Special When to use and not to use (adhesive) primers and/or damp screens: the benefits and drawbacks

ADHESIVE PRIMERS ARE OFTEN ESSENTIAL FOR GLUEING

THE ‘PERFECT SUBSTRATE’ IS STILL SOMETHING OF AN ILLUSION

Photo – Stauf

Primers can solve various ‘problems’, but they are usually associated with renovation. That view is sometimes right, but certainly not always. For instance, an adhesive primer is designed to even out the absorption capacity of the screed over the entire surface. The need for this will arise more often with renovation, but certainly not exclusively with renovation. Let’s be honest here: You know how it is in the building sector? The sector where lots of things can be done, but not always ‘properly’.

Adhesion primer and absorption capacity The absorption capacity or porosity of the covering floor is vital for glueing parquet. That porosity can cause problems for floor fitters in many ways. A floor can be too porous so the glue cannot stick. In this case, the floor is probably not strong enough for glueing. A floor can be inadequately porous. If a covering floor is pressed so that it is too smooth, that can impede the glueing or you might need an adapted adhesive. Finally, a floor can show uneven porosity resulting in uneven adhesive bonding. In all the above cases, it is necessary to use a

primer. It is possible to detect differences in porosity by wetting the screed with a damp cloth. If the floor dries unevenly, that is a sign of uneven porosity.

Other functions Apart from improving porosity with a view to glueing, primers also have a number of other functions. Let’s consider the various functions of primers.

Damp screen A damp screen can be fitted to combat residual building damp in a new building or if there is a risk of rising damp (but it’s best in that case not to fit parquet). There are various chemical compositions for this. PU primers can often be used for certain residual moisture percentages. Everyone agrees that epoxy damp screens are the most effective damp screens. And so, there is no doubt that epoxy offers an excellent solution in this way. Major benefits (properties) are the uniform and sealing film, the good adhesion, and the excellent combination with dual-component adhesives.

As reinforcement The strength of a screed is also important for glueing quality. With a new building the composition of the screed (cement/sand) plays a part, whilst older screeds may show signs of old age in the form of local ‘weak spots’. A reinforcement primer can provide a solution for powdery substrates or screeds which lack strength. This fixes the covering layer as it were. Some producers draw a distinction between primers for porous or for non-porous substrates, whilst others offer universal primers.

As an adhesion bridge for quartz sand If it is necessary to sprinkle in some quartz sand to improve the adhesion with a levelling agent or with the adhesive, the primer serves to fix the quartz sand. This can be necessary for applying a leveller after fitting an epoxy screen.

Activation of tiles Ceramic tiles and natural stone such as marble are hardly porous at all. Nevertheless, clients often request with renovation that the glueing be done directly onto those existing floor coverings. The primer then serves as the degreaser and activator of the ceramic tile.

Some specialists

Chimiver PRYMER SF 1105 is a two-component water-based epoxy primer developed for dusty subfloor, with a multi-layer application, it works as a moisture barrier. It is resistant to the inverse hydrostatic pressure according to the law UNI 8298 part 8. PRYMER SF 1105 is suitable for consolidation of subfloors on radiant heating. It is also recommend as a promoter of adhesion for anhydrite subfloors.

Emfi The most common problems with the bearer are rising damp and brittleness. To improve cohesion they offer EMFIPRIM PU MONO, which is applied in a coat of about 150 g/m². To protect the surface from damp, they recommend EMFIPRIM EPOXY, which is applied in two crossed coats (the final one is sandblasted), with a total consumption of about 500 g/m² (300g + 200g). Their primers are compatible with the mastic adhesives in their range. For the use of an adhesive with a different brand of mastic they recommend a compatibility test in advance. EMFIPRIM PU MONO accounts for about 1.5% and EMFIPRIM EPOXY for about 8% of the total end price of the fitted parquet. This is certainly acceptable when it includes a guarantee of durable work. The most effective primer in their range is EMFIPRIM EPOXY because it reinforces the surface of the bearer and forms a barrier against rising damp.

STAUF

The primer to save friable screeds: STAUF WEP 180 Adhesives specialist STAUF has developed a primer that is capable of safely re-consolidating even friable screeds. The multipurpose, solvent-free, dispersion-based, 2-component epoxy resin primer STAUF WEP 180 reinforces unstable substrates and significantly improves the strength of materials thanks to its extremely high level of penetration into mineral mortar systems. In addition, STAUF WEP 180 dries and films very quickly within approx. 2 hours. STAUF WEP 180 can also be used as a dispersion-based, two-component epoxy resin primer on cement screeds with a higher residual moisture content of up to 4 CM%. It also features very low consumption (1:1 dilution with water depending on the application) and is suitable for direct bonding with almost all STAUF reactive adhesives. After being sprinkled with silica sand or having an intermediate primer coat of STAUF VDP 160 applied, it can be filled or plastered over. The container size allows direct mixing of the 2K product pure or with water without the need for an additional container.