Advice please! DPM for underground pond filter housing?

[Jeff Davenport]

I am constructing a Koi pond and the (gravity fed) filter housing will be underground. It's going to be approx 7' X 7' X 4' 6" deep, 6" concrete foundation with high density blockwork walls. Access to the cavity will be via decking panels and removable crossbeams.

Having read as much as I can find on the subject I haven't come across anything which refers to the use of a DPM under the base and behind the walls. Does anyone here have experience of building a similar structure or views/advice on how I would best proceed?

My inclination is to install a DPM between the earth and concrete all around. Part of the cavity will be constructed and used as a 'dry area' for pump, UV and associated electrics.

I have tried the 'pond groups' but they tend to be a little quiet on this issue :-)

Many thanks!

Jeff To email me just take the MICK out of my addy!

[Rick Dipper]

Sir

Based on my experience with DPM in an underground structure you are looking at something like ProofexEngage for below the slab, and a different compatable product for the walls. At 300+ quid a roll you might decide do leave it without a DPM.

Rick

[Dave Liquorice]

I'd have thought a sutiably sized sheet of the heaviest builders poly you can get laid in the hole on a bed of sand (similar to the butyl pond liner) then folded and tucked at the corners would do. But any water that got in, (rain?), would not be able to get out...

[Rob Graham]

Jeff I necessary question for those of not familiar with what you are trying to do is whether the DPM is to keep the water in or keep it out ? Is the concrete cavity to then contain a filter unit?

The reason I ask is that I have a small pond (500 gallons) with Koi in it and have a below ground filter which is one of the proprietary pressure ones and all that it is in is a 2x2x2 foot hole which is lined with an plastic box that happened to be about the right size and I don't have any problems with that. Now you're on a bigger scale I can see (!!!).

Rob

[Jeff Davenport]

My concern is really to keep water out and the brickwork/concrete in good condition. The construction is not to be a filter in itself but a housing for a commercial filter called a Nexus (1.1m high X 1.4m wide) and ancilliary equipment like pipes; pump, UV etc.

As I intend to use the area above the filter housing as a BBQ area I shall be 'close boarding' above with decking so the walls will need to support this.

Incorporated in the design of the filter housing is a 'wet sump' with a sumbersible pump to the drains to remove waste, spillages and overflow from the pond system.

Thanks for your comments!

Jeff To email me just take the MICK out of my addy!

[Pete C]

Hi,

What you want is Bondaglass G4 eg:

cheers, Pete.