How to Choose Pond Sealants.
For quite some years now the trend in garden pond construction has been to move away from building methods using concrete as the main lining material. Streams and waterfall sections too are available in lighter more convenient pre-formed units and kits and both ponds and watercourses are commonly made from flexible lining materials. Because of this the use of pond Sealants has decreased significantly but several are available and are sometimes very useful in new construction work or when repairing older ponds and water features. Below are detailed several types of pond sealant together with their uses.

Polyurethane Sealants.
Polyurethane sealants are very versatile and can be used to seal concrete, natural stone materials and brick. Because of their versatility they are one of the best selling type of sealants and the market leader of this type is G4 by Bondaglass Voss. Apart from being able to seal a variety of materials a great advantage to this type of sealant is that they are moisture cured so can be applied to damp surfaces. Curing is affected at temperatures as low as 38f (3C). Two to three coats are recommended. The standard colour option is clear (When cured dries a slightly darker shade than un-treated material but this is only evident on mortar and lighter coloured stone). Colours are available in pre-mixed form with the addition of pigment giving a solid, dense colour in Green, Red or black. Coloured G4 is slightly more expensive than clear. At least 21 to 28 days should elapse before applying any sealant to new mortar finishes. Wear gloves when using, as Polyurethane sealants will also bond to human skin!! This type of sealant can be used to seal an entire pond but this would work out quite expensive, certainly more than using a flexible pond liner. The most common use is for sealing the exposed mortar around flags, brickwork and stonework around the pond, stream and waterfall areas. This will ensure that harmful lime does not leach into the pond and will also improve the resistance of the treated surface to weathering.

Pond Paints.
Pond paints, as the name suggests are a coloured finish applied to both seal and create an effect to a cement or mortar surface. As garden ornamental ponds are now usually made to look more natural they are not as popular as they once where and the majority of sales are to re-finish or repair existing installations. Interpet-Blagdon distributes a range of these Acrylic paints in clear, light blue, stone and black colour options. Pond paints can only be applied to clean, dry surfaces and existing paint should be abraded to supply a “key” to assist adhesion of the new application. As for Polyurethane sealants above allow new mortar to cure for at least 21 to 28 days before painting. At least two coats are usually required. Perhaps with the current home décor trends leaning towards contemporary designs, there may be resurgence in formal ponds with coloured finishes resulting in a greater interest in these particular sealants.

Pond Glazes.
Pond glazes are a soluble powder mixed with water that then reacts chemically with cement to both neutralise the harmful lime content and harden off to an impervious surface. Although inexpensive, quite a large area can be treated for little outlay, they are laborious in application as four coats are required over four consecutive days. This makes them perhaps the least popular of the pond sealants. As for other sealants allow at least 21 to 28 days for new mortar to cure before applying glazes.

Bitumen Paints.
Bitumen Paints are a fairly inexpensive method of sealing concrete ponds and Mortar skims but are quite messy to apply. The liquid is brown when wet and dries to an almost black, slightly textured finish. It is very important to choose Bitumen that is to drinking water quality standard, as this will ensure that the finish is non-toxic when cured. Aquaseal 40 is available in the UK for this purpose and is not usually stocked by retailers of aquatic goods but is available from the larger plumbers merchants. The 21 to 28 day rule applies as above.

Mortar Additives.
The final mortar skim of a rendered pond, stream or waterfall can be made less porous by adding a material to the mix. Mortar additives improve the mix making it smoother to apply and although a totally waterproof finish is not achieved it does make ideal preparation for a surface that is to be later coated with a sealant. Mortar additives or “Waterproofing Powders” are recommended for a totally professional finish.

When using any Pond Sealant always follow manufacturers instructions to the letter and wear gloves to prevent skin contact. Cover the treated area after application to protect from rain and once fully cured thoroughly hose down, empty and re-fill.