Concrete disaster

[River Runner]

Good Day,

After missing out on concrete last year due to supply issues and weather I finally got my 40x64 shop floor poured a week ago. While I am not a dedicated concrete guy I have poured dozens of slabs and they usually turn out pretty decent but maybe not perfect. Because this was a big pour I had two other contractors and their crew with me along with a 35 year finisher to run the power trowel. I was feeling very confident with all the man power and experience I had at my disposal.

Everything was great until it wasn't. It was 10 am and 40 degrees outside and we were using a 6 bag mix with 3/8" aggregate. I informed the batch plant that we would be pumping the mud because we didn't think a truck could fit into the shop. The mix was as requested by the pumper.

We had immediate clogging right away and spent the first hour breaking hoses and trying to deal with the mud not pumping. After an hour of only pumping about a yard I rejected the truck and told the pumper to clean up. At this point the 2nd truck was already on site. I thought about calling the whole thing off but I knew that it would be months or longer before I could get scheduled again. I noticed that the 2nd truck was shorter than the other and we were able to back the truck in with about 2" of clearance, so we just started raking like dogs as we had the man power. From that point on the job went smooth and we had all 5 trucks dumped in a few hours. The batch plant is only about 1/2 a mile away so waiting between trucks was minimal.

After we had let the mud set up we started working it. I noticed right away that it was incredibly sticky. So sticky that when I went out on my skates I would get stuck and the cream would tear from the surface. The mud also never really had any bleed water, which I have not seen before. So, we busted out the power trowel and every time we tried to spin the blades it would kill the engine because it was so sticky. We finally got it going and didn't dare turn it off out of fear we couldn't get it moving again.

The mud that the 2nd truck dumped was not setting so we had to work around it. After a while I started to notice blistering on the surface on the last pass with the trowel. My finisher said it was the worst mud he has seen in 35 years of finishing concrete and that it was loaded with air. The mud from the 2nd truck was still not setting after finishing all the rest. Eventually we called it at 1 am because all it would do is smear across the surface of the adjacent set concrete, basically looking like troweled drywall mud with a skipped trowel finish.

I know that blistering occurs when you finish it too soon while its still bleeding air and water but I can tell you that was not the case. The surface was getting so stiff that we couldn't even mag it, there was so little cream and again, it was incredibly sticky. Its been a little over a week and the surface *****. Blisters all over the slab and a wavy surface in the area that wouldn't set up.

I have since spoken to the batch plant and expressed my disapproval with regards to the mud. They have however already charged my credit card and I also have the bill from the pumper. I am hoping to at best get my money back from them for the mud. It was record high cost, $229 a yard! I have a $4,000 40' trench drain in the shop and the slab is 6" thick with #4 rebar.

I'm not sure where to go from here as I have never had a pour go bad. I can chip out the blisters by smacking them with a hammer leaving a 1/8" - 1/4" deep crater. I think my only option at this point is to grind the whole surface down 1/4" and resurface? Because of my drain I can't really take off material without adding something. The floor will be subject to all sorts of abuse ranging from copious amounts of water from a bridge saw, sparks from welding, heavy traffic from a skid steer and fluids from vehicles, its my do all shop.

I am thinking I can gain the 1/4" height back by tiling the whole shop with a porcelain tile. I am looking for ideas on ways to polish the expensive turd surface that I will have. I can't really do a full overlay as it will mess up my header heights for the doors. The shop has block walls so I am not about to change the header height.
I've also looked at the Supratiles and they seem like a good option but may not hold up to sparks or molten metal from cutting and welding?

All the options seem to be about as expensive as the concrete itself was but the thought of tearing out 46 yards of concrete with rebar seems awful. Hopefully I can get Knife River to own up to crappy mud and share some expense on a repair option. Sorry for the novel but I don't have experience resurfacing a concrete floor subject to shop use. Thanks!

