Shotcrete day - another quasi panic

[dotbombjoe]

Raised bond beam pool. They appear to be using backer board as the framing material. Everything I’ve read said this is common practice but not adequate because it is firm enough and moves when the shotcrete is applied. It is tied to a staked frame, but it still isn’t how I read it should be done.

Panic? Or not?

 

[PoolGate]

It's the builder's dime on the hook so I'd let them do what they do. Too late at this point to change anything.

 

[dotbombjoe]

That was where I landed as well. I really wish I had done an owner build.

Feels like all I can do is hope we don’t have problems down the road.

 

[duraleigh]

+1 what pool gate said. Not likely you could get him to do it your way (or any other way) at this point. Relax and enjoy the process and stay on good terms with him (always holding financial leverage, of course)

 

[ajw22]

Just take pics/videos and document the work done in case there are problems.

 

[JamesW]

With the shotcrete process, the concrete is shot in place, so the weight of concrete is carried by the concrete itself. There is little or no lateral pressure because the shotcrete is essentially self-supporting and doesn’t “flow” like fresh concrete does.

https://www.shotcrete.org/media/Archive/2011Sum_Sustainability.pdf

The formwork looks a little bit weak but it should be doable if the crew knows what they are doing.

Also, note that the front of the concrete has no forms at all, which proves that the concrete doesn't rely on the forms for support.

The back forms are mostly for reference to know where the back should be.

The other issue is the impact from the concrete being shot from the nozzle. The formwork should be able to withstand the impact without deforming.

If the gunite or shotcrete is built up, the concrete is mostly impacting at an angle, which reduces the impact on the formwork.

 

[SacPoolPros]

As a owner of a gunite company we use the same stuff to set pup i buy peg board by the pallet the thing to look for is do the strip it when they are done and take the forms away that's what we do sometimes i even use sheetrock just depends on what's cheaper material at the time its just used as a backer to shoot against once finished we always trip the boards/form off the gunite and throw them away.

 

[dotbombjoe]

As a owner of a gunite company we use the same stuff to set pup i buy peg board by the pallet the thing to look for is do the strip it when they are done and take the forms away that's what we do sometimes i even use sheetrock just depends on what's cheaper material at the time its just used as a backer to shoot against once finished we always trip the boards/form off the gunite and throw them away.

The stuff I read, mostly from the American Shotcrete Association, said the most important thing is that the form not move. For that reason, they generally don’t consider backer/peg board a good option, especially for large areas, but if it doesn’t move, that’s what matters.

Not sure it was a huge issue for my raised bond beam which seemed in most places to be decently supported by the 2x4 framing, but I could see the spa wall backer board deflect from 30’ away. I’ll upload a video when I can.

Another concern was they shot the wall first, which I think is typical, but the ASA seems to say is bad practice because it generally means the slough from the walls just falls to the floor rather than discarded as waste. I didn’t see any waste on my shoot — they simply applied loose material wherever they saw fit.

And then timing-wise, there was one section of material (pool-side corner between spa/pool) that sat there for probably an hour or more undisturbed until they restarted on that area. It didn’t look like they kept it wet during that time or before they started shooting it again but I could have missed it. They were wetting other areas...so, hopefully I just missed it.

The ASA seems to suggest all of these bad practices are fairly common if not typical in the industry and are a common cause of pool failures. But I’ll emphasize reading a few technical articles does not make me any sort of an expert — maybe I’m misunderstanding the articles I’ve read; just doesn’t seem like I am.

Thanks for everyone’s comments, I appreciate it. It’s good to hear from someone that does this for a living that some of these practices seem to be working well for them.

Here’s to hoping it was done well enough to hold up until the earthquake hits!

 

[JamesW]

Rebound is concrete that does not stick to the wall. Loose concrete should be discarded and not used in the pool.

Proper placement is at velocity to create the correct compaction.

Rebound is the material that ricochets off the application surface during the gunite operation. Rebound is typically made up of the larger and harder particles (which tend to ricochet) and does not contain adequate cement, water or density to develop significant strength. Rebound, therefore, should not be used in any application where strength, hardness or durability is needed.

