UNRAVELLING LINERS

Liners are the most cost effective method of making a waterproof pool in your garden, but what is there really to choose between all the makes and materials?

Peter May tells you what will help you make it neat or natural.

Don’t you hate all those fancy scientific names and acronyms; those strings of letters that only mean anything to ‘them that’s in the know’. Somehow you feel excluded from all the information. But then again all you are after is to make a hole in the ground waterproof. You have already vaguely contemplated going ‘au naturelle’ by puddling it in clay, but then there was the mess.

And then you thought of manufacturing the pool itself in concrete, but a few sums quickly made you realise not only the muck and disruption involved but also the expense. So then you continue your investigations down the aquatic centre and find a huge range of products that all have different names but all look pretty much the same: black, some are shiny, some are not.

Admittedly some are rigid and already pool shaped. They will tell you these are made from are generally HDPE (High Density Polyethylene) or ABS (Acrylonitrile Butadiene Styrene) and those are also fibreglass – mostly bigger heavier pools.

Others liners look like sheets of plastic, whilst some look like rubber. And its here you discover all these exotic names like Pondalene, Aqualast, Maxipool or possibly Alfafol. Despite the variety of brand names most of the liners available are one of several quite distinctly different materials that will all do the same job, and as individual materials they only come from 2 and 3 factories around the world. So it is highly likely that products, or at least the raw materials, with similar specifications will have come from the same factories in America, Belgium or Sweden.

The flexible sheets of material are either PVC (Polyvinyl Chloride) or Polyethylene – those are the shiny ones – and matt coloured ones are EPDM rubber (Ethylene Propylene Diene Monomar) or Butyl rubber. Well as your eyes are glazing over and you feel no the wiser, you still aren’t finding the choice any easier. Once upon a time that choice was much easier.

THE HISTORY OF THE WORLD OF RIGID POOLS

If we talk about rigid pools for a moment, harking back to 1982 when there were only pools made of fibreglass. There were good and bad brands, as fibreglass pools are products that require manual skill produce. But on the whole if the pools survived the delivery and installation process, they generally lasted longer than their owners. Then came pools made from ABS and HDPE: more robust in storage at the garden centres and vastly cheaper. These seemed like a shotgun blast to the head of a business that was just beginning to boom. They were a moulded product, which although they could be produced in vast quantities at the touch of a button, their limitation was in the physics of making moulds and the sizes of the sheets of raw material. Once it was realised that you only could get small pools from these materials, fibreglass re-emerged into a new niche, offering highly durable pools that were larger and deeper than the plastic competition. A particularly attractive proposition for people interested in creating water gardens for fish, even Koi carp keepers (especially when they were pandered to with the dimples and grooves built into the shape to take the pipe work and fittings for the very best type of biological filtration, when it is ‘gravity fed’ from a sump in the bottom of the pool.)

Rigid pools represent ‘the cheap and cheerful’ end of the market on a par with the moderately priced flexible liners in terms of price per square foot of surface area and if there is a shape and size that suits the space you had in mind they are worth considering. They are easy to clean because of their smoothness, which on the other hand gives them a clinical look that only weathers to an extent required for a suburban patio pool. Even fully laden with plants could never be mistaken for a ‘natural feature’, and because of their size they can easily look lost or out of place if there is enough room in the garden for other distractions.

Ifs….NO BUTS

If you are looking for something to waterproof your hole in the ground the way you have designed it and if you want it to look natural or to look purpose built with brick or stone facing, not just outside, but inside as well then a flexible liner is imperative. If you have the intention of creating more than 6 square metres of water surface and a depth that suits you, the plants and the fish, again you must use a flexible waterproof sheet of some kind.

THE HISTORY OF THE WORLD OF FLEXIBLE LINERS

Back again to 25 years ago the choice was easy. If you were serious about water gardens and you wanted to see water in the ground after 9 years then butyl was the only consideration. Why 9 years? I don’t know but that was the guarantee for it then. PVC and polyethylene, under the glare of ultra violet rays from the sun would self-destruct after 5 years at the most, turning to crispy flakes around the exposed edge at water level. With PVC, it was ok if the liner was completely obscured and then it would last indefinitely but then it seemed so fragile. In fact all the liners for domestic ponds seemed very thin, butyl 0.75mm and PVC only 0.3mm, but there was a huge demand for thicker longer lasting materials for huge projects from the building industry, water, and sewage industries (the channel tunnel after all was lined with PVC –and it only had a 9 year guarantee then). This in turn brought about competition to supply that demand and the effects filtered down to the domestic market.

Well, the end result, if this is the end, is the range of liners that you see now, some of them with LIFETIME GUARANTEES, with 15 years as the cheap end of the market. It is my guess that retailers are banking on the natural ergonomics of people moving around and growing old and dying before they are likely to reclaim their money back for a duff liner.

Oase offer a service to take back and ‘professionally reclaim or dispose’ any old liner that you give them.

Nevertheless I think we can still regard the guarantees as the best yardstick for quality and from there we can assess the different products according to the characteristics of the individual materials. This means you are now at liberty to choose the most suitable material for the project and be confident it will do its job for as long as you want. To cut your costs by choosing a liner with a limited guarantee for the sake of expense, particularly on a large project, is not sensible. Better to shrink the size of the project to a size where you afford the best materials. Also ignore the bargains that may come from the building trade or ‘off the back of a lorry’. Some formulations of these products leech chemicals into the water that will kill wildlife and fish (generally slowly and painfully). They are made for roofing or tarpaulins not pools.

CHARACTERISTICS THAT SUIT WATER GARDEN STYLES

So what are the characteristics of these materials and how do they perform in certain situations?

