Sealing Paving

Many homeowners choose to seal their new paving to protect it from accidental staining and to reduce the risk of allowing algae and lichens to establish themselves on the surface and joints, discolouring the paving and masking the natural beauty of the completed work.

There are many different sealants on the market, providing different finishes and often changing the appearance of the paving. High gloss sealants rarely look ‘natural’ and can sometimes make the treated surface slippery and unsafe. Polyurethane sealants are best suited to concrete block paving rather than natural stone, but if the semi-glossy, slightly waxy finish is admired, there is no reason why they should not be used. Fluoropolymer sealants are completely invisible: you wouldn’t know they were there until someone spills a glass of red wine and you are able to clean it off with nothing more complicated than a paper kitchen towel.

There are also specific sealants for specific stones. Sandstone is often more porous than, say, granite, and so some manufacturers offer sealants designed to suit the characteristics of individual stone types. These are often very good quality products, but invariably expensive (cost of treatment in excess of £5 per square metre).

One of the best products for many types of stone is Lithofin MN StainStop. This is a top quality sealant suitable for use both indoors and out, and will protect your paving for 2-5 years depending on how heavily used it might be. For those that prefer the richer colours that appear when paving is damp, Lithofin MN Colour Impregnator will give a permanent damp look and can be applied before using the StainStop sealant. Apply sparingly: it is better to build up the ‘damp look’ to the desired level in a series of stages rather than overdo it in one application and find that the effect is “too much”. Once a satisfactory ‘damp look’ has been achieved, it can be ‘fixed’ by applying one or two coats of the StainStop.

As with any surface treatment, the finished effect will depend on a range of factors such as stone type and condition, but also on less obvious factors such as whether it is in a shady or sunny position, so it’s a good idea to try out the treatment in an out-of-the-way corner before treating the whole patio or driveway.

Obviously, all paving should be in pristine condition prior to sealing. There is little sense in sealing in stains and empty joints, and so preserving them for several seasons more. Prior to sealing, the paving should be thoroughly cleaned, and checked for any defects. Ensure joints are full and that there are no loose pavers or flagstones. Because faults and minor defects rarely show up straight away with new paving, as well as the possibility of efflorescence developing on a small number of installations, it is strongly recommended that all paving is left untreated for at least 6 weeks. Sealing immediately upon completion tends to seal-in problems and make them much more difficult to rectify.

It’s essential that the paving is completely dry before applying colour enhancers and/or sealants, and so it is never a good idea to attempt sealing during the damper, cooler months of October to April. Try to choose a time when there have been at least two days without rain or precipitation, and remember that users will not be able to access the paving for several hours following sealing. Also, avoid breezy days when there is a risk of dust and detritus being blown onto the freshly sealed surface.

If using a colour enhancer/impregnator, this must be done FIRST. It’s not possible to enhance the colour of a newly-sealed driveway. Follow the manufacturer’s instructions to the letter. Don’t cut corners, and if it says to leave off any further treatments for two hours, make sure it really is at least two hours. On those occasions when sealant treatments go wrong, the manufacturers will not entertain any claim where they suspect the application procedure was not followed rigorously.

Many sealants will require two coats to achieve full cover. This is especially true with new stone and paving that has not received any other treatment. The first coat tends to soak in and coverage can be worryingly low, just a couple of square metres per litre in some cases. However, the second or subsequent coat usually goes much further, 5-8 square metres per litre is not unusual, and the coverage rates reported by manufacturers often aggregate the rates for the two coats.

Many sealants will dry or cure in 2-6 hours. Protect the paving with flutter tape, temporary fencing or barriers during this time as visitors to your home may not be aware that you’ve just spent all day (and several hundred pounds) treating the surface of your driveway.

A good quality sealant will usually provide 3-7 years of protection before it will need re-doing. Cheaper sealants are often a false economy as they may last only one season. Generally speaking, it’s a good idea to use the same type/brand of sealant when the time comes to re-seal, so keep a record of what was used, when, and from where it was sourced.

General Maintenance

Despite what is claimed by some suppliers and installers, there’s no such thing as maintenance free paving. All paving needs a little bit of care and attention to keep it in tip-top condition, but by choosing Global Stone paving, you have started with the very best, so the maintenance requirements will be lesser than those of cheaper offerings.

Weekly brushing:
The simplest maintenance is brushing. Regular sweeping will remove detritus before it has a chance to accumulate and stain or damage the paving, and in these days of obesity-consciousness, is an ideal low-impact workout for a normally-horizontal teenager. Autumn leaves may look stunning on the trees, but when they fall and land on the paving, they may stain if allowed to lie there over the winter. This is even more important for berries, hips, drupes and other fruits. Remove these as soon as they are spotted.

Stains:
Where stains have occurred there are many and varied proprietary products that are claimed to be the perfect cleaning solution. However, care is required as some of these cleaning products, particularly those that are based on or include hydrochloric acid, can damage the paving surface, make worse the existing stain, or even create a whole new stain! As with all surface treatments, test the product on a discreet corner before using it elsewhere.

Most stains can be removed with soap and water. Hot water sometimes is more effective than cold, and many experienced cleaning contractors prefer to use a mild soap, such as those found in baby shampoos, rather than a harsh, floor-cleaning type product which may adversely affect the colouring of the stone.

