History of the UV Filling Lines
The UV Filling Lines are designed to seal small cracks which appear on the surface of certain stone through the application of photosensitive mastic.

This process, commonly known as “surface filling”, is aimed at merely hiding holes, pores and pinholes. However, it must be very, very clear that photosensitive mastics have no reinforcing effect; and accordingly surface filling should be never confused with proper Resin Treatment.

It may be worth noticing that the first UV Filling Lines date back to the early ‘90s, nonetheless there are machinery producers trying to launch ovens for surface filling as an innovative technology.

The low prevalence of the UV Filling Lines is due to the modest benefits given by their use and the narrowness of their scope.

Workings of the UV Filling Lines
The basic components of any UV Filling Line are two tunnel ovens and a couple of worktables for mastic application. The Drying Tunnel is a horizontal oven with forced warm air ventilation aimed to dry the surfaces to be enhanced with photosensitive mastic. The UV Tunnel contains a series of lamps which generate ultraviolet radiations. Exposure to ultraviolet radiations causes an almost instantaneous hardening of the mastic coating.

Most UV Filling Lines are installed between honing machines and polishing lines, to have the slabs honed, filled and polished uninterruptedly. However, any UV Filling Line can be complete of loading and unloading workstations and used separately from other machines.

Concluding remarks on the UV Filling Lines
Our long-standing experience in the construction of Filling Lines enables us to evaluate competently their utility and efficacy, and to advise customers on the do’s and don’ts of surface UV filling.

As explained above, surface filling has little to do with Resin Treatment, because unlike that it is completely ineffective at strengthening fragile material. UV filling is nothing but a straightforward operation aimed at hiding small superficial defects and it might be even defined as a “cosmetic treatment”.

Furthermore, the duration of effectiveness of surface filling remains uncertain, because nobody can a priori exclude the possibility that the mastic will chip and leave the holes open after a few months. In this regard, it is worth bearing in mind that unfavourable weather and climatic conditions may increase the risk of problems. Therefore, mastic filled stone is not recommended for exterior use.

Another subject that is not always well understood is the difference between “surface filling” and “filling of cracks with resin”. The application of photosensitive mastic makes it possible to hide superficial defects such as tiny holes which are only a few millimetres deep; but when it comes to the repair of fractured materials, there is no other way than coating the stone with epoxy resin. Trying to fill deeper faults with photosensitive mastic is pointless indeed, as the parts of mastic which are not directly exposed to ultraviolet radiations cannot harden.

Summing up, using photosensitive mastic makes sense only if the polished material can present small imperfections despite it was resin coated. The best example is represented by the surface treatment of traveronyx slabs that consists of honing, resin coating, fine honing, UV surface filling and polishing. This processing method can be applied to the very few types of marble, breccia and limestone with similar problems.

The latest UV Filling Lines from S.E.I.
The S.E.I. UV Filling Lines can be combined to honing and polishing machines to form high-automation comprehensive production lines designed according to the required productivity levels and the availability of space.

Worthy of mention are the “Res Pol UV” models. These multipurpose plants allow stone processors using any polyester resin, epoxy resin and photosensitive mastic. Indeed, they are equipped with truly unique “Polymerization and Hardening Tunnels” characterized by the inclusion of both a heating and ventilation system to accelerate the resin polymerization and a set of ultraviolet lamps aimed at forcing the photosensitive mastic to harden in the blink of an eye.

The only relevant difference that lies between the plants for slabs and the lines for strip and tile filling is the size of the components.