LSU or glass-magnesium sheet: application and characteristics, comparison

Recommendation points

• The essence of the scandal around LSU
• Characteristics and classification
• Technical purpose of glass-magnesium sheets
• Used types of adhesives and binders
• Installation and operating conditions

Today we will talk about the use in construction of LSU, or glass-magnesium sheet. There are quite a few examples of the successful use of LSU, and therefore it is time to understand what leads to such a result: the right choice and application, or just a coincidence.

The essence of the scandal around LSU

The first practice of using glass-magnesium sheets caused a lot of negative reviews. The cladding made by them was subject to swelling and warping in a very short time, often the only solution to the problem was a new installation of the entire finish. The negative reputation of LSU was firmly entrenched, even now very rare masters undertake to work with this material.

Magnesium glass sheet has been present in the range of hardware stores for about ten years. Have there been any positive changes in product quality during this period? Of course, yes, at the same time, many developers are deprived of understanding the rules for working with such material, while designers are reluctant to learn to use the strengths of LSU.

The main reason why glass-magnesium sheet is not widely used is the lack of consistent quality. Only half a dozen Russian enterprises are working on the manufacture of LSU, while there are much more of them in the Chinese industrial space. As a rule, there is no marking on the sheets, which makes it impossible to unambiguously determine the source of the product and the main properties: density, composition, resistance to high humidity..

Characteristics and classification

In our review, we will pay attention to two types of products: domestic and imported from China. Let us note in advance that it makes no sense to consider such LSU categories as illiquid sheets and packing panels sold at a cost 3-5 times lower than that of products tested by the Quality Control Department. It was this trick that many developers fell for, tempted by the low price and decided to replace the gypsum board with less expensive sheathing material. However, it is important to remember: a high-quality LSU in all respects surpasses GCR and GVL, it has a more complex production technology, which means that it simply cannot be cheaper..

Products from the Celestial Empire enter the Russian market in three variations. These are sheets of classes “Standard” for roughing and preparatory work, “Premium” for finishing, as well as “Premium +” or “Ultra” – moisture resistant and suitable for painting. It is quite simple to distinguish them – for each class there is an established density range: standard ones have 700-800 kg / m³, “Premium” – 950-1100 kg / m³, well and the highest quality – up to 1250 kg / m³. If there is only one LSU class in the assortment, you will have to trust the data of the product certificate (and it must be), or weigh a small piece of sheet and recalculate the density. If sheets of several grades are available, the difference in density is easy to determine, even visually and by touch.

Russian suppliers use their own classification and periodically change the selling rates at their discretion. This is due to the fact that about 90% of Russian LSUs are produced exclusively for internal use, therefore, it is very rare to encounter the use of such sheets in repair practice. The quality of LSU of domestic production is somewhat better: this is mainly due to the fact that domestic enterprises do not produce plates for the device of intermediate non-critical layers and packaging. When tested by soaking for a day and burning with a gas burner, almost all samples of local production cope with a bang, while a Chinese leaf in two cases out of three swells in water and crumbles. It is believed that this trend is partly due to long delivery times from China, as well as related violations of storage and transportation rules..

Since LSU is most often compared with gypsum plasterboard, gypsum plasterboard, GSP and other cladding materials, it is on this comparison that we will briefly consider the qualities of glass-magnesium plates. In terms of impact strength, they are second only to DSP, GSP and chipboards. In terms of weight, only sheets of the “Standard” class can be compared with gypsum board and gypsum plasterboard, higher quality ones have a specific weight of 1.3-1.5 times more. LSU of “Premium” and “Ultra” classes is the absolute leader in terms of hydrophobicity, in this regard, glass magnesite surpasses even varnished OSB and moisture-resistant plywood. Whether a glass-magnesium sheet has the required water resistance can be determined right at the warehouse: the edges must be even, hard, without a hint of chipping, attempts to crush a cut of a solid LSU with your fingers always end in failure. You should also pay attention to the color of the filler: in cheap sheets it is almost white, in high-quality sheets it has a beige or pinkish tint..

Technical purpose of glass-magnesium sheets

We hope that we have managed to dispel the main myth about LSU: this material is not an equivalent replacement for other types of sheathing sheets. Glass-magnesium plates have a much narrower scope of application, determined by their special properties..

