Sandy concrete what to do for Epoxy?

[kyles974]

Sandy concrete what to do for Epoxy? Need help ASAP!

I had a new slab poured a little over a month ago. I acid etched it a few days ago. (metal building comming Tuesday, so I wanted to etch prior to)

Any how, I noticed in areas, there is alot of sand on the suface. If I take my fingers and rub, the sand comes loose. I'm thinking that I will have to take a sander or a wire wheel to the surface prior to epoxy to take any loose sand of the top???

The 1st pic is a close up of the surface.

The 2nd pic is where I took quarter and scraped the surface and you can see where some sand came loose. (left and right was scraped)(not a good pic but you can get the idea of what I mean)

The 3rd pic is where a hole appeared. My concrete guy is comming out Tuesday to look at it. It looks like something didn't get mixed right from the truck? Anyone ever seen this before????
I'm not worried about the hole, easy fix for the concrete guy, but it does mke me concerned for other areas this may have hppend that I can not see at this time?

(I'm more worried about the sandy surface and the prep prior to epoxy?)

Also, I live in Florida, so maybe they use more sand here in the mix?(stupid thought?)

 

[cowboy73]

Hate to tell you this, but that slab is toast. It will never be able hold epoxy and it's way too soft to hold a steel building. If you created that hole with a quarter, you have a big problem. It's going to have to ripped up and redone. Your concrete guy hopefully will make it right.

 

[kyles974]

Hate to tell you this, but that slab is toast. It will never be able hold epoxy and it's way too soft to hold a steel building. If you created that hole with a quarter, you have a big problem. It's going to have to ripped up and redone. Your concrete guy hopefully will make it right.

You did not understand me.

First I stated, a "metal building" and NOT a steel building.

Second, I didn't say I caused the hole from a quarter. Read agin there sir.

Also, if you know why the concrete will not hold epoxy, please explain, instead of saying what you did. Your comment does me or anyone else that reads this in the future NO help, please, don't take this the wrong way, I'm very frustrated just looking for help.
Thank you.

 

[jhelrey]

Concrete seems like it was not mixed right and seems awful soft. I don't know that epoxy will hold.

 

[kyles974]

I've been doing a little searching on the net. I have found that this would or can be caused from to much water in the mix.

Hopefully, Monday (business day) someone(s) with expertise on this matter can help me?

 

[ConCretin]

Sorry but it is unlikely that anyone on here is going to be able to definitively say what might be wrong with your slab from a few photos.

I wouldn't invest in am expensive epoxy floor until I had an expert evaluation of the slab. The hole in particular is very odd. It could be something isolated and simple such as a chunk of unmixed aggregate or something more serious.

It wouldn't be cheap but a testing lab could do a spectroscopic analysis of your surface to determine it's potential durability. Good luck.

 

[kyles974]

Sorry but it is unlikely that anyone on here is going to be able to definitively say what might be wrong with your slab from a few photos.

I understand that, but
you would be suprised.

I wouldn't invest in am expensive epoxy floor until I had an expert evaluation of the slab. The hole in particular is very odd. It could be something isolated and simple such as a chunk of unmixed aggregate or something more serious.

Ya, no kidding. I was just about to order up the epoxy. (going to put that on hold for a few)

I just emailed my concrete guy and told him I will be calling him in the morning. (didn't want to call him on Sunday) But need him out here Monday. In case I need to put the delvery date on the metal building on hold.

Concrete seems like it was not mixed right and seems awful soft. I don't know that epoxy will hold.

You are right about being soft:**********
I just went outside and tried something. (I know this maybe a bad idea)
but I tried hitting the concrete with a light to medium hit with the hammer.

Well, it put a dent into the concrete.

I know there are alot of factors that can be here, weather, temp., etc., for curing, but after 30+ days, I don't think hitting it with a hammer light to a medium hit should cause a dent???

 

[LegacyIndustrial]

Kyle:
Absolutely, too much water will make it sandy.
Normally I would say go ahead and grind it. However, that hole is troubling.
You need to tap that floor and unearth all the voids and make a judgement call.

If it's just here or there you may be able to repair yourself.
However, if it's everywhere you may have structural issues.

Glad to hear you have the contractor coming back to look at it with you.

 

[kyles974]

Glad to hear you have the contractor coming back to look at it with you.

I've like this guy (my concrete guy) from the first few minutes on the phone with him. Very professional. BUT, we will see. This is when a business in the "service business" succeeds or fails.

 

[Edger]

Kyle, he might sound professional, but that is far from a professional finish, it appears there was too much water and also very poor mixing.