The small informal garden pool. In terms of the thinner materials, 0.75mm butyl rubber has always been considered the ‘Rolls-Royce’ of materials. It folds well into place and has a certain stretch-ability or give that finds the contours of the smaller awkward shape. It evolves a certain patina over time that gives it an almost natural stone look and for some people this may be a disqualification. For people keen on cleanliness and godliness, they will find PVC and Polyethylene easier to clean. EPDM rubber is too thick at 1mm and folds awkwardly in tight spaces. Some of the more robust PVC and Polyethylene don’t seem to want to fold down at all and you end up holding flaps of liner down with planting baskets.

Large pools. In my experience, as long as the size is within a dimension that can actually be transported to site and then the rolls of material manoeuvred to be laid, EPDM rubber performs as well as butyl. It is much heavier because it tends to be thicker for the same resilience value, but this gives it the ability to smooth itself out to a certain extent as the water fills the pool. With butyl and PVC the folds become exaggerated as the weight of the water takes effect. EPDM it is quite resilient to puncturing, but not as resilient as butyl to impact, as from heavy stones. PVC is not good with impact but on the other hand it is very difficult to pierce with gradual pressure as from a blade or spike. All these idiosyncrasies are evened out with a good layer of sand under the liner as well as a fabric underlay.

It is interesting to note that for the construction of wildlife or conservation pools, the BTCV, the national conservation volunteer group, use EPDM rubber in the ponds they create all around the country, some in areas exposed to spates of vandalism. These have the added protection of a geomembrane on top of the liner as well as below and then perhaps a 15cm a layer of subsoil over that.

Very large pools need to be welded from strips on site because of the weight factor. EPDM has to be factory welded. Butyl and PVC can be welded and polyethylene can even be taped. Polyethylene has a poor reputation from the past to live down and although it is very popular in other continents – in South Africa they use nothing else – I would be very averse to using it on a large project. Mainly because of its price, farmers love it in this country using it for everything from silage pits to slurry lagoons.

When price becomes the crucial factor on these large sites, butyl cannot keep up. Over the years the prices have been falling on all the products as the alleged performance goes up, but it has now reached a point that butyl can no longer compete particularly when it needs to be 1mm or over.

Stream and waterfalls are projects with which I always prefer to be using butyl. Creating them using natural stone and cement, theoretically the stonework should be self supporting, but there is a bit of grip that you get from butyl rubber and cement mortar that ensures that it says where its put until it goes off. As I’ve said before, it has resilience to stone impact, which served it well when I was building waterfalls before the idea of protective underlay over the liner was ever thought of.

Other factors that may have relevance are:

weather conditions. PVC does not perform well in extremes of temperature. In the very cold it can crack if it is folded tightly. In extreme heat it can become very flimsy. These are only factors that affect its installation. Once it is installed, it seems to be ok.

Root penetration. PVC seems impervious to the most rampant plant growth from willow to bamboo, from bindweed to Japanese knotweed. As for butyl especially when it ages, some plants seem to sense there is water the other side of it and head straight through.

Burrowing beasties: Mice and moles have only affected butyl installations from below in my experience. It may be just my experience, but I will ‘throw it into the hat’ for consideration.

Extending pools. I might have given you the idea that because you can weld PVC and butyl on site that you could easily extend your water garden at a future date. Unfortunately the welding machinery is difficult to come by, even more difficult to use on dirty pond liner and simply does not work on butyl that has been in the ground for more than a year. PVC I would not like to vouch for, but by the time you have had skilled contractor in to assess and do the job it will probably be better to have a completely new liner installed.

IN CONCLUSION

The ultimate choice must be down to availability and price. If you have a supplier on your doorstep, or there is a price in a magazine or on the Internet from a reputable company that suits you, then go for it. The important thing is that it is suitable for the project you have in mind. Here are 10 top tips to bear in mind in your budget considerations.

TOP TEN TIPS TO HELP YOU WITH THE LINER YOU NEED

1.Budget – Consider the whole project; budget for all the materials you are going to use. Then consider the type of liner you think you can afford, but don’t penny pinch on anything over 6sqmtrs. Minimum 0.5mm.

2.Familiarize yourself with what is available. See what they feel like and try to see them in the ground. Gauge opinion from other pond owners.

3.Buy ‘off the roll’ unless there are any end of rolls or off-cuts that suit you.

4. To estimate the size of the liner:

length of liner = (length + (2 x depth))+10%
width of liner = (width + (2 x depth))+10%

Estimate stream liners roughly:

Length of liner =Length along the horizontal + (2 x height of the head)

Width of liner = width of widest header pool + (2 X depth)

5.Plan your pool with a dimension that plus the depth times 2, equals a standard width of liner off the rolls. EPDM generally comes in multiples of 5feet up to about 25feet (American you see), PVC and butyl in 2 metre widths up to 8metres in some places.

6.Dramatic indentations in the shape use up extra liner. Measure along the contour of the pool excavation just to check before you try to install it. In desperation you can gain a few inches by laying it in skew, using the extra length of the diagonal. Risky though.

7. Don’t stretch it into place. I don’t care how many books tell you. It needs to be tucked and folded into place. Just before you cut too much off around the top, then you can make sure it is properly fitted by filling it with water.

8. Use underlay and sand especially in gravely and stony situations. The pressure of water magically causes stones to float up through the sand and press against the liner. Very odd.

9.You also need to double the underlay for conservation projects or projects where the liner is going to be totally obscured by stone work.

10. Having considered everything, you though you might have a bash at going ‘au naturelle’ clay puddling after all, or even using concrete. Well, my advice is put a liner underneath as an insurance. It will also mean that you wont have to use the proper 15cm thickness of concrete or clay as you run out funds or energy!

Site Map copyright 2004 - 2006