CMU pool without liner questions (edited)

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RussMaGuss

Active member
Feb 6, 2023
29
IL zone 5
Hi all!

I'm planning a concrete block pool build for this spring. I am a mason contractor by trade so I am doing it this way instead of hiring a pool company to shotcrete/gunnite.

I have looked up a few posts here about CMU pools and it seems like everyone uses a liner. I am planning to pour a concrete bottom and then plaster. Are there any examples floating around of pools like this?


I edited this post to thin it out a little and keep my questions simple:

Does anyone know of any pool finish suppliers that ship to IL? I called SMG and after getting phone number after phone number I got a salesperson's phone number in Indianapolis that sounds like is the person in charge of distribution in my area but got their voicemail only. Looking to use diamond brite.

For the actual application: I do not have access to a $50,000 shotcrete machine :ROFLMAO:. Will a standard hand held stucco sprayer be enough, or would I be wasting my time and better off just applying it by hand in the first place? Application video suggests that wetting the surface and then spraying is the only way, but I figure if I take the mason's approach of scratch coating, it should be fine, right? I figure for the square footage, me and my laborer could do it in about half a day if we had to do it all by trowel (16x32 rectangle, 6' deep end and shallow is split between sun shelf and 40" deep area.)

Plumbing packages: I hear that 2" pvc is a lot better, but maybe overkill for my pool size? Mine will be roughly 16,000 gallons I figure.
For plumbing layout, I have figured 1 skimmer between the deep and shallow end, close to the pump, and then 2 floor drains. I am thinking 2 return lines would be fine also--1 in the deep and 1 in the middle area.

Thanks for any advice!
 
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Good morning Russ and welcome to TFP! :wave: Afraid I'm no help on your technical questions, but we do have some members that might. Traffic is picking up a bit here on the forum so stick close to this thread and watch for replies. Post back as much as needed to help encourage responses. Stick around and enjoy the forum. :swim:
 
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Texas Splash said:
Good morning Russ and welcome to TFP! :wave: Afraid I'm no help on your technical questions, but we do have some members that might. Traffic is picking up a bit here on the forum so stick close to this thread and watch for replies. Post back as much as needed to help encourage responses. Stick around and enjoy the forum. :swim:
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Thanks for the reply. I have been looking into diamond bright and it seems like that by itself is water tight? Just spray it on and trowel it on 3/8-1/2” thickness. Found a very helpful tutorial of theirs. I guess I don’t need to worry about waterproofing with that stuff.
 
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I am no expert by far, but I do follow Jimmy Reed from Rock Solid Tile and read a lot of his posts and articles. - Rock Solid Tile - Mosaic Tile Contractor

Now, he does glass tile, and he is not cheap. He gets called in on quite a few jobs where people have gone with a cheaper company and now the glass tile in the pool is failing. This is often because they did not properly waterproof behind the tile. It fails, not because the pool leaks OUT, but because the groundwater infiltrates IN and causes the tile to fail.

If you read the installation specs for Diamond Brite it specifically says to prevent the infiltration of ground water. If I were doing this, I would put on a fluid applied membrane first, and then float it out, and then diamond brite over that.
 
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phonedave said:
I am no expert by far, but I do follow Jimmy Reed from Rock Solid Tile and read a lot of his posts and articles. - Rock Solid Tile - Mosaic Tile Contractor

Now, he does glass tile, and he is not cheap. He gets called in on quite a few jobs where people have gone with a cheaper company and now the glass tile in the pool is failing. This is often because they did not properly waterproof behind the tile. It fails, not because the pool leaks OUT, but because the groundwater infiltrates IN and causes the tile to fail.

If you read the installation specs for Diamond Brite it specifically says to prevent the infiltration of ground water. If I were doing this, I would put on a fluid applied membrane first, and then float it out, and then diamond brite over that.
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I am planning to damp proof the outer cmu walls. I wonder what I can do to damp proof under the pool floor/slab though. For my basement slab pour we used thick plastic, I imagine that would work just as well

New question for folks reading this: The vertical inside corner radius’ of the pool walls—how should I go about that? I imagine too small of a radius would be impossible for a robot cleaner to do it’s job, but if I take a 90° inside corner and do a big radius, I feel like those corners would be likely to fail. Maybe during install of the block, i will take some ladder wire and curve it to the desired radius creating a wire cage, and drop a rebar behind it so when I do the concrete and plaster it will have something to bond to? How big of a radius do the robots need?
 
