Plinth finish for natural stone

Recommendation points

• What is imitation stone
• Used plaster solutions
• Preparation of the foundation before finishing
• Plastering
• Joining and invoicing methods
• Final processing of the simulation

Something in between basement siding and natural stone is an imitation of the latter. We offer an overview of the most common techniques for performing this type of finishing, their advantages and weaknesses, as well as recommendations for doing work with your own hands..

What is imitation stone

Natural stone, be it hewn granite or façade tiles, requires exceptional bricklaying skills. The cost of such a finish is very high, but it is this type of foundation that looks the most natural and solid. If you do not take into account the physical and mechanical qualities of the stone cladding, but only its appearance, there is a finishing method that can quite plausibly imitate the stone.

We are talking about special artistic methods designed to give the surface of the plaster the look of masonry. Due to the network of deep grooves, a visual imitation of masonry, either rubble or hewn stones, is performed. At the same time, flat areas between the seams are also processed with a set of techniques, because the surface of even very high-quality processed stones cannot be perfectly flat.

The main advantage of this technique can be called the availability of development by beginners from construction, not particularly experienced in plastering and painting craft. It is possible to simulate a stone on a plinth with the help of the most primitive tools, while there is always a margin for error: if the appearance is unsatisfactory, the plaster can be re-leveled, and then re-applied the texture and jointing. There are, however, and professional techniques that require careful selection of the composition of the plaster mix and a number of special devices..

The disadvantages of imitating a stone basement are the same as for ordinary plaster: high hygroscopicity, low frost resistance, a tendency to overgrowing with moss and algae with limited ventilation. Most of these “diseases” are quite easy to eliminate through the use of special construction chemicals, because even when using the highest quality materials, the finish differs extremely favorably in price from natural stone.

Used plaster solutions

The most suitable composition for plaster imitation stone is considered commercial sand concrete of the M150 brand, mixed with a W / C ratio of not more than 0.35. Washed river sand of fraction 1–2 will be most suitable as a filler..

When preparing a mortar for plastering on your own, you should use cement of a grade of at least M400 in a ratio to the filler of at least 1: 4.5 or grade M500 in a ratio of 1: 6. The sand must be carefully prepared: cleaned from organic impurities, dried and sieved through a sieve with a mesh of 2-3 mm.

With the recommended W / C ratio, the mixture will not be plastic enough, it is recommended to increase its mobility by adding surfactants to the water in a ratio of about 0.02% by weight. It also shows the use of frost resistance modifiers, which provide a closed pore structure in conditions of impossibility of compaction of the mixture by vibration. For these purposes, the most suitable is the use of aqueous solutions of potassium and sodium silicates.

Replacing part of the filler with porous materials of a fine fraction (perlite, vermiculite) is possible with the understanding of how such inclusions will affect the final appearance. Improving the heat-saving properties of the plinth finish is a fully justified practice, however, adding foam crumbs to the solution should be avoided.

Preparation of the foundation before finishing

There are two special cases of finishing the basement – with and without insulation. It should be understood that in any case, the concrete surface must have reinforcement of the trimmed plane, anticipating the formation of cracks. Their appearance on the finished finish will give out a fake of natural stone due to the pattern of cracks, which is not typical for real masonry.

So, the reinforcement of the outer plane can be performed with a steel reinforcing mesh with a cell of the order of 150-200 mm, which is laid in a concrete layer with a protective layer of at least 20 mm. If the foundation plane has not been reinforced, the mesh is installed in the outer plaster layer. In this case, it is imperative to pre-spray with a layer of about 10–15 mm, and then fix the mesh. In this case, it is better to choose a smaller cell size – about 120-150 mm.

The preparation of the insulated basement is carried out using a fiberglass facade mesh. It is laid in two layers: the first one immediately after preliminary spraying with a thickness of 20 mm, the second – after another 20 mm. After laying the second layer of reinforcement, the plaster “crust” is fastened through the insulation using disc dowels with a spacer. Final preparation – throwing another 25-30 mm of plaster, thus, the final thickness of the plaster increases to 70 mm.

The preparatory layers can be thrown both along the lighthouses and without them with the alignment of the baseline line along the berth. The final plaster cast is carried out without thorough mashing, but deep cracks and voids are not allowed through which air and moisture can penetrate to the reinforcing elements. The plaster is kept for 4 weeks, then covered with 1–2 layers of quartz reinforcing soil, after having removed the crumbling filler particles from the surface. The surface is now completely ready for decorative finishing.