The hardness of concrete depends on the water to cement ratio - softer concrete has almost twice the water of very hard concrete. If a contractor adds more water to make it flow easier when laying he will end up with a softer mix which looks like what you have. Certainly the top surface has lost its protective paste and strength.

Epoxy will adhere to it very well because it soaks into the surface so no trouble with adhesion, however the epoxy will not last because it will be stuck to soft concrete and you will find very quickly that you have big bubbles under the epoxy where there is any traffic on it. If you break those bubbles the underside of the epoxy will have a generous layer of concrete stuck to it, but the concrete will have separated from the slab.

You could try grinding it to the stone aggregate and applying a concrete hardener before epoxy, but it may not harden sufficiently, it is an unknown because nobody can tell without expensive testing how hard it is now. Soft concrete also cracks very readily with any ground movement so it will very likely develop cracks that are wider than "hairline".

All this means that if the slab surface is restored with processes and products the rest of the slab will probably crack anyway. These are just guesses based on experience, but it gives you some ideas.

 

[nehog]

You are right about being soft:**********
I just went outside and tried something. (I know this maybe a bad idea)
but I tried hitting the concrete with a light to medium hit with the hammer.

Well, it put a dent into the concrete.

I know there are alot of factors that can be here, weather, temp., etc., for curing, but after 30+ days, I don't think hitting it with a hammer light to a medium hit should cause a dent???

Hammer should have bounced off the concrete, with (perhaps) a chip. Dents are not good.

I wonder if they used beach sand in the mix, or just way too much sand. Was it a ready mix truck, or did they mix it on site?

 

[dcs Inc]

I think Florida uses crushed shell for sand. If the surface was blessed (with water) at time of finishing, this could be ground down to a more stable surface.... and should be. If they added too much water to the entire mix at time of pour then it can cause a weak slab through out. Find the supplier and request a batch ticket for that job. That will tell you the mix design and how much water was ordered in the mix and how much was added at the job. This looks as if it was poured on a wet substrate in regards to the pic showing the hole. Looks like the base material was squished up by a boot when pouring, meaning a really wet sub grade when the concrete was placed. There could be a bunch of areas like that. Also, if the sub grade was wet and they drove the concrete truck onto it, that could have left huge ruts that the concrete crew need to regrade as the truck backed out of the pouring area. This isn't normally not a bad thing if they regraded and compacted before pouring over it.

If you were not around when this was placed, pull up a weather history a couple days before and during the day of pour. A soft surface does not mean the concrete is not salvageable. I would demand a core sample done by an independent. It's all he said, she said until the facts are in. gene ec-Indy

 

[kyles974]

Edger

Thank you, all what you said makes sence.

I wonder if putting a "sealer" down prior to an epoxy would help prevent this?


nehog
it was a ready mix truck


dcs Inc
I was there when poured. No, the truck didnt drive on the area being poured.



I just got off the phone with my concrete guy. He will be comming out later today. He also will make the concrete company have someone come out.

One thing my guy said was they might have put fly ash in the mix. This can cause a slower time for curing. (?)

I thank you all for your replies. I will let you know what he says later tonight. If they refuse to get the oncrete tested for hardness, does anyone know how much this can cost me?

 

[Edger]

Hi Kyles,

A sealer will not work for the same reasons as epoxy. I am not an expert in concrete, but I thought fly ash was a good thing in it and that most concrete had it. See http://www.flyash.com/flyashconcrete.asp

 

[ConCretin]

Fly ash is a cementious material that replaces a portion of Portland cement. It will retard set times early in the process but by 28 days the concrete will have 'caught up'

To be honest, I think some of the guys may be jumping to conclusions here. Granted the hole is odd but there is nothing in the pictures or your hammer test that definitively proves anything about water content or concrete strength.

If you were there during the placement, you would have seen excessive slump or water added during finishing. What do you remember seeing?

I would ask for an in-situ test for concrete strength such as a Windsor probe. If the compressive strength is there and you didn't observe any major issues, you may be fine.

The acid etching you did removed some of the concrete paste that held the fine aggregate (sand) together. I'm not shocked that you can dislodge some of the sand with the sharp edge of a quarter.

 

[Edger]

The acid etching you did removed some of the concrete paste that held the fine aggregate (sand) together. I'm not shocked that you can dislodge some of the sand with the sharp edge of a quarter.

Hi Willysfan,

On the forums, most people have trouble getting any profile at all with acid etching and some do it more than once just to get a fine sand finish, but their concrete is never softened by the process, it is still very hard and solid, not sandy.

