- When the plastering method is suitable
- When is it better to give preference to gypsum board
- Preparing the base layer
- Lighthouse plaster – a brief educational program
- False-wall device
- Combining methods
The durability and quality of the bathroom finish depends almost entirely on the quality of the base preparation. Today we will analyze two main finishing methods, the possibility of combining them in one room, the differences, disadvantages and advantages of plaster and sheet cladding..
When the plastering method is suitable
The choice between dry and wet finishing is a lively and popular topic of discussion. Basically, this issue is considered from a purely practical point of view:
- is it appropriate to use a cement-sand mixture in the conditions of a particular facility?
- which alignment method will be the least material intensive?
- which option will allow you to complete the work as soon as possible?
- what type of building material is more convenient to deliver directly to the place of work?
In the context of preparation for tiling, plaster has one main advantage and disadvantage. The main advantage of plastering walls under tiles is the highest possible moisture resistance. Alignment with sheet materials, even moisture resistant and of high quality, cannot guarantee that in the event of water penetration under the tiles, the finish will retain its appearance and integrity.
The disadvantage of plaster is its low resistance to cracking under the influence of phenomena associated with the settlement of buildings and the movement of walls. In addition, one cannot remain silent about the rather high complexity of the work: while the gypsum board cladding is quite easy to master in absentia in master classes, working with plaster requires extraordinary skills and experience.
When is it better to give preference to gypsum board
So, the main reason for using plaster for leveling under the tiles is the durability of this kind of finish. However, there are a number of arguments in favor of moisture resistant gypsum plasterboard (GKLV) or gypsum fiber (GVLV) boards..
Mainly, sheathing is attractive in terms of ease and speed of installation, as well as due to the absence of the need to prepare large portions of cement mortar. This alignment provides a higher work culture and does not entail time-consuming cleaning..
Sheet materials make it possible to level rooms with highly distorted geometry, where a very large amount of plaster would be needed when using plaster. Sometimes the blockage of the walls simply does not allow you to apply such a thick layer, in which the durability of the walls in high humidity conditions will exceed the finish with sheet materials. In extreme cases, plastering work has to be performed in several passes of 10–20 mm, which greatly delays the repair.
Finally, for buildings on unstable soils and in areas with high seismic activity, dry preparation of walls for tiling provides excellent opportunities to maintain the appearance of the cladding for a long time. With proper installation, such a finish will be completely independent of the main walls and their deformation. But you have to pay for everything: the installation of false walls eats up the space in the room much more, and where a minimum layer of 10-15 mm is sufficient for plaster, the sheathing will require at least 60 mm.
Preparing the base layer
Difficulties in applying plaster appear already at the stage of preparing the rough surfaces. Very high adhesion and high-quality adhesion of the cement mortar to the surface is required. This is achieved without significant efforts only if the carrier layer is exposed, has a sufficiently high porosity, roughness and absorbs moisture well, but not too much..
In this case, a single treatment with a deep penetration primer such as Ceresit ST-19 is sufficient. If the substrate is in materials such as granite or heavy duty concrete, it may be necessary to roughen the surface. For these purposes, you can use primers containing marble or quartzite dust..
However, most often the conditions at the facility are far from ideal. If the renovation is not carried out in a new building, then most likely some type of bathroom finish is already in place, and this can be a significant obstacle to tiling. Usually, the old finishing coating is completely dismantled in order to expose the layer of carrier material and then carry out the work as if the finishing was done for the first time.
Removing the top layer without fail requires walls with “coiling” plaster, whitewashed, painted or already tiled. In the latter case, you need to remove not only the tile, but also all the remnants of glue or cement mortar. Removing the surface layer only on the hand: this way the room narrows much less and the influence of mistakes made in the process of previous finishing work is leveled.
Lighthouse plaster – a brief educational program
First, you need to measure the room, establishing its true geometric shape and dimensional deviation. In this case, the violation of the plane of each wall should be taken into account, having previously determined the points of the surface that protrude as much as possible towards the center, and taking them as zero.
