# Concrete/Fiberglass Mix - Your thoughts?



## 747 (Feb 11, 2005)

you can go either way rebar or the fiber mixed into the concrete. Seeing how its a garage i say fiber if its cheaper.


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## joasis (May 28, 2006)

Old school versus new school thought: I pour a lot of mud, and we lay steel in the footings, whether it needs it or not (some local building codes still rquire it). I leave it to the customer on the issue of steel rebars or remesh in the floor, or adding fibers. 

Now the truth (in my opinion) is concrete is going to crack, it is the nature of the material...sometimes it doesn't crack for years, but it will crack. If fiberglass reinforcement is blended well in the truck, I think it is as good as remesh, and according to engineering, it will have greater strength then rebar in flat work (floors). It is tougher to finish, since as you machine or hand trowel concrete, you will float cement up, and the fibers with them. I have found it is almost impossible to burn a finish with a trowel when fiber is used, but you can still get a nice finish. Some guys say the floor is "hairy" with fibers, and uncomfortable to lay on....truth is the fibers that are exposed will wear away in no time, and I know of a contractor that uses a propane torch to "lightly" burn the floor after it is set. So there you have it.

In my own home that I am building, it is getting steel in the footings, and fiber in the floor.


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## concretemasonry (Oct 10, 2006)

Are you doing a structural slab "foundation" or a floating slab inside a footing/stem wall?

I love the "name" of confib - con as in convince and fib as in lie.

Fiber mesh concrete is good for its application and it is certainly beneficial if used properly. It is not a do-all substitute. There are many types of fibers used in fiber concrete.

There are many materials/admixtures that can be economically added to concrete to improve the properties. Fortunately, the cost is low, but unfortunately, you have to know how to produce or use them.

As Joasis said, there is no replacement for rebar for structural purposes in concrete - footings, columns, grade beams and continuous thickened edge footings/beams.

Fiber mesh concrete will crack less than concrete without fibermesh if it is mixed and place properly. At best, it will work as well as concrete with 6x6 steel mesh. There are different ideas about the cost difference. The finishing of fiber mesh is more critical and the advantages can be lost easily if not properly placed and finished.

With a good contractor, The IDEAL (with little extra cost - really in the big picture) is to use both. If you plan, have the steel mesh stop on either side of where you saw a control joint the next day. Yes - concrete will crack, so plan ahead. Fiber mesh without steel mesh makes controlling the location of cracks more difficuly. The extra cost of the mesh is peanuts compared to the standard of concrete with wire mesh (6x6).

What ever you do, there is always the possiblity of the fibers coming to the surface, but they are very friable and will wear off or be destroyed quickly. The problem is that they leave a void.