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Let me be a contrarian- there’s a reason why CMU block pools use liners and, as a mason, you know why … what do CMU block walls look like after a couple of years? They look like this -

CE3EBABA-5442-4C86-9774-100C01BAAF51.jpeg

The c-blocks, even when tied with rebar vertically and horizontally, will move and cracks will always propagate along the joints where the cement is. You can not stop it. For masonry walls, it’s ok because you can always fill the cracks and repaint. But for a pool … instant leak.

Cement pools are manufactured using shotcrete or gunite process because you need to create a monolithic, continuous structure to be able to handle the intense mechanical pressure created by hundreds of thousands of pounds of water. There is no way c-block can do that without cracks developing. Heck, even shotcrete pools can crack …

@AQUA~HOLICS @JamesW @MAPR-Austin … am I wrong? Can you build a plaster pool using CMU ?
 
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JoyfulNoise said:
Let me be a contrarian- there’s a reason why CMU block pools use liners and, as a mason, you know why … what do CMU block walls look like after a couple of years? They look like this -

View attachment 472799

The c-blocks, even when tied with rebar vertically and horizontally, will move and cracks will always propagate along the joints where the cement is. You can not stop it. For masonry walls, it’s ok because you can always fill the cracks and repaint. But for a pool … instant leak.

Cement pools are manufactured using shotcrete or gunite process because you need to create a monolithic, continuous structure to be able to handle the intense mechanical pressure created by hundreds of thousands of pounds of water. There is no way c-block can do that without cracks developing. Heck, even shotcrete pools can crack …

@AQUA~HOLICS @JamesW @MAPR-Austin … am I wrong? Can you build a plaster pool using CMU ?
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So the way I’m building it is by grouting every block solid, #4 rebar 8”O.C. (Every cell), and several bondbeam courses including the top course and bottom with continuous rebar all the way around. Footer is going to be 20x10 with rebar keyed into it. Slab is getting rebar drilled and epoxied minimum 2’ o.c.
By “c” block, do you mean bondbeam?
I’m thinking the walls should be just as strong as shotcrete considering they are 8” thick.
I also plan on adding a few pilasters to the outer wall for extra strength even though it only goes 6’ at the deep end. Walls will be 6’ high even in the shallow end to give the deep end walls added strength

Absolute worst case I see is that it leaks and i have to go with a liner, but for $1,000 in plaster and a days work I think it’s worth it to try

I do appreciate the contrarianism though, it keeps me on my toes to make sure I don’t overlook anything on a large project like this!
 

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I’m an “existence proof” kind of thinker on these matters … if it could be made to work, then why aren’t builders doing it all the time? Your plan sounds great but CMU, cement, rebar, pools, etc, have been around a long time. If CMU walled plaster pools were possible, I would think one would already exist … but hey, I’m happy to be proven wrong and I’m wrong way more often than I’m right.

One final thought - hand application of pool plaster is not really effective or practical. If you’re looking to save money, then skimping on the plaster application is not where you want to go. Hand applied plaster will look horrible, it will not have the density/compaction needed that pump-applied will, and I can easily see it failing from voids and lack of adhesion. Find other ways to save money and then pay a real plaster crew to do the job right. It’s not a one-man job.
 
JoyfulNoise said:
I’m an “existence proof” kind of thinker on these matters … if it could be made to work, then why aren’t builders doing it all the time? Your plan sounds great but CMU, cement, rebar, pools, etc, have been around a long time. If CMU walled plaster pools were possible, I would think one would already exist … but hey, I’m happy to be proven wrong and I’m wrong way more often than I’m right.

One final thought - hand application of pool plaster is not really effective or practical. If you’re looking to save money, then skimping on the plaster application is not where you want to go. Hand applied plaster will look horrible, it will not have the density/compaction needed that pump-applied will, and I can easily see it failing from voids and lack of adhesion. Find other ways to save money and then pay a real plaster crew to do the job right. It’s not a one-man job.
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For what it’s worth, i do plan to spray it on, just not with a shotcrete machine. If I could find a shotcrete machine to rent i’d do that instead of cmu, but the only people that have them are the pool builders who laugh at you when you ask if they want to sub out their crew and machine for a day (I don’t blame them, the money lies in the whole project and the shotcrete shell is only 1 piece of the puzzle) I’ll probably use a sprayer with a hopper for the plaster. I imagine me and my laborer can get it done in half a day, it’s only 16x32. The diamond brite gets hand troweled and brushed regardless of application medium though, so it seems like pumping it is just the faster route. I talked on the phone with the sales rep and he said hand troweling it on is fine. I plan to lightly wet the wall and then either “burn” in the first skim coat and then build up from there, or just spray the whole thing and then finish it.

