Ask the Expert : limestone floors in toilets
In this regular column, Consultant Barry Hunt answers reader enquiries. If you have a question you would like to put to Barry, email it to: nss@qmj.co.uk marked for Barry’s attention. The answer will be sent to you and may be used in Barry's column in Natural Stone Specialist.
Q: I want to use limestone as a toilet floor. Am I asking for trouble?
You could be creating a situation where there is not only a high risk of failure but also the necessity for regular intensive maintenance that may not prevent ongoing staining and discoloration.
There is also the potential problem of not being able to use aggressive disinfecting and cleaning chemicals that are typically needed to provide sufficient cleanliness.
The principal problem with using limestone in a toilet area is the fact that it is readily attacked by acidic materials. Unless there is a protective coating, no amount of surface treatment can prevent surface dissolution by spilt human waste, notably uric acid.
Toilets that men use are more liable to suffer spillage problems and dissolution often follows obvious patterns.
The need for cleanliness demands strong chemicals to neutralise germs and wastes and help remove them. Chemicals typically contain highly alkaline materials that act as bleaching agents and which can strip some of the natural materials from the stone. Salts may also be promoted that can lead to surface damage.
Exposed limestone surfaces typically become rougher and lighten in appearance under the action of aggressive cleaning chemicals, thus reducing and often losing their aesthetic appeal.
Secondary effects can be the harbouring of waste products, as limestone is denuded and the typically porous structure opened up, regardless of any sealing treatments that have been applied. Some limestones may contain dark organic matter that can be stripped from the stone, leading to the development of dark surface discolorations.
The potential problems with limestones can be reduced by selecting types with low porosity, as these tend to be more crystalline and potentially more resistant to dissolution.
It would be even better to find limestones that have been altered so that their carbonate minerals comprise dolomite rather than calcite, as dolomite is considerably more resistant to acidic dissolution.
Limestones of very light colour are best avoided as these generally more readily exhibit discoloration.
The last resort would be to apply a chemically resistant coating to the stone such as a urethane or acrylic resin, but the compromise will be a potentially major and undesirable change in the appearance of the stone .
Overall it would be better to use dense materials such as granites, or siliceous materials such as quartzites, that would provide good resistance to attack from both spillage and chemical attack.
However, I would be wary of some basalts, calcite-bearing sandstones, verde marbles and any other stones that contain carbonate.
There is no official test available for determining a stone’s suitability for use in a toilet. However, it is relatively straightforward to determine if a stone is suitable by applying bleaching agents and toilet descalers to their surfaces, washing them off and seeing if the stone has changed.
As much as I like to promote stone use, this is one situation where I believe the choice of limestone does not do the stone industry any favours.