Outdoor pool - should I insulate?

[richie967]

Hi forum,

I'm currently in the process of designing a small paddling pool for the garden (Water volume 5m x 3m x 1.2m). I'm considering a fairly traditional pool construction including:

6" C35 concrete base reinforced with a single layer of a142 steel mesh
Dense hollow concrete block for the walls with rebar and filled with C35
Rendered with waterproof render
Waterproofed with Chlorinated pool paint or a two part epoxy paint.
Hayward fittings throughout.

I have done some excavation to investigate the quality of the ground, and it looks like there is about 300mm of topsoil and then it is clay with bedrock.

Initially, I will just run a sand filter with skimmer. But I may want to eventually want to heat it with an Air Source Heat pump. Here is my question..

1. Looking at the Schematic attached, does anyone see any issues with the construction method?
2. Should I add 100mm or so of kingspan beneath the concrete slab? and around the outside of the block walls?

Note, I am aware of block and liner builds, however I am fairly happy to paint the pool every few years with Epoxy or Chlorinated paint. It's only small so wont be too much trouble.



Cheers, rich

[Teapot]

Hi Rich,
Comment on the construction, you may already be doing this, the top course of block should have a full ring of rebar to form a ring beam.
You should insulate the floor and walls but absolutely not with kingspan, use extruded polystyrene or Wedi panel etc. Kingspan takes on water despite what their adverts may say, I personal experience of kingspan failure due to water ingress.

I hate chlorinated rubber paint and epoxy but it's your job, have you considered glass fiber or polyurea?

[richie967]

Hi Rich,
Comment on the construction, you may already be doing this, the top course of block should have a full ring of rebar to form a ring beam.
You should insulate the floor and walls but absolutely not with kingspan, use extruded polystyrene or Wedi panel etc. Kingspan takes on water despite what their adverts may say, I personal experience of kingspan failure due to water ingress.

I hate chlorinated rubber paint and epoxy but it's your job, have you considered glass fiber or polyurea?

Hi Teapot, Thank you for the speedy response. I hadn't considered a full ring of rebar in the top course of block. I may do a full ring in every course for a belt and braces approach! good advice.

RE: insulation, i'll stay away from Kingspan. Upon doing some further research into pool insulation, I have discovered something called Cellecta Hexatherm XPool Swimming Pool Insulation Board 50mm. It is fairly pricey at ~£120 (~$120) for 6sqm. One more question on the insulation. I guess this sits on top of a 75mm gravel base, then the insulation, then the damp proof membrane. is the damp proof membrane necessary?

RE: paint, Noted about the paint and epoxy. In my limited experience I have not heard of using glass fiber or polyurea. I'll look them up now!

A few questions on the slab, Is it okay to do a 150mm slab for the entire base, and build the wall on top of it. I could drill the rebar into the slab to tie the walls and the floor together. second question, how much concrete slab should there be around the base of the wall? I was planning on an additional 100mm around the base of the wall.

Here is a picture of the current excavation, doing it all by hand is quite challenging!



Cheers!

[Teapot]

Hi Rich, just googled Cellecta Hexatherm and it's extruded polystyrene as suggested so forget brand names and just go for whats value and has a good load rating.
I would put damp proof membrane under the insulation or under the concrete slab.
150mm will be fine but I would go wider than 100m on the perimeter, I usually go 300-500mm depending on the size of the pool. I also go thicker on the edge of the slab only, another 100mm to back up the rebar.
If possible I would sink short 90 bends of rebar into the base and wire to those. My first pool I drilled and chemfixed the rebar and it moved whilst filling, I have never forgotten this and still have trouble explaining how it could do it but the wall went off plumb!

[Teapot]

Rich, take a look at Eco finish as well, as known as Aquabright.

[richie967]

Hi Rich, just googled Cellecta Hexatherm and it's extruded polystyrene as suggested so forget brand names and just go for whats value and has a good load rating.
I would put damp proof membrane under the insulation or under the concrete slab.
150mm will be fine but I would go wider than 100m on the perimeter, I usually go 300-500mm depending on the size of the pool. I also go thicker on the edge of the slab only, another 100mm to back up the rebar.
If possible I would sink short 90 bends of rebar into the base and wire to those. My first pool I drilled and chemfixed the rebar and it moved whilst filling, I have never forgotten this and still have trouble explaining how it could do it but the wall went off plumb!

Hi Teapot,

Thanks for the advice, I have added the XPS to the drawing, and also made a note to add the ringbeam. I have also found a decent reasonably priced 50mm XPS insulation that works out at £11 per square meter delivered. So ill go with that.

The pool is only small, 5m x 3m x 1.2m. I was going to make the slab 3.6 wide, and i can also just use the standard A142 mesh in 3600 size as well. But ill note what you said, and consider making the slab go 300mm-500mm larger than the wall.

Regarding sinking short 90 rebar into the walls. I am guessing this means you need to know where your holes in your blocks are going to be? so you can place the block over the rebar, or do you pour found foundation with the first course of blocks in place?

Cheers, rich

[Teapot]

Hi Rich,
Yes you'll need to know the block dimensions to position the rebar. It's a std problem on sites.

[richie967]

Hi Rich,
Yes you'll need to know the block dimensions to position the rebar. It's a std problem on sites.

Fantastic, thanks so much for all the helpful information. One final question. You mentioned that it's good to go 300-500mm larger on the slab in comparison to the walls. If the pool is relatively small, 3m x 5m x 1.2m, could i go on the lower end of that?

