Exposed Concrete Slab and Expansion/ Control Joints

[nirajbrisbane]

Hi all, my concreter has poured an Exposed Concrete Slab for me in my patio - 60 meters total. After finishing the job on Tuesday he says he will come back on Friday for the expansion joints because there will be chipping flying if he do too early using the saw cut method on the day or next day. So to avoid chipping from exposed gravel he says Friday is good.

Then he message me on Friday and says he will do it on Saturday, then again on Sat he message saying he had family thing he didn't know so he say he will do it on Monday. It will be day 6 on Monday.

I called him and he say he will do it in the afternoon as he has another job of concrete to be poured so he will come after that, he also offered me to come tomorrow first thing if I want (which is day 7 - Tuesday to Tuesday)

I told him clearly that it has to happen today (Monday - Day 6 of pouring) he say ok.

I am panicking if it is too late or on border line, I unfortunately paid him in full for the job on day he poured because I could see he did a good job, hard work and he gave me very good cash price.

I am not a concrete expert but learning from google and AI results, it says day 6 is still acceptable for the saw cut but no later then that. Is that right? I have not seen any cracks etc so far. and I am wetting concrete since poured every 2 hours as a wet curing to keep it moist (does it help or it goes against me?)

Day 1 when he poured, obviously I did not wet it for first 6 hours and then very slight spray on that evening.

Please let me know your expert views on this.

 

[Firebrick43]

If you don't cut them a few hours after power troweling, its too late. The next day is definitely too late. 6 days later is just plain stupid.

https://www.concrete.org/frequentlyaskedquestions.aspx?faqid=915#:~:text=Timing is critical, and cuts,conditions requiring cuts even sooner.

If someone tells you that it can be done later and its ok, they just want to go home and drink instead of cutting that day later.

 

[Sumboodie]

Usually done the day after.

 

[ConCretin]

Yea, probably too late to do much good now when it comes to controlling shrinkage cracks, which generally occur pretty early in the setting process but what does that mean? If you're lucky, it might not matter at all and the slab doesn't crack. Depending on the size and shape, some slabs are less likely to crack than others. Worst case you get a few visible surface shrinkage cracks. This is an aesthetic issue rather than a structural one. The slab has cracks either way.

Hopefully you kept mix water under control, which will limit shrinkage as will and your ongoing curing efforts. If you used fiber mesh, that will further limit the amount of cracking. If you installed steel reinforcing, the cracks shouldn't get too wide.

There is still a small chance that the slab could crack so cutting the joints late might be better than not at all. Your contractor definitely dropped the ball here so if you get cracking you can't live with, it's on him. It's almost impossible to achieve invisible repairs to shrinkage cracks so be prepared to live with them or fight for a new slab.

 

[nirajbrisbane]

Yea, probably too late to do much good now when it comes to controlling shrinkage cracks, which generally occur pretty early in the setting process but what does that mean? If you're lucky, it might not matter at all and the slab doesn't crack. Depending on the size and shape, some slabs are less likely to crack than others. Worst case you get a few visible surface shrinkage cracks. This is an aesthetic issue rather than a structural one. The slab has cracks either way.

Hopefully you kept mix water under control, which will limit shrinkage as will and your ongoing curing efforts. If you used fiber mesh, that will further limit the amount of cracking. If you installed steel reinforcing, the cracks shouldn't get too wide.

There is still a small chance that the slab could crack so cutting the joints late might be better than not at all. Your contractor definitely dropped the ball here so if you get cracking you can't live with, it's on him. It's almost impossible to achieve invisible repairs to shrinkage cracks so be prepared to live with them or fight for a new slab.

It was a cash job, no warranty I think but I see no cracks so far. Due to me being proactive and watering the slab every 1.5 to 2 hours whole 6 days. Looks good so far. He is hopefully coming today. I read a blog that 6 days is still ok for the exposed concrete slab, not 7 days on wards.

