Rebar placement / process

[dotbombjoe]

So, I know the rebar size/placement depends on the engineering...my question is what should I be looking for to make sure it is being done correctly?

For example, I've read that there should be spacers on the walls and floor to make sure the rebar is properly encapsulated. There are no spacers in place yet. Is that typically done towards the end of the rebar placement or should I start to worry that my crew isn't doing it properly? (see pic below)

They are using metal ties where rebar crosses -- should these ties be at every 'cross'? Does it matter which piece of rebar is above the other? I'm thinking about the corners where the rebar is heading up the wall -- should the rebar along the floor in that section be above or below the rebar that curves up the wall? And for the general lattice or rebar in the floor, should a given run of rebar always be below (or above) the crosses or should each length of rebar be interlaced (above and then below) at crosses?

When two lengths meet, they are bound by metal ties and overlapping by at least 2-2.5 "crosses".

Anyway, I obviously don't know anything about this; I'm just trying to build confidence that the crew is doing it properly. The lack of spacers was a red flag to me although I'm guessing/hoping it may just be that they add them in later after they've tied everything together.

 

[BMK]

This isnt my area of expertise either, but I can tell you from my experience that the spacers or 'chairs' were inserted at the end of the whole rebar process just prior to the the shoot or pour.
One reason is that this allows crew to work and easily move around without the tripping hazard of raised rebar.

 

[bdavis466]

It looks like they aren't done yet

The transition from the shallow to deep end should have #3 bars at 6" O.C.

Once they are finished none of the rebar should be closer than 3" to the earth. They'll add the dobies (spacers) to raise the cage off the floor and from the walls.

Pool only? No spa?

 

[dotbombjoe]

It looks like they aren't done yet

The transition from the shallow to deep end should have #3 bars at 6" O.C.

Once they are finished none of the rebar should be closer than 3" to the earth. They'll add the dobies (spacers) to raise the cage off the floor and from the walls.

Pool only? No spa?

Yea, That was my guess re: the spacers coming later but it’s good to hear.

I’ll have to measure again but I don’t think the bars on slope are 6” OC. More like 9”. Pool is 4 - 5 - 4, so two slopes roughly 1’ drop over 5’ length. I was assuming this would get inspected and checked against the engineering plans but maybe that is wishful thinking?

My architect just really made it seem like I was going to get screwed because I didn’t go with any of their recommended vendors...scare tactic for sure but does have me doing extra diligence.

You don’t even want to know how much I’ve read about proper shotcrete application! Lol

We do have a spa, I’m assuming they’ll have to build the form for the spa wall that is shared with the pool — that hasn’t been built yet.

The pool and spa will be raised 18” from grade.

Thanks for the input!

 

[bdavis466]

Yea, That was my guess re: the spacers coming later but it’s good to hear.

I’ll have to measure again but I don’t think the bars on slope are 6” OC. More like 9”. Pool is 4 - 5 - 4, so two slopes roughly 1’ drop over 5’ length. I was assuming this would get inspected and checked against the engineering plans but maybe that is wishful thinking?

My architect just really made it seem like I was going to get screwed because I didn’t go with any of their recommended vendors...scare tactic for sure but does have me doing extra diligence.

You don’t even want to know how much I’ve read about proper shotcrete application! Lol

We do have a spa, I’m assuming they’ll have to build the form for the spa wall that is shared with the pool — that hasn’t been built yet.

The pool and spa will be raised 18” from grade.

Thanks for the input!

There is an inspection for the rebar and rough plumbing/electrical and your city is known to be particularly particular. Who's doing the rebar?

 

[dotbombjoe]

There is an inspection for the rebar and rough plumbing/electrical and your city is known to be particularly particular. Who's doing the rebar?

South County Steel is doing the rebar.

We are in unincorporated territory here so permitting/inspections through the county (Orange).

 

[kimkats]

If you want you can take a tape measure out there. Add about 8" to both walls and floor for the shell and plaster. The water depth will be to the middle of the skimmer face.

This is one of those trust yet verify times.

Kim

 

[dotbombjoe]

If you want you can take a tape measure out there. Add about 8" to both walls and floor for the shell and plaster. The water depth will be to the middle of the skimmer face.

This is one of those trust yet verify times.

Kim

Re: the skimmer and water height... Pool is raised 18”, with coping and a few inches gap between coping and water, I’d guess that middle of the skimmer probably needs to be about 12” (+/-2 inches); does that mean I may have to raise/lower the skimmer to get the water line where it needs to be? I’ll have to look up dimensions on the pentair 520.

Thanks again all!