Cheers, Rich

[Teapot]

Hi Rich, Yes I am sure that will be fine, it's the turning moment denoted by the height of the walls so it doesn't break the edge of the floor. Whilst I and your good self try to do everything right, I am reminded of my neighbours pool where the concrete ran out at one edge so the tickness couldnt be more than 30mm. Just as an aside, do not be tempted to backfil with the spoil you have removed, use a self compacting gravel or pea shingle. The spoil take years to settle and causes fractured pipe work etc.
Good luck with the project and please keep us informed of how it's going.

[GregAAmin]

I wish to make a pool near my house. Actually I'm unaware of the construction procedure as well as the budget. Is my place is fit for the pool? I have many doubts regarding the pool construction. Anyone please advice me. I really wish to make a pool.
Thank you!

[richie967]

Hi Rich, Yes I am sure that will be fine, it's the turning moment denoted by the height of the walls so it doesn't break the edge of the floor. Whilst I and your good self try to do everything right, I am reminded of my neighbours pool where the concrete ran out at one edge so the tickness couldnt be more than 30mm. Just as an aside, do not be tempted to backfil with the spoil you have removed, use a self compacting gravel or pea shingle. The spoil take years to settle and causes fractured pipe work etc.
Good luck with the project and please keep us informed of how it's going.

Hi Teapot,

Thanks for the information on the pool construction, I will ensure I use a pea gravel material when backfilling, I was wondering, is backfilling necessary? What purpose does it serve? If I was going to deck around the coping tiles, would id matter if it was backfilled?

After more reading around the subject, I am also considering a block and liner approach, I am about to make the decision as I am now ordering all of the plumbing and fittings. And need to choose liner or concrete fittings! Regarding the fittings, I have established that I need the following:

2 main drains
1 return inlet
1 light
4 concrete conduits (1 for main drain, 1 for light, 1 for inlet)
13 elbows
1 T piece
1 skimmer with extension throat

That doesnt seem like much in comparison to what you get with these DIY block and liner kits! Is there anything obvious I have missed?

I am considering ordering all of the pool fittings from Bosta. There appears to be 2 main manufacturers, Hayward and Certikin, have you any experience with either? And finally, It looks like a 50mm diameter pipe is the way to go as well.

Below is a Cad rendering of my proposed plumbing, showing main drains, return inlet, light (not connected).

Cheers, Rich

[Teapot]

Hi Rich, obviously I am not looking at the site so backfill is a general comment. You want to avoid landslides and ground movement so traditionally we backfill to stabilise.
Have you looked at ICF (Nudura etc) Personally I like liners, the chemistry is easier to manage, smoother finish less alage hiding places. Like wallpaper you can change the design to reflect modern advances, pattern and styles as time goes on.
I don't have a main drain on my pool which is twice the size, never needed one. They can be the source of leaks, they really do not do much at all to help with the water as all dirt enters from above, that's the best place to remove it before it sinks! 2 returns per skimmer, the returns help push the dirt towards the skimmer as skimmers do not draw in much beyond 6 inches in front of them. No issue with Bosta, Hatward likewise. I don't like Certikin or their ethics, they behave like the mafia and their HD100 skimmer is junk.
If you decide to go with two main drains, connect the two with min 2" pipe, this ensures the entrapment hold down is way less than a single 1 1/2" but if it were me and the customer insisted I would plumb the MD's as inlets switchable via valves to MD outlets and then you can plum the heated water into the bottom.
Don't use elbows, use bends and you get a lot more flow or use less energy like I do.

What are you doing filtration and pump wise?

[richie967]

Hi Teapot,

Thanks again for the speedy reply. I've dug down to 1.2m across the entire base. I hit layers of rock after about 75cm and now it's all bedrock. Which is solid to break up. But a few hours a day is doing the job nicely ! I'll post a picture tomorrow !



I've been looking at the ICF blocks and they do look appealing, it'll come down to cost (as time is something I have at the moment !). I was looking at the mega pool building blocks on the Bosta site earlier today.

Interesting point about the main drains. I figured they were fairly critical in ensuring you suck out the coldest water and heat it up ensuring complete circulation. I'm not attached to the idea at all and not installing them would be a nice win! I guess in order to ensure that there is ample circulation of heated water, and a good relationship between return inlets and skimmers, there are set places that these items should be placed for best results? Is there a schematic for an average rectangular pool for placement of inlets in relation to skimmer?

I get your point about the bends and not elbows. So basically I'll replace all the elbows with 45 degree bends for better flow. Good advice that!

I actually had the Certikin hd100 on my shopping list. Ill scrub it and look at Hayward or Mega's options.

Regarding filtration, was planning on going with the mega 535mm diameter sand filter which is designed for pools around 20 cubic meters and I believe it comes with a matching pump of about 0.75hp.

Eventually I'd like a 10kw heat pump or similar.

Thanks again for the insight, very helpful indeed !

[alicechen745]

Hi Richie,

What would be your final dimensions of pool? Or what would be the Pool volume? Will you cover it with a pool cover? I can guide you with selecting a best Heatpump.

[richie967]

Hi Richie,

What would be your final dimensions of pool? Or what would be the Pool volume? Will you cover it with a pool cover? I can guide you with selecting a best Heatpump.

Hi Alicchen,

The Final dimensions are 5 x 3 x 1.2 = 18,000 Liters. I'm contemplating going with a 10kw heat pump. But that wont be for a few years. I am in a bit of a conundrum about how to build the walls for the pool. I was going to go with hollow dense concrete block, with rebar down each hollow, and filled with concrete. However I am now considering going with the more traditional method using regular building blocks laid on their side.

Do you think i would need to put a pillar every 2.5m if doing it this way? The Wall would need to be 1.4m high to allow for a screed floor and a bit of a gap at the top so the water line starts about 10cm down from the coping.

Cheers, Rich