(tile bowing effect)
Bowing or curvature is one of the most common imperfections however bowed tiles are deemed acceptable if they are within specified tolerances. As an example under ISO13006 the tolerances are;
Maximum deviation from square edge is +/-0.5% of length of tile. For example if you have a 400 mm square tile, then the maximum gap between the straight edge and the tile cannot be more than 2 mm.
Modern porcelain tiles, or large, rectified wall tiles generally need to be as flat as possible in order to avoid joint lips which are protuding tile edges that can occur with bowed tiles. Curvatures are much more pronounced on rectified edge tiles laid with narrow joints. Modern production technologies allow a tile be exceptionally flat and of uniform size. However a small percentage of products fail this requirement and the result is hard to live with so it is best avoided before installation.
To test for excessive tile curvature you will need a long, straight edge, such as a spirit level, a long ruler, of a straight edge tool. In order to measure the gap, you can use a set of mechanic’s feeler gauges (pictured) or a pair of measuring calipers.
A) Pick up the piece and look down each edge and see if it is curved.
B) Place two tiles face to face and see if any gap exists.
C) Stand a stack of tiles on one end (as in check 2 above) and check that all of the tile edge profiles conform to one another.
If you are satisfied skip to the check number 5)
If you suspect curvature may be excessive (remember that tolerances exist that make minor curvature acceptable) a measurement will need to be made of the gaps to check if the tile is within specification or not.
NOTE; DO NOT USE ANOTHER TILE AS A STRAIGHT EDGE OR FACE WHEN MEASURING.
Steps to take if curvature is visible
A) Notify your supplier and get them involved
With curvature it is important to establish if the amount of curvature is excessive. In ceramic products some tolerance for visible curvature may form part of the specification and therefore is not considered to be excessive. Remember that your options are greater if the tiles are not yet laid. The answer depends on the practical aspects of lipping, laying and seating the tiles on a flat surface as well as aesthetics. The standards are a fallback when it is difficult to assess the validity of the complaint.
B) Using feeler gauges (One can buy a set for a few dollars at a discount auto parts retailer) measure the size of the maximum gap between the straight edge and the tile surface by the insertion of different combinations of gauges (example 0.88 mm + 0.83 mm + 0.55 mm = 2.26 mm gap). If you have no gauges then a good photo of the gap alongside a millimetre ruler for scale. Use a macro setting if available.
It is important to note that maximum curvature can occur along the long dimension or the short dimension, or just occur at one extremity. Excessive curvature can also be localised at the corners and may be a curl up (or kickup) or kick down as per the example in the photo below.
What the above photo illustrates is that a measurement of the gap is required to determine whether or not the curvature really exceeds acceptable tolerances. Also note that the impact of the curvature on the final installation may differ according to each product and the installation .
B) Record the measured departured from straight which is the maximum gap between the straight edge and the tile and take digital photos
C) Count the occurrences within your panel you used in check 1 above, and then from the other cartons and pallets.
See if there is a pattern to the occurence of bowed tiles within your batch?
– Within Cartons?
– Between Cartons?
– Between Pallets?
In my experience excessive curvatures where whole tiles are bowed require a more complete inspection of the entire batch to determine occurrence.
Once measured and quantified:
– Set aside any affected pieces and only lay flat tiles. Replace the affected pieces OR
– Return the product and replace with another batch OR
– If the issue is mild and after getting expert advice that determines that it is possible to go ahead anyway.