Highly controlled and automated production methods should result in good quality tiles that match sizes perfectly, however sizing is also controlled by selection. The selection itself is determined by the standards the factory advertises. In common use today is the ISO13006 standards although you need to ask about this as each manufacturer can actually specify its own standards if they choose. Most factories will list the standards they conform with on the packaging (ISO or perhaps a regional standard).
As an example the ISO13006 standard lists the maximum size variance as being 1% of the length or a maximum of 2 mm for a cushion edge tile. The maximum of 2 mm applies to large tiles, hence a 600 mm tile would have a maximum variance of +/- 0.33%.
First – check quickly that thickness differences are not in evidence. With modern dust-pressed tiles this type of defect is very rare.
Now on to size variation;
If the tiles are rectified then it is controlled by the finishing process of rectification. Rectified tiles are those that have been trimmed to size with dressed (or finely finished) edges using special cutting tools.
Excessive ceramic tile size variation and squareness problems occur differently in a stamped (moulded) tile than a rectified edge tile. This also apples to the uniformity of the bevel.
Tolerances for modern rectified edge tiles are expected to be extremely tight. If your tile has a rectified (machine trimmed) edge then there is a higher requirement for size control as the joint gaps will be narrow.
Using the panel of loose tiles you laid out earlier for the shade see if there are there any visible sizing or “out of square”issues. Rectified tiles should meet squarely at the corners, and the lines formed should be straight.
If they are moulded or cushion edge (non-rectified) tiles, some variation is inherent. To check, create a space beween each tile so that the gaps represent the actual size of the intended grout joints. If possible you should use spacers (small plastic crosses) which are used by tilers to keep tiles at the right distance from each other when laying – see image above;
Then take three pieces from each of the other cartons you are inspecting and put them into your panel. They should fit, if not, then that other pallet may have a portion of tiles that are of a different calibre.
Another quick method to test this is where all of tiles in a carton are stood together on end ( on a surface that is absolutely flat) allowing one to easily count pieces and measure the variability in sizes. Stand all of the tiles on edge and see if any of them vary in length. Then roll them on to the next edge and see if they are all the same.
Then take random tiles from other cartons and pallets and compare them with your first carton to ensure a size match.
If you are satisfied, skip to the next check number 3. If not then read on:
Steps if size variation is a concern;
A) Using a ruler or a caliper gauge measure the size variation in several pieces from random cartons and determine if the variation is consistent and if there is a pattern.
TIP:The “standing on end” method makes counting the number of outsized/undersized tiles in each carton very easy.
You can also measure each tile in both directions and record the results on a ruled sheet with the product code as the header. (note the pallet number and the measured size) You will need to be accurate to the nearest millimeter.
If the measured tile size variance is within the tolerance specified by the manufacturer you will have to use the joint gap size recommended by the manufacturer.
If the measured variation appears to be excessive then;
B) Notify and then discuss with your supplier
C) Try to determine if the occurrence has a pattern;
Between different cartons?
Between different pallets?
TIP: To make sorting easier check the “calibre” or “caliber” or “CAL” numbers in case they are different . It is possible to receive different calibres with the same shade and batch. Although strictly speaking this is not normal it remains a possibility. These markings make it possible to count and separate different sized products without having to open every carton.
If the excessive size variation occurs randomly and throughout the entire quantity you may be able to question the “1st quality” selection status.
Remember that the quantity and the pattern of occurrence influences the solution.
- If it is possible to sort into different lots, try to separate these for replacement OR to be installed into different areas
- If the occurence is a set percentage in each carton, one can estimate the amount that is affected, and have the tiler set aside the wrong sized pieces as the job proceeds for installation in a different room or area (note that here the different sized pieces have to all the same size!)
- If the occurence is a set percentage in each carton and the above is not applicable, have the tiler set aside pieces for return, and negotiate with your supplier to replace this quantity OR
- Return the entire batch for replacement OR
- Get a refund and reselect
3) Squareness (rectangularity) and Shape test;
Of all of the possible ceramic tile defects rectangularity or shape defects issues are the easiest to spot in a panel because the lines between each tile should should show no changes in gap size. They generally occur with rectified tiles if the cutting equipment is not properly calibrated. They occasionally occur with regular edge tiles because sometimes these are also cut from larger pieces.
Using the example of ISO13006 as the specified standard then the maximum rectangularity deviation is +/- 1% of the edge length
By performing the size variation check in the previous step you would also have noticed any squareness issues. If none were detected, skip to the next check – number 4. If any issues were detected read on;
Steps: As in sizing, try to determine the pattern of occurence
- Within cartons
- Between Cartons
- Between pallets
- Localized in just one portion of your order
The out of square tile can only be used for cutting into the pieces required at the edges of the area being tiled. A mis-shaped or “out of square” piece should never be laid.
– Have the tiler set aside all out of square pieces AND
– Use affected tiles for “cuts” and return the unused balance to the supplier AND/OR
– Replacement of the affected tiles
– If the occurence is significant and throughout the batch then
– Return the whole order AND
– Replace with a different batch OR
– Reselect another product
The important information to report is an estimate of the number of affected pieces based on a random count. The more cartons you select and count, the more accurate the estimate will be! Once you have from each pallet a random selection a good average of the occurence should be possible to calculate.