Tiles convince not only by their attractive appearance and durability, but above all by their durability. Optimum adhesion to the substrate is the be-all and end-all – and for this you need the right conditions. In this article, you will learn how to ensure that your tiles have a lasting hold and what a decisive role the primer plays in this context.
The right substrate for tiles
Whether cement, concrete, plaster or even tile on tile in the bathroom – in principle, you can lay tiles on almost any surface. The prerequisite, however, is that they are clean, dry, flat and stable.
For example, when laying a new screed, it is essential to allow time for the tiles to fall below a certain residual moisture content and for the floor to be ready for laying. While, on the other hand, when laying tiles on top of tiles, you must first create a sufficiently even surface – preferably by using tile levelling compound, which you use to cover the old tiles.
But that’s not all. Because in most cases, an optimally prepared substrate also includes the right primer.
Primer – why actually?
If we were to ask you what actually makes tiles stick, tile adhesive would probably be your first answer. Basically, this is not wrong of course – after all, you can use it to attach the tiles to the wall or floor. But then it is not quite right either. Because the adhesive alone does not provide good adhesion.
In order to ensure that the tiles actually remain permanently bonded, you must first ensure that the substrate is evenly absorbent to increase the effect of the tile adhesive or even create it in the first place. And that is exactly what the primer is for.
Which primer for which substrate?
In principle, a distinction is made between the categories of deep primer and adhesive primer. The various products, which are available in a wide range of ready-to-use products in specialist shops, differ both in their composition and in the type of surface on which they can be applied:
Deep base for highly absorbent material
Highly absorbent substrates, such as plaster or cement, draw water from the tile adhesive – with potentially unpleasant consequences during and after installation. On the one hand, the adhesive hardens faster, leaving you less time to install the wall or floor tiles. On the other hand, the adhesive effect can be impaired, which in turn leads to less adhesion of the tiles. In these cases, therefore, a pre-treatment with Tiefengrund forms the basis for a permanently perfect result when tiling.
Tiefengrund is usually a liquid primer based on synthetic resin, which is applied to the substrate diluted with water or undiluted, depending on the manufacturer’s information. It penetrates deep into the surface, solidifies the material and thus reduces its absorbency. In this way, the primer not only helps the tiles to adhere better, but also protects against too much penetrating moisture under the tiles.
Primer for smooth surfaces
In contrast, primer is used on non-absorbent or only weakly absorbent, smooth surfaces on which bonded tiles would normally not hold sufficiently.
This type of primer provides optimal conditions, especially for surfaces made of concrete, metal or even screeds made of mastic asphalt. In addition, existing tiles can also be treated with primer to ensure the necessary adhesion when laying tile on tile.
Adhesion primer consists of coarse-grained mortar with binding agents, which serves as a bonding agent between tile and adhesive. Unlike Tiefengrund, Haftgrund does not penetrate very deeply into the surface.
The best tips for an optimal primer
1. determine the absorbency of the substrate
Before priming your wall or floor, you should first test the absorbency of your substrate. With the so-called scratch test this can be tested well and easily: The easier and deeper you can prick the surface with a screwdriver or other sharp object, the more absorbent it is.
Another possibility is the water test, in which you moisten a small area of the substrate. If a dark discoloration is visible, you are also dealing with a highly absorbent material.
2. choose a suitable primer
On the shelves of DIY stores, but also in various online shops, you will find countless different products for priming. You can find out which of these is the right one for the condition of your surface from the manufacturer’s information. In addition, the primer and adhesive must be compatible. Ideally, therefore, only products of a system should end up in your shopping cart.
3. apply primer step by step
Before the primer can be applied, dust, dirt and material residues must be carefully removed from floors or walls. For the priming itself, it is best to use a paint roller or ceiling brush to achieve the most even result. Alternatively, you can also use a brush or a spray bottle.
In case of highly absorbent surfaces or larger damages, it is recommended to apply at least two coats of primer (first diluted and then undiluted) – more if necessary. Make sure that the first layer is sufficiently dry before applying the next one. All necessary information about the drying time can be found in the manufacturer’s instructions. When the primer is dry, you can start laying the tiles.
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