In this regular column, Consultant Barry Hunt answers reader enquiries. If you have a question, email it to: nss@qmj.co.uk marked for Barry’s attention.

Q: More resins seem to be used in association with stone finishing all the time. What do you think of resins and their use with stone?

The word ‘resin’ covers a great many different materials, from natural secretions from trees to man-made petro-chemical products.

The many different formulations of resin are among the reasons the top-end producers of quartz composites claim their products are superior to cheaper versions.

With natural stone, resins are a bit of a Jeckyll and Hyde material. They are increasingly used but can cause problems.

On the plus side, they have been used for many years to fill small imperfections that would otherwise make some stones undesirable, reducing the waste of an essentially non-replaceable resource.

The modern drive to decrease waste has meant more elaborate and widespread use of resins, some of which cause new problems that you will want to avoid.

Whole blocks of more friable stones are now being impregnated with resins before cutting so they do not break as they are sawn. I see no problem with this when the slabs are cut into floor tiling, where a failure would be unlikely to be much more than an aesthetic issue, but if formed into cladding panels, the design, assessment and testing regime would have to take account of the treatment.

It should also be remembered that if resin forms more than 1% of the finished product it will require testing to establish its fire resistance rating.

Resins are now commonly applied to tiles and slabs prior to finishing, not just to fill imperfections but also to enhance appearance. Dull stones that do not easily take a high polish may become more reflective with a surface impregnation of resin.

However, this resin also presents a potential barrier to treatments that would hope to protect the stone, especially when used for counter tops.

The highly reflective resinous surface can disappear with use, leaving a dulled surface that is difficult to restore. Refinishing an otherwise acceptable site repair could inadvertently result in a larger patch that is unable to be polished back to the condition of the surrounding surface because the resin has inevitably been removed in making the repair.

There are cases where excessive resin use, both to fill cracks and voids and to provide a more lustrous or even appearance, has led to excessive re-cracking and an uneven appearance. I know of one case where more than a third of the stone received was rejected for this reason.

Sometimes a resinous impression of matting can be left on the surface of a stone that has been packed in a crate with polished faces touching the reverse of slabs and tiles that have been given a mat and resin backing – a strengthening process often used on weaker stones such as breccias and serpentinites.

Some travertine suppliers rely heavily on resins to fill voids, which is fine for wall tiling and cladding, but as flooring has caused a spate of failures as hidden voids collapse under foot. It is always worth looking at the untreated back of a stone to get an idea of the amount of resin that has been used on the front – as long as the back has not also been treated.

One issue that has arisen with the application of resinous backings to stone tiles is the loss of suction when fixing them using cement-based adhesives. A film of water forms at the contact between the resin and the adhesive when the stone is pressed on to the adhesive, compressing it.

To counter this, ­the mechanical interlock can be increased by thicker matting or, more laboriously, the surface to be bonded can be roughened by grinding – not something you want to find necessary once you have started fixing tiles on site.