Did your PB's shotcrete sub reuse the shotcrete rebound?

[Titanium]

This is a question directed at either those who have a background in building pools (waste !) or those who watched the shotcrete sub-contractor shoot their pool.

Did the shotcrete sub-contractor reuse the shotcrete rebound, or was the rebound hauled away as debris?


Evidently the reuse or recycling of shotcrete rebound is very common among shotcrete contractors who mainly work on residential pools. Very common, and a very bad practice. Here are some relevant quotes from an expert on both pools and shotcrete.

Inside Rebound

Aside from it being a waste product of pneumatic application, what’s wrong with using rebound as a structural material?

Think of a baseball that’s coated with cement and thrown very fast against a rigid wall. The result is that the baseball ricochets off the rigid wall but, as this happens, a substantial amount of the cement that coated the ball becomes splattered against the wall. The ball, now lacking a good part of its cement coating, falls to the most convenient landing spot.

Similarly with gunite and shotcrete, a portion of the high velocity shot material— primarily the larger aggregates—ricochets or rebounds off the receiving surface and lands on the nearest horizontal plane.

The key point of this comparison is that, like the ball, the “rebound” aggregate has lost a substantial amount of its cement and is therefore no longer viable as a structural material. This is so widely recognized that, in fact, uniform building codes do not permit the use of rebound in structures.

Not using rebound as a structural material is a baseline workmanship principle that should never be violated, but, unfortunately, that’s just not the case in a large number of (mostly residential) swimming pool/spa projects.

The good news is that the fix is simple: don’t use rebound or trimmings to form steps or benches anywhere in a pool/spa shell—end of discussion!

The bad news is that this practice is so common in the industry that it’s hard to imagine things changing without some sort of concerted information campaign and increased education in workmanship and good construction practices. The simple fact is that there is a right way to apply shotcrete and that guidance in doing so is available from the American Concrete Institute (ACI) and the American Shotcrete Association (ASA).

http://www.shotcrete.org/pdf_files/Spri ... yMix%2Epdf


Even Ben Powell of Pool Forum/Pool Solutions did not like the idea of reusing shotcrete rebound when he was musing about his dream pool. http://www.poolsolutions.com/letter.html

All gunite rebound would be discarded.

I would be interested to hear stories or anecdotes of how the shotcrete guys did your pool. Thanks!

Titanium

 

[DLSDO]

No rebound used in our pool. We had so much waste that had to be hauled off it was a job in itself.

 

[Titanium]

DLSDO,

Thanks for the feedback. Sounds like you had a great shotcrete contractor.

Were you able to watch the shotcrete contractor in action? How did they keep the rebound and trimmings from falling and becoming part of the pool floor?

Titanium

 

[DLSDO]

Certainly some of the rebound and trimming ended up on the floor but they did not use these to form steps or swim outs. They did make some effort to throw out trimmings. It created hundreds of little mounds outside the perimeter of the pool. I was a little unhappy about the mess but they came back the following 2 days and hauled it all away.

 

[Titanium]

This is something interesting. It seems that the city I live in actually has a pool ordnance that deals with this issue.

Pool wall construction.

In gunite pools, the portion of the floor adjacent to the walls shall be placed before any material is deposited in the wall. A sufficient width shall be placed to facilitate the removal of rebound from the wall section.

Do the city ordnances of any other TFP members address this issue?

Titanium

 

[DLSDO]

Hmm. Interesting. How did you find that ordinance? I wouldn't know where to look.

I looked back at my build pics to refresh my memory. I can't tell if they did the walls or floor first.

Here is a pic of some of the mess after the shoot that surrounded the pool in piles.

 

[waste]

Titanium, thanks for the thread, it brings back memories from my shotcrete days. I spent many an hour shoveling out rebound from pools Our floors were poured, not shot!, and obviously done before the walls. The ONLY time we would use the rebound was if there were stairs or a 'swimout/ love seat' that would need 3+' of material to fill the bottom/ backend of it. All other rebound was tossed over the walls (this can be a real PITA in a 10' deep pool, so we wheelbarrowed the excess material up to the shallow end for removal). One thing you haven't brought up is when the walls collapse (the guy shooting the crete goes too high too fast and the shot crete is too heavy for the slump and comes crashing down, when that happened, we WOULD 'hand stack' a portion of the wall (though I can not throw a shovelfull of crete into a wall @ 1600psi, which is what the hose would apply the mix). This material is NOT rebound, but still isn't the same as having the 'gun' apply it - does that factor in?

Dave, looking at that picture, most of what I see (the white- gray piles) is from where they broke apart the hoses, the smaller 'chunks' which are darker, look to be rebound that was shoveled out of the pool.

