Slab pour in cold weather with night freeze.

[EddieWalker]

Eddie,
If I am reading this correctly, you're saying the higher the concrete piles up on its self, the stronger the concrete will be.

But it reads in my mind just the opposite...the more slump the stronger the concrete.

People who don't know much about concrete might misunderstand.

Slump is an odd word, and I might be using it wrong. The way I look at it is like building a sand castle on the beach. You fill up the bucket with sand and flip it over. Really good slump is like a really good bucket of sand that holds it's shape. The more it collapse, or sinks, the worse it is.
Slump is measured by how much the concrete "slumps" after you fill a bucket and turn it over. The taller it remains, the better it is!

The very worse thing you can do is add so much water that it flows like soup. Some of the YouTube videos are really bad. The so called experts on there will either ignore how soupy it is when showing off their work, or they will say that they have added special chemicals to it so it's OK to have it so wet. I'm not aware of those chemicals, but it seems to me that it's better to not have to add anything to correct what you are doing wrong in the first place.

 

[EddieWalker]

Residential concrete contractors, you mean guys pouring driveways and walkways, and commercial concrete contractors, you mean construction companies ?

When a house is built, the General Contractor will hire a Concrete Crew to pour the concrete for the foundation. That same crew will also do the driveway and sidewalks, and any other concrete work. Most of them are "hacks" that will add as much water to the mix as the can to make it as easy as they can.

When a commercial building is built, there are engineers, teams of inspectors, architects and every other expert you can think of there making sure it's perfect. Rebar is tied, lifted, held in position and clean. I don't think welded wire is ever used in a commercial job. Same with highways and bridges. These are the "Pros" who know concrete inside and out. They are expensive, but when it's done, it doesn't crack, and it's there for all eternity.

The trick is finding a Contractor that does work for homes and farms that isn't a Hack, and understands the importance of doing it right. Sadly, most of the people who do this type of work do not even speak English, and they are rarely in the same city for a full year. In the last 20 years, I've never been able to hire the same Concrete Crew twice. They just move on and it's a search all over again to find a new crew.

 

[BlueKnife]

The taller it remains, the better it is!

It's not quite that simple. When pouring a wall, for example, if the slump is too high, the concrete won't fill out the wall properly, leaving air pockets. When doing flat work, it doesn't need to flow as easily, so the slump can be higher.

I'm not aware of those chemicals, but it seems to me that it's better to not have to add anything to correct what you are doing wrong in the first place.

Again, it's not that simple. "Doing it wrong" and pouring concrete in a situation where it needs to flow aren't necessarily the same thing.

It is certainly possible, and not uncommon, to add too much water to concrete, but just because a contractor has some water added in the truck doesn't automatically make him a hack. Sometimes more water is needed in order to do the job properly. Just out of curiosity, how much concrete work and what type have you done?

 

[EddieWalker]

I'm mostly a remodel and repair contractor. Most of my issues with concrete come from doing repairs related to issues caused by cracked slabs. I built a few spec houses, and I've done quite a few additions too. Probably the most common thing that I do in bathroom remodels is cut out the concrete to relocate drain lines. 100% of every house that I've done this in over the last several decades, that has wire instead of rebar, has the wire on the dirt, or the plastic, under the slab.

I've also done a fair amount of block work and agree that when filling them, the concrete needs more water in it to flow all the way to the bottom, and around the rebar in the block. But in that case, I'm not too concerned with it cracking once it cures. It's not really the same thing as pouring a slab for a building, or a driveway.

As you can tell, I'm not hiding my real name, or how to find me. One of the things that sends out red flags to me is people that are afraid to give their real names. Feel free to look up my Facebook page and search through my photo's if you want to find proof that I'm who I say I am.

I'm not a concrete contractor, and I'm aware that nothing is absolute. My comments on concrete work is directed at slab work. I understand that there are exceptions to everything, but in general, those who do poor work, tend to use those exemptions to justify what they are doing when they know they are cutting corners, and doing sloppy work.

The best example of this is when welded wire is used in a slab. It's very common on here for somebody to post pics of a slab being poured for a workshop. Their contractor told them that they will lift the wire as the spread it, and usually there is a picture of this happening when the pour begins. But then there are more pictures where it's obvious that they quite playing that game and they are walking on top of the wire. It's also obvious that the concrete is spreading on it's own, and more like soup then it should be.

My reason for dividing hacks from pros came to me last year when I was watching a YouTube video of a highway being poured. The rebar was amazing to see. It was perfect!!! That's really when it hit me how different concrete work is done where it's engineered and inspected multiple times, compared to what everyone gets when they are building a house or workshop.

 

[BlueKnife]

I've also done a fair amount of block work and agree that when filling them, the concrete needs more water in it to flow all the way to the bottom, and around the rebar in the block. But in that case, I'm not too concerned with it cracking once it cures.

I was talking about pouring a formed concrete wall, not just filling block cores, but the principle is similar. The difference is that you most certainly do need to be concerned with cracking once it's cured.

