Sealing a masonry "pond"?

[Jeremy Harris]

To disguise our borehole, which is a raised concrete section 600 x 450 inspection chamber, we've built a circular stone wall around it, about 1500mm in diameter (about the smallest diameter we could manage).  This is built on a hefty concrete footing, that seals to the pre-cast concrete inspection chamber section.  I've added another inspection chamber section, so the borehole casing, inside the stone ring is now about 30mm above it and I have capped it with a 900 x 600 sandstone.  The stone ring is around 400mm high, and we're now left with an annular space around the borehole head chamber and are thinking of turning it into a water feature.

There's no risk of contaminating the borehole, as the borehole itself has a sealed cap, plus there's a 100mm  drain leading from the base of the head chamber to a soakaway.  All the electrics in the head chamber are IP66 sealed.

What I'm looking at is the best way to seal both the outside of the precast chamber sections, the concrete base and the inside face of the stone wall.  My initial thoughts are to parge coat the inside of the masonry to get it smooth and fill any bigger voids in the mortar, add a strong mortar radius around the base of both the inner face of the outer wall and the base, and between the outer face of the chamber section and the base.

Once I have the surfaces fairly smooth, I was then thinking of using something like G4 PU sealant to seal the whole of the inside.

I'll build in an overflow pipe and also a fill pipe, and as there's power there we may well add a pump and some form of gentle water feature later.  The "pond" will be planted, with raised platforms for things like water lilies, maybe some irises, but won't have fish in it.

Does the above sound sensible?

I'll try and take a photo tomorrow, to show how it looks at the moment.

[PeterW]

Jeremy - I would have thought that parging / radius with mortar and then using GRP would be the most secure way..? Not that difficult either as it doesn't need to look pretty ..?

[Mikey_1980]

Would something like the below just drop straight in?

http://www.watergardeningdirect.com/acatalog/Dove-Preformed-Pond-Lotus-Toughline.html

[TheMitchells]

Sounds like a lovely idea; just be aware that most waterlilies do not like moving water.  So keep it at the opposite end from the water feature. 

[Ferdinand]

I think that 45-50 sqft is the recommended minimum surface area for a pool which will self-maintain (eg stay slime free) which is 3-4 times your size ignoring the island in the middle.

That number is from The Garden Expert by DG Hessayon. 

SO I wonder if a non-pond water feature would be more appropriate and less time consuming? That could be a fountain onto rocks, possible incorporating a bird bath, or something more plant-based.

Here I would like to make a bird fountain from two or three defunct satellite dishes but have not got round to it yet.

My mischevious side wants to see a JSH garden gnome wielding some sort of borehole management crowbar or kitchen plunger, but that won't happen in an oasis of good taste.

Ferdinand

 

Edited June 10, 2016 by Ferdinand

[Jeremy Harris]

Thanks for the thoughts, they are much appreciated.  Lining the inside with GRP may well be a better bet, especially as I have rolls of CSM and glass cloth in various weights, left over from boat and aircraft building, so all I'd need is some resin and concrete primer (as, IIRC, polyester resins are cure inhibited by alkaline materials like concrete). 

The drop in pond idea won't work because of the 600 x 450 chamber that pokes up in the middle, unfortunately.  This is what the thing looks like now I've added another chamber section and put the sandstone slab over the top as a lid over the borehole head chamber:

The pond is on the small side, so it may well be better to look at a non-pond water feature, using the annular space as a water reservoir with a small submersible pump in it.  It'd be pretty easy to put a layer of heavy duty mesh in there, spaced off the bottom, and then have something like some rounded cobblestones  interspersed with planting. 

I would like to make a small drilling rig, with a fountain spraying over a couple of models of drillers, but that would not go down at all well...................... 

Whatever we put on the stone slab needs to be removable, to gain occasional (as in every few years) access to the borehole head chamber, and a fountain type thing would probably look a bit naff.  Something like a bird bath that gently overflows all around the edge and trickles over the stone slab and back down to the reservoir would work OK.  I could easily drill a hole in the centre of the slab and seal a pipe in it for a water feed.  In fact I could go one better if I fibreglass the inside of the reservoir, as I could also make a lipped GRP lid to fit under the stone slab (with a moulded in vertical pipe in the centre) and that would ensure that no water ran back under and into the borehole head chamber.

Sadly it's not going to be big enough for our resident ducks:

[Ferdinand]

Somewhere under the mesh I would put a 2x2 stack of breezeblocks so that there is somewhere on your mesh where you can stand to have a good look or lift without leaning from the edge, without having to dismantle and drain first. Make it tall enough to stand proud of the water level.

Perhaps both sides so two people can lift the slab easily.

Can you do a complementary bird feeder support with fat balls, Niger seeds etc to be close by that you could see from your window?

Ferdinand

Edited June 10, 2016 by Ferdinand

[Jeremy Harris]

I was thinking of just standing the mesh on some left over blocks (wasteful, but they'll probably be bigger jumper blocks of that Bradstone Buff, as I still have around two pallet loads of it left over).  Somewhere I have some galvanised gratings that I could probably cut to fit; they are the stuff often used as elevated walkways and I scrounged some years ago and stacked it somewhere at home.  That would be ideal, as it would take the weight of some cobblestones and also being walked on.

There will be some sort of bird feeder nearby, along with some nest boxes, probably on the garage at the end of the garden in the shade, up near the eaves.  SWMBO isn't keen on the resident ducks, because of the mess they make, but I'm just thankful they now crap on the newly laid lawn, as before that was laid they used to sit on the steps to the front door and crap there, so I had to clean it up practically every day.

[Siochair]

Hi JSH have you considered using garden pond liner? Should be both cheap and easy to get and will be easy to revert to what you already have if you change your mind in the water feature.