 

[LegacyIndustrial]

Grinding 1/4" is a herculean job. This would be a "grinding forever" proposition without full-size 460V 3P polisher/grinders.
Grind off the weakness the best that you can, fill the craters with an Epoxy Patch Material , we have one, FIVETON EPOXY PATCH.

Once ground, coat with a Full Flake System, will help to hide the surface imperfections.

Cover your welding/torching areas with a welding blanket as needed.

Good luck and sorry to hear of your issues.

 

[LXCam]

Man that’s a sad story. If you do decide to go with tile you’ll need a scrabbler to get that much material gone.

 

[mepstein]

Call your credit card company and file a dispute. Credit card companies protect the buyer. At least talk to them and go over options.

 

[River Runner]

Good thought on calling the credit card company.

The surface feels pretty weak. I don’t feel like it would take much to grind it down with a scarifier.

 

[ConCretin]

First off, this ***** River Runner. Sorry you are having to deal with this.

In my experience, defective ready mix is rare. Modern QC, batching methods and equipment are pretty dependable but there is always room for human error.

impossible to diagnose what happened based on the available information but it seems clear there was something wrong with the mix in one or more of the loads. Something was going on with the load that didn't set and while stickiness is subjective, it could be an indication of deeper problems. Stickiness generally results when there isn't enough water relative to other constituents

What admixtures were used? water reducers? retarder? air entrainment?

Was there slag or fly ash in the mix?

What was the approximate slump the concrete was placed at? Was water added to bring back that second load?

Was a vapor barrier installed under the slab?

I'm not thrilled with the 3/8 stone due to shrinkage issues but it probably didn't contribute directly to the finishing issues. While we're on the subject, are there any visible shrinkage cracks on the surface or in the bottom of control joints?

Given the costs involved, it might be worthwhile to engage a materials testing lab to come out and do an evaluation. There are a number of tests that can be performed from compressive strength all the way to petrographic analysis that can determine the material makeup of the concrete. This could help determine the cause of the problem and whether the slab is worth repairing. You might also get some ammunition for a case against the supplier if it comes to that.

I'll just add that the pic you posted doesn't look like de-lamination to me. You correctly described the cause of de-lamination but it generally manifests as thin sheets of surface concrete that come up, not large divots. That just looks like a chunk of unmixed cement.

In any case, good luck. I hope it works out and you can get on with your new shop.

 

[thebmrust]

Get statements from the whole crew asap. Details diminish over time.

 

[River Runner]

I was able to talk to the regional manager at knife River today. She said that they went out and looked at the job and stated in their opinion it was a combination of issues.

They feel that we got on the mud to soon causing the blistering. There was air in the mix and that it delayed the bleeding process.

However, they admitted that the driver of the 2nd truck gave the load a heavy dose of Delvo and that mistake was on them. As of now they are agreeing to cut out that area and have it redone.

I am not seeing any unusual cracking. As for the 3/8” aggregate it was required by the pumper that didn’t even work.

I did a small 5 yard pour this morning by myself for a customer and it was great, I kept thinking how much easier the mud was to finish and move on. I relayed this information to her.

I felt as though she was truly interesting in helping but reliant upon the direct advice and decision making of her boss. Today I’m supposed to have a call with him.

They were no other additives to the mix. I keep thinking that perhaps it was either given a big dose of air or that perhaps the aggregate wasn’t washed properly. I have a hard time believing we got on it too soon, it was incredibly sticky.

 

[River Runner]

Btw, there was no vapor barrier, it was poured directly on compacted base. I called for a 6” slump.

The picture I posted is of a surface blister that I chipped out with a hammer. The area is crusty and very loose. I did a chain drag and everything sounds ok. The blistering is throughout with some areas of great concentration and more sporadic in others.

In hindsight if I had known we could have backed in the trucks I would have called for standard aggregate and no air, but the mix was tailored for pumping.