My reason for dividing hacks from pros came to me last year when I was watching a YouTube video of a highway being poured. The rebar was amazing to see. It was perfect!!! That's really when it hit me how different concrete work is done where it's engineered and inspected multiple times, compared to what everyone gets when they are building a house or workshop.

You're not wrong. Commercial jobs like that are under far more scrutiny than residential or agricultural jobs. What I'm getting at here though is that I think we need to be careful about making sort of blanket statements about contractors being "hacks" if they use things like re-mesh (the "wire" you reference). If a person wants to pay for a commercial level driveway, they can certainly do so. Their driveway will last a really long time and cost many times as much. The person who doesn't want to pay that much can hire a contractor who does good prep work (remove topsoil, put down proper aggregate, compact in lifts) and uses mesh. Their driveway will last a really long time and cost far less. Is there a higher chance that a crack will form in the second driveway? Yes. It's not likely, if the prep work was done right (no amount of rebar will prevent cracking if the prep work wasn't done correctly). Is it worth (potentially) many thousands of dollars more to not have that crack? That's up to the individual. For most, it isn't worth it. The contractor who is giving the client what they paid for is not automatically a hack, just because they used mesh or a superplasticizer (the "special chemicals" you mentioned). I've worked for several commercial concrete contractors (one was the lead concrete guy for several pro sports stadiums in the great lakes region) and they all used mesh for residential driveways.

What I don't want to see happen here is for a homeowner to read some posts on an internet forum and then try to tell a concrete contractor how to do their job.

 

[Renze]

Slump is measured by how much the concrete "slumps" after you fill a bucket and turn it over. The taller it remains, the better it is!

Not entirely. We did sometimes use "tamp-concrete" very dry to put in the V slots of cattle slats. We put them upside down and filled them with very dry concrete with lots of gravel in it. Then the next day we would use wetter concrete to make an enclosed floor, so the wet stuff would fill the pores of this "tamp concrete" that is stiff as bulls't when dumped.

When concrete is too dry and doesnt flow at all, you need to tamp it in place to get rid of pores: too dry concrete causes air inclusions, which is just as bad as dry cracks from soup concrete...

But i agree with you, when you dump a wheel barrow of concrete it should look like a dairy cow took a dump. Beef cow dumps are too stiff, and calf diarrhea is too wet.

The so called experts on there will either ignore how soupy it is when showing off their work, or they will say that they have added special chemicals to it so it's OK to have it so wet. I'm not aware of those chemicals, but it seems to me that it's better to not have to add anything to correct what you are doing wrong in the first place.

Calcium is added to bricklaying mortar so you can squish the stone to the correct seam height, without it floating away after stacking 6 or 7 layers of brick in a day. Ive never used in concrete. As a kid i once layd bricks in a slurry pit, just leaving the 2 parts gravel out of the 1-2-3 concrete i had mixed for the floor 2 weeks prior when the rest of the family was wheelbarrowing it into an existing pig barn being coverted from nursery to pregnant sow housing. Laying bricks without calcium wasnt a success, the mortar didnt spread nice when squished into place, it just came out the side instead of spreading through the seam nicely.

People too lazy to use a levelling tool would add water to make it easier. When you pour too wet, the water (with cement) runs off as soon as you dump the wheelbarrow.

Anyways, the cow dung metaphore is pretty spot on to allow a farmer to mix the right concrete

 

[bigtiller]

Video of how to measure slump

 

[EddieWalker]

Good video. That explains slump a lot better then I did!!!!

 

[MAX-24-Dean]

It's not quite that simple. When pouring a wall, for example, if the slump is too high, the concrete won't fill out the wall properly, leaving air pockets. When doing flat work, it doesn't need to flow as easily, so the slump can be higher.

Again, it's not that simple. "Doing it wrong" and pouring concrete in a situation where it needs to flow aren't necessarily the same thing.

It is certainly possible, and not uncommon, to add too much water to concrete, but just because a contractor has some water added in the truck doesn't automatically make him a hack. Sometimes more water is needed in order to do the job properly. Just out of curiosity, how much concrete work and what type have you done?

Most of the commercial high rise projects I worked on used plastizers (called self consolidating concrete) in the mix for columns and walls to get it to flow better. So again it comes down to engineering decisions or certified concrete professionals to make it all work and maintain the structural integrity because of thier knowledge base.

 

[Streetcar]

Slump is an odd word, and I might be using it wrong. The way I look at it is like building a sand castle on the beach. You fill up the bucket with sand and flip it over. Really good slump is like a really good bucket of sand that holds it's shape. The more it collapse, or sinks, the worse it is.
Slump is measured by how much the concrete "slumps" after you fill a bucket and turn it over. The taller it remains, the better it is!

The very worse thing you can do is add so much water that it flows like soup. Some of the YouTube videos are really bad. The so called experts on there will either ignore how soupy it is when showing off their work, or they will say that they have added special chemicals to it so it's OK to have it so wet. I'm not aware of those chemicals, but it seems to me that it's better to not have to add anything to correct what you are doing wrong in the first place.

Eddie
Superplasticizer will increase slump without lowering the strength of concrete. It is used on many bridge decks