[Jeremy Harris]

I did look at using an EPDM liner, but because it's an annular space I'd have to have at least one welded joint, and it didn't look at all straightforward to fit.  There would have been a lot of wastage, too, and I'd have had to bond the EPDM to the concrete, as there's no easy way to hold it in place.  I'd also need to do a fair bit of work to get the inside smooth enough to not damage the liner, so thought that if I was going that far I may as well make whatever the smooth layer was, watertight.

[ProDave]

Is the wall strong enough to withstand the water presure?  I am not doubting your bricklaying, it looks very good, but fill that with water and you have an outward pressure on the wall, and cement is not very good in tension.

For that reason alone I would be loking at a fibreglass pond liner cast in place, if nothing else to add to the strength of the wall.

[Nickfromwales]

Good idea. Plus 1 to fibreglass. 

[Nickfromwales]

1 hour ago, Siochair said:

Hi JSH have you considered using garden pond liner? Should be both cheap and easy to get and will be easy to revert to what you already have if you change your mind in the water feature.

Deffo a good choice for a straightforward shape  

Oh, and welcome aboard ! 

[Jeremy Harris]

55 minutes ago, ProDave said:

Is the wall strong enough to withstand the water presure?  I am not doubting your bricklaying, it looks very good, but fill that with water and you have an outward pressure on the wall, and cement is not very god in tension.

For that reason alone I would be loking at a fibreglass pond liner cast in place, if nothing else to add to the strength of the wall.

Assuming 400mm depth (it'll probably be around 350mm depth in practice) then the static pressure at the base of the wall will be 0.0392 bar, or about 0.576 psi in imperial units.  That's roughly 15% of the pressure an air bed might be inflated to.  The pressure from filling it with pea shingle would be very roughly 50% higher, allowing for the internal friction angle and increased density of rounded shingle.

The fibreglass skin won't increase the strength to any significant degree, as the wall will be far stiffer so will take 99%+ of the resistance to overturning, but priming with G4 and then laying up a GRP skin, finished with a gelcoat with added wax to ensure a tack-free cure (gel coat being a resin that will only properly cure under anaerobic conditions) does make a great deal of sense.  I've not used G4 before, but a nephew worked at CFS for years and gave me masses of info on it, and other stuff, when two of us decided to do a garage roof in GRP (easy, tough, long-lasting, probably the best way, bar none, of doing a flat roof IMHO).  I still have a big folder of info he gave me from all those years ago and looking through it nothing much seems to have changed.

[Siochair]

1 hour ago, Nickfromwales said:

Oh, and welcome aboard ! 

Thankyou

[Construction Channel]

why can't you just put a whole load of waterproofer into your render mix? e.g tanking slurry

just speculating but would that not work?

[Construction Channel]

9 hours ago, JSHarris said:

 

So......... what's with the brick at 5o/c?  

[Stones]

I think you could do something very simple and avoid having to line the entire well. If you could live with some kind of water feature on top of the slab (overflowing bird bath, stone with hole drilled through it etc) all you need is a collection tray sitting on the slab and discharge that into a small reservoir, a bucket say, in which you submerge a low power pump to trickle water back up into the water feature. A cheap shower tray, trap and bit of drainage pipe could do the job nicely in terms of a collection tray and discharge. Disguise everything with cobbles and plants (using blocks and some of the metal grating you mentioned to raise the 'ground' level between borehole chamber and stone wall)

[Jeremy Harris]

54 minutes ago, Construction Channel said:

So......... whats with the brick at 5o/c?  

It's called a cock-up, when you put the Bradstone in the wrong way around..........................

(they are faced one side, or both sides, and either one or both ends, sort of randomly)

[Construction Channel]

30 minutes ago, JSHarris said:

It's called a cock-up, when you put the Bradstone in the wrong way around..........................

(they are faced one side, or both sides, and either one or both ends, sort of randomly)

 I almost felt bad bringing it up. We've all been there...

problem is Building apprenticeship 101: finding the faults in others' work so you feel better about your own

[Ferdinand]

I can confirm that a well done fibreglass roof can be expected to last 35 years or more.

My father did various roof gullies and valleys from the late 1970s in our mainly 17c house.

The most common failure modes would be due to mechanical stress ie standing on joints, edges not sealed down properly giving water seepage, or potentially deterioration of the resin in sunlight over decades.

Ferdinand

[Ferdinand]

23 hours ago, Construction Channel said:

 I almost felt bad bringing it up. We've all been there...

problem is Building apprenticeship 101: finding the faults in others' work so you feel better about your own

That surely is the one thread wrong in the Persian rug equivalent.

Edited June 11, 2016 by Ferdinand

[SteamyTea]

Just GRP it and you won't have to worry about it again.

I made a pond in the mid 70's for my parents, as far as I know it is still there.

[Jeremy Harris]

1 hour ago, SteamyTea said:

Just GRP is and you won't have to worry about it again.

I made a pond in the mid 70's for my parents, as far as I know it is still there.

You're right.  I'm planning on calling in at CFS next time I'm down your way and picking up some G4 and loads of resin and gel coat.  I have rolls of cloth and CSM already.  The biggest job is going to be cleaning back the rough internal side of the stonework to get a half decent surface to prime and glass to.

[SteamyTea]

Get some cobalt accelerator while your down, paint that on the masonry first and then paint some resin on.  It will set so quick that you won't have a problem.  Then lay up as usual.

I always found Llewellen Rylands Lavander grey a good colour for ponds.  It seemed to withstand UV better too.

I also found that the self etching environmental resins pretty good, Cray Valley (Encore 30) was a good one.  It withstood a bit of damp too.