 

[Titanium]

DLSDO,

Our city has links to the city ordinances right on the city website. Regarding your picture, it reminds of my last visit to the elephant exhibit at the zoo. :-D


waste,

"we WOULD 'hand stack' a portion of the wall"

What is involved in this? I'm having trouble understanding this.

The ONLY time we would use the rebound was if there were stairs or a 'swimout/ love seat' that would need 3+' of material to fill the bottom/ backend of it.

I'm not a shotcrete engineer, but I would think that the rebound used in this manner could only be considered as "fill" and not any sort of structural element. From reading the various articles I have come across on rebound, the rebound apparently, with so much aggregate and so little cement, has no structural characteristics whatsoever.

I've been hoping that you would offer your opinions and observations on this subject. How did you end up removing shotcrete rebound yourself? Were you working for a shotcrete sub, or did your poolbuilder employer shoot the pool shell with his own employees?

Also, how widespread would you say this problem is among today's poolbuilders and shotcrete subcontractors?

And how should a prospective pool owner try and prevent this problem?

It seems to me the problem, as a prospective pool owner contemplating a pool build, is that you are trying to control the quality and workmanship of the various subcontractors even though these subcontractors don't work directly for you and they work directly for the pool builder. It would be great if there were a set of plumbing, electrical, shotcrete, excavation, tile, and decking specifications that the pool owner could insist be incorporated into the contract the pool owner has with the pool builder. These specifications could not cover everything, of course, but hopefully would place some kind of minimum on the workmanship of the pool in the event of later problems. Evidently NSPI (or is it APSA?) has some specifications on pools, but I have not seen a copy of them.

Titanium

 

[waste]

Titanium,

The 'hand stacking' of which I speak is done when a section of wall that's being shot collapses (an area ~ 5' long and 2' high at the top of the most recently applied shotcrete) and ends up on the floor. This is usually caused by the crete itself being too wet (honestly, some drivers don't know jack about getting the right slump), or the 'gunner' going just a little too high with the fresh stuff. When the wall collapses, the laborers stop scraping the rebound off of the floor and set to work on the big pile of good crete - being careful not to mix rebound in with the good stuff, they heave shovels full of crete onto the section which collapsed (the best way I can describe this is like throwing a lacross ball, except instead of a ball, you have a shovel full of crete) You can reapply ~1/2 of the lost material this way - the rest goes either into the stair/ loveseat void or over the wall. (I hope that this answers your ? but if it doesn't I'll try to give a decent primer on shooting concrete - however, it's been over 12 years since I shot any crete )

Having only worked for one company which did shotcrete pools, I can't say how many out there are using inferior methods - what I will say is for any potential pool buyer to go with a company that has an established history and plenty of references and few bad marks with the local BBB (I say few because some people will file a complaint over negligable things which will still show up as a negative on the report) Even as I was typing this last bit, one exception came to mind - every pool company has to start somewhere, usually it's a guy, or a couple of guys, that have been doing the same work for someone else and just got tired of being the foreman/ doing all the work and driving a Hundai while the boss drives a Cadilac - he's been doing all the work to make someone else rich while getting a $.50 raise every year and a $500 Xmas bonus - once he/ they leave the company, most of the experience is lost but they still don't have a 'track record' of their own -- they will probably undercut their former employer to gain some business and one may get a quality job for a discount :blah: (enough of my "how to pick a pool builder" )

I've taken up enough of everyone's time, including my own , with this - If I can be of further service, or share a few chapters out of one of my 'books', I'll gladly do it for this 'library' :lol:

 

[Titanium]

waste,

Thanks for your description of "hand-stacking", which explained the operation very well.

I hope that this answers your ? but if it doesn't I'll try to give a decent primer on shooting concrete - however, it's been over 12 years since I shot any crete

You answered the question, but the "library" here at TFP could always use a decent primer if you have the time and inclination.

So your poolbuilder employer did the shotcrete inhouse as versus subcontracting it out to a dedicated shotcrete company?

Titanium

 

[cliff_s]

From what I have observed here in AZ the floor is shot last and anything that is left over is just
buried in the floor. As far as the slump is concerned the truck drivers speak English and the workers
speak Spanish(and NO English), so the just shoot what they get. Contractors love cheap help(skill
optional) so if the mud sticks to the sides thats good enough, the finish guys will fix the problems.

Cliff s

 

[waste]

Cliff, MERRY CHRISTMAS!!! (If you don't celebrate Christmas, insert the appropriate holiday/ reason )

I see you've posted many times today, my wife sends her well wishes to/ for you as do I-- no offense, but would you like to talk?, you seem to have no reason not to be posting today (PM me with a phone # if you'd like to hear another persons voice tonight ) If I'm being too presumptuous, tell me to 'bugger off', I just want everyone to have a reason to be joyous on this day (if only because it's Jimmy Buffetts birthday )

 

[repair_guy]

I used my rebound to backfill the plumbing trenches.