They're Coming After Your Holidays...
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No best answer has yet been selected by erik. Once a best answer has been selected, it will be shown here.
For more on marking an answer as the "Best Answer", please visit our FAQ.These sound like the hard ceramic tiles which are often used in industrial floor areas, The only way to get through is use a new good quality drill bit, set the slowest speed on your drill, use no hammer, and keep a small water flow running on the drill end and around the hole to cool/lub the drill bit.
If you stiill can't get through then you will have to use a hammer drill but before doing so try banging on the tiles with something hard and listen to the sound, if they give a hard sound and not a dull thud, they are probably well fixed and will not break if using hammer, use the hammer drill with a low pressure and with water again.
Start with the smallest masonry drill you can find/buy and make a small hole first using hammer action and then go to the actual size you want to make and open it up using no hammer if possible.
If you still can't get through then the final answer is to find a diamond tipped drill as used on glass, not easy to find and not cheap and not easy to use either. see this site for some info.
hi , sorry but I have just seen this thread and thought i'd give you a usefule tip. For hard materials such as porcelain etc, u must use a diamond core drill bit like the one in the screwfix link below
http://www.screwfix.com/app/sfd/cat/cat.jsp?id=100211>se=gtuk>kw=diamond+core+drill+bit
U can not hammer drill a tile as 9 times out of 10, u will crack the tile. These drill bits, are excelent and will cut through your tiles with ease (U must keep cooling the bit with water). a 10 mm thick tile will take less than 40 secs
its
http://www.screwfix.com/app/sfd/cat/cat.jsp?id=100211>se=gtuk>kw=diamond+core+drill+bit
The only answer is to use the right drill bit. The above link is to a diamond core drill bit that is specifically designed to the job.