 

[ConCretin]

You are obviously pretty knowledgable about concrete and I don't want to armchair quarterback here but I'll share a couple thoughts.

The excess retarder in the second truck seems to make sense. The driver saw you fighting with the pump and tried to save the load but human error reared it's ugly head and he added too much. It's not ideal but at least the plant is stepping up to address that issue. A partial slab replacement should be serviceable and hopefully won't be too noticeable.

Honestly the blistering makes sense if the concrete was air entrained. I know people do it all the time but we never use air entrained concrete on an interior steel troweled finish. As you correctly mentioned, air and bleed water can pool under the surface creating voids and de-lamination of the surface layer of concrete. This most often occurs when steel blades are used too soon in hot or windy conditions sealing the surface and trapping air and bleed water.

Since the primary purpose of air entrainment is to help the concrete resist freeze/thaw damage from moisture, I don't believe it's worth the risk to use it on interior slabs where it won't be exposed to weather. It's best left to exterior, broom finished concrete. We had a near catastrophe on a hundred thousand square feet of parking garage a while back and I still haven't recovered. lol.

I struggled with this issue when I built the Concrete Underground since my interior slabs would be exposed for an entire Maine winter. Since we were placing in warmer weather I was very concerned about de-lamination. In the end I opted not to use air and the slabs survived the winter just fine.

Since the purpose of dragging a chain over the slab is to locate areas of de-lamination, yours must be relatively minor if you aren't hearing changes in tone as the chain passes over.

In fairness to you, I think you would have had an excellent chance of avoiding de-lamination if not for other issues. No vapor barrier and temps in the 40's should have been a recipe for success.

With regard to the stickiness, something still isn't adding up. If you asked the plant for a 6' slump, you almost certainly would have gotten a water reducer. If you asked the driver, you would have got more water. If a 6" slump was achieved with water, you should have seen bleed water. If chemical water reducer was used, it's not that surprising you didn't unless you were on the slab with steel blades before it appeared.

I don't recall if you mentioned the psi of the concrete but presumably 3500 or 4000? Either mix should have enough cement to avoid stickiness. It makes me wonder if a water reducer was used and the mix suffered from a lack of actual mix water. Purely speculation on my part but maybe something to look into.

Sorry for the long winded post but I'm feeling your pain. You don't get a do-over with a concrete slab and you have to live with it for a long time.

 

[yelchevelle]

Like you, I have done a few pours. Not everyday, but enough to be comfortable with it. What you described is exactly why I hate concrete. I have had two jobs that went bad, and it had everything to do with what came off the truck in my opinion. I personally think that they were hot loads. Completely different companies and markets in both situations. In my case , the concrete was kicking before we could get it out of the truck good. Both times we were able to get it done but it about killed us. Unlike you, finish was not that important because of what the concrete was used for.

If you are going to coat or tile it, I might would see what it would cost to have core samples done for it. At least see what you got

 

[PCustoms]

If you are going to coat or tile it, I might would see what it would cost to have core samples done for it. At least see what you got

Question for the pros: say the OP cores a few samples and tests at 2,000psi when he paid for 4k.

Then what?

 

[yelchevelle]

Question for the pros: say the OP cores a few samples and tests at 2,000psi when he paid for 4k.

Then what?

If it were mine, I would have a discussion with the concrete plant. I feel like they would owe him a slab. I think in the court of law, they should lose. I have little faith when lawyers are involved is why I said should. On commercial jobs where they know they are going to be tested, and they seem to bring their A game because they know they own it if it doesn’t test. Typically get a lot higher psi than you are buying too. I think that concrete plants are pretty relaxed on residential because they don’t expect to be tested.

I have a friend with a mix on site concrete company. They had an “experienced” new driver come out and do a night pour. I think total they had 6-8 trucks, with the new guy pouring 2. Calibration on the new guys truck was off, and he didn’t think anything about having most of his Portland at the end of each truck. They could not even get like 500 psi on the initial break. My friend replaced it all. It wasn’t worth the bad reputation to fight over only fixing the bad sections.