To strengthen the structure of the plaster and its reliable adhesion to the base of the wall, it is necessary to cover it with a plaster mesh or a chain-link with cells of 30–40 mm. It is recommended to use the chain-link if the total thickness of the plaster is more than 50 mm, otherwise a flat mesh will help save an additional 5-7 mm under the beacons. It is better to fix the mesh with plastic dowels, threading a nail into a wide washer. The overlap between the netting should be at least 10-15 cm.
The lighthouses are adjusted before installation, and then fixed with small clods from a mixture of cement mortar and alabaster. The purpose of the preliminary adjustment is to describe a regular parallelepiped (or other spatial figure) inside the room – with right angles, verticality / horizontality and equality of opposite edges. This is done using a temporary fastening on self-tapping screws with plastic plugs. It is convenient to use ordinary washers as spacers. The distance between the beacons is 20-30 cm less than the length of the rule that will be used to pull the solution.
For plastering under tiles, DSP with a ratio of 3 parts of sand to one part of M400 cement is optimal. To improve the plasticity of the solution, you can add 1–2 teaspoons of detergent to a bucket of water, and use this solution to dilute the dry mixture. Adhesion to the base can be improved by replacing the water with a diluted 1:50 PVA glue or “Bustilat”. To be able to throw a layer of more than 30 mm in one pass, you should use ready-made plaster mixtures with the inclusion of polymer binders.
The plaster should be cast out of the bucket, so that the solution is compressed with high quality and gets rid of air pockets during impacts. Throw it over until the solution protrudes above the plane of the beacons about 10–20 mm. After completing the throw in one strip between the beacons, the solution is allowed to settle for about 10 minutes and then the excess is cut off with the wedge-shaped part of the rule. After the plaster has dried within 24-48 hours, the beacons must be selected and the remaining grooves should be sealed with cement mortar.
It is not necessary to grind the plaster under the tiles. Plastering on beacons allows alignment with an accuracy of 3-5 mm with a tile laying tolerance of 0.5 mm / m. If you need to bring out the walls with a better quality, and there is no desire to level the tiles with the thickness of the adhesive seam, you can pre-fill with the adhesive mixture with a layer of up to 3-4 mm.
Walls made of gypsum plasterboard under lining with tiles are erected according to the general technology, but there are a number of recommendations:
- Sewing sheets for tiles must be carried out in two layers with a breakdown and a total thickness of at least 14 mm.
- CD-60 profiles (ceiling) are not suitable for laying tiles from ceiling to floor, only under panels up to 120 cm or under a kitchen apron.
- When installing the guides, gluing with compensation tape is strictly mandatory..
- Rack profile step – no more than 40 cm.
- Before patching, even moisture-resistant sheets are recommended to be treated with an antiseptic and a hydrophobic primer such as Knauf Flachendicht with a consumption rate of 350 ml / m2.
- Ideally, if the cladding, or at least its top layer, will be made of moisture resistant cement boards such as KNAUF “Aquapanel”.
Sometimes only one of the dimensions of the bathroom does not allow the use of sheet cladding under the tiles due to the impossibility, for example, to install a bathtub. Another special case is the sewing of the rear false wall in the toilet to hide communications, while the rest of the surfaces are finished with cement plaster.
This approach is quite rational, and for implementation you need to take into account only a couple of technical subtleties. First of all, the correct sequence of work is important: first, leveling with plaster, then installation of false walls. In this case, the frame should be framed by a guide profile not only from above and below, but also on the sides as well. Plus, it is recommended to add a couple of jumpers with an interval of one meter between the vertical rails and the nearest rack profiles..
The conjugation of drywall and plaster needs to be cut a little: from the end of the gypsum board or gypsum board, remove the chamfer at 45 and peel off the cardboard with a strip of about 30 mm, prime the corner well. To seal the joint, use paper or strips of plaster fiberglass mesh and tile adhesive.
It is recommended to seal fillet joints with elastic compounds when grouting tiles. And not only when switching from sheet cladding to plaster, but also in the corners between false walls. A good example of a composition suitable for grouting corners is Ceresit CE-40, flat joints up to 6 mm can be safely sealed with KNAUF Fugenbunt aggregate.