Plastering

The final layer of plaster, which will be decorated to imitate stone, is performed with the same composition that was used in the preparation. For the most believable appearance, a joining depth of about 15–20 mm is required, while a whole layer of about 10 mm should remain at the bottom of the joints. Thus, spraying is done with a total layer of about 30–35 mm..

For the finishing layer, careful alignment is not particularly important, much more critical indicator is the density of the fill and its thorough compaction. For this reason, it is recommended to use a trowel or trowel instead of a plastering bucket. Carefully pushing through the plaster, layer by layer, a common plane is brought out, which is leveled purely visually.

It is optimal if the finishing work is carried out by 2-3 people. One applies the finishing layer, the other two follow and perform textured surface treatment. If such a strategy of actions is not possible, plaster should be carried out in sections of 3.5-4 m², after all, decorative processing should be carried out on a still fresh layer of plaster.

Joining and invoicing methods

After drying, the cement plaster becomes granular and fine-pored, which is not quite natural for most types of rocks. Removing texture and applying jointing is the most creative and delicate part of the finishing process, which determines the believability of the appearance..

It is required that the surface has acquired some semblance of a glossy film, which is possible by squeezing a small portion of the dissolved cement onto the surface. The best way to achieve this effect is to sprinkle the freshly applied solution with a small portion of water and cover the surface with a film about 10-15 microns thick. The film is laid on the surface and rolled with an effort with a hard roller, without smoothing out the folds. At the same time, through the transparent shell it is clearly visible how cement milk accumulates on the surface.

When the film is rolled, it is unevenly pressed with a large dense sponge or rag, setting the primary surface relief. Then the film is kept for 15–20 minutes and torn off the surface in a horizontal direction. You need to act carefully so that the finish layer does not leave the base.

You can add additional variety of texture in the following ways:

1. With the help of a damp sponge or brush, with which light movements wipe the most protruding parts of the relief.
2. A fleecy roller, with which the edges of future “stones” are lightly rolled.
3. A spatula, which is stretched in random places, forming nodules that simulate chips.
4. Textured PVC film or a piece of fabric pre-impregnated with silicone.

When the general texture and relief are set, the surface is embroidered. In the simplest case, this is done with a sliver or a sharpened paint brush handle. Joining can be done either under a ruler or by random lines forming a non-repeating pattern.

When scraping the furrows, their edges will crumble and crumble. To make the appearance of the seams more natural, the loose plaster is removed with a metal or hard synthetic brush. It is also possible to punch the seams with a soft wedge with a smooth surface. It must be remembered that the lines of the seams should not intersect large protrusions or depressions of the relief, which in a natural finish never pass from stone to stone.

An alternative method of applying jointing is to use special stencils. They are applied to the plaster immediately after applying the texture, having previously moistened the inner surface with water, then tapped with a mallet. The resulting impression is almost completely finished jointing, it remains only to check the seams for defects and eliminate them. The disadvantage of this method is the repetition of the pattern and the difficulty in aligning the seams in adjacent areas..

Final processing of the simulation

Almost no type of natural stone has a uniform gray color. To imitate the appearance of the rock, you should use latex facade paint, tinted in several tones from brick red to sand or black..

The paint is applied in several layers, overlapping each other, and then rolled out with a roller to partially mix the color. If the established color composition does not meet expectations, you can wait until dry and apply several coats over the existing ones. It is quite simple to choose the main tones for tinting from photographs of rocks, one thing is important – not to use too bright and saturated colors.

There are two techniques to simulate graininess. The first is spraying small drops of diluted paint with a brush. The second method is to unwind a roller with a long nap, slightly moistened with paint, 20-30 cm from the finish surface.

You can add a more noble look with a patina effect. To do this, you will need a very light color paint and a wide brush with a long bristle. With its help, with light sliding movements, scuffs are applied to the most protruding parts of the imitation, it is only important not to overdo it with lightening.

When the staining of the stones is over, you should remove the traces of paint inside the seams. Here, the coloring is carried out in a single uniform tone, while the darker the tinting, the more noticeable the seams will be and the more pronounced their visual depth will become. If the entire plaster surface is covered with at least 1–2 layers of paint, the base can be considered reliably protected from frost and atmospheric moisture. Additional processing is possible, if desired, to give the stones a glossy shine, for which a transparent deep penetration primer is optimal.