For those who don’t know, when they test commercially on the front end they take multiple samples and they break them at like 7, 14, and 30 days. I can’t remember exactly how often, but I know they do multiple breaks so they can see where they are. Usually 30 days is considered fully cured, even though technically concrete continues curing for a really long time, if not forever.

 

[River Runner]

Thanks for all the input. There was no water reducer and the driver added water to achieve a 6” slump. Concrete was 4,000 psi.

 

[ConCretin]

Question for the pros: say the OP cores a few samples and tests at 2,000psi when he paid for 4k.

Then what?

Assuming the concrete was placed at the specified slump, the ready mix companies I deal with would remove and replace the slab without question. With that said, I've been doing this on a fairly large scale for 30+ years and I've never seen it actually happen. We've had the occasional low break but ACI allows for some modest deviation and the concrete is eventually accepted.

 

[ConCretin]

Thanks for all the input. There was no water reducer and the driver added water to achieve a 6” slump. Concrete was 4,000 psi.

Adding mix water to get the slump that high isn't ideal but I don't think it lead to your issues and doesn't solve the stickiness mystery.

I guess it comes down to whether the slab is serviceable and whether the ready mix supplier is responsible if it isn't. The answer to both questions can only be answered by a testing lab. It would probably run into the thousand of dollars but if there is something fundamentally wrong with the concrete, you will deal with it down the road. Best of luck and please let us know what happens.

 

[River Runner]

I met with Knife River today. They have agreed to remove and replace one side of the shop that had a truck what was overdosed with Delvo. This side has a trench drain running down the middle of it, so they would also replace the drain. As far as the rest of the floor they are standing by their decision to not do anything for it as they are convinced that I got on it too early. Its understandable that we both have our opinion on that issue and since they weren't there its essentially a he said she said situation. I don't really think that testing and litigation would be worth it for $6,000 in material and a weeks worth of work for me to redo.


The other option that was discussed was that they don't remove any concrete and have a specialized company come in and grind and patch the floor as necessary and provide an epoxy coating over the whole shop. They said they need to do some due diligence on it first.

I have broken this down to essentially 3 options in my mind....

1. They replace half the floor and I replace the other half
2. They replace half the floor and place it about 1/2" higher than the other side. I then prep the surface and put down a self leveler of sorts on the other side. I'll have a mismatched floor color but I could potentially put down epoxy or a different floor covering at a future date.
3. All the concrete stays and a company comes in that specializes in concrete repair and epoxy coating and does the whole floor on Knife River's dime. This is TBD. My only concern is cold joints from the truck with Delvo.

When I asked about he stickiness of the mud they had no explanation for it and said that concrete varies on any given day due to the weather. They did state that the mud had about 6% air entrainment. In my opinion, this is the root of my problem. I think that if it had a broomed finish I wouldn't have had the blisters. The stickiness of the mud made it near impossible for us to get a good finish, it just wasn't going to happen.

The pumper is sticking with its guns on saying the mud was poor quality and is still charging me for the pumper at a reduced cost. Knife River is sticking with its opinion that it was pumper error and that they were necking it down too much.

 

[ConCretin]

It seems as though Knife River is being reasonable. I wouldn't expect any more from most suppliers unless there was proof that the concrete was defective, which generally involves compressive strength. It's a lot more complicated to assign blame for surface defects.

I think all of your options are workable. I wouldn't be too concerned about the cold joints. It's mostly an aesthetic issue. There is plenty of bond plus the rebar to hold it all together. I'd just encourage you to think about what you really want for your floor. Don't let frustration or impatience lead to a decision you'll regret. If you wanted a nice durable exposed concrete floor rather than epoxy, go with option 1.

