Hidden problems of using stone for facade decoration in cold regions
Cast stone and many types of natural stone are among the most difficult facade finishing materials in cold climates.
Surprisingly, all the major manufacturers and sellers of cast stone do not touch the real difficulties of installing their tiles on the walls of cottages, although they give many colorful pictures of these houses. You will not find them to recommend assemblies and technical solutions for finishing facades. Can you guess why? Our article may be the most complete overview of the problems of installation of cast stone.
If you study the manufacturers instructions for installing the stone, it appears that the sources of possible problems are: bad glue (read "not our glue"), a weak base and can be grout. In real practice, everything is more complicated. To make sense of it, you need to understand several things at once.
What happens in cold regions
An important physical process takes place in cold regions. Water vapor from warm areas is pushed outside, including continuously through the walls of the house. Because the absolute humidity at sub-zero temperatures outside is several times lower than the humidity inside a heated living house.
In fact, warm moist air (gas) penetrates the walls of the house and on its way out, at a certain point, as it cools, can even condense into real water (dew point).
And so with this moisture inside the walls engineers have to reckon with, especially when installing stone. In some cases, it must be helped to get out, in other cases it must be prevented.
What a modern private home is built of
In all likelihood, your house is made of autoclaved aerated concrete. It may well be ceramic block, hollow brick, timber or concrete. These are all vapor-permeable structures that actively move moisture through the walls in the winter.
What is cast stone
It is, in fact, a heavy concrete tile, with fillers (sand, screenings of different fractions). Tile is low-porous, as it is specially vibrated on the shaping table/platform.
Vapor permeability of such a stone is very low, like all heavy concretes.
Бетонная плитка, может весить от 16 кг/м² (под кирпич) и до 80 кг/м² (под дикий камень) — такой плитки много в ассортименте любого производителя. Итак, до 80 кг/м², и это без клея и затирки. Еще тяжелей натуральный камень — гранит, гнейс, базальт, травертин, мрамор, и у них так же плохо с паропроницанием.
In general, cast stone is a barrier to steam.
Imagine an 80 kg/m² stone glued with the best adhesive on the gable of an entryway where your loved ones are constantly passing through. You want safeguards just in case, don't you? It could happen that the adhesive and stone will get significantly wet from the inside and the water will freeze with expansion. And maybe not immediately (because the glue is good), but after many cycles of wet freezing and rapid heating in the sun, the stone will peel off.
Masonry joints help a little
УYou can lay stone with or without seams. If there are seams, you can use a grout that lets the steam through. The larger the area of an individual stone in such a masonry, the smaller the area of seams on the wall. Conversely, the smaller the tiles and the greater the width of the joints, the greater the area of vapor permeable through the grout.
Now let's look at the options of the finishing pie, because in each case the details are important. In each case, we will assume that the load-bearing wall is made of vapor-permeable materials, the house in a cold region. First, let's consider two "bonded" systems, where all the layers are in tight contact with each other.
Stone directly on the wall
Gluing tiles directly over the wall is risky.
The plane of maximum moisture will be right behind the stone. Part of the load-bearing wall, the adhesive and the inner surface of the stone will freeze in a water-saturated state, weakening the structure.
We have to install an additional metal system to hold the stone on the facade, with a thick mesh, dowel, pierons, piercing the stone to connect with the mounting system. All this immerse in a solution with a liquid initial phase, because of the extra water during curing, the layer turns out loose, in the cavities in the winter, the ice is formed.
There seems to be a simple solution: to prevent water from accumulating in the outside under the stone, it is necessary to prevent it from the inside into the wall. To do this, use vinyl wallpaper, paint with vapor-proof paints (their choice is small), covered with vapor-proof membranes. But this idea is almost impossible and expensive, because you will have not only the walls but also the ceiling / floor vapor barrier throughout the house.