Btw, in case anyone else has rebar questions, I’ve read a few things of interest to those who may want more details:

When a single length of rebar is too short for the required pool length, additional lengths can be ‘joined’. There are two way to do so: connected and not. Not connected actually appears to be desired from an engineering perspective but connected is more frequently done in the field.

Either should be fine provided it is done well.

Connected involves overlapping the ends of two lengths and using the metal snips to bind them. The ‘risk’ in this approach is primarily related to shotcrete — it wouldn’t arise for poured concrete for example. Basically, the double wide section of rebar can introduce voids/shadowing as the shotcrete is being applied. What I’ve read suggests the risk is mitigated by tying the bars so they are stacked on top of each other based on the direction the shotcrete will be applied in...

The length of overlap is based on many factors but based on what I read it is common for 2-3’ of overlap.

Unconnected rebar is preferred from an engineering standpoint because it avoids the shadowing/void problem. In this approach, the bars must still overlap but they are separated by a few inches. This appears less commonly leveraged either due to lack of training or concerns re: ensuring the stability of the frame (ie, harder to tie it all together and prevent movement of the rebar).

Again, either seems fine if done properly, at least from what I read.

I feel like I should have GC’ed this project myself with everything I’ve learned! Lol

 

[bdavis466]

The top of the skimmer mouth should be flush with the top of the form. Usually a piece of rebar is tied from form to form right across the top of the skimmer to hold it in place

 

[dotbombjoe]

The top of the skimmer mouth should be flush with the top of the form. Usually a piece of rebar is tied from form to form right across the top of the skimmer to hold it in place

lol, ok, ok, I get what you are saying now...I was very confused re: misunderstanding what you meant by skimmer. My previous experience is with large fish tanks and we use the term skimmer for our filtration systems and I still find myself thinking the wrong thing.

Is there anything else important re: skimmers? Re: how many there should be or where physically they should be? I'm assuming we'll be locating them on the far side of my pool away from my house (toward our slope) so the associated plumbing is hidden from view...right? Is it ok that they would all be on the same side of the pool? Is two sufficient?

 

[bdavis466]

One skimmer is plenty for that small of a pool and all the associated plumbing will be under the ground and unseen. It should be positioned on the side of the pool opposite the predominant wind.

Who do you plan on using for the plumbing?

 

[dotbombjoe]

One skimmer is plenty for that small of a pool and all the associated plumbing will be under the ground and unseen. It should be positioned on the side of the pool opposite the predominant wind.

Who do you plan on using for the plumbing?

Gotcha, ok, so house side then...the wind comes straight up the slope into the house — that makes sense re: skimmer location now that you point out the wind. We’re having an automatic pool cover put on so I’m hoping the skimmer won’t have a ton of work to do in general.

So I shouldn’t worry about redundancy re: skimmer? It’s a habit I’m in because of my fish tank...

The PB hasn’t shared who he is using for plumbing. I’ve asked him for the plumbing plan a few times and he’s said he would let me know but I have t seen anything yet.

I did explain to him that I prefer to oversize my plumbing but his thoughts on that may not be the same as mine.

 

[dotbombjoe]

Ok, so the steel crew wrapped up day 2. I'm looking at the work and I'm seeing some of the issues raised as "common problems" by the documents I've been reading.

Specifically, I see the rebar stacked side by side instead of on top of each other where there are contact lap splices.



Everything I've read basically says that shotcrete is regular concrete -- what makes it special is that it is pneumatically slammed onto the surface. The concrete isn't strong because its better concrete, it is strong because of the application to the surface. And that's why it is so important that the rebar doesn't impede/block the shot concrete...even if it doesn't result in a void it probably won't be 'shot' it could/would be rebound and trimmings/slop which won't have the necessary strength.

I'm guessing a really good shotcrete crew could potentially still shoot it well with a non-optimal steel installation but I'm feeling like I shouldn't/can't rely on that...

The same pic also shows a rather short contact lap splice -- a single overlap of probably 6-9" with only a tie at a single cross point. That doesn't seem right to me either. Most places seem to be better in that regard but they should all be "right"...right?

I'm just someone that's read a bunch of online content mostly from engineers describing good/bad pool construction practices so it isn't like I really know what I'm talking about...but do others agree this is something I should have my PB address right rather than trusting a shotcrete crew is going to do a great job anyway?

For what it's worth, I found another article by the engineer describing these issues and he said in most jurisdiction that there has to be 2.5" of space between parallel bars. What I'm not clear about is whether he meant when using contact lap splices or non-contact lap splices. Meaning, does the 2.5" of space refer to when rebar is overlapped but not in contact with each other or does he mean 2.5" between bundles of rebar tied together.