First of all, glass magnesite is used in fire protection systems for the construction of type 1 and type 2 firewalls. For the same purposes, the sheets are quite successfully used for arranging fire compartments over openings when insulating facades with expanded polystyrene plates. It is worth emphasizing that almost all, including low-grade types of LSU, have a very high fire resistance.

Another use case is a floating floor device. Traditionally, GVL is used for this purpose, which implies a low resistance of the entire system to flooding. Glass-magnesium sheets of the “Standard” class, although they cannot be operated under permanent exposure to high humidity, they tolerate a one-time short-term wetness quite well. At the same time, high impact and bending strength makes LSU one of the priority materials for such use..

The so-called “technical” types of sheets are not without reason considered disposable. They are used for the device of fixed formwork, for the conservation of building objects for the winter, as well as for various kinds of preparatory layers and interlayers. For example, LSU can be successfully used to separate armored belts and bridges over openings in order to partially or completely eliminate cold bridges. At the same time, the small thickness of the material allows them to be installed between the reinforcement lines, forming 4 or more separated layers. When installing a roof, LSU is often used as a heat insulator, protecting the waterproofing coating from overheating on unshaded slopes..

LSU is rarely used in interior decoration. It is simply pointless to use a glass-magnesium sheet for cladding suspended ceiling structures and flooring devices: there are lighter and cheaper materials. Again, the exception is objects with increased requirements for fire safety: kitchens, switchboards, fireplaces and fireplaces themselves, as well as some types of industrial premises. Almost the same trend applies to walls, but high-quality magnesia glass allows you to provide moisture resistance, which is guaranteed to be sufficient for bathrooms, saunas and basements..

As for external use, only Premium and Premium + sheets are suitable for it. Such types of LSU can also be used in systems of hinged ventilated facades and wet facades. The benefit from the use of glass-magnesium sheets lies in their highest suitability for such operating conditions, which even OSB 1 and 2 classes cannot always boast of. In addition, LSU perceives seasonal temperature fluctuations well, and it is also not a breeding ground for the development of harmful organic matter. For these reasons, LSU is increasingly used as a shell of sandwich panels..

Used types of adhesives and binders

Like drywall, LSU allows two mounting methods: glue and mechanical fastening to the frame subsystem. In the latter case, everything is quite simple: the step and type of fastening is the same, although for material with a density of more than 800 kg / m³ recommend preliminary drilling, without which it is possible to wind reinforcing threads on the self-tapping screw and the occurrence of problems with the embedding of the caps. An additional reservation should be made regarding the storage conditions of sheets: if there is no complete confidence in the quality and origin of the material, LSU should be kept for 1-2 days at room temperature and humidity, otherwise, during the drying process, the edges may break at the attachment points.

The situation is a little more complicated with the adhesive fastening of LSU. On the one hand, the sheets have excellent adhesion, but the behavior of the adhesive and the sheets when external factors change is of great importance. It is necessary that the glue retains its plasticity after hardening and acts as a damper, eliminating the transfer of vibrations from the carrier layer to the skin, and compensating for the shrinkage of the glass-magnesium sheets. Not the best solution would be to use polyurethane foam or liquid nails as the main method of fixing.

The adhesive must be selected according to the operating conditions. So, “Perlfix” is well suited for gluing LSU to walls in dry rooms, however, at high humidity, the gypsum included in the composition swells, which leads to the appearance of blisters. The right decision would be to give preference to UNIKOL 402 glue on a rubber binder, or universal mixtures Ceresit CM 17 or CM 117 for facade finishing. The sheets are glued with the back rough side, having previously treated them with two types of primers: deeply penetrating from the inside to increase adhesion, with the front side – with a water repellent.

Installation and operating conditions

From the moment of delivery to the construction site and until the start of installation, LSU should be stored in a horizontal position, and also be isolated from the floor with plastic wrap and linings. SML cutting is performed with a conventional hacksaw or jigsaw, while it is recommended to use a respirator to avoid inhaling small particles of fiberglass. When fixing sheets to walls, their vertical orientation is preferable. A prerequisite for installation is to ensure a joint width equal to half the thickness of the sheets used.

The earlier the finishing is carried out, the better it is for glass magnesite. And although there are examples when LSU stood in the open air for 1–2 years without irreversible loss of properties, nevertheless, due to the unstable situation with the quality of the material, this approach is always a lottery. It will be much more correct to store the sheets until the moment when it is possible to consistently and in a short time to carry out covering, sealing joints with plastic filler, re-priming and finishing, thus protecting LSU from possible harmful effects.