Jon's pond build

[Jon W]

Hi Guys
Need a bit of advice re preparing to lay concrete base. The whole has been dug as deep as possible (5'-6').



The substrate is red shale and pretty hard - couldn't go down any further with an 8-ton digger.I have the following questions;

Should I put a visqueen membrane down to stop water ingress or is this only required if you have a high water table?

I've made a b*lls up and dug the filter pit out too far (by a mere 3'). What is the best way of rectifying this so that I can lay a slab within the next few months?

Cheers

Jon

[Gazza]

Hi Jon,

Looks good mate and a nice size

Yes i would put a membrane down fist just in case and then you can build on top and know it will all be sound.

I am not sure what you mean on the filter house is it to deep or too long can you not fill it back in

[Jon W]

Hi Gazza

The far end of the hole in the picture is where the filter house should be. It's been dug down 5 foot when it probably should only be about 2'-2'6". What I wonder is how best to go about filling it back in. If I tip a load of shale back down that end it's going to take a while to settle, so it might be a bit dodgy putting a concrete base and the weight of the filters back on top for a while. Just wondered if anyone knew the best way to build it back up without having to worry about settlement.

Cheers

Jon

[eds]

Jon I think you're going to have to refill it with either some gravel or hardcore and pack it down really well so it won't consolidate after you've laid the floor. Soil is out as it will settle a lot. What filters are you putting in there? Could you just build plinths and decking to walk on in there and just have the deep section of the filter chamber as an underfloor sump so all your waste water just gets dumped in there and then a sump pump dumps the waste water onto the garden?

[Jon W]

Hi Ed

I think you may be right. I have distributed about 120 tons of red shale which makes pretty good hardcore all round a field so I have got the material - it will just mean another day hiring a digger and dumper. What I'm not sure about is exactly how to go about consolidating it properly.

I could build plinths and decking but the plinths would need to be about 4ft high!. Maybe I could do a 2 storey fish house! Hadn't thought of creating a waste sump. Or perhaps use it or storing conditioned water. Because we weren't able to dig down quite as far as I would have like due to hardness of the rock the streamflow may go out of the window. I'm still going to use showers as primary filtration and use a Nexus or bead for polishing (a few people have warned me off beads but I've never had a problem with one). I'm leaning back towards conventional bottom drains with skimmers to feed the filters. I've given myself a week to make a final decision.

Cheers

Jon

[Yorkie]

Hi Jon,

i'll keep this answer short as imdoing a couple of bits

Right forget about putting any "red shale" back in waste of time & effort.

Your ground is probaly stable & will not consolidate any further, probably been there 1000's of yrs already, take yourself of to the sand pit/ builders mechant & get "reject sand" others call it fennit sand & is used for blinding out oversites etc before pouring concrete.

Cover your entire base with around 3" or so & hire a good size wacker plate & compact it with that, if you then need to top up any low spots same rule as before......................... ensure that its fairly level it will make your life easier when you pour your floor.

As to plastic/visqueen do you suffer with water ingress at that depth?.... If you do then you will have to put visqueen up the walls to help prevent water ingress & tank the block work wioth a sealer & divert as much ground water away from the pond.

But yes do use visqueen or similar under your base pour at a min of 8" deep with steel mesh for strenght.

Hope that helps

[Jon W]

Hi Yorkie

Thanks very much for the reply.

To what depth do you think I can use sand to raise the level? Having done some more measurements I'm looking at possibly 4 feet!

Re water ingress; there is some, so I was planning on having a continuous sheet of visqueen up the walls to ground level. I've got a sump pump on standby in case the water situation gets serious.

Cheers

Jon

[Yorkie]

Jon,

Not bieng funny mate but why would you want to raise the floor level by almost a foot??

What are your overall idea's for the pond................... ultimate finished depth........... all in ground, some below & some above?

Backfilling the floor by that amount with sand will just leave you wide open to problems especallly if you have some water ingress.............basically it will wash away leaving a void below the slab which will break up with that amount of water on top,

sorry for the questions just want to make sure you get it right first time

[Jon W]

Hi Yorkie

Reason I want to raise the level by 4-5 feet is because there was a bit of a cock up and the area for the filter has been dug nearly as deep as the pond. Given that the pond will be nearly 7 feet deep with 2 foot above ground it means the filter room will be 6 foot deep at water level. Not ideal. Hence the need to backfill by several feet. Either that or have a 2 storey filter house!.