If you don't mind one more question. Everyone seems to be in agreement that the air entrainment is a major contributor to the de-lamination. It's an admixture that needs to be requested. You don't seem happy it was in there. Who ordered it?

 

[River Runner]

LLWillysfan,

Thanks for the input. I had no original intention of a surface other than a polished concrete but I'm also open to an epoxy. My only concern about the epoxy was welding and cutting plus its expensive if I had to pay for it. My wife says to just put down a welding blanket.

I did not request air, they just put it in. Because of our climate here they said everything gets air unless we ask for it to not be added. That is an educational error on my part. I've ordered dozens of times from the local batch plant and I never had that conversation. The dispatcher never asked if I wanted it or not. I'm a bit frustrated about that. I assumed that I was not getting air entrainment.

 

[River Runner]

I got a quote on supra tiles delivered to the shop. Its just shy of $17k for 6.5mm with adhesive and edging. I am also waiting on quotes for a full bodied porcelain tile. I think that the price range will be very similar between the two. I'm inclined to think a tiled floor would hold up better over time to an epoxy but I'm not very experienced with either setup for a shop floor.

 

[LXCam]

Epoxy coatings are great and can last with the following exceptions. No welding and or heavy grinding. Dropping heavy loads and or dragging anything with an edge. The most critical aspect is the condition of the substrate and in your case you didn’t install a moisture barrier all though this can be mitigated with the correct primer. And more importantly the chance of de lamination of the substrate which in your case may be the a major issue. Personally if it were me doing a coating or tile, I’d scrabble the surface to eliminate that potential.

 

[ConCretin]

I did not request air, they just put it in. Because of our climate here they said everything gets air unless we ask for it to not be added. That is an educational error on my part. I've ordered dozens of times from the local batch plant and I never had that conversation. The dispatcher never asked if I wanted it or not. I'm a bit frustrated about that. I assumed that I was not getting air entrainment

Quite frankly, that's stunning. I'm in Maine, which I suspect has worse winters than Idaho and our suppliers would never presume to add air entrainment admixture unless specifically requested. I'll have to remember this if I ever do some concrete in your neck of the woods.

 

[Armorpoxy]

Hi if you can get the slab repaired to your liking with re-pour, grinding or scarifying (they are very different processes) you may want to consider coating the floor with our Ballistix Coating System which gives the look of polished concrete but will protect the floor from fluids, chemicals, etc which polished concrete won't, hence why it's not used in shop environments. The Ballistix gives the best of both worlds at 1/4 of the work and cost.
Contact us directly at below, and search for some of our prior Ballistix postings for more info.

 

[River Runner]

Due to the insane backlog of contractors and my need to get this done so that I can move my CNC inside, Knife River has asked if I would take a refund on the concrete and leave it as is and I can do with it as I please. I have decided that this option will work for me. Best case scenario is 3 months till a crew could do the work and I just don't have that much time with snow flying in October most years.

So I decided I will rent a large grinder and see what happens. I'm hoping I can clean things up and then go around and patch the bad areas. I did another chain drag and I don't feel that the whole surface will delaminate but just the blisters. Then I have to decide if I want to tile the floor or do a roll on coating of sorts. I'm inclined to do tile but it sure is expensive, most tile is around $4-5 a sf. If I can find a tile for $2.50 a square foot that would be great. Ideally I don't spend more than $10k as my concrete refund will be about that amount plus a bunch of work.

 

[River Runner]

I started the grinding process this weekend. Its been a chore. I rented a dual disc EDCO unit with the Dyma Serts. Its working but is very slow and messy. The area that was dosed with Delvo is by far the worse and I will not be able to get it flat as the highs and lows are too extreme. This are is also sloping to my trench drain. Any ideas or products to use as a screed layer? If the floor wasn't sloping to the drain I'd use a self leveler but I don't think it will work in my case, although the slope is very minimal at about 1/8". I've considered losing my slope to the drain and just pouring it level and raising the grates to match the new height.