Exterior insulation and finish system (EIFS)
Now the most popular method of insulation and finishing of private capital houses - EIFS (known in Europe as External Wall Insulation System (EWIS) and External Thermal Insulation Cladding System (ETICS)), but it is, at the same time, a complex system for the application of stone. In each case, you need to calculate the protection against over-wetting and crystallization of water, taking into account the material walls, the geographical location of the house, the area of the joints between the stone, with the selection of the type and thickness of insulation - to prevent moisture concentration in the vulnerable parts of the cake, such as wall, adhesive layers, rockwool.
In most cases, stone cladding requires slowing the removal of moisture by using non-wetting insulation with low vapor permeability, such as EPS, PIR. You can select the thickness and density (for EPS), so that the dew point falls on the body of the insulation, without damaging the structure. With sufficient insulation, the load-bearing wall will not condense moisture, or will be only in a small part of it. And the temperature is always positive there, so there will be no weakening of the structure.
However, there is a problem with the insulation fixing the finish layer. The stone is attached to the outer plaster layer, on top of the insulation, reinforced with steel or composite mesh (not to be confused with the plaster mesh). Reinforced mesh is attached to the wall through the insulation with galvanized steel screws in the expansion or chemical anchors.
In this case, the effective anti-moisture thickness of EPS - 100-200 mm. It turns out that we need to keep the structure weighing up to 100 kg / m on the shoulder of about 20 cm, with point fixing in the loose wall of the gas, ceramic block or frame.
Some stones and especially dark slabs of granite are so heavy and large in area that their thermal expansion and weight are already a problem for any adhesive. Therefore, they, too, are hung with steel hooks, pins and staples, followed by grouting the reinforcement space between the wall and the slabs.
There are also solutions to selectively support the glued stones with stainless steel screws that are supported on the head.
Such measures are particularly relevant in dangerous passageways above people's heads.
In addition to the static load, there is a ripple load from the wind through the «sail» of the outer layer on the anchors in the wall. You have to carefully select anchors for each of the available wall materials.
In order to reduce the lever load, with thick insulation, it is advisable to use MERK (Sormat) pendulum hooks, used for thick plaster, but the installation of such fastening system is more complicated and has its disadvantages. When pendulum fastening it is necessary to take into account the resistance to compression of the insulation.
The peculiarity of the situation is that in the technical albums of the well-known developers of EIFS solutions for concrete tiles on the facade is not at all. Ceresit has a solution for "breathable" ceramic tiles up to 25 kg/m2.
It turns out that the possible solutions for working with stone when insulating the facade using the EIFS method are not confirmed by official tests of manufacturers or suppliers of products, are the private opinion and the risk of individual planners, foremen and bold builders.
Next, consider options «unbound», «screen» finishing, solving the problem of moisture, but have their own weaknesses.
Ventilated facade system on cement board
This is a «self-made» ventilated facade by Knauf, although it is not drawn there in detail. On wooden or metal rails mounted on a plane of cement slabs (usually Knauf Aquapanel Outdoor), on which the reinforced layer of adhesive is applied with a coating, and then lined with stone. Solid wall can be insulated with rockwool, freely withdrawing moisture, with a ventilation gap. Solid wall can be insulated with mineral wool, freely withdrawing moisture, with a ventilation gap. Burning insulation is not used because of the high fire hazard of air "wells". Disadvantages of this system, the additional weight of the structure, sailing (wind can sway the wall in both directions, loosen fasteners). Cement boards, depending on the substrate, may eventually crack at the joints, which complicates the use in areas with a fine stone finish (majolica, mosaic). Very illustrative of this occurs on stucco facade.
Ventilated facade with tile rails
System type Ronson-House (with wooden uprights) and Ronson-500 (with a metal substructure) requires a special shape of stone and therefore is limited to a set of products. The stones themselves are close to rectangular. There is no capping and aesthetically this is not always a good thing. There is also a limit to the decorations, which also have to be special and made to order. At close range, as in private homes, the "noodle" stones, laid seamlessly, look good.
Three-layer facades with ventilation gap and stone finish
It is a reliable system if everything is done correctly.
The outer wall is usually made of face bricks, but cheap ordinary bricks can be used, which can then be faced with artificial stone or clinker tiles. The wall requires air holes at the bottom and top for moisture to escape from the inner cavity.
