Pouring the slab next week, cement additives?

[Willypu]

So, this is my first post but I have been lurking a while waiting for permits.

The build crew plans to pour the 6" slab for my new 60' x 30' shop next week. The foundation guys suggest adding some type of fiberglass (?) additive and a chemical to make the concrete harder and less resistant to cracking.

The increase in cost is about $1k to the total pour. I am really not familiar with concrete additives, am I being sold "snake oil" or is this really needed to prevent the concrete from cracking?

The attached photo is the from the back of the shop looking to the front, there will be 2 single bays on each end and a double bay in the middle.

Thanks,

Jim

 

[Kaizen]

I used the mesh in mine and no metal in the middle. Two years later still no cracks. Are they talking about ordering 4K psi vs 3k? It’s a different mix not an additive. I highly recommend it if that is what they are talking about.
If it’s some other additive I wouldn’t. The fiberglass mesh isn’t very expensive. Get more details.

As for how hard 4K psi cement is? The truck left me a one six inch to a foot thick pile when they cleaned out. I couldn’t chip it with a sledge. Had to use a jack hammer for a few hours to break it up.


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[JoeMcGov]

Your concrete contractor is referring to a fiber mesh type of "additive." This is technically a reinforcement that in theory (if dosed correctly) is to replace the more traditional reinforcement such as rebar or steel mesh (mentioned above). I have fiber mesh in my garage slab at home (24 years old) and not a crack in it. If you decide to do fiber mesh I would suggest you get the fiber mesh manufacturers installation instruction. Read them and understand them. Then confirm that your concrete contractor, for the additional price quoted, is set to comply with those manufacturer's requirements.

Have no idea what the concrete contractor may be referring to as an "additive" to make it harder. Stay away.

 

[Toomanytools?]

Fiber mesh runs about $10/ yard.

 

[Willypu]

Thanks everyone! Yes to all above. He wants to use the fiber mesh, rebar and 4k psi. He plans to pour next Tuesday and then I will start a build thread.

Thanks!

Jim

 

[Kaizen]

Thanks everyone! Yes to all above. He wants to use the fiber mesh, rebar and 4k psi. He plans to pour next Tuesday and then I will start a build thread.

Thanks!

Jim

worth the money imo. what is he doing for expansion joints? i did not want the ones they do that has a dip so i cut mine myself the next day.

nothing more impressive then seeing an entire cement truck empty in a few minutes.

 

[Willypu]

For the expansion joints he suggested they use a process he called cut and cover. The joint is cut and then lightly covered. This will allow rolling cabinets, creepers etc to move smoothly but will eventually have some small cracking.

Yes, it is like Christmas for me to see thing thing actually happening! There will be quite a bit of cement poured, in addition to the 60' x 30' shop slab I am having a 60' x 10' apron poured in front of the garage and a 6' x30' side patio poured.

 

[ConCretin]

I'm not sure what cut and cover is..... Maybe he is referring covering the slab for curing purposes after the joints are cut. The important thing with regard to cutting control joints is the timing. To avoid random cracks, it's vital the joints are cut with an early entry saw immediately after finishing.

If this is done properly, it mitigates the need for fiber mesh whose sole purpose is to delay the onset of shrinkage cracks. Saw cuts create a weak spot in the floor to induce cracks where they are hidden. Personally, I'd focus on the saw cutting and pocket the money fiber would cost you.

The only additive that I'd look for is a mid range water reducer. This chemical is added at the concrete plant and provides a workable slump without the need for additional water. This will maximize the compressive strength of the concrete but even more impoortantly, it will help ensure a durable surface. Water is the enemy here.

 

[jack stand]

So, this is my first post but I have been lurking a while waiting for permits.
Jim

Welcome to GJ
LLWlliesfan is the man with concrete in his blood, bones and everything else. I listen to his concrete advice, help & experience very closly
If your curious as why: https://www.garagejournal.com/forum/showthread.php?t=145073
but be careful, it's only 100+ pages long!

 

[like2wheel]

Welcome to GJ
LLWlliesfan is the man with concrete in his blood, bones and everything else. I listen to his concrete advice, help & experience very closly
If your curious as why: https://www.garagejournal.com/forum/showthread.php?t=145073
but be careful, it's only 100+ pages long!

I'll second that; he's down to earth & gives honest, factual advice. I've learned a lot reading his posts.

I only wish he was local to me as I'll be ready for a floor soon.

 

[Kaizen]

For the expansion joints he suggested they use a process he called cut and cover. The joint is cut and then lightly covered. This will allow rolling cabinets, creepers etc to move smoothly but will eventually have some small cracking.

Yes, it is like Christmas for me to see thing thing actually happening! There will be quite a bit of cement poured, in addition to the 60' x 30' shop slab I am having a 60' x 10' apron poured in front of the garage and a 6' x30' side patio poured.

Sounds like he is putting concrete in the cracks?? I used a circular saw diamond blade for 20 bucks and mine were an eighth inch wide. I filled with caulk stuff before doing epoxy. Rolling over it is not noticeable. I’ve never heard of this cover and would worry the cement (if that’s what he is using) will bond the sides making it like there wasn’t ever a cut.


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[ConCretin]

For the expansion joints he suggested they use a process he called cut and cover. The joint is cut and then lightly covered. This will allow rolling cabinets, creepers etc to move smoothly but will eventually have some small cracking.

Sounds like he is putting concrete in the cracks??

I re read the original post Kaizen and I think you are right. It sounds like he wants to cut the joints and them fill over them. That sounds a little dubious. The purpose of the joint is to hide the cracks. If the thin 'cover' is going to crack anyway, I'm not sure what you have gained.

I'd probably cut traditional joints and fill them with sealant.

And thanks Jack Stand and Like2wheel. I appreciate the kind comments.

 

[Willypu]

So the concrete was poured today. I asked about leaving the cracks and filling them later. He said that his process of cutting the joints and then covering works well. He said to expect a hairline crack to form along the joint line but not much more.

Based on the experience from the group I am a bit skeptical as well but it is done and we will see how it holds up.

Thanks for all the insight!

Here is a picture of the pour today.

Jim
My Garage Build
https://www.garagejournal.com/forum/showthread.php?t=402633

 

[c39er]

Looks very nice!
I like "zip" strips for crack control.... clean and nice.

 

[Turbo]

I had the slab i put my lift on done with the cut and cover method. My concrete guy explained it the same way, he said all i would see is a hairline crack, and a year later all i have is a hairline crack. Terry

 

[Willypu]

Thanks Terry, I had to trust the foundation guys on this one as I am used to the traditional expansion joints. Time will tell how it works, but it looks really nice right now. If it does work well, it will be great to roll tool cabinets and things around

 

[James-W]

Looking super nice so far. I can hardly wait to see pictures of the build.

 

[jack stand]

Nothing like fresh "green" concrete! Looks very nice Jim.