And to answer why most people don’t do it this way I think is because for others it would be really expensive, but since this is what I do for a living, it’s mostly just materials + my laborer’s wages for a few days (22k for everything) VS the pool companies whose base price is $100k+
 
AQUA~HOLICS said:
20’ X 40’ 8 men in the hole and 2 at the hopper, 7 hours with no breaks.View attachment 472825View attachment 472827
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Yes yes … but we all know you SoCal types will only do plaster work in your most expensive Louis Vuitton spiked shoes! Oooo … is that fellow on the hopper wearing his grey Manolo Blahnik high rise boots … bold fashion choice … very trendy. I see you sub out to only the best 😉
 
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Those sqft per man numbers don’t seem to jive with mine, and that’s a little (not a ton) bigger than what I’m doing, but I appreciate the input/reality check and will definitely make sure I have more than 1 helper. Can’t hurt if we finish early anyways, right? It looks like I’ll have about a pallet to do, so 14 bags/man is like 2/hr which is right there with my numbers. I’ll double check all my surface measurements before ordering materials though
 
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RussMaGuss said:
Those sqft per man numbers don’t seem to jive with mine, and that’s a little (not a ton) bigger than what I’m doing, but I appreciate the input/reality check and will definitely make sure I have more than 1 helper. Can’t hurt if we finish early anyways, right? It looks like I’ll have about a pallet to do, so 14 bags/man is like 2/hr which is right there with my numbers. I’ll double check all my surface measurements before ordering materials though
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From watching in person, the laying down of material was done quickly. The rest is all a coordinated art. That pump in the middle is for hydration/slurry removal. The process with exposed aggregate is more than spread and trowel Each man has a different job and it's all done simultaneously to make an aggregate finish uniform in aggregate exposure and color. Outside of the guy with the nozzle, others are troweling, others are removing water and cream and hauling off, others are washing while still wet and not set, while others are going behind and finishing and forming as it starts to set. End goal is having uniform hydration, compaction, and surface coat so that color will be uniform. Even then, with darker colors, even differences in troweling and hydration/drying rate in areas will throw different shading in final color, mottling. That's why you see they use spiked boots, it's not done in stages but as a whole.
 
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I'm glad I asked here first so that I could get great input.
Now, as a person not afraid to ask dumb questions because this is the internet (And allow me to preface it by saying this is basically kicking rocks around because I'm still open to doing either a liner or tile): Is it totally sacrilegious to do a plaster job in 2 days vs 1 if we take too long? I imagine big pools either have to, or they would just use a different medium like tile. Feathering the edges down to the cmu walls at the end of the session instead of what would essentially be a cold joint would be the best way to prevent any cracking. I don't imagine there would be any issues bonding--I was always taught and it was proven to me in the field that "mortar likes to stick to mortar" so it seems that logic would work here as well since there would be exposed aggregate for the fresh plaster to bond to. And it would still be fresh. Unless the finish is not rough enough, then it would definitely be an idea to bail on. If the bond was not an issue, would the only other main issue be color mismatch possibilities? Not going to even consider this as an option until I get more input, but want to kick the idea around. It’s probably a dumb idea, but I had to ask. Would rather get scolded and avoid it now, than try it and be surprised if it fails after 1 season or something.

Ultimately though: If a plaster job needs re-finishing after 20 years anyways and a liner lasts 10-15, maybe the liner is just the smart way to go? I could do tile, but my budget also says liner over tile. Heck, maybe I do a liner now, and when it’s time to replace it I can tile it then
 
Plaster needs to be laid down in one day and then, depending on the plaster type, the pool needs to be filled within a few hours of the final troweling (if aggregate exposure is required then sometimes the plaster is left overnight and the exposure is done the following morning). If it’s left for days before filling, the plaster will not properly cure and the lack of carbonate exposure from the water will not allow the plaster chemistry to happen. You risk creating a porous and weak plaster that will likely fail well before 15-20 years. You will also create lots of “cold joints” between the plaster layers which will ultimately affect appearance. This is why I suggested that you save money elsewhere in the project and not skimp on the plaster job. Paying a crew of experienced plaster applicators $8k-$12k (depends on your area) to do the job right and get you the longest possible plaster life (along with whatever warranty they’re willing to give for an unconventional pool structure) is worth it. And you save yourself days of back breaking labor hauling around mud and troweling plaster.

I honestly think you’d be much better off with a liner pool. Given your location in a cold northern mid-west climate, plaster is not really an optimal surface.
 
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