6 Editoriale - Su quali basi decidere se retinare le lastre o meno[1]

Editorial – On what basis should stone processors decide to mesh back their slabs or not?

Anyone who has some familiarity with stone restoration knows the difference between materials which need to be treated on both sides, that means mesh backed first and then resin coated, and those which only need to be resin coated.

In most people’s opinion fractured slabs should be reinforced with fibreglass, while mesh backing stone with no visible cracking seems pointless. This classification is only partially correct, as the issue of reinforcement is far too complex to be reduced to the two equations: ‘presence of large cracks = mesh backing is necessary’ and ‘absence of large cracks = mesh backing is unnecessary’.

There certainly are materials which are so sound in their natural state that they do not need any reinforcement, and this is the case of much granite. However, in order to avoid big mistakes it is worth clarifying the exact meaning of the adjective “sound”.

In fact, so many machinery makers misinterpret the significance of mesh backing and even worse diffuse misconceptions among slab producers. If you take a look to various catalogues, blogs and websites, you will find explanations according to which “mesh reinforcement is required when it comes to the treatment of slabs that present numerous cracks”. Whoever writes this undervalues or simply doesn’t know a crucial point: the absence of huge cracks does not in itself mean that the slabs are sturdy. Therefore, it is absolutely wrong to believe that stone free from extensive fractures and large irregular voids should not be mesh backed, because there are a number of varieties of marble and limestone – as well as some types of granite – that have hairline cracks which although fine and narrow can weaken the slabs and eventually be the cause of their breakage.

Obviously, hairline cracks’ worsening takes time, and yet this is not a good reason to neglect to carry out a proper reinforcement. In fact, once polished the slabs have to be moved to specialized workshops, where they are transformed into made-to-measure stone coverings, pavings, bathrooms, kitchens, tables, fireplaces, to name but a few. In the vast majority of cases, this means that the slabs have to be bundled, loaded into trailers or containers, transported over great distances (the transport can take weeks), unloaded and unpacked. Besides, small and medium scale companies source slabs from large importers and dealers, and accordingly have to collect their stone from warehouses, and transport the material using A-frame supports secured to the bed of a truck with the slabs tightly strapped and fastened to the support frame.

The production of made to measure items involves a repeated number of handling operations too, as the slabs are moved from the store and loaded on the worktables of bridge saws, contouring machines or waterjet cutting machines.

In summary, the polished slabs are subject to mechanical stress that may cause a small fault to turn into a huge crack; and hence to strengthen stone tending to break is a necessity. To whoever raises objections this leads to increased production costs, we reply that spending a few Dollars more per square metre is far preferable to bearing huge financial losses due to breakage of slabs.

Notwithstanding the above, we do not purport that slabs with hairline cracks or micro fissures should be always and in all cases mesh backed. For example, tiny fractures are not a problem for stone processors operating factories where the slabs are polished and nearly immediately cut to size. As well, companies dealing in cheap stone are simply forced to keep production costs down, and thus they are right not to reinforce relatively sound slabs.

The decision on whether or not to carry out a mesh backing should be also based on the intended use of the slabs. Indeed, there are situations where the use of mesh backed stone is advisable and cases when fibreglass looks unsightly or hampers the work of stone installers and tilers. In this regard, it is noteworthy to mention that fitting teams often complain about the incompatibility between the resin/fibreglass reinforcement and adhesives for the installation of natural stone. However, this is not a major obstacle because real experts in marble fitting know various methods to bypass it.

Other factors to be taken into account are thickness and dimensions of the slabs to be processed. Needless to say, 2 cm-thick long narrow slabs (e.g. 320 cm X 100 cm) will break much more easily than compact-sized (e.g. 220 cm X 160 cm) 3 cm-thick slabs.