Cannot disagree with anything else in your post though and you probably know a lot more about concrete and placement than me. However, my experience comes from many jobs where we had to try and fix concrete problems with surface treatments and part of that was to work out the cause of the problem so we could try and remedy it.

I saw what happened to bad pours after they were put into use.

 

[ConCretin]

Edger, I'll certainly defer on the effects of etching and requirements for an epoxy floor. Not an expert here at all.

I'm just trying to provide a counterpoint to the 'rip it out' crowd. There is reason to be concerned but the OP may have a serviceable slab.

Thanks for the clarification.

 

[kyles974]

Well, I just got done meeting with my concrete guy. He took a hammer to the hole, and it only went about a 1/2 inch deep. He said this had him worried. If had had went all the way through he said it could mean trouble. So, easy patch.

As for the "sandy" surface, he said the following:

(first let me say he did ask me when he was finishing, I told him it did not have to be sleak smooth, for I was going to epoxy.) He rented a power trowel that had all purpose blades, he said to get the smooth finish, he would have to get the finishing baldes,..... I told him that it was not a big deal)

He told me that he wished he would had not worried about getting the machine back for the 1/2 day rental and stayed and went over the surface 1-2 more times. So, he told me he will be back with a sanding machine that he uses. He said it has stones that is used for the sanding and then has a good pressure washer to make sure any loose sand gets taking care of.

(He also stated that word of mouth is everything, and wants to make sure I'm happy)

As for the denting in the concrete from the hammer, he showed me how it was just the surface being "packed" down. After I can easily see that, since it was not "burt" down.

I will let everyone know how the sanding goes.


Last thing......... My metal building just got dropped off!!!!
They will be back in the morning to start the build.
I wanted to take a pic of the metal on the trailer, but it was right at dark.

 

[kyles974]

Edger, I'll certainly defer on the effects of etching and requirements for an epoxy floor. Not an expert here at all.

I'm just trying to provide a counterpoint to the 'rip it out' crowd. There is reason to be concerned but the OP may have a serviceable slab.

Thanks for the clarification.

yes, thank you both

 

[Edger]

Kyle,

Sorry to hear about this problem, but I have to say it seems a bit odd that the contractor would hire a trowel and not own one, also he will use stones to sand instead of diamonds which is very old technology these days.

I do know that your sandy finish problem can also be caused by finishing too early and bringing up too much water during the process. All the bleed water must be gone before troweling to avoid this otherwise you will have a strong slab with a soft topping which is also what happens when a slab gets rain damaged.

Just another possible cause.

 

[kyles974]

Edger
ya, I kinda thought the same, not owning one. (he is a 2-3 man crew)

as for the stone vs diamond, again, I thought the same, but as long as he not charging me and it doea the job.

thanks

 

[kyles974]

Scotty/Legacy

After my concrete guy sands the surface, do you think it would be a good idea to use Lagacy's Concrete Hardener as a "safe side", if I think my slab might be on the soft side?

(this my have been brought up before, but I've got many things going on, so the memory isn't there at the moment,LOL)

Thanks

 

[LegacyIndustrial]

Yes, it would be wise. Use the Plus formula, here is the link:
http://legacyindustrial.net/cart/concrete-densifier-plus-1-gallon-p-143.html

 

[wingzjd]

Do you live near Fort Walton? I had a similar situation, where it dents very easily and looks like a lot of sand. That cement guys name isn't Charles? If you got the same stuff I did, I would have him tear it out and go with someone else. I'm living with mine and might put race dek or something down so I don't have to be so careful about dropping tools on it. I think epoxy would start to pull up with parts of the concrete surface stuck to it. Well, hopefully yours is better. Let us know how things worked out.

 

[kyles974]

Do you live near Fort Walton? I had a similar situation, where it dents very easily and looks like a lot of sand. That cement guys name isn't Charles? If you got the same stuff I did, I would have him tear it out and go with someone else. I'm living with mine and might put race dek or something down so I don't have to be so careful about dropping tools on it. I think epoxy would start to pull up with parts of the concrete surface stuck to it. Well, hopefully yours is better. Let us know how things worked out.

I live near Pensacola and no, my guy's name is Don.

I have not been out there in about two weeks. Busy at work. Just got done with my last fishing charter trip or at least the last one "on the books" for the year.(I'm a deck hand on fishing charter boat) Now I might be getting a damn head cold. (wife and kids been sick for a week or two)

Any how, I will let everyone know how it goes.
I did order Legacy's Concrete Hardener. (Just went online and orderd and paid with paypal. Got item less than a week)

As long as I feel better in the morning, I'm going to go back out there and check the hardness again with a hammer.

