New slab already having problems.

[z28dad]

I was so proud of the way that my new slab turned out until today. I noticed that it has several x pattern cracks about the size of my hand. I knew it was going get some cracks, but what bothers me is when you tap around the cracks, its very solid, but when tapping over the crack you can tell that its sounds like a hollow sound as if about an 1/8 inch of concrete the size of a silver dollar would bust out. I have not tried it, but you can tell by the sound.

I will tell my contractors about it tomorrow. They subbed the pour of the floor out. Its 4000psi, with mesh and alot of rebar. My cousin said that they either got on the floor to early with the finish machine, or got it too wet/soupy when finishing it.

Not sure what my options are. Let me know what you think, so I can maybe consider it with my contractors.

Kinda bummed out right now.. Thanks Russ

 

[Salem747]

Was it kept wet during the first 7 days? That looks like it dried out too fast.

 

[z28dad]

Yes, they covered it with black plastic, I waited a week and it was still wet in places when I took it up.

 

[z28dad]

Well my contractors talked to the concrete guy. He said he had been having this problem for a few weeks and we needed to talk to the concrete company. I hope I'm not going to get the run around. There is nothing that gets me more upset than someone pointing the blame instead of just acknowledging the problem and determining a solution. As for now, more waiting to see what the concrete rep says.

Speaking of solutions, what do you guys think is the best method of repairing surface imperfections. When these places do pop up it will look like concrete that has been salted.

 

[LegacyIndustrial]

Epoxy resin, flat bladed.
It's the same process we use prior to polishing.

 

[z28dad]

Epoxy resin, flat bladed.
It's the same process we use prior to polishing.

Legacy Industrial, Thanks for the reply. Please give me some more details on the resin and the process. Is this something that I can do myself? Thanks, Russ

 

[Mel M]

How close was the rebar to the surface? Do any of the cracks follow where the rebar was laid out?

 

[LegacyIndustrial]

Legacy Industrial, Thanks for the reply. Please give me some more details on the resin and the process. Is this something that I can do myself? Thanks, Russ

We fill the pores of the concrete with a clear epoxy resin prior to polishing.
We use HD-380 Seamless Binder. It costs $ 165.00 + shipping for a 3 gallon kit.

It is flat bladed across the pores. Naturally, we grind the excess off through the polishing process. You would have to do the same or coat the entire floor with an epoxy coating after.

It's fine for thin cracks and small bug holes, etc...

 

[AlphaGarage]

Knock out the loose stuff, then fill with an epoxy binder mixed with sand. The finished area will be considerably more durable then the rest of teh floor. With a good binder (such as TrowelEase 1161) figure about 50 pounds sand mixed with 1 gallon epoxy will yield enough to fill 16 ft2 to 1/4" deep.

It's self priming, just pour in and smooth out.

 

[Teamchevy]

Russ,

Did you have the fibre re-enforced concrete?

Dave

 

[z28dad]

Thanks for the info guys. I may let it sit until spring and repair those spots. I will epoxy the whole floor afterwards. This should make my floor better than new. I have alot of other work to do in the meantime.

Dave, no fiber, just rebar and mesh. It has alot of rebar in it. Mel, the cracks are random at best, but do seem to be mainly in the more center part of the slab.

 

[z28dad]

The slab is about 50 days old. I never got any info from the guys that finished the floor, or the concrete company. After my research I also think it cured a little quick. It was really hot that weekend, I was going to water it, they said it was no need with the plastic over it. I wish I would have done it anyway, but we went out of town. I have had a few more of those tiny cracks surface. I just hope this is a cosmetic issue and nothing more. The concrete has been wet when these pics where taken so they do show up a little more. Most of the time you don't even notice them, because they are so small. I'm still concerned that the finish will pop up in certain areas.

Funny thing is these hairline cracks seem to be in the middle area of the slab. If I knew that this was all that the slab was going to do, and it would not get any worse, I could live with it.

I did have one of my friends that builds houses ask if it was 4000psi which it was. He said he did a slab once using 4000psi and it did the same thing. He thought that might have been an issue.

Here are some pics before the slab was poured. These pics are not great. It was late when I got in and it was dark. They were not finished tying all the rebar together yet.

 

[green.bubbly]

Hopefully it is only cosmetic.

What is with all the bad concrete jobs being posted today?

 

[LegacyIndustrial]

Franky, I have seen plenty of fine cracks like the ones pictured.
I would leave it alone, unless they get bigger.

If you are not going to coat it, then at least densify it for added surface strength and no dusting.

 

[jkeyser14]

I wouldn't settle for that, I would start talking to the sub contractors insurance to have it replaced. What if you wanted to put a lift in sometime down the road and there's a hidden thin spot? You could wind up dead or destroy an expensive car.

 

[z28dad]

I wouldn't settle for that, I would start talking to the sub contractors insurance to have it replaced. What if you wanted to put a lift in sometime down the road and there's a hidden thin spot? You could wind up dead or destroy an expensive car.

