Richard Osborne of LTP Ecoprotec looks at the options for sealing outdoor surfaces, and the benefits that each can bring to projects.

limestone floor or a granite worktop. After all, who actually seals an outdoor surface? The average patio or terrace may get the occasional jet wash to blast away slippery algae, but outdoor slabs are basically left to their own devices, aren’t they? This view is now, however, being reassessed, and it’s driven to an extent by the popularity of the ‘seamless’ inside-to-outside installation. When the same material is used inside and outside, it doesn’t take long for the two areas to show a contrast. This is particularly evident in stone installations, where flush surfaces are continued through bi-fold doors. Generally, the indoor slabs are sealed and the outdoor surface isn’t, so it very quickly becomes darker, and dirtier. One reason for a reluctance to contemplate external sealing is that traditional spirit-based products can make outdoor sealing almost impossible; they’re best applied when a surface is bone dry and free of any residual moisture. If they were applied in damp conditions, moisture could


hen discussing the best sealer for a job, it’s generally assumed that it’s for use indoors – for a

become trapped between the surface and sealer, and this could create an unpleasant, milky appearance.

SPIRIT-BASED VS WATER-BASED Today, there’s a new breed of water-based sealers on the market that eliminate these issues. They are equal in performance to spirit-based sealers, with the added benefit that they can be applied over moisture. Once applied and cured, water and spirit-based sealers actually function in a similar way. They’re both tough, durable and provide stain protection. Spirit and water-based solvents are simply used to facilitate application. Once a surface has dried, the spirit evaporates into the air and releases VOCs into the atmos- phere, so they don’t actually contribute to a treatment’s ongoing performance. Water-based treatments enter a stone’s pores in the same way, but as they tend to be VOC free, they don’t have the same negative impact. One key difference worth mentioning, however, is their appearance. Spirit-based sealers tend to be clear as the sealer

polymer and the solvent form a continuous clear solution, whereas water-based sealers appear white. This is because the polymers are present as separate particles and scatter visible light differently than the water in which they are dispersed. However, this original appearance does not create the permanent milky look caused by trapped moisture under a spirit-based solvent.

Despite the huge leaps that have been made in water-based technology, so many companies remain unconvinced about outdoor sealing. As well as the weather issue, they claim that it’s simply a waste of money, that there will be logistical difficulties, that it will change the stone’s appearance and create a patchy surface. However, a quality, natural-finish, water-based impregnator is actually easy to apply, will not change appearance, and will not create a patchy surface. It will, however, protect both areas and retain that seamless look.

As well as facilitating treatment in any

season, a quality water-based sealer will offer greater protection against the elements. It will provide some UV resistance, offer protection against frost, lichen and algae, and prevent staining from pets and wildlife, plants and leaf matter, and barbecues.

There are other less obvious benefits of switching to a spirit-free product. They are safer to transport, handle and store, which is a plus as there can be a vast amount of admin involved in the storage of ‘hazardous’ spirit-based products, including completion of reams of paperwork and the requirement for secure fireproof locked


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