I am keeping fingers crossed. If this is just hairline cracking, I can live with it. just hoping for it to do the job structurally strong. They used Rio Mesh and 25 mpa.

Knowing Rio Mesh, 25 MPA, and constant watering for wet curing, what you say? if he do the joint cut today. should be ok?

 

[nirajbrisbane]

If you don't cut them a few hours after power troweling, its too late. The next day is definitely too late. 6 days later is just plain stupid.

https://www.concrete.org/frequentlyaskedquestions.aspx?faqid=915#:~:text=Timing is critical, and cuts,conditions requiring cuts even sooner.

If someone tells you that it can be done later and its ok, they just want to go home and drink instead of cutting that day later.

I got it. I think I should have not pay him and ask him to do it but he says chipping issue if done same day.

 

[nirajbrisbane]

Yea, probably too late to do much good now when it comes to controlling shrinkage cracks, which generally occur pretty early in the setting process but what does that mean? If you're lucky, it might not matter at all and the slab doesn't crack. Depending on the size and shape, some slabs are less likely to crack than others. Worst case you get a few visible surface shrinkage cracks. This is an aesthetic issue rather than a structural one. The slab has cracks either way.

Hopefully you kept mix water under control, which will limit shrinkage as will and your ongoing curing efforts. If you used fiber mesh, that will further limit the amount of cracking. If you installed steel reinforcing, the cracks shouldn't get too wide.

There is still a small chance that the slab could crack so cutting the joints late might be better than not at all. Your contractor definitely dropped the ball here so if you get cracking you can't live with, it's on him. It's almost impossible to achieve invisible repairs to shrinkage cracks so be prepared to live with them or fight for a new slab.

He used Reo Mesh and 25 MPA exposed concrete and washed the slurry same day with water hose and brush.

 

[Firebrick43]

I got it. I think I should have not pay him and ask him to do it but he says chipping issue if done same day.

There is no chipping issue I have ever had when cutting concrete with a stihl gas saw. He was just making BS excuses so he didn't have to wait on site.

The article I listed is the American concrete institute, the premier source on concrete, probably in the world.

On the interstates, they cut just an hour behind the screed when its warm out. Of course with them the saws are bridge saws that straddle the lane so no one or thing is actually on the concrete.

 

[nirajbrisbane]

There is no chipping issue I have ever had when cutting concrete with a stihl gas saw. He was just making BS excuses so he didn't have to wait on site.

The article I listed is the American concrete institute, the premier source on concrete, probably in the world.

On the interstates, they cut just an hour behind the screed when its warm out. Of course with them the saws are bridge saws that straddle the lane so no one or thing is actually on the concrete.

Thanks mate I agree with BS. I googled and it says up to 6 days is still OK to cut So I did not push him for same day or next day where he told me he will do it on Friday which is day 3 and I keep it moist all the time and it was mild sun.

He is a small concrete installer and doesn't have machine like you showing in the video.

Okay, what's the worst that could happen if he cuts today (day 6)? Knowing it had Rio Bars, 25 mpa, and I kept it moist most of the time to get wet curing.

Is it a hairline crack in worst case or affects the overall structure? I am surely not happy with the guy but he did very good cash price for me. Lets say he did 8500 compare to 10500 Cash quotes. Some guys even gave me 12500 or 13500 quotes. I checked the material itself cost around 5.5K, rest 2.5 k is labour for 3 people for 2 full day work. Thats pretty cheap but they give me this stress in return.

 

[nirajbrisbane]

If you don't cut them a few hours after power troweling, its too late. The next day is definitely too late. 6 days later is just plain stupid.

https://www.concrete.org/frequentlyaskedquestions.aspx?faqid=915#:~:text=Timing is critical, and cuts,conditions requiring cuts even sooner.

If someone tells you that it can be done later and its ok, they just want to go home and drink instead of cutting that day later.

Got it thanks. Whats the worse can happen then? is it just hairline cracks that may appear over time
or structural issue too?