Most everybody just seems to think its a cosmetic issue. I'm guessing if any of the finish does pop up it would only be about 1/16-1/8"thick. Nothing that would cause a car to turn over. If I knew for sure that it was a structure or a strength issue that would cause me serious problems I would rip it out in the morning.

Today my neighbor up the road had a two slabs poured. I stopped by and talked to the contractor that was doing the work. Its all he has ever done. I explain the types of cracks that had developed, the first thing he ask was if most of them were out in the open , I said most of them are in the middle of the slab. He asked was it real hot, I told him that it was. Especially for this time of year. It was 90-95 every day. He said it was that heat that did it, and that I should have put a sprinkler on it. He did say that he thought I would be fine. I just hope he is right.

I'm still thinking about coating it in the spring. I have mainly been just keeping an eye on it during the rest of the build.

 

[Massive Overkill]

My ordeal: http://www.garagejournal.com/forum/showthread.php?t=43451

I'm glad I had my whole slab repoured. Listen to the tapping in my videos.

 

[Tommydogg]

Looks like mine did, it's called spauling. My builder had a different concrete dood come in and chip out the spauled spots and spot patch with Renew Coat, then they re- surfaced the entire floor with Renew Coat. It's been almost two months, and it's ho;ding up fine! Here is my original post:

http://www.garagejournal.com/forum/showthread.php?t=73025

 

[z28dad]

My ordeal: http://www.garagejournal.com/forum/showthread.php?t=43451

I'm glad I had my whole slab repoured. Listen to the tapping in my videos.

WOW!, sorry to hear you had to go through that. After watching your video, I went out to the garage and did the same thing to my floor. There is no change in sound using the same method with a 2x4 on the spots that I have marked. I will check the whole floor tomorrow. The only way I can get a different sound is by tapping with my knuckle. I have tapped this floor until my fingers hurt.. I have a couple of spots that you can see the cracks barely move and produce a slightly different sound.

 

[z28dad]

Looks like mine did, it's called spauling. My builder had a different concrete dood come in and chip out the spauled spots and spot patch with Renew Coat, then they re- surfaced the entire floor with Renew Coat. It's been almost two months, and it's ho;ding up fine! Here is my original post:

http://www.garagejournal.com/forum/showthread.php?t=73025

I have that site bookmarked. Do you have any updated pics of the repair.

 

[Tommydogg]

I have that site bookmarked. Do you have any updated pics of the repair.

no, but it looks perfect! I had to move all my garage stuff in from my storage unit. I just bought a shed, and hope to disribute stuff from the garage to spare bedroos and the shed soon so I can epoxy the floor.

 

[z28dad]

Well I'm about ready to start working on the floor. The cracks haven't got any bigger and I don't think there are any new ones. Some of the cracks I believe are fine. I say this because some of them there is no change in sound when tapped on. I do have about 10 that are loose. In the picture below, the larger area was loose, and there were some hairline cracks as well. The loose stuff came up pretty easy, but to be honest I could have left the other part. It was actually pretty solid. But now I have an idea of what needs to be fixed and what can be left.

The pic makes it look worst than it actually is. Its just the finish coat that is loose, about an 1/8 inch deep. I'm looking for a product that I can fill this with. I have a few questions. When I knock out the loose stuff, should I cut the edges smooth or leave them as they are. As stated its about an 1/8 inch deep, but as it gets to the edges its less. I plan to epoxy the floor and I don't want to see the patches once the is down. As far as the hairline cracks that are not loose I guess I should put something over them as well. I would like to do this in small increments while working on other parts of the garage.
Also does epoxy make the floor surface stronger?

Thanks, for any help. Russ

 

[3x9RT/SE]

The same thing happened to me,my floor was poured without the building on it,therefore open to the sunlight,and yes,was hot that day also.Mine is way worse than yours,hairline cracks,but not patches popping up like you show.Had numerous people look at it and say its not structual,just cosmetically annoying,and that those cracks don't go all the way to the bottom of the slab,they are are just surface,maybe alittle down but not deep.Cured to fast on the top,and yes,I did put a sprinkler right away on it when they were done,for a week or two and still ended up with cracks.Also,I have radiant floor heat,5 loops,250' each,none of which any of those cracks affected.I had 80psi of air in the lines as they poured and did'nt hook up the tubing for nearly 2 years after,and the lines NEVER leaked out,so there shows you the cracks did'nt go down into breaking my tubing,for what its worth.

