Is it ok to shoot gunnite pool in the middle of winter?

[FireDean]

HI
I am researching potential probs for a gunnite pool shoot scheduled for this weekend (Dec 17) from a reputable pool contractor. That said, the contractor subs out this part of the pool build project. I am a landscape designer and in this case acting as GC for the project as well. My instincts tell me its too cold to do anything with a concrete mix now but ive been assured that they do this all winter long without it ever being an issue. Can anyone provide a short list of questions I should have them answer before they start? Thanks
PS - I did read the now defunct thread on a similar topic posted in this forum years back but it didnt really provide any type of clear cut check list . The concensus was that it could be done but that 'precautions had to be taken' . Im wondering what specifically those precautions might be.
Thanks so much, ive installed hundreds of hardscapes , a few of which were structurally quite complicated, but never a pool so Im a bit nervous.

 

[Bperry]

HI
I am researching potential probs for a gunnite pool shoot scheduled for this weekend (Dec 17) from a reputable pool contractor. That said, the contractor subs out this part of the pool build project. I am a landscape designer and in this case acting as GC for the project as well. My instincts tell me its too cold to do anything with a concrete mix now but ive been assured that they do this all winter long without it ever being an issue. Can anyone provide a short list of questions I should have them answer before they start? Thanks
PS - I did read the now defunct thread on a similar topic posted in this forum years back but it didnt really provide any type of clear cut check list . The concensus was that it could be done but that 'precautions had to be taken' . Im wondering what specifically those precautions might be.
Thanks so much, ive installed hundreds of hardscapes , a few of which were structurally quite complicated, but never a pool so Im a bit nervous.

I don’t have any of the precautions for it, but I’ve seen concrete being poured and finished with snow on the ground so it’s not out of the question, just they typically use accelerants to speed up the curing, but not sure if gunite gets the same treatment.

That said, are they aware of the blizzard is coming that way this weekend over the dakotas which is likely to push snow and rain through update NY? Seems like waiting a week might be wise, but that’s just me and I’m not a pool builder.

Edit: maybe upstate NY has a different enough climate that it’s less of a concern.

 

[Leebo]

Pool Plaster Tips for the Average Homeowner

A quality plaster job can last a homeowner for decades. We help share basic steps that can be taken before, during, and after the plastering of a pool.

www.troublefreepool.com

You’re asking for some large issues attempting to plaster your pool now. One of the largest hurdles the contractor won’t speak of is the upkeep of things after he leaves. How are you gonna keep the pH under control when the pool is a block of ice?

 

[Foxer]

Not the same type of weather as you'd have now, but I had my pool shot last March, and temperatures were still getting into the 30's. The company that did mine suggested covering the pool with a tarp and putting a heater in it to keep it above 40 degrees. He did say it would probably be fine without doing that, but if it was his pool he would do it. At the end of the day I figured the cost to keep it warm for a week was worth the peace of mind.

Other than that, they do add some kind of accelerant or something as part of the winter mix, but I don't specifically know what it was.

 

[JoyfulNoise]

The shotcrete should not be done unless the air temps are over 40F. If there’s any chance of freezing occurring within a few days after the shoot, cracking damage can occur from the water inside the concrete freezing.

Usually with a winter pour, you try to cover and keep the concrete as warm as possible. Tenting and using contractor lights (halogen lamps) to keep the space warm is not out of the question.

 

[Bperry]

Pool Plaster Tips for the Average Homeowner

A quality plaster job can last a homeowner for decades. We help share basic steps that can be taken before, during, and after the plastering of a pool.

www.troublefreepool.com

You’re asking for some large issues attempting to plaster your pool now. One of the largest hurdles the contractor won’t speak of is the upkeep of things after he leaves. How are you gonna keep the pH under control when the pool is a block of ice?

I think he’s just at the gunite stage right now. Plaster for sure would be best to wait out the freezing weather.

 

[JoyfulNoise]

The gunite/shotcrete subcontracted crew is unlikely to do anything but setup their screening/masking tents for the work site, shoot the shell, screed and trowel the surfaces and then cleanup the rebound & leave. You do know about not reusing rebound, right? You should be there when the crew is working and make sure as little rebound is reused as is possible. Since you are the GC, ordering and ensuring that the concrete mix from the yard is appropriate for the environment is on you. Someone needs to look at the concrete trucks ticket to make sure the proper mix was delivered and that the concrete hasn’t been sitting in the truck for more than 45mins to an hour. Someone should also do a slump test of the concrete from the truck BEFORE it is shot to ensure that it passes. Normally a PB would be there to either do these things or witness them being done so that they can verify the materials are correct.

As the GC, it will fall on you to do any additional tenting and put out heaters of the concrete is going to be exposed to freezing weather.

