5 Aspects to Fix Tile Hollowing(EASY!)

As a home decoration material, improper construction of Fliesenkleber will cause tile hollowing and the grassroots due to poor bonding and weak bonding.

So what are the hazards of tile hollowing?

1. The part of the tile hollowing is not sticky, and it is easy to break when the external force is significant in the future.
2. The area of the tile hollowing may gradually expand, and finally, the tiles will lift or fall off.
3. Tile hollowing will cause difficulty to drill the wall and easily break (for example, when installing water heaters, mirrors, pendants, cabinets, and bathroom cabinets).
4. Hollow tiles will cause water to accumulate on the bathroom floor, which will eventually rot and smell.
We analyze the reasons for the tile hollow and the corresponding solutions from the following 5 aspects.

1. Unqualified base layer

• The base layer is loosing, the wall peeling off after the tiles are attached.
• The unevenness of the base layer results in different amounts of tile adhesive in each position of the same tile. The tile adhesive shrinks unevenly during the hardening process, so there will be a gap between the base layer, causing hollow tiles.
• The surface of the base layer has not been cleaned up and is covered with dust, loose material, oil stains, etc. The mortar is actually in direct contact with the dirt and is not integrated with the base layer, so it is prone to hollowing after a long time.

Therefore, it is necessary to carefully check the base layer before application to determine whether the surface is dirty or uneven or cracks or looseness. If so, use a spatula to remove the easy-to-peel areas on the surface of the base layer. And then repair the cracked areas to ensure that the surface of the base layer is clean, flat, and firm. It can reduce the probability of tiles falling off and hollow sounding tile on concrete. The painted base layer should be roughened.

2. Improper operation during construction

• There is no compaction during the tile-laying process. During the pasting process, fully press or hammer with rubber is needed in order to squeeze out the remaining air in the bonding layer, to completely engage the base layer. Generally, the thickness of tile adhesive for paving wall tiles is 7-10mm, and that for floor tiles is 10-20mm. It is advisable to have tile adhesive extruded around the tiles.
• There are no gaps between the tiles, or the gaps are too small. Some people will require the gap between the tiles to be as small as possible to pursue beauty. When the temperature changes, the tiles will not have enough space for thermal expansion and contraction. And they will squeeze each other, cause bumps or tile hollowing.
• Add too much water when mixing the tile adhesive. After the water evaporates, the volume of the adhesive will shrink too much. This will leaving a gap between the base layer and the tiles, and the tiles will bulge or fall.
• The tile adhesive did not cover the entire tile during construction in order to save materials and time, resulting in a partial gap between the tile and the substrate.
• Too much tile adhesive is used. The thicker the tile adhesive, the greater the expansion and contraction rate of the material itself. it will cause uneven shrinkage between the adhesive layer, the tile, and the wall. And it will reduce the interface bonding strength, resulting in hollow spots under tile.
• After paving, the tile adhesive is not completely cured (usually 1~2 days) before being subjected to external force, such as walking on it, knocking, etc., causing the tiles to loosen and fall off.
• After the tile adhesive was applied, the tiles were not laid in time. The surface of the mortar has been condensed, and the viscosity is significantly reduced, causing hollow sounding.
• Mix the tile adhesive unevenly or add cement by yourself. To speed up the drying time of the tile adhesive, there may be workers who add cement to the tile adhesive privately. It can better knead and reduce costs. However, this destroys the ratio of tile collagen and dramatically reduces the adhesion force, eventually resulting in hollowing.
• Add water to the adhesive and continue using even it begins to harden. At this moment, the cement hydration reaction is over and can not be used anymore.

3. Inappropriate temperature

Excessively high or low temperature during construction will affect the viscosity of the tile adhesive. Tile adhesive is generally used at 5-35°C. When the temperature is lower than 5℃, the hydration reaction of cement is too slow, and it can not fully react in the original time. Moreover, when the temperature is lower than 0°C, the water in the tile adhesive freezes, and the volume increases. After the temperature rises above 0°, the ice cubes absorb heat and re-form into the water, and the tile adhesive returns to its original volume.

Changes in temperature and volume will seriously affect the tile adhesive’s coagulation effectiveness and bonding strength, resulting in weak tile bonding and tile hollowing. Generally, when the temperature is lower than 15℃, we can see that the hardening speed of the tile adhesive is significantly reduced, but this does not affect the viscosity of the tile adhesive. If the temperature is too high, the moisture will evaporate too fast. It will result in an insufficient cement hydration reaction and affect the bonding strength.