 

[Killer95Stang]

You understand the ties putting the rebar together arent structual...right? The ties keep the rebar in the proper location until the concrete is "shot", "poured" and "shoveled" into place. All those engineering articles you are reading are probably associated with the construction of skyscrapers, bridges and freeway overpasses. A residential pool does not meet most of those requirements. And why even use shotcrete or gunite methods for pool construction... ? mainly because concrete applied in those two methods does a nice job of sticking to vertical surfaces like walls of the pool. You cant exactly poor concrete in the traditional method without forms and expect to be able to build a pool.

My 4 inch thick garage slab has been in place without rebar for 60 years with no cracks... im not worried about my 8" -12" thick pool.

 

[bdavis466]

Where is that picture in the pool? Is that a keyway?

 

[dotbombjoe]

You understand the ties putting the rebar together arent structual...right? The ties keep the rebar in the proper location until the concrete is "shot", "poured" and "shoveled" into place. All those engineering articles you are reading are probably associated with the construction of skyscrapers, bridges and freeway overpasses. A residential pool does not meet most of those requirements. And why even use shotcrete or gunite methods for pool construction... ? mainly because concrete applied in those two methods does a nice job of sticking to vertical surfaces like walls of the pool. You cant exactly poor concrete in the traditional method without forms and expect to be able to build a pool.

My 4 inch thick garage slab has been in place without rebar for 60 years with no cracks... im not worried about my 8" -12" thick pool.

I'm not talking about the "ties" -- maybe you are equating "ties" to my references to the "contact" splices? Yes, I understand the ties are just to keep the bars in place...firmly because it is important the bars don't move if they're going to be properly encapsulated by the concrete.

Contact and non-contact splices are not "the ties" -- they are the term used to describe how to join two pieces of rebar lengthwise in cases where a single length of rebar isn't long enough for the requirement. Either of these techniques can be executed so the strength of the rebar is retained throughout the desired length.

Further, there are right and wrong ways to execute on these splices. I can understand that it probably doesn't interest you, but I shared because I thought maybe someone else will someday find this thread and think the information useful.

All the articles I'm referencing are specifically about residential pools.

I don't remember suggesting a residential pool requires the same engineering that skyscrapers, bridges and freeway overpasses require. From the limited reading I've done, the shotcrete we use for our residential purposes is a far cry from the same product and application used in commercial applications.

I never asked the question why shotcrete is the preferred mechanism to create the shell of residential pools -- that's just what my pool builder told me he was planning to do. My interest now is to make sure it is done properly, and to share what I think I've learned about that with anyone else on this forum that may find the information useful.

Shotcrete isn't magic. It doesn't guarantee the structural integrity of whatever structure it was being used to create. If it isn't applied properly, it will fail. I know a ton of people in California have experienced such failures in their residential pools that were built with shotcrete. The articles I found from engineers who are brought in to identify the cause of such failures have pointed out that improper rebar installation resulting in poor shotcrete application is one of the most common reasons for the most common pool failures.

I'm happy to hear your garage slab has been working so well. I'd guess it was properly engineered and installed. I'm certain if it were not properly engineered or installed, you very well may have had to dig it up and have it redone. I'm not suggesting you have to worry about your 8-12" thick pool, but I am going to "worry" about mine because I'm paying a ton of freakin' money and I expect the job to be done right. Improperly installed 8-12" thick reinforced concrete will and does fail, all the time...you can see a ton of examples if you do a search right here on this website.

 

[dotbombjoe]

Yes, that particular one is a keyway. There are similar situations elsewhere, not in a keyway. It is also where they left off, so the issue re: the short length of rebar with only a single tie, that may just be unfinished work.

I'm more concerned with the use of side-by-side rebar instead of stacked. I don't know how concerned to be because in most areas there are still a few inches of space around the area so I would think a decent shotcrete crew could shoot it without voids. But a careless crew might not. And from what people have told me, the folks shooting residential pools aren't as consistently good as commercial applicators...and again, the docs I've read suggest every splice should be stacked instead of side-by-side so I'm inclined to push them to address it.

 

[dotbombjoe]

Turns out several of the articles I’ve been reading are by the engineer that did my pool (it’s who my PB uses).

My PB says there is plenty of room to shoot properly. He might be right...

I’m going to see if the engineer will provide some guidance.

 

[kimkats]

You have dug deeper into the steel placement than I have seen before. I am learning a lot just reading what you are saying. I am VERY interested to see what the engineer has to say especially since it is his articles you are using as a bases for your ideas.

Kim

 

[Arizonarob]

Yeah, I’ll ditto what Kim said. Kutos to you for going the extra mile and keeping an eye on your build!!