 

[FireDean]

The gunite/shotcrete subcontracted crew is unlikely to do anything but setup their screening/masking tents for the work site, shoot the shell, screed and trowel the surfaces and then cleanup the rebound & leave. You do know about not reusing rebound, right? You should be there when the crew is working and make sure as little rebound is reused as is possible. Since you are the GC, ordering and ensuring that the concrete mix from the yard is appropriate for the environment is on you. Someone needs to look at the concrete trucks ticket to make sure the proper mix was delivered and that the concrete hasn’t been sitting in the truck for more than 45mins to an hour. Someone should also do a slump test of the concrete from the truck BEFORE it is shot to ensure that it passes. Normally a PB would be there to either do these things or witness them being done so that they can verify the materials are correct.

As the GC, it will fall on you to do any additional tenting and put out heaters of the concrete is going to be exposed to freezing weather.

Super helpful. Thankyou Joyful Noise! This is the first pool project ive ever had to manage . I have no idea what 'rebound' is and would welcome your explanation of what it is and further experience with what to look out for in regards to its use or non-use.

 

[JoyfulNoise]

Super helpful. Thankyou Joyful Noise! This is the first pool project ive ever had to manage . I have no idea what 'rebound' is and would welcome your explanation of what it is and further experience with what to look out for in regards to its use or non-use.

When a shotcrete crew starts to pump concrete at the rebar cage, the concrete builds up into the intended form. As the more concrete is shot (at high pressure and higher velocity), some of the concrete will stick and some will fall away as "rebound". In an effort to minimize "waste", some of the crew will scoop up the rebound to use it to fill in hollow spots or build up areas. This is BAD shotcrete practice. The entire point of using a high pressure concrete pump is to "shoot" the concrete into place so that it forms a highly densified structure. Think about how when holes are backfilled and you want to make sure that proper compaction of the soil is achieved - you don't just dump in a bunch of dirt, tap it with a shovel and then walk away. That will cause serious settling. You add the soil in lifts and between each lift you use some kind of compaction device (either a tamping pole or a jumping jack or a water barrel) to make sure the soil is set in place at the highest density possible. This results in a firm ground that can be built upon. Same idea goes with shotcrete - you want to make sure the walls and floors have good compaction and density so that there no voids and the concrete that is set into place has the highest possible strength. If a guy just take a blob of concrete sitting off the floor and throws it up onto the wall to fill in spots, then those areas are going to be significantly less dense. There's even a good chance that the rebound material will not stick properly and fall away as the concrete cures.

Now there's some situation where one can use a little bit of rebound to help smooth over an area but, by and large, the walls should be shot and any rebound moved away quickly.

Be sure to discuss it with the shotcrete foreman and insist that his crew not use rebound in any of the structural segments of the wall. You want your walls shot with the highest possible density.

 

[FireDean]

Super helpful. Thankyou Joyful Noise! This is the first pool project ive ever had to manage . I have no idea what 'rebound' is and would welcome your explanation of what it is and further experience with what to look out for in regards to its use or non-use.

Pool Plaster Tips for the Average Homeowner

A quality plaster job can last a homeowner for decades. We help share basic steps that can be taken before, during, and after the plastering of a pool.

www.troublefreepool.com

You’re asking for some large issues attempting to plaster your pool now. One of the largest hurdles the contractor won’t speak of is the upkeep of things after he leaves. How are you gonna keep the pH under control when the pool is a block of ice?

Hi, thanks I wasnt asking about maintenance or plaster. We just finished the nest phase and now Im trying to get educated about next phase (gunnite / shotcrete application ). Looking at industry standards so I can I ask my Pool Builder (who I trust btw) reasonable questions and create a check list BEFORE they start.

 

[ajw22]

Rebound waste scraped off of walls when shaping it are often used to form steps and ledges. You do not want that and as GC you should not only discuss it with the shotcrete foreman but keep an eye on the way the crew is working. Especially on the way steps and ledges are being formed.

Rebound does not have the structural strength of shotcrete and we see cracks in the plaster on steps a few years after build due to the base under the plaster crumbling because rebound was used to form it.

Rebound scraped off in shaping the shotcrete should be loaded into buckets and hauled away from the job site. As you can imagine some crews would rather use the rebound then be hauling it away.

 

[FireDean]

When a shotcrete crew starts to pump concrete at the rebar cage, the concrete builds up into the intended form. As the more concrete is shot (at high pressure and higher velocity), some of the concrete will stick and some will fall away as "rebound". In an effort to minimize "waste", some of the crew will scoop up the rebound to use it to fill in hollow spots or build up areas. This is BAD shotcrete practice. The entire point of using a high pressure concrete pump is to "shoot" the concrete into place so that it forms a highly densified structure. Think about how when holes are backfilled and you want to make sure that proper compaction of the soil is achieved - you don't just dump in a bunch of dirt, tap it with a shovel and then walk away. That will cause serious settling. You add the soil in lifts and between each lift you use some kind of compaction device (either a tamping pole or a jumping jack or a water barrel) to make sure the soil is set in place at the highest density possible. This results in a firm ground that can be built upon. Same idea goes with shotcrete - you want to make sure the walls and floors have good compaction and density so that there no voids and the concrete that is set into place has the highest possible strength. If a guy just take a blob of concrete sitting off the floor and throws it up onto the wall to fill in spots, then those areas are going to be significantly less dense. There's even a good chance that the rebound material will not stick properly and fall away as the concrete cures.