Power washers:
While hosing down a paved area every few weeks is unlikely to do any long-term damage to the paving, power washers can, and do, seriously damage some pavements. The force of the water exploits any minor cracks or weaknesses and blasts out loose stone or slightly weak jointing. While they can rejuvenate tired, dirty paving, regular use will often do more harm than good. If you find that your paving gets dirty very quickly (overhanging trees or close to a busy road) consider using a quality sealant to protect it rather than abrade the surface on a weekly basis with a power washer.

Running repairs:
Regular brushing also offers the opportunity to inspect the paving for any minor defects. The jointing is the most likely element of the pavement to suffer. Cement mortars degrade over time, while sand jointing can be lost due to scour from wind and water. Lost jointing may allow damaging surface water to find its way into the sub-layers and further weaken the structure, so it makes sense to repair as soon as a problem is identified.

Cut out any damaged mortar jointing, and replace it with fresh 3:1 mortar to a depth of not less than 25mm (any less is unlikely to bond properly). Polymeric-filled joints rarely degrade or come loose, but if it was to happen, the affected area should be cut out and replaced to full depth. Lost jointing sand is a more common defect and easily remedied by topping-up with fresh kiln-dried sand. When jointing sand is repeatedly lost from a pavement, it may be a good idea to consider a joint stabiliser or even a sealant to ‘fix’ the jointing in place once and for all.

Algae, mosses and lichens:
Where lichens (black spots) and/or algae (green discolouring) are a problem, regular swilling of the surface using a weak bleach is often beneficial. Wet the paving first, then apply diluted bleach via a fine rose from a watering can, and allow 10-20 minutes before washing off. Don’t allow the bleach to dry on the surface: wash off sooner if the surface is drying out more quickly than anticipated, and repeat the treatment. This regime has been found to be very effective at keeping algae, lichens and mosses off unsealed stone paving, without damaging the surface and at minimal cost.

Efflorescence

Efflorescence was traditionally a problem associated with concrete products but the growth in use of stone paving has seen an increased incidence of efflorescence, and efflorescence-like problems, occasionally affecting several different types of stone paving.

The phenomenon has only come to prominence in the last few years and as research into its causes is still ongoing, and given the vast range of stone now being supplied to the residential paving market, there is no definitive answer for how it is caused. It is thought by most to be related to the porosity of the stone, which would partly explain why it affects some stones and not others, but there is also a strong indication that local aggregates used in the laying course and/or the mortar jointing can have a significant effect. For example, it is now well-documented that some of the strongly coloured red/orange/yellow sands used by the building trade in SE England have a tendency to discolour light coloured sandstones and limestones.

Some installers are now claiming that the very light granites, sandstones and limestones should only be laid onto mortar made using a silver or granite sand, as these contain no iron minerals that could cause discolouration. Global Stone will be able to supply you with a washed, silver sand if you prefer to use this method.

Most of the problems involving discolouration and picture framing occur with relatively porous stone types (many of the sandstones plus silver-grey granite) when they’ve been allowed to dry out completely. Having stone sat in the summer sun causes it to lose all of its moisture content by evaporation. When it is then laid on a wet mortar bed or pointed with a wet mortar, it ‘sucks in’ moisture, bringing cement particles, clay fines and iron minerals with it, which are later deposited on the surface as further evaporation dries out the paving once more.

A few techniques that can reduce (but not eliminate) the incidence of these problems:

1. soak the paving with clean water a day or two before laying. It’s best if the soaked paving is given enough time to become ‘surface dry’, as this makes it easier to lay, but the recent soaking should have rendered it less ‘thirsty’ and therefore less inclined to absorb moisture from the bedding and jointing.
2. prime the underside and edges with a ‘moisture barrier’. This has the effect of limiting the amount of moisture that can be absorbed by the paving following installation. One method relies on neat PVA being painted onto the underside and edges prior to laying. Another favoured technique uses PVA mixed with cement and a small quantity of water to make a slurry paste that is daubed onto the underside and edges, while some contractors prefer to use a SBR/cement slurry. Most installers lay the paving immediately after ‘priming’ although some contractors claim better results with the PVA-only technique if they allow it to dry overnight. Care is required as all of these products can stain paving and make it difficult, if not impossible to clean off stains that have been allowed to harden. Wash off any accidental stains and spills immediately with clean water.
3. use a stiffer (less wet) mortar for the bed and a barely damp mortar for the pointing. Alternatively, use a polymeric mortar for jointing as these have no cement or mineral content that can stain.

Regardless of which stone is being used and regardless of technique, it’s important to remember that stone is a wholly natural product and as such there is an inherent variation in porosity, colour, texture and grain size. It’s not unknown for one flagstone to discolour while its immediate neighbour remains completely unaffected. This does not mean there is a problem with the stone: it’s just the way things are with natural stone paving.

While discolouration and picture framing can look unattractive when first encountered, the effect and its visual impact do lessen over time and it’s quite likely that in 12 months time the problem will have lessened significantly or disappeared completely. Don’t be panicked into ripping up and replacing affected paving immediately. Give it time, allow nature to run its course and review the situation the following year.