Metal building got put up a couple of weeks ago. Once finished with the epoxy, I will post a new thread on my floor and build. This would be the least I can do, since I have got so much help from this site. (because we all know, a forum can be only as good as what we put into it, right?)
I would guess this all will happen in the next couple of weeks. (weather permitting)

Also, first I need to see how the sanding goes. anyhow, I will post an update as soon as the work is done.
Thanks

 

[wingzjd]

Yeah, Don sounds like the name of the guy that worked with him. I don't know if these are the same people but PM me if you want to hear about my experience.

I'm just wondering if this is some new low standard in this area for the type of mix. It's like grout with rocks in it and seems like a very little cement.

Hopefully, that hardener works for you. I thought about it myself but already have a solid color stain on mine. I just want a floor that where I can work on and not have to worry about it being torn up. Maybe my next place I'll have better luck.

 

[kyles974]

well, I hate to say this, but yesturday I went out and it seems to be softer. Now when I scratch the sueface with the hammer claw, after a few scrapes boack and fourth, it seems to be chaulky. Like drywall but a little harder and gray in color.

Don called me last night and left a message after I emailed him saying I was ready for him to come out to see what he can do when he is ready, so I'll let GJ know what happens.

I have I hard time believing the slab can be made right, but he seems to think there is nothing to worry about. So he is really good at over comming the objective or knows his stuff? ......we will see....

(His name is Don Schesny DS Construction )

 

[kyles974]

well, my concrete did the stone grinding/sanding today. I seemed to all good untill I kneeled down to a spot right outside the door. As I scraped the surface with the claw hammer, it seemed to easily scrap up. Then it seems to have a mud type texture.(I forgot to say this was right after he left and I rinced it all off)
Almost like when ya finishing concrete and water comes up.

Of course he comes out with nothing to fix the whole but just to sand/grind. ANYHOW,
I called him back up and he said he will get the supplier of the concrete to come out Monday morning.

As I hit the concrete it is still putting dents into the concrete.

Please if you are going to commit, please be kind, since I'm pretty ticked off right now.

 

[kyles974]

Do you live near Fort Walton? I had a similar situation, where it dents very easily and looks like a lot of sand. That cement guys name isn't Charles? If you got the same stuff I did, I would have him tear it out and go with someone else. I'm living with mine and might put race dek or something down so I don't have to be so careful about dropping tools on it. I think epoxy would start to pull up with parts of the concrete surface stuck to it. Well, hopefully yours is better. Let us know how things worked out.

ya, I'm seeing the picture now in to the above statement.


I don't think mine is as bad, but bad enough.

 

[kyles974]

All reality, people say, have hime tear it out and do it again.

....well if I had that kind of money, I wouldn't be here asking for help.

....just some words for thought

 

[kyles974]

ok, I'm over being mad. so if anyone wants to post; tear it out and start over, I promise not to get mad

I do appreciate everyones commits and help with this issue.

One thing I dont understand is how, if they do decided the concrete is bad and needs to be redone, but how? My metal building is up.

This is also why I'm so mad at my concrete man. I called him up before the building was up to make sure and to see if I needed to delay the build. He told me not to worry that it's just the surface from him not "burnning" the surface.

Anyhow, Monday afternoon he and the concrete mixing company's rep will be comming out to look at it. I will post an update.

 

[kyles974]

here my metal building or garage

 

[nmanitou]

My recommendation is that you stop relying on the contractor's theory and stories, and get some actual facts from an independent testing service.

Google or phone book search for a "construction materials testing" company. They can come to your site, conduct non-destructive, or more reliable destructive testing (core sample), and provide you with definitive answers. They can also review the mix design from the concrete company. (Don't forget to ask if they added water to the mix at the job site - this is often a cause of problems in concrete quality)

This will cost some money, but is really the only way to know if your slab is repairable or needs to be removed and replaced. Good Luck.

 

[kyles974]

My recommendation is that you stop relying on the contractor's theory and stories, and get some actual facts from an independent testing service.

Google or phone book search for a "construction materials testing" company. They can come to your site, conduct non-destructive, or more reliable destructive testing (core sample), and provide you with definitive answers. They can also review the mix design from the concrete company. (Don't forget to ask if they added water to the mix at the job site - this is often a cause of problems in concrete quality)

This will cost some money, but is really the only way to know if your slab is repairable or needs to be removed and replaced. Good Luck.

I think others have said this, so I have to give them credit also...... but you are correct

I'm going to search the yellow pages.

