Seal the deal

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

When discussing the best sealer for a job, it’s generally assumed that it’s for use indoors – for a 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 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 atmosphere, 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 containers. Also, as a general rule, water- based sealers tend to go further, with a typical extra coverage of between 10 and 20 per cent on most surfaces.

It’s also worth mentioning that sealing, as opposed to not sealing, provides its own environmental advantages. The main one being that a sealed surface requires much less cleaning. This, in turn, reduces associated waste and water consumption, and eliminates the need for more drastic intervention with harsh chemicals.

Other external surfaces

Advances in stone-effect porcelain finishes have resulted in wider specification – and as well as installation in homes, these surfaces are now being continued onto patios.

Just like stone, external porcelain does require protection – but for different reasons. While most matt porcelains are stain-resistant, they can still be marked during the fixing process. This is often caused by grouts or joint sealing compounds, which have an oily resin that can be very hard to remove. In order to prevent this, a sacrificial seal should be applied before fixing.

Protecting outdoor surfaces offers many benefits – and the new breed of sealers makes treatment completely feasible, whatever the weather and whatever the finish. In terms of the ‘seamless surface’ it’s a must. And having reassessed this area – armed with a new arsenal of eco-treatments – maybe it’s time to look at other external surfaces too?

Richard Osborne is director of LTP Ecoprotec