 

[BuickFarmer]

Best I can tell from the pictures is that those appear to be shrinkage cracks typically caused by high strength concrete being poured in hot weather. I'll bet the slump of the concrete was pretty high too. In other words they added water at the site to allow more time to work the concrete. I use to tell my guys that you PLACE concrete, if you pour concrete then there is too much water in it. Excess water (which in itself weakens the concrete) and high cement content (anything over 3000 psi, I consider high cement content) will create shrinkage cracking when the concrete starts the hydration process. Hydration = heat. Covering with black pvc on a hot day probably increased the heat thereby contributing to the cracking. I would consider it strucrual but only to the top probably 1/2 inch or so. The overall strength of the floor has probably not been compromised. My suggestion for a fix (and this is looking at it from where I am sitting) would be to grind the surface of the areas that are cracked (plus a foot or so additional) down 1/8 to 1/4 inch and apply a self leveling epoxy conrete patch material as has been suggested before. Do this in neat squared off areas. You can rent heavy duty grinders that grind about 8 inchs wide and however deep you want to go at a time. If you plan to paint/cover the entire surface of the floor later there will likely be some small reflective cracking come through the surfacing. But if you do a neat job of repair, squaring up the patches that you repair now it shouldn't look bad.

 

[LegacyIndustrial]

Well I'm about ready to start working on the floor. The cracks haven't got any bigger and I don't think there are any new ones. Some of the cracks I believe are fine. I say this because some of them there is no change in sound when tapped on. I do have about 10 that are loose. In the picture below, the larger area was loose, and there were some hairline cracks as well. The loose stuff came up pretty easy, but to be honest I could have left the other part. It was actually pretty solid. But now I have an idea of what needs to be fixed and what can be left.

The pic makes it look worst than it actually is. Its just the finish coat that is loose, about an 1/8 inch deep. I'm looking for a product that I can fill this with. I have a few questions. When I knock out the loose stuff, should I cut the edges smooth or leave them as they are. As stated its about an 1/8 inch deep, but as it gets to the edges its less. I plan to epoxy the floor and I don't want to see the patches once the is down. As far as the hairline cracks that are not loose I guess I should put something over them as well. I would like to do this in small increments while working on other parts of the garage.
Also does epoxy make the floor surface stronger?

Thanks, for any help. Russ

Epoxy needs a solid substrate. It is stronger than concrete in thin thicknesses.

Our epoxy patch can be used here. Square off the repair area, mix the material leaving it slightly resinous. Trowel it in butting up the edges.

Once cured you can run a sander over it and get it really flat. Use the flake when you coat your epoxy and it will disappear.

Link:

http://legacyindustrial.net/cart/epoxy-concrete-patch-1-gal-hd110-p-6.html

 

[z28dad]

Epoxy needs a solid substrate. It is stronger than concrete in thin thicknesses.

Our epoxy patch can be used here. Square off the repair area, mix the material leaving it slightly resinous. Trowel it in butting up the edges.

Once cured you can run a sander over it and get it really flat. Use the flake when you coat your epoxy and it will disappear.

Link:

http://legacyindustrial.net/cart/epoxy-concrete-patch-1-gal-hd110-p-6.html

Thanks for the replies guys. Scotty, I have a few questions about your products. Can I cut the mix down to do small areas. As long as I mix the resin 1:1. I'm sure once I do a few of them I will have an idea of how much to mix up for a given amount of repair areas. Also what about when I prep the floor for epoxy. I plan to acid wash the floor. How will that affect the repaired areas? Should I try to keep the acid away from the repaired areas?

As far as the fine line cracks that are solid, and nothing on the surface seems to be loose, I was thinking of flat blading the 821 product over the cracks. What do you think? Do you sell this product in sizes less than 1 gallon? Also how would you prep these areas for epoxy?

Also on the sanding what grit should I sand with? I suppose a DA sander would get the job done. I have some 80 grit.

I'm guessing I should shoot for a moderate to heavy broadcast on the flakes. Will the hd110 ever shrink over time?

 

[LegacyIndustrial]

Thanks for the replies guys. Scotty, I have a few questions about your products. Can I cut the mix down to do small areas. As long as I mix the resin 1:1. I'm sure once I do a few of them I will have an idea of how much to mix up for a given amount of repair areas. Also what about when I prep the floor for epoxy. I plan to acid wash the floor. How will that affect the repaired areas? Should I try to keep the acid away from the repaired areas?

As far as the fine line cracks that are solid, and nothing on the surface seems to be loose, I was thinking of flat blading the 821 product over the cracks. What do you think? Do you sell this product in sizes less than 1 gallon? Also how would you prep these areas for epoxy?

Also on the sanding what grit should I sand with? I suppose a DA sander would get the job done. I have some 80 grit.

I'm guessing I should shoot for a moderate to heavy broadcast on the flakes. Will the hd110 ever shrink over time?

I'll answer in reverse:
The HD-110 will never shrink. It will stay exactly the same as when your trowel left it for the last time.

The D/A would be good, a belt sander or orbital would work too.

You can flat blade the 821, we don't sell it any smaller.

The HD-110 is not 1:1. Plan out your repairs and if you want to do it piece-meal, purchase the one gallon units, very easy to work with.

This product does not kick that fast, in fact if you do it now it will slow the cure giving you even more time to work with it.

Good luck and if you go for it, please post some pics for everyone.
We send out golf-shirts for pics.

 

[z28dad]

Thanks. I just ordered 2, 1 gallon kits. I hope to work on it in a week or so. I will keep you guys posted. Thanks, Russ