Cheers

Jon

[Glenn]

Hi Jon, might be of some help but I did the same by a depth of about 3 feet so what I did was concrete the base (with some reinforcing in) and built some sleeper walls with concrete blocks. I then installed some 9" x 3" timber joists and boarded the floor out with timber. I left a void underneath the floor to act as big sump with alcho drains laid underneath in the concrete base taking any excess water away to waste. I fixed a 4" inch pipe to the underneath of the timber joist and dropped and connected each 4" filter waste through holes I made in the floor to the 4" pipe with a "T" so none of the waste pipes are seen. I cursed at the cock up of leaving the base too low but it worked out to the good in the end. All the filters are then installed on top of the timber floor, it worked for me, hope this helps,

Regards

Glenn

[Jon W]

Hi Glenn

Thanks for that. It gives me some hope that I rectify things without having to ship in 30-40 tons of hardcore. The sump sounds a good idea. Sorry to sound a bit thick but what are "sleeper walls"? And what sort of depth did you have for the concrete base?

I was thinking that I could maybe put down a foot of hardcore and about 18" inches of concrete. This would retrieve the situation byt 2 1/2 foot. I could then build up from there. Also it might be possible to leave the very front part at almost the same height and install a window so that you can see through the pond at normal standing height. It might even look like this was a done by design rather than cock up.

Regards

Jon

[Glenn]

Ho Jon, sleeper walls are just walls built to support the timber joists. I would only put about 9" of hardcore and a 9" concrete slab with heavy guage steel mesh reinforcing which should be more than adequate (although some would disagree) but it has worked for me. You could even build the joist into the outside walls if you wanted but I would still put a wall down the middle to take the weight of the filters. I have created a section of the floor on hinges so it can be lifted up so I can get to the alcho drains if they get blocked. If your ever Reading way give us a call and I will show you what I have done which will give you a better idea,

Regards

Glenn

[Jon W]

Hi Glenn

Sorry, not too up on building terminology; I see what you mean. To be honest if it was perfectly flat, it would probably be possible to build straight off the floor - the ground is solid rock! However just to be on the safe side I think I will follow the hardcore/concrete route. I still can't quite believe I've been such an arse and dug out too much. The hole is 48 feet long and the internal dimensions of the pond were 20ftx10ft. I'm now thinking of going a bit longer...

I do shoot up and down the M4 every so often to visit my parents in Surrey so perhaps I could send you a pm sometime to have a look.

Thanks very much for your help.

Regards

Jon

[Yorkie]

Jon,

Sorry mate didn;t fully read/understand your situation re filter house.

You wont end up with a 2 storey filter house mate & savbe yourself a lot of stres at this point.

OK way to go.......................... you know your pond dims Z x Y your filter pit is beyond that point & i assume youir gravity feeding your filtration? Pour your floor in the normal way and as i have suggested blind out the floor with sand & visqueen that pour 8" of crete over that with re-inforcing mesh in aswell.

Put your block work up................ strart at the end your filter pit is going to be & take it up as high as you can go leave for a week or so allowing the mortar to cure & not be "green"...................... then use some of your excavated shale to back fill that void area, you must know your finished hieght out of the ground so put up a Datum Stick with finish pond level on,

From that F/P/L you will be able to measure down to give you the finish floor level in your filter house depending on wjhat filter you are using.

Just had a thought here why not have a filter house below ground & build plinth's for your filters to stand on fror gravity feeding? that way you'll end up with a great room everything protected from those nasty welsh elements.


Pm me your email addy & i'll send you some sketch's of the differant ways to go you'll have to bear with me for a couple of day as ive got a s***e load on

[Jon W]

Hi Yorkie

Definitely going gravity fed - still pontificating on exactly where the bottom drains are going to emerge into the filter house area due to couple of possible configurations. Filters will be in the far end of the pond pit.
Re. pouring the base - do you think it will make any difference if I a fibre concrete - I was going to use a structural grade and dispense with mesh (I've found it quite hard to get up here in the past)?

I'm still working out the final water level. Because the rock was so hard the pond base area isn't completely flat - I've got to work out exactly what depth of sand and concrete I will need to ensure volume of concrete is require for a minimum base depth of 11 inches.

I was going to go for a partially sunken filter house - I want to put a window within and be able to view it from a comfortable standing height. Part of the reason for this is to be able to view the fish despite the wonderful weather we get here on the Welsh Riviera - at least 3 days a year without torrential rain!

Thanks very much for the offer of some sketches. I'll send you a pm.

Regards

Jon