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 garden ponds and 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 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 the UK 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 me 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:
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.
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.
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 and water garden ponds
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.
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.