 

[smallbloc]

Years ago I worked for a county engineers testing lab, testing road materials.
From what I've read here the problem is one or many....

Bad batch from the plant, a test cylinder would confirm this.
excessive slump,too much water added
the surface was worked to much, bringing sand and water to the surface

A testing service can drill a cylinder out and test the psi now that it's cured.


good luck

 

[kyles974]

Years ago I worked for a county engineers testing lab, testing road materials.
From what I've read here the problem is one or many....

Bad batch from the plant, a test cylinder would confirm this.
excessive slump,too much water added
the surface was worked to much, bringing sand and water to the surface

A testing service can drill a cylinder out and test the psi now that it's cured.


good luck

Good info.

(I was nervouse that the "cylinders" had to be poured while pouring the slab)

Do you know or can give me an idea of what kind of cost that would be?
(if not......I'll know in the morning when I call)

I'm going to try and get some more pics up showing what I see. One thing that puzzels me is that if I chip off a piece on the corner (I did this after I rinced it the other day) but I could easily break the piece up, and it kinda broke up into crumbs than pieces. I tried doing the same thing about 1hr later and it was harder to break up. So I then got that piece wet with water and it did the same thing, and it broke up into more crumbs than pieces. So, it seems to be more fragile when any water is introduced. The color of the inside part of the concrete is more darker color in gray.

(off the top of my head the slab is 50 plus days old)

 

[ConCretin]

kyles974, as I and others have mentioned, the only way to get definitive answers is to test the slab.

Tests such as a Windsor probe or breaking a core are going to tell you the approximate compressive strength of the concrete. This is obviously very important but may or may not be related to your surface issues.

Your observations of hammer dents, etc may be indicative of a problem but testing is the only way to get the information you need to make good decisions on how to proceed.

If the compressive strength is found to be low, the ready mix company is responsible for any remedial action UNLESS your concrete finisher added too much water on site. Hopefully the driver wrote this information on the batch ticket.

 

[Kevin54]

Denting the concrete is not a good test as to whether or not your slab is good. I can dent 80 year old concrete with a 1 1/2" ball bearing bounced off of a slab. If it were me, I would get in touch with a concrete coring company and have them core out a piece of your slab then have that tested. It sounds to me like the mix was incorrect. You shouldn't be able to break up a piece of it in your hand after this amount of time. Using the claw of a hammer isn't a good sign either. If the concrete has any roughness to it at all, the sharp claw of a hammer will scuff up any concrete, hard or otherwise.

It will be interesting to see what your concrete guy has to say, but I'd be more interested in a core sample to see what the concrete actually looks like. If he had to replace the slab, he could by cutting alond the sides, back, and front with a concrete saw then hammering out the middle. What is bad about that though is that they have to pin the slab to the now made curb and pur inside. This still lets the metal building sit on bad concrete, if in fact it is bad.

 

[CaptainRay]

I don't like Epoxy, it has been a waste of money for me and a frustration that doesn't go away. I'm looking at this stuff http://www.rubberflooringinc.com/garage/coin-grid-loc-tiles.html It's a little pricy but cheaper than most of the snap together stuff on the market and has mostly 5.0 ratings. I weld, grind and fabricate so will either leave have a spot open for that or use a welding blanket (harbor Freight). Something to consider... check out YouTube they have some videos on the various snap together flooring...
That sandy slab won't hold epoxy or any other pain on stuff. But you can make it look nice without repacing the cement.

 

[kyles974]

I don't like Epoxy, it has been a waste of money for me and a frustration that doesn't go away. I'm looking at this stuff http://www.rubberflooringinc.com/garage/coin-grid-loc-tiles.html It's a little pricy but cheaper than most of the snap together stuff on the market and has mostly 5.0 ratings. I weld, grind and fabricate so will either leave have a spot open for that or use a welding blanket (harbor Freight). Something to consider... check out YouTube they have some videos on the various snap together flooring...
That sandy slab won't hold epoxy or any other pain on stuff. But you can make it look nice without repacing the cement.

I think I just read about this in another thread, maybe you posted?

anyhow, yes, I was thinking about having to go this route. Because I doubt the concrete people are going to put my building and blocks, tear out the concrete and replace it?

My only concern is that 5,10,15yrs down the road, I would be nervous because of having problem with the footing and the building starts to????
It is a cheap style metal uilding and not your heavy red iron steel, so it is lighter, but I guess it would be a chance I would have to take.

I don't have the money, but I will be getting my money back from these guys if they don't do something. I could use that money for the flooring.

I should find out later today when they come out.
thanks