In the same way, if the tiles are laid close to the heat source or are subjected to short-term temperature changes caused by over-cooling and over-heating, thermal expansion and contraction of tile adhesive and tiles will also cause tile hollowing.

How to apply tile adhesive:

First, you should know tile adhesive formulation. Pour the tile adhesive powder into clean water and stir it into a paste. Put the water first and then the powder. It is best to use an electric agitator when mixing to have sufficient blending. The mixing time of the machine should not be less than 2-3min so that the material can be fully hydrated without agglomeration. After stirring, let it stand for about ten minutes and then stir again before using.

Use a toothed scraper to spread the grout evenly on the base layer and form a toothed shape (the tile adhesive should be evenly and thoroughly applied, and the thickness is about half the height of the tooth pitch of the scraper). Apply about 1 square meter each time, and then lay the tiles within 5-15 minutes (adjustment needs to be carried out within 20-25 minutes).

Choose a suitable tooth scraper according to the flatness of the base layer and the degree of convexity on the back of the tile. If the gap on the back of the tile is deep or the stone or tile is more extensive and heavier, apply mortar to the base layer as well as the back of the tile.

Pay attention to leave proper gaps between the tiles, it is generally recommended to reserve an expansion joint of 1-3mm. After laying, wait for the grout to harden completely (approximately 24 hours) to fill the joints. Clean the surface of the tiles with a damp cloth or sponge before the grout hardens. If it hardens for more than 24 hours, the stains on the surface of the tiles can be cleaned with tile and stone cleaners (do not use acid cleaners).

If it is a rainy day, waterproof measures are needed to ensure that the tiles will not be exposed to rain within 24 hours.

4. Tile characteristics

• The sizes of the tiles becomes more extensive( the shrinkage expansion rate is about 4×10-6) and heavier. When the mortar hardens and shrinks, it is more likely to tile hollowing because adhesive has larger volume change (the shrinkage rate of the adhesive is more than twice as than tiles’). Therefore, the tile adhesive must have good flexibility.
• The water absorption rate of the tiles is reduced, and the adsorption force between the tiles and the tile adhesive is weakened. tiles can be divided into porcelain tiles, stoneware tiles, fine stoneware tiles, and ceramic tiles according to different materials. Nowadays, porcelain tiles are more and more common, It have best quality, the lowest water absorption, and weakest adhesion to the base. Therefore, high-quality porcelain tiles must use professional tile adhesive to avoid tile hollowing.
• Porcelain tiles have high strength and more sensitive to temperature changes. As the temperature changes in different seasons, ceramic tiles and grouts shrink to different degrees, which will decreases bonding strength. The bonding structure between the ceramic tiles and the base layer is destroyed, resulting in the hollowing of the tiles.
• When buying tiles, we have to consider their water absorption and volume. If they are relatively sizeable full tiles with poor water absorption, it is recommended to use tile back glue and tile adhesive simultaneously. The primary raw material of tile back glue is a compound of high-quality polymer emulsion materials and inorganic silicate, mainly for tiles with non-water absorption and low water absorption, microcrystalline stone, marble, etc..

When tiling, clean the tiles’ back, apply glue on the surface, and wait for it to set. And then we can tile it on the wall with tile adhesive. Because the glue can adapt to the thermal expansion and contraction of the tiles and other external factors, tiles, and the mortar can be firmly bonded together, effectively reducing or even avoiding the tile hollowing.

5. Poor quality of tile adhesive

Suppose the quality of the tile adhesive is poor and its adhesive force is not enough. In that case, it is easy to cause tile hollowing, falling off, and internal water accumulation.

To ensure the quality of tile adhesive, we can do a small test before large-scale construction.

The high-quality tile adhesive becomes a thick uniform paste after thoroughly stirring, then sticking two test materials. After the tile adhesive is cured, tear them apart along the bonding interface. If the adhered material is damaged, it proves that the adhesive strength is sufficient. If only the bonding interface separates, it indicates insufficient adhesive strength. It can also be tested in high or low-temperature environments, such as grilled on fire or placed in the refrigerator.

During the test, we can also:

①Look at the water retention of tile adhesive. The too-fast water loss will cause insufficient cement hydration and insufficient strength. Therefore, a suitable tile adhesive must have excellent water retention.

②Feeling it during construction. The tile adhesive has a delicate and smooth hand feel and also saves time and effort in construction.

In following video, MELACOLL team introduce to you what is the tile hollowing, which can help you quickly understand the tile hollowing , and summarize and supplement the three reasons of tile hollowing in addition to the five reasons mentioned above. If you want to learn more, please watch our video.