Such a system can be insulated with rockwool, but the air gap is mandatory.
Finishing layer is fully protected from the inner moisture and the wall and insulation is always dry - the properties of thermal insulation is not deteriorated.
Disadvantages of the system - requires a more secure reinforced foundation, and then - flying monolithic slab or a wide plinth, the outer part of which should form a horizontal support belt-excess for the erection of a heavy wall at the attitude (not including facing stone).
If the design of the foundation is good, you can build a reinforced support belt on the anchors in the already built house.
Exterior wall of half a brick or even thinner (Euroformats) - is an unstable structure, especially if it is built to a height of two or more stories (gable zone). Therefore, it must be reinforced and properly connected by flexible ties to the main wall.
It is necessary to provide and perform expansion joints, both vertical and horizontal.
Grouting the stone
The grout must be vapor permeable. The larger the joints, such as when masonry multifaceted stone, the more elastic the grout must be. Grout is used in the mixes. A common problem - efflorescence from mineral grout and mineral adhesive, it is just the result of the discussed transfer of moisture from the walls or washout when it rains.
It also happens at joints with poorly made flat roofs or pads - when snow melts water is filtered through the wall to the lining.
Modern expensive adhesives and grouting materials can cope with this problem. On facades, you must use adhesives class C2 on the European marking and grouting material class CG2.
Pauses in installation
The installation of artificial stone requires long process pauses that the customer may have to pay for. For example, after applying the base coat according to the technical instructions, it is required to wait 7 days for sufficient strength to build up. Grouting of the joints is possible after 14 days. It takes another 24 days to hydrophobize the stone. This process requires the preliminary development of a plan of works at the site to avoid downtime.
Stone finish strongly slows down the exit of moisture from the pie wall, so it is better to postpone the wet finishing work inside the house to the summer, when you can actively ventilate the house and through the open windows. Wet work inside the house in winter can lead to weakening and contamination of the finishing layer, the rockwool insulation will get wet, and moisture can protrude into the insufficiently sealed seams of the EPS and dowel fixing points.
For the spring and autumn period is important that the stone is already covered with hydrophobisator, cut off the flow of moisture from the outside.
In summer, you also need to dry the basement cavities, if any. Open the grids on all sides of the house, and make sure they are not blocked by gardening tools, boxes, etc.
If the house has radius walls in plan, finishing them with stone is a separate engineering task depending on the insulation and installation system. One important requirement is that the layer of glue should not exceed the thickness of the finishing material. And the smaller the size of the covering element, the smoother the roundness of the finish, A thick layer of glue on the edges of a long tile has a significant amount of shrinkage, which leads to tearing off or breaking the stone.
Additional operations with artificial stone
It is very rare for artificial stone to be made colored in mass. Care is needed in tiling and subsequent use. When purchasing stone for cladding, we recommend taking a couple of packs for routine repairs, replacement in pass-through areas, on the plinth. It is desirable to protect the cladding from rain sufficiently wide roof overhangs, plinth and facade eaves; from slanting rain will protect a quality hydrophobizer, which must be renewed after 5-7 years.
Before laying an artificial stone on the back side of the need to mechanically remove the «cement milk», this cement foam that appears during the vibration of a wet fraction of the concrete (specified cement layer should not be confused with a mixture prepared for the ironing of concrete). Frozen «milk» on the tile becomes an obstacle to the adhesion of the adhesive with the tile. Over time, the reaction with carbon dioxide turns into limestone.
Cleaning the cement slurry from the tiles is time-consuming, but necessary.
Filling the joints (dilation) of artificial stone is recommended to do sour creamy mass of the construction syringe. The risk of soiling the face of the stone is thus significantly reduced.
Our customers often comment on the durability of stone compared to decorative plaster, for example. We ourselves use stone all the time in the design (and supervise during supervised installation).
This review is not intended to turn customers away from stone, but for a general understanding of the complexities of using this beautiful material. We wanted to show that underneath the layer of reliable stone, there is always a supporting, compromised structure that is a weaker link than the stone itself, especially with design and construction errors.