Now there's some situation where one can use a little bit of rebound to help smooth over an area but, by and large, the walls should be shot and any rebound moved away quickly.

Be sure to discuss it with the shotcrete foreman and insist that his crew not use rebound in any of the structural segments of the wall. You want your walls shot with the highest possible density.

Makes complete sense JoyfulNoise. Appreciate your analogy , thanks for taking the time to explain.

 

[FireDean]

Rebound waste scraped off of walls when shaping it are often used to form steps and ledges. You do not want that and as GC you should not only discuss it with the shotcrete foreman but keep an eye on the way the crew is working. Especially on the way steps and ledges are being formed.

Rebound does not have the structural strength of shotcrete and we see cracks in the plaster on steps a few years after build due to the base under the plaster crumbling because rebound was used to form it.

Rebound scraped off in shaping the shotcrete should be loaded into buckets and hauled away from the job site. As you can imagine some crews would rather use the rebound then be hauling it away.

Thankyou, all helpfull...affirms what others have said.

 

[kimkats]

Be sure to discuss it with the shotcrete foreman and insist that his crew not use rebound in any of the structural segments of the wall. You want your walls shot with the highest possible density.

I am very glad you trust your GC. That is a huge plus. Saying that I would make sure you could be there to hand out drinks and snacks *wink, wink* aka keep an eye on them while doing the work. Nothing wrong with setting up a comfy chair by the cooler.

 

[FireDean]

Hysterical...exactly my style free pizza and stupid war stories interrupted by the occasional tape measure / level check

 

[generessler]

I've never done shotcrete but lots of paving with conventional concrete. It's extra easy to create a future disaster when placing in freezing weather. The base cannot be frozen, so it must be heated until thawed all the way through before pour day. Many base materials should then be re-compacted. As has been mentioned, special mixes are used to ensure curing in reasonable time and provide more heat to the base. They're generically called "high-early." Recommended slumps are usually different for high-early mixes. Pouring and finishing concrete in cold weather is grueling work. People doing it must be extra conscientious; it's easy for keeping hands warm to trump important details. Surface freezing must be avoided absolutely. Insulation or heat tents are needed; details depend on temperature, slab thickness, and mix. There are handbooks and tables for all of this. A paving foreman who knows their business will use them.

tl;dr is avoid winter pours like the plague. They can turn out all right, but the risk is significant.

All this is for slabs on grade. I can only imagine that shotcrete is harder. It would be interesting to know if the guy who said "they do this all winter long" has a pool and when it was poured

 

[JoyfulNoise]

… It would be interesting to know if the guy who said "they do this all winter long" has a pool and when it was poured

When he used the word “We” he meant the “royal We” as in, “I pay guys to do this all the time while I sit in my warm truck playing Wordle on my iPhone …”

 

[AQUA~HOLICS]

Shotcrete application is one of the most critical steps in the construction of the swimming pool.
Rebound is only one of many concerns that need to be looked at.
The delivery ticket has lots of info that needs to be confirmed, the dirt shell needs to be properly prepared to accept the Shotcrete, crew needs to be informed of what plaster is going to be installed so they can cut the edges properly and so on. As earlier said , you have taken on a lot of responsibility.

 

[FireDean]

I've never done shotcrete but lots of paving with conventional concrete. It's extra easy to create a future disaster when placing in freezing weather. The base cannot be frozen, so it must be heated until thawed all the way through before pour day. Many base materials should then be re-compacted. As has been mentioned, special mixes are used to ensure curing in reasonable time and provide more heat to the base. They're generically called "high-early." Recommended slumps are usually different for high-early mixes. Pouring and finishing concrete in cold weather is grueling work. People doing it must be extra conscientious; it's easy for keeping hands warm to trump important details. Surface freezing must be avoided like the plague. Insulation or heat tents are needed; details depend on temperature, slab thickness, and mix. There are handbooks and tables for all of this. A paving foreman who knows their business will use them.

tl;dr is avoid winter pours like the plague. They can turn out all right, but the risk is significant.

All this is for slabs on grade. I can only imagine that shotcrete is harder. It would be interesting to know if the guy who said "they do this all winter long" has a pool and when it was poured

Thankyou generessler...lots common sense to apply..

 

[FireDean]

Shotcrete application is one of the most critical steps in the construction of the swimming pool.
Rebound is only one of many concerns that need to be looked at.
The delivery ticket has lots of info that needs to be confirmed, the dirt shell needs to be properly prepared to accept the Shotcrete, crew needs to be informed of what plaster is going to be installed so they can cut the edges properly and so on. As earlier said , you have taken on a lot of responsibility.

Got it Aqua-holics....I advised my client that I thought we needed to wait till things warmed up...Clearly that is this groups concensus and I'm incredibly grateful for the collective expertise made available here.