SUBSTRATE DIAGNOSIS BEFORE TILING

for Efficient Adhesion of Adhesive and Grout

Problem

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For efficient adhesion of adhesive and grout. The substrate diagnosis before tiling is so important. How to check the flatness of the substrate?

How to check the flatness of the substrate?

The substrate should be flat without dust or any residues.

1. The flatness can be checked by placing a 2 m straight edge onto the substrate

The flatness can be checked by placing a 2 m straight edge onto the substrate, the straight edge should lay flat without any gaps.

  • If there are some gaps, they should not be bigger than ±5 mm.
  • The gap should not exceed ± 3 mm in the heavy-traffic areas or the areas using ready-mixed adhesive for tiling.
2. The area has to be leveled with mortar cement mixed with weberneo latex.
  • If more than 80% of the area conforms to the above standards, it is considered to be in a normal condition. If more than 20% of the area is not as the standards, the area has to be leveled with mortar cement mixed with weberneo latex.

How to check the stability of the substrate?

1. This check mainly concerns wooden floors laid on joists or battens
  • This check mainly concerns wooden floors laid on joists or battens, wooden panels and, more rarely, partitions.
2. The flooring strips or wooden panels should not move when they are stepped on.
  • The flooring strips or wooden panels should not move when they are stepped on.Partitions should not flex when press by hand.
3. If this is not the case, reinforce the floor, replace the boards, or brace unstable partitions.

How to check the hardness of the substrate?

The substrate should be both hard and resistant in order to avoid cracking or disbonding at a later stage.

How to check the hardness of the substrate?

1. Check the surface hardness by scratching it with a pointed tool e.g. a nail, in several places.
  • The scratch has to be superficial.
  • If the surface peels off, it is not hard enough for tiling.
2. Plaster walls should be brushed with a stiff brush and then wiped to remove any loose material.
  • Plaster walls should be brushed with a stiff brush and then wiped to remove any loose material. Also check the in-depth hardness of existing screed or plaster walls.
3. The defective surfaces have to be removed until sound material is reached.

How to check the porosity of the substrates?

Cement-based substrates should have normal absorption in order to avoid premature water loss from the cement-based adhesive and to ensure that the bond can develop correctly.

How to check the porosity of the substrates?

1. Pour a little amount of water onto the substrate.
2. If the water is absorbed in less than 1 minute, the substrate is considered as excessive porous and requires priming.

How to check the adhesion of the existing tiles be

The substrate has to be cohesive and resistant in order to ensure the cement-based adhesive bonds properly.

How to check the adhesion of the existing tiles before tiling?

How to check the adhesion of the existing tiles before tiling?

1. Check the adhesion of existing tiles by tapping with a hammer.
2. Any hollow sounding tiles or tiles with poor adhesion have to be removed.
3. Replace by similar tiles or tiles with the same pro-perties.

How to check the adhesion of the existing paint before tiling?

1. To check the adhesion of existing paint, carry out a cross-hatch test using a suitable knife or cutter.

2. Score the paint in small 2 x 2 mm squares over a total area of 10 x 10 cm. Use transparent tape to stick onto the area and then pull off quickly.

3. The paint is considered suitable for tiling if 80% of the area of the small squares remain bonded. If not, the paint has to be removed mechanically.

How to clean the substrates?

The substrate has to be clean in order to ensure the adhesive bonds properly.

How to clean the substrates?

1. Eliminate any traces of plaster with a scraper. Carefully remove any dust and any other stains.

  • Apply weber.prim 2 primer, if necessary, on existing tiles, paint, wood or PVC tiles to increase the bonding property.
  • When do the tiling on existing paint, remove any traces of varnish or wax and apply weberprim 2 primer to ensure a good adhesion.

2. For cement, light-weight concrete or gypsum-based substrates; a primer to decrease water absorption should be applied.

How to check if the substrate is dry?

  • To check the humidity of the substrate, wipe it until dry and then use a humidity checking device.
  • Plaster substrates and the substrates for tiling should not have more than 3% residual moisture during application depending on the ambient conditions, the residual moisture could last longer than 2 weeks - several months in some conditions.
  • The residual moisture of anhydrite substrates (with the mixture of calcium sulfate) should be less than 1%, and less than 0.5% for PVC substrates.