 

[Firebrick43]

Got it thanks. Whats the worse can happen then? is it just hairline cracks that may appear over time
or structural issue too?

Did he use chairs to hold the wire up? Or throw it on the ground and try to pull it up with a hook while standing on it?

What type and size of sub base? How deep of sub base? Did he use an actually compactor to compact it in lifts appropriate for the size of compactor?

What was the slump of the concrete? Did he add water to it?

 

[nirajbrisbane]

Keeping it wet curing, so far no cracks.

 

[nirajbrisbane]

Did he use chairs to hold the wire up? Or throw it on the ground and try to pull it up with a hook while standing on it?

What type and size of sub base? How deep of sub base? Did he use an actually compactor to compact it in lifts appropriate for the size of compactor?

What was the slump of the concrete? Did he add water to it?

All those good questions mate, thanks. Yes he used the chairs to support the mesh lifted, the ground was prep worked 3 months ago and then there was rain so the ground was compacted I think that way, however to prep it further he did use very fine grawel dirt mix I don't know what we call it but it was like sand, cement and very fine gravel mix and they watered it and then chairs, mesh on top. After few hours I check that started getting firm so I belive there must be some sort of cement in it to hold the gravel dirt and soil and this was day before pouring concrete. No compactor was used to compact these fine gravel but obviously they walked on it while preparing it.

What type and size of sub base? means? you mean what I explained above?

On top of this, it is 100 mm Concrete Slab sitting on those gravel dir mix I explained above. Hope this help to clarify further.

 

[Firebrick43]

Sub base is the gravel/stone.

While concrete can be designed to span voids with proper thickness, rebar, and or grade beams, the biggest factor if a slab settles and moves after it cracks causing uneven level, or even cause the slab to break up.

Wold class is 1” and smaller clean crushed stone 3 times the thickness of the slab that is well packed by equipment.

As the compaction, thickness of the sub base, and type of sub base gets less optimal the chances of voids happening under the slab increase and the possibility of undesired cracking/settling.

This is not to say that some undisturbed soils that are very well drained can’t support the slab, as some can.

But in every case I have removed slabs that are excessively broke up and uneven there is little to no sub base under it and piss poor prep. Almost always the wire is also on the bottom where it should not be because they didn’t put it on chairs and try to lift it while standing on it.

 

[nirajbrisbane]

Sub base is the gravel/stone.

While concrete can be designed to span voids with proper thickness, rebar, and or grade beams, the biggest factor if a slab settles and moves after it cracks causing uneven level, or even cause the slab to break up.

Wold class is 1” and smaller clean crushed stone 3 times the thickness of the slab that is well packed by equipment.

As the compaction, thickness of the sub base, and type of sub base gets less optimal the chances of voids happening under the slab increase and the possibility of undesired cracking/settling.

This is not to say that some undisturbed soils that are very well drained can’t support the slab, as some can.

But in every case I have removed slabs that are excessively broke up and uneven there is little to no sub base under it and piss poor prep. Almost always the wire is also on the bottom where it should not be because they didn’t put it on chairs and try to lift it while standing on it.

What a great explanation mate, yes so they used crushed stone mix probably equal thick as slab (100 mm) and they watered it down, I feel like it had some cement type material mixed to bond it well overnight before they pour concrete.

They did not compact it with machine, but with hand tools they leveled it by tapping it down as they level It and then they watered it well and then they put the chairs and then the Rio Mesh. so Rio was sitting somewhere in between the total slab may be more towards the bottom 25 mm out of 100 mm.

He did come today (Day 7) and did the saw cutting every 3 meters about 20 mm deep, and I see NO crack so far anywhere, not even hair line.

I have been regularly wetting it since day 1 evening (4 hours after the handover of the slab (poured, washed the slurry and tidy the site). It was poured just before mid day and I started watering (sprinkled) around 6 PM.

I think I did well by wetting it regularly, from next day I have done about 10 time spraying during the whole day. If no cracks until now, and saw cut done every 3 meters, Am I good to go?