Concrete Pond Construction

Q. My pond is nearing completion.The walls are rendered and I regularly get koi carp magazine and have contacted a fibreglass supplier who has sent me an estimate,can you answer the following questions for me please?
[1] Is it normal to use G4 on render before applying fibreglass as the supplier I contacted plans to sell me some as well as resin ETC.
[2] I have fitted a bottom drain and an Olympic in wall skimmer do I still use the rubber seal behind the fibreglass and on top of the fibreglass before fitting the retaining plate on the skimmer.
[3] Can I still use the retaining plate and screws on top of the fibreglass when it is been applied wet to the bottom drain as I have reservations of just sticking the glass to the plastic on its own.
[4] How do I seal my pond pump return pipe to the fibreglass,does it stick to plastic OK.

A. The following is my answers to your questions.
1). Using G4 on the render before fibreglassing is a deluxe way of doing it, but of all the ponds fibreglassed in our club (over 15) none have done this.
2). No. The retaining plate and screws are removed and not used. The whole lot is then rendered level, and the fibreglass is taken down into the bottom drain. In some cases the whole internal of the bottom drain is covered.
3). This is not necessary. The fibreglass is usually talen into the bottom drain to seal it
4). The fibreglass just adheres to the pipe which is sticking through the wall. The professionals do not appear to have problems with this.

Q. Is the best method fibreglassing rather than fitting a butyl liner?

A. We feel in this area that fibreglass is better. The cost of fibreglassing a concrete pond is more expensive. If you have a 6ft deep pond with vertical sides the walls must be of concrete blocks to prevent the walls falling in even with a liner. You cannot just put the liner in a hole in the ground, and it is best to use a boxed liner which is more expensive. We use Mick Whitehall from near Birmingham to do the fibreglassing.

Q. Some messages on the Forum seem to suggest it is best to build a pond using a liner, but I'm not sure why. Or was it suggested that the liner is sandwiched between the 9" thick retaining wall and in effect seals off the soil of the excavated hole.

A. All of the correspondence recently in the Forum are favouring the use of liners, but most koi-keepers in South Wales seem to prefer to use cement render. It is a matter of choice and sometimes cost as a liner is cheaper if you do not use a boxed liner.

Q. Render and G4 is the other option but I have (probably unfounded) reservations about concrete ponds.

A. To fibreglass the pond it first has to be rendered. For the fibreglassing we use a person who lives just south of Birmingham, and the cost of fibreglassing is not much more than just buying the G4.
Although the fibreglass forms its own skin the walls and foundations have to be reasonable strong enough to support the weight, but of course small cracks will not affect the fibreglass as it would with a pond coated with G4.
It must be realised that this is the same size as a small swimming pool, and just think of the heavy construction they use for them when professionally built.

Q. I have finished the major parts in the construction of the pond , so I am wondering what kind of paint sould I use to seal the concrete blocks , and sould I use muriatic acid to clean the blocks before I paint and waterproof the pond?

A. The usual way to continue after completing the blockwork is to render the pond as described on http://www.bogus.net/koi/const9c.htm
After completing the blockwork you will need to render (plaster) the walls to give a smooth surface unless you intend to use a liner.

Q. Do I need to neutralize the toxic from the cement once the pond is completed? If yes, what is the product use in doing so.

A.Yes, you definitely must neutralize the cement when the pond is complete. There are several types of paint, and polyurethane varnish which can be used, but it is very important to check with the manufacturer that it is not toxic to fish. What we use is G4, and this is described by the manufacturer as a polyurethane based sealer for brick, concrete, cement, plaster, and wood. Three coats are required.
P1 and Koi-kote are other suitable products. Aquaseal 40 is no longer suitable for koi ponds.