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View Full Version : Shotcrete or Gunnite - which one's best for the pool?



MagicMtnDan
08-10-2005, 06:59 AM
Which is best?
Here's what I've been told:
* Gunnite is mixed on-site by the contractor.
* Shotcrete is pre-mixed by the manufacturer.
* The difference, as I've been told, is that shotcrete is more consistent and gunnite quality will vary with the contractor.
Sounds like shotcrete is the better way (and more expensive). Is that right?
Found this online (http://www.itsa.info/Shotcrete.shtml ):
Concrete is the material that gives a thin-shell it's rigidity. While the concrete can in theory be entirely mixed and applied by hand, that seldom is economical. There are two popular methods of applying the concrete to the structure of the building: shotcrete and gunnite. The end result is the same in each case--concrete provides tremendous compressive strength while the rebar provides the tensile strength. But the means of handling the materials is slightly different.
Shotcrete is typically applied with a pneumatically driven pump. Concrete that is either site-mixed or delivered from a redi-mix plant is poured into a large hopper, from where it's pumped through a hose and sprayed by high air pressure (100-120 psi) and air volume (185 cfm or so) against the formwork. The best of the professional systems are able to move 6-to-12 or more yards of low-slump concrete (2" slump or less) through 2" hoses to produce a wall in excess of 4000 psi, though individual contractors will have their own specifications and preferences. Most concrete plants should have a recipe for a shotcrete mix that they can prepare at a moment's notice.
Gunnite is an equally suitable method of applying concrete. It is most frequently used when building swimming pools, and differs from shotcrete in that the ingredients are dumped separately into the gunnite truck, and then pumped through hoses, where they mix at the nozzle and project onto the wall. This method is not inherently better or worse than shotcrete--each work well as long as the rebar is properly encased.
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Hey Roz, I got the excavator's info and will PM it to you later today. (He's got 18 years of experience and is great to work with).

plaster dave
08-10-2005, 07:02 AM
Go with what your contractor uses.

HOSS
08-10-2005, 07:02 AM
My pool is gunite. Don`t know if its better or not but I do know its most common.

MagicMtnDan
08-10-2005, 07:04 AM
Go with what your contractor uses.
Uh, I have a choice as to material and contractor :)

PHX ATC
08-10-2005, 07:06 AM
These days they are just about the same. It all depends upon the "mix" of concrete: what psi, fiberglass shreds in it, etc. I've always used shotcrete in all the pools I've built. Never had a problem one.
Just make sure it is "shot" in and kept wet for about 5 days afterwards. You gotta water it 4 to 5 times a day and keep it wet. Sometimes the installer forgets to tell you that. It keeps it from cracking.

plaster dave
08-10-2005, 09:11 AM
What I mean is go with what your contractor recomends cause then if something go's wrong it's on him not you. .02 good luck
It's summer it's hot and it's concrete so it's gonna crack.

MagicMtnDan
08-10-2005, 11:31 AM
How about the know-all pool guys out there? Roz?

RiverDave
08-10-2005, 12:27 PM
Is this your boat money that your building this pool with.. ;) :D
RD

al cole'holic
08-10-2005, 12:41 PM
...when I added on to my existing pool I went with shotcrete...as they were spraying it they were forming the steps and walking on it while they worked! Sets up really fast... :)

ROZ
08-10-2005, 02:59 PM
Shotcrete.... I didn't think anyone used gunnite anymore...
Shotcrete mix is more consistant. The mix is comupter controlled at the batch plant to exact and controlled standards. It's a much stronger material ... Heck it's what CalTrans now mandates on all it's briges :)
Hope this helped

mmered8299
08-10-2005, 03:30 PM
Shotcrete can be good because it is mix at the plant. Downsize is if the concrete truck is stuck in traffic on a hot day the contractor adds water to the mix so the mud can go through the pump. Any time you add extra water to the concrete you weaken it. Gunite seams to be the way to go these days. Nozzle men have to be certified before they can shoot pools. Gunite out here in Vegas is going for $140-145yd. I wouldn't worrie to much either way. It's just a hole in the ground. :(

ROZ
08-10-2005, 03:43 PM
Shotcrete can be good because it is mix at the plant. Downsize is if the concrete truck is stuck in traffic on a hot day the contractor adds water to the mix so the mud can go through the pump. Any time you add extra water to the concrete you weaken it. Gunite seams to be the way to go these days. Nozzle men have to be certified before they can shoot pools. Gunite out here in Vegas is going for $140-145yd. I wouldn't worrie to much either way. It's just a hole in the ground. :(
Build pools in the winter :D
The heat may be the reason you guys use gunnite up there...
As long as your pool cage has the correct amount of steel in it, I wouldn't worry too much.. :messedup:

NashvilleBound
08-10-2005, 04:04 PM
Gunite is sand and cement only. Shotcrete is sand cement AND rock. HUGE difference. I would ONLY build a pool with shotcrete. Lots of contractors, where its still permittable, use shotcrete to save money and its a little easier to fix problems and work with. You can easily drive a nail into gunite where shotcrete is almost impossible. Go with shotcrete if you can....pay the difference (@$5 p/y) its worth it! Your article is misleading at best.

NashvilleBound
08-10-2005, 06:01 PM
LOL... the only thing that would do, if it was even possible or cost effective would be make the gunite, or shotcrete for that matter, is go off faster. Making the concrete powder hot is dangerous..... cold joints....cracking.... besides being harder to work with. I would like to see them expand sand and rock by 25% by heating.

BigDoug
08-10-2005, 09:50 PM
HM, im laughing with ya, cause i got it the first time :hammerhea

ROZ
08-10-2005, 10:24 PM
You can easily drive a nail into gunite where shotcrete is almost impossible.
Got that right!... Driving nails in the wood to attach the foam coping forms really sucked, didn't it :D :supp:

mmered8299
08-11-2005, 05:31 AM
Not to badmouth shotcrete or anything but one time we were shotcreteing a pool and the batch plant computer put too much retarder in the truck. So, as we were placing the concrete in the pool we were noticing that the mud wasn't setting up. We had to cancel the rest of the trucks. The next day the concrete in the pool was still loose/wet. :notam:

RNEW15
08-11-2005, 07:15 AM
been in the business 20+ years , shotcrete is stronger but harder to finish. This makes it tough to for the plaster company to apply final finish. Over 90% of all new pool construction is done using gunite. In So Cal typically the only time they use shot is when they are looking for psi ratings over 4500
2cents

ROZ
08-11-2005, 07:17 AM
Not to badmouth shotcrete or anything but one time we were shotcreteing a pool and the batch plant computer put too much retarder in the truck. So, as we were placing the concrete in the pool we were noticing that the mud wasn't setting up. We had to cancel the rest of the trucks. The next day the concrete in the pool was still loose/wet. :notam:
That's not badmouthing shotcrete, that's badmouthing batch plant operations :)
I'm sure you're seen gunnite mixed too wet as well...Maybe not that extreme, but wet nonetheless...
Like NB said, its composition is what makes shotcrete stronger and batch mixing usually makes it more consistant.