The 2006 International Building Code states in section 1913.6:

1913.6 Rebound. Any rebound or accumulated loose aggregate shall be removed from the surfaces to be covered prior to placing the initial or any succeeding layers of shotcrete. Rebound shall not be reused as aggregate.

This Section of the International Building Code basically reinforces the fact that “rebound” cannot be used as a construction material. In fact, the code does not even permit “rebound” to be used as aggregate.

Use of Rebound in Swimming Pool Construction

https://www.shotcrete.org/media/Archive/2016Sum_PoolRecCorner.pdf

 

[dotbombjoe]

So, not the shotcrete guys fault but it became mighty obvious that there is no bench between the pool and spa. PB admits he missed that (we talked about it on many occasions, both agreeing that would be the most used bench)...he just didn’t catch the mistake on the rebar...

Doesn’t make me feel any better.

I’m not sure what a recently shot pool is supposed to look like but I’m pretty sure there shouldn’t be exposed rebar if it was shot well:

...the wall gets noticeably thinner there too. It’s the only place I noticed an obvious issue, but why am I the one finding that issue? Anyone know what should be done about it now?

On a separate note, I’m assuming it’s fine/normal that the concrete isn’t at all smooth? The floor of the pool is downright ragged...guessing that gets sanded down? I wondered because there are several sections where it is indeed very smooth looking. Guessing the difference is how the form came off. Is it an issue?

 

[dotbombjoe]

Here is a video from this morning...I'm not saying this is ok or not ok, but when they start shooting against the spa/pool wall, you can see that wall moves from the pressure...not an immense amount or anything, but it definitely moves wherever the shotcrete is being applied -- maybe that isn't so much that its a problem, but what i read suggested it really shouldn't move at all.

http://reefmaster.synology.me/photo/share/K9xtuQ7K/video_706f6f6c32303138_494d475f363139352e4d4f56

I haven't posted a video like this before so not entirely sure that will work.

 

[ajw22]

Roughness is not an issue. It all gets smoothed out by the plaster coat on top of it.

 

[dotbombjoe]

Also, my pool builder has in his contract that I have to water the gunite while it cures. Verbally, he said it probably doesn't matter. He hasn't told me what it means to water it...how wet is this supposed to be?

Do I go buy soaker hoses and a sprinkler or something and set it on a time or something? I don't want him using this to point fingers at me saying I didn't do what I was supposed to do. I'll search but if anyone has guidance I'd appreciate it.

 

[ajw22]

Also, my pool builder has in his contract that I have to water the gunite while it cures. Verbally, he said it probably doesn't matter. He hasn't told me what it means to water it...how wet is this supposed to be?

Do I go buy soaker hoses and a sprinkler or something and set it on a time or something? I don't want him using this to point fingers at me saying I didn't do what I was supposed to do. I'll search but if anyone has guidance I'd appreciate it.

Swan Pools - Procedure for Watering the Swimming Pool Gunite After Installation

 

[dotbombjoe]

Swan Pools - Procedure for Watering the Swimming Pool Gunite After Installation

Awesome, thanks!

 

[RoyR]

Why are those spa walls so much thinner, what is the width?

 

[dotbombjoe]

Why are those spa walls so much thinner, what is the width?

Might just be the way the pic looks. Not sure which photo you are looking at, but the spa walls are the same width as everywhere else except for that outside corner at spa/pool where there is a tiny bit of exposed rebar — that wall is thin right there.

The last pic it can be hard to distinguish between the bench in the pool and the wall; maybe that’s what you were seeing?

 

[kimkats]

Missing bench. They can drill in to the walls and put rebar in to make the bench.

 

[SacPoolPros]

Shotcrete is different then Gunite here is a pic of a gunite job we just did to give you a idea of the finish quality difference that finish looked quite messy

 

[JamesW]

Gunite and shotcrete should give the same quality finish.

Any weakness is due to application processes.

The original poster's shotcrete does look a little bit sloppy.

Probably poor technique and maybe improper mix.

Apparently, there was extensive use of rebound and cuttings, which create areas where the concrete is not properly compacted and not dense enough.

I wouldn't be surprised if the pool gets some cracks.