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Great question Dan...interested to hear what others think
What type of stone are you planning to use?
It would definately depend on the type of stone being used. I have seen riven Indian sandstone laid around pools both sealed and unsealed and not heard of any negative stories. We have also supplied different types of sawn sandstone, limestone and Yorkstone for use around pools. In this case we will always advise sealing, not just because its round a pool but because we reccomend that sawn paving is sealed regardless
Belt and braces would be to soak the coping stones in a stabilising agent. After the stabilising agent has cured you could then additionally apply a couple of coats of an impregnating paving sealant. If you followed these steps then you would have no issues whatsoever but as I have said it might be a bit OTT.
Also bear in mind that Travertines and limestones are regularly used for internal pool applications. I would imagine that in this circumstance the stone would always be sealed as internal stone always is
What is the stone in question Dan, or is it just an general enquiry?
Never ever use sealant on natural stone outside, and especially around pools. The only time you might use it is with a granite or other exceptionally hard and non-porous stone and then only to assist maintenance and prevent staining from oil spillage for example. What will happen is salts will inevitably enter underneath the stone and then try to get out and usually concentrate below the surface causing it to blow. This can happen in months, not years. There are many other problems as well. Another issue is that these materials can reduce slip resistance around the pool if not used correctly, and I have been involved in large accident claims due to slip into pool where people have broken their necks amongst other things. I am currently writing a guide on the use of stone around swimming pools for the Stone Federation Great Britain, and this and much other advice will eventually be included in it. I have spent 25 years investigating natural stone problems and sealants used externally are one of the most common. Do not believe the manufacturer's claims for these materials such as vapour permeability, externally this is too slow and frost attack and other issues can result. Organisms feeding on the sealant materials is another and it is often impossible to get them to penetrate properly in the first instance due to pervasive dam in the stone. Apologies, but I am going to be blunt,any one who recommends these products for stone externally does not know what they are talking about. I could list many other issues and problems but I had better leave that for the guide rather than ramming the point home. Sealants equals problems for external stone…
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Internally, then generally there are far fewer problems, but be mindful of the potential drop in slip resistance. Limestones can be eaten away by acidification that can occur when trying to constantly balance the pool and not mixing properly, and we have used CCC resin to provide a sacrificial coating. Otherwise the Lithofin range of products is one it is difficult to go wrong with. Avoid eco products that generally do not have the penetration and do not work. Follow the instructions and often it is best to ring the manufacturer for more specific advice./p>
The problem with most sealants is that they penetrate the stone and stop moisture flow to a degree. However, they do not stop the surface from being chemically attacked where it is in direct contact with water and the chemicals it may contain. Limestone is particularly susceptible to acidic attack, as is any other carbonate-based stone which includes travertine and most marbles. Dolomitic marbles and limestones are less susceptible but when mild acid is warmed up in a heated pool the reaction is increased. Most pool owners have no idea what they are doing to the stone until it is too late. If you are going to put a sealer on a stone, acrylic or urethane is probably king.
The use of sawn stone around pools is not recommended for health and safety reasons as there is insufficient macro-texture. It just takes a little bit of algae or other organic growth in the pores at the surface and the stone will be more like a skating rink. Sealing the stone also increases the potential for aquaplaning. Sandstone should always be used with a naturally riven finish or with a strong tooled finish.
No matter what Clients are asking for, the slip resistance must be the first consideration around a pool, then aesthetics. The stone must comply with either BS EN 12057, BS EN 12058 or BS EN 1341 for starters and if slip results for the finish are not available for consideration, it should not be used. Since 01 July 2013 natural stone must be CE marked. You could become liable for any accidents caused. Slip testing must be undertaken with any treatment applied, otherwise they may be invalid.
Quite simply, you should never seal natural stone,as it needs to breath. Such is the doctrine from English Heritage which, if you think about it, is entirely logical.
Because it is a natural product,sealing stone will simply fill the pores. This will prevent it aerating, and will seal any moisture inside.
Also , any moisture from beneath will have nowhere to go.
During a hard winter the moisture that is trapped inside the stone, will expand during periods when the temperatures are sub zero, the moisture will expand and "blow" the surface of the stone, damaging it irrevocably.
A further disadvantage of sealing stone is that it will lose it's no slip effect.
If you are trying to prevent Patio Black Spots, ie lichen growth or green algae, the the sensible option is to apply, "Patio Black Spot Preventer" annually.
The Patio Black Spot Preventer is applied to new stone, and leave an invisible residue which kills the spores as they land on the stone. Applied in Spring, by simply spraying it on the stone and leaving it to cure, the Patio Black Spot Preventer will last for up to 12 months. Always use it on new stone, or stone which has been treated with Patio Black Spot Remover.
The Patio Black Spot Preventer will preserve the stone, maintaining the colours, without the use of damaging sealers.
It's so difficult to bite my tongue reading some of the advice being given on this topic. Please please please if you are going to give opinions on the suitability and/or the performance of sealing products it's very important that you distinguish between Topical sealers, common Impregnating sealers and permanent bond sealers. At Dry-Treat for instance we have spent over twenty years developing a completely unique range of permanent bond products that DO NOT change the slip resistance even 1% and are still 97/98% breathable and then you can get "experts" on this site just dismissing that twenty years of development in a two minute blog post! Although I agree that 95% of products sold in the UK for paving can cause more issue than they solve you also shouldn't ever just dismiss the use of sealers externally across the board.
More than happy to let people try and test for themselves and equally delighted to meet any sceptics as I know when people question a hole in someone's "knowledge" that the default setting will be to be dismissive.
In fact I'd be delighted to set up a demonstration of the technology for LJN members at London Stone at anytime if Steve is in agreement as I understand that they are a stockist of some of the products we manufacture. I am not trying to sell you anything I am just offering to show you the advances in technology that you may or may not want to use.
I know that everyone posting on here is just trying to helpful but let's remember we once believed the Earth to be flat and that Smoking was a great way to stay slim.
David
David,
Equally important to distinguish between what a sealer achieves and what a "Preventer" achieves.
Both have their benefits.
Far from knocking what you are selling, we manufacture and market The Patio Black Spot Removal System, purely to remove and prevent the growth of Lichen and Algae, which sealers will not.
Equally, our System is not intended to seal (so it doesn't) it purely "prevents" the deterioration of stone without changing it's makeup, which a sealer does.
It's also organic and solvent free.
What are the HSE Pendulum Test results for your product applied to York Stone or Indian Sandstone, for instance in both wet and dry conditions?
Will your product prevent red wine stains?
Regards,
Simon
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