DIY Cement Block IG New project

GerryUK

Bronze Supporter
#1
Hi to all!

After 5 years of ‘trouble free’ enjoyment of my Intex 16ft round AG pool, installed below ground, the liner is on its last legs and this time around I would like to go for a ‘proper’, albeit DIY, in-ground pool. I plan to use the already excavated 16ft circle and increase the overall size a little to make an irregular kidney shape. I live in a part of South America where Gunite/shotcrete etc are not an option, nor is the possibility of getting a liner fitted and therefore I have opted for cement/blocks. The ground is solid, never before dug earth, the climate is tropical, so no frosts, no waterline to consider and there are no zoning/permit issues.

Right now, I am at the digging/planning stage and the provisional method and options have been selected as a result of several weeks reading previous posts and advice.

At this early stage I will limit my questions to the first decisions I have to make.


  1. The pool shape will be approx. 26’ x 12’ x 4’6” throughout except for a 10” deep sun ledge about 4’x6’. Approximate volume will be just under 10,000 gallons. The plan is to dig 4” footings around the edge, use vertical ½” rebar at 8” intervals curved in to the floor connecting with metal reinforced mesh on the floor, raised 2”. I would a dig trench for a bottom drain, positioned in the centre and then ‘pour’ the footings and cement floor in one go (so total thickness of footings 8”, floor 4”). I say pour, it will be a crew of locals mixing and passing down mixed cement and this may have to be done in two or more goes. Does this spec and method appear to be sound?
  2. I would then construct the walls, slotting each block (8x8x16”) over the vertical rebars. As the pool is curved in places, half blocks would be used. Then, drill holes to fit 1 ½” pipe for two jets out and a bubbler on the sun ledge, plus a single pool light. Once points of entry for plumbing and electrics are in place, fill each block with cement around the rebars already in place.
  3. The inner surface of the pool will be plaster and/or tile. Tile and tilers are relatively inexpensive here, but I am unsure if plaster is necessary if the finished surface will be tile?
  4. Will it be necessary to ‘seal’ the join between the floor and the cement blocks or will the tile and grout do this sufficiently?

No doubt I will have more questions in the future with regards to pump, filter etc and I plan to post photos but at this stage I would be very grateful for your thoughts on the above. Thanks in advance

EDIT September 2018: Construction and final photos posted on page 2 of this post
 

kimkats

Mod Squad
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Jul 10, 2012
36,038
Tallahassee, FL
#2
I would think you need to seal the whole thing before you put the tile on as grout is not waterproof. Especially the wall to floor joint.

Kim:kim:
 

GerryUK

Bronze Supporter
#3
Thank you - the tile grout will be waterproof epoxy grout, made specifically for pools, but is the concensus that a waterproof plaster should be applied to the cement blocks prior to tiling? Also, any input on the proposed wall/floor construction method would be much appreciated
 

duraleigh

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Apr 1, 2007
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#4
Your idea for a concrete floor is problematic. Concrete cracks and concrete poured on separate days creates the same thing as a crack. Subsequently, your tile or plaster will crack.

I think you should consider a liner insert if you stay with a concrete floor.
 

GerryUK

Bronze Supporter
#5
Moving forward a little, in order to get them shipped here in good time, I have selected a Hayward C500 Star Clear cartridge filter (50 sq ft) and a 1HP two speed pump 3450/1700RPM, 4350 gph to plumb with 1.5" PVC - any observations before I make the purchase? (there will be suction from one skimmer + main bottom drain and two return jets plus option include two bubblers in the return - each with their own pipe run approx 10-15 ft from the pump).
 

GerryUK

Bronze Supporter
#6
Hi Dave, Your comments duly noted (I have studied your project in detail). The issue would be getting a liner measured and then delivered here - no one uses them - everything locally is cement block and tile, though I have yet to find anyone who actually had anything to do with the building of their own pool. Given the limitations, I assume making sure the floor is poured in one day will be the way to go? Can you tell me what precautions, metal mesh, thickness of concrete you would recommend? Does connecting the cement blocks with curved rebars into the floor make sense to you?
 

duraleigh

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#7
Using rebar to hold your structure together makes perfect, almost mandatory, sense. The concrete will still crack.

A good rule of thumb is any concrete space being fifteen feet or longer in either one or both directions will crack.......it's a pretty good rule.

I know that many pools in Europe are bigger than that and yet they are covered with plaster and often tile. How they deal with that is beyond my scope.

