, quite a lot of force is required, so a screwdriver with an attachment for the screw head is used.

Installation of frame dowels and sleeves

Metal fasteners are traditionally used on a concrete ceiling slab. On walls, steel frame dowels are used as an exception. Firstly, this is a one-time fastener; after installation, it is almost impossible to remove the deformed frame without destroying the foam block material.

Secondly, after installing the fastener, cracks appear. Therefore, frame dowels are used on foam block walls only where very high fastening strength is required.

To install, you need to drill a hole along the diameter of the insert, place the frame inside the foam block, secure it with one key and screw the head with the second.

The second type of metal dowels - sleeve ones, are used en masse for any finishing and facing work on the surface of the foam block. For example, for assembling sheathing.

To install the dowel, you need to drill a hole in the wall; the diameter can be found on the marking. But most often, craftsmen simply measure the diameter in the middle part of the split sleeve. After drilling, insert the sleeve into the hole by hand (about half will go in), and then hammer it in to the wall level with a regular hammer.

Unlike frame models, sleeve split dowels never break the foam block material.

Folk method of fastening for foam blocks

Many craftsmen use old proven methods of fastening with homemade dowel plugs. Despite their somewhat archaic nature, such homemade products can easily withstand the weight of heavy objects. With their help, it is easy to attach hanging furniture to the foam block. Homemade dowels are often used to fasten door frames and they serve no worse, and sometimes better, than plastic ones.

The traditional fastening method involves the use of homemade plugs cut from a wooden strip.Initially, you need to cut blanks from a square strip of 20x20 mm, 80-90 mm long. The back part (the one that will fit into the hole) is cut 3-4 cm in length and lightly trimmed into a cone with a knife. The cut is needed to wedge inside the foam block after tightening the self-tapping screw.

Next, at the fastening point on the foam concrete, a hole with a diameter of 19 mm is drilled to a depth equal to the length of the plug. All that remains is to drive the plug into the foam block to its full depth and screw in a screw or hammer in a nail.

Such a wooden insert holds up much better than plastic, and if you have to install a door in an opening, the plugs can be coated with glue so that they do not dry out over time. And although it takes much more time to install a fastener in foam concrete, it is almost impossible to tear such a fastener out of the wall, which cannot be said about plugs made of plastic or metal.

Results

Choosing which dowel is best to use will not be difficult if you know exactly for what purpose the fastener will be used. The size and shape of the plug and the method of its installation in the wall are selected accordingly. The method has long been worked out and tested in practice, so it is almost impossible to “miss” the reliability of fastening.

Tell us about your experience in choosing fasteners for foam concrete. Which ones do you think are the best? Also, bookmark the article and share it on social networks by reposting.