No matter how flat a floor appears visually, you can guarantee that its not completely 100%. Here and there the floor levels might be out by as little as a couple of millimeters. It may not sound very much, but it can have an impact on a flooring installation.

 

floor levels tiling and floating floors

 

An example of this came about recently, when a customer laid cork tiles straight over a plywood floor. Glue wasn’t required, and underlay although optional, was not used. However, the customer experienced loud noises when she walked over it. When the cork boards are clicked together, you are basically creating on big flat piece of flexible cork. When loose laid it will find its own level depending on the level of the floor, meaning it will rest on the highest points of the floor, and sink in the lower points if the distance between the two will allow.

floor

This image gives an example of a floor, with 2 peaks at each end and a dip in the centre. The dotted line is the average floor level. Due to the flatness of the boards, you will notice as the boards sink to the lowest point. But due to the rigidity and lightness of the boards, there are also areas where the cork is not physically in contact with the substrate. These areas are known as voids.

The noise that the customer is experiencing occurs when weight is placed on the tile above the void, causing the tile to be pushed with force into the substrate, making impact noise. This is resonated further due to the adjacent boards moving in unison, creating a bounce effect. An underlay, albeit not essential, will to an extent fill these voids and cushion weight loads as it is walked on, thus reducing the amount of noise.

 

Undulating floors can also have an adverse affect on normal tiled floors also. As the tiles don’t click together, getting each one the correct level is a little trickier and if the floor isn’t flat, will cause problems from voids to lipping (height differences between adjacent tiles).

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This image shows how lippage can occur. A peak in the floor has pushed the tile up on one side. When the next tile is laid on a flatter surface next to it, it sits much lower.

floor-2

A dip in the floor can also create lippage when a tile is compressed into it. In this instance to prevent the lip, the dip would need to be filled with extra adhesive. But if the adhesive when spread just follows the contours of the floor, either A, the tile would sit lower, or B, the tile will be made level with the adjacent tile and leave a void beneath it as below:

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The first thing to do before any flooring project is to ensure the floor is as level as possible. Lay a spirit level in all directions, covering as much of the floor as possible, to see where the peaks and dips may be located. If the floor has just a few lumps in it, these can be sanded down with a large sander, or an angle-grinder with a grinding cup attachment. This can suitable flatten small areas of the floor.

However if the floor is out of true in multiple areas, the use of a Self Levelling Compound (SLC) can make the tiling easier. It can be used to fill any dips or completely raise the whole floor level up to meet the highest points. Once the SLC is mixed, it is extremely runny, meaning it can be poured and will find its own level to a certain extent, but may need to be flattened with a plasterers trowel to take out any ripples. The most effective way to flatten the levelling compound is by using a “Straight Edge”. These are quite simply long bits of metal, approximately 2m long, with a perfectly flat edge. Like a spirit level but without the bubble. With the compound poured, the straight edge can be used to skim the area and give more accuracy over larger areas.

Voids beneath ceramic, porcelain or stone tiles, can cause tiles to crack over time, due to the weight exerted onto them and the lack of support. It is therefore critical that in addition to a flat surface being in place, each tile laid has a full coverage of adhesive beneath it. This can be done by skimming the back of the tile with the flat edge of the trowel to fill in any undulations that may be debossed. This is also known as back-buttering and can also increase the bond strength of the adhesive with the tile.

For more advice and technical help on tiling projects, visit our Help Centre. It's the Wikipedia of tile related queries and knowledge!

 

 

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