I would suggest you take the trouble to research this thoroughly with someone experienced in this application...........it is pretty unusual to find a concrete bottomed pool here in the US.
 

keithw

Well-known member
Mar 30, 2007
303
Virginia Beach
#9
Gerry,

You might want to do some looking around on the Koiphen forum. It is geared around Koi fish ponds not pools but many of the builds there are similar to what you describe.
 

duraleigh

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#10
I would suggest a 100 sq ft filter. Especially with a cartridge type, bigger is always better. You will do less cleaning and you will get better flow from a large filter.

Your pump seems the correct size but the rating of 4350 gph bugs me a little. Most good pumps here in the US are rated in GPM......not GPH. What brand is it?

Pump and filter are almost "lifetime" purchases so be very sure of the quality.

You didn't ask, but many, many folks here in the US are building without bottom drains.......that's what I would do with a pool your size.
 

SBall

Well-known member
Jun 27, 2017
160
Nashville, TN
#11
Gerry, is Line-X available in your area? It is a poly-based spray on material that can be used to a variety of things, and lining potable water tanks is one of them. I have often thought that it would be ideal for this type of setup. If that is not an option, I would look into DITRA/Schluter tiling products. They have developed isolation membranes that are waterproof, basically, it is a waterproof liner that is installed in pieces to fit any shape, and you tile over it. The isolation piece separates the tile from the substrate (in this case, concrete floor and block), which means that if the concrete cracks or shifts, it is "isolated" from the tile and should not disturb it. I think that would also be a great option.

Protective CoatingsLineX

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tiling a pool with Kerdi - Ceramic Tile Advice Forums - John Bridge Ceramic Tile

Check this thread out
 

GerryUK

Bronze Supporter
#13
Hi Dave, Again thank you. Noted re the filter, so I will look for the next option up. The pump is unbranded but has very good reviews but again your comments duly noted. With regard to bottom drain, is there a particular reason why they are not so common now and would a skimmer be sufficient on it's own or would there need to be additional intakes?

Keith, Thank you, I will check out the forum you have suggested today - as you say, there will be a lot of similarities I think.

SBall, Thank you too, I checked the LineX and DITRA/Schluter websites but they are not in Colombia, yet, but good info for those in countries that do have this option I'm sure.
 

borjis

LifeTime Supporter
Aug 19, 2014
2,643
Pacific NW
#15
I'm not sure why it's common to NOT have a main drain these days, but my pool was
built in the early 80's and does not have one.

I've had pools with and without maindrains. They don't seem to make any difference
to be without except for the rare need to drain water you have to figure out another way.
 

GerryUK

Bronze Supporter
#16
Our pools that we build with concrete floor, we do 8" with 1'2" bar on 1' centers
Thanks for that, duly noted

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Look into “basecrete” proprietary products..
Thanks, Unfortunately Basecrete is not available here in Colombia but I will see what equivalents there may be.

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I'm not sure why it's common to NOT have a main drain these days, but my pool was
built in the early 80's and does not have one.

I've had pools with and without maindrains. They don't seem to make any difference
to be without except for the rare need to drain water you have to figure out another way.
Thanks borjis - so the only intake is the skimmer, or should there be other intakes plumbed in?
 

PoolguyinCT

In The Industry
Jul 21, 2014
2,718
Connecticut
#18
Thanks for that, duly noted

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Thanks, Unfortunately Basecrete is not available here in Colombia but I will see what equivalents there may be.

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Thanks borjis - so the only intake is the skimmer, or should there be other intakes plumbed in?
Do a little digging & find Vito. He owns basecrete and has provided it throughout the globe. He is active on LinkedIn- & an easy guy to find.
I know his product has landed in West Indies, Africa, south and Central America- and of course Europe.
 

pushin glass

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Jun 16, 2016
117
East Central MS
#20
My pool has a concrete floor with concrete block walls and was built in the 1970's. It is still sound and performing well today. I agree with swimcmp about the thickness of the floor. I would definitely go much thicker than your proposed 4" and would make the footings much thicker than 4" as well. I'm not sure how thick my floor or footings are, but I know they are thick. Typical house foundation footings are 24" wide by 12" deep. I do know that my walls are 12" CMU block with rebar spaced at 4" intervals within the footings and traveling to the top of the walls, meaning that every hole in the blocks has rebar in it, and then the blocks were backfilled with concrete. I would definitely suggest one pour for the footings and slab (monolithic). Then lay the block and backfill the concrete. I can tell that the backfilled concrete was somehow allowed to seep out the bottom of the blocks because I can see it at the joints at the bottom of my pool. They do not leak by the way. If you can use epoxy-coated rebar, that might even be better. You might consider a rectangular shape rather than kidney bean as it will be much easier to design and construct. Concrete is a great material but definitely requires skill and expertise to get it right. If you have any concern about the labor you are hiring, using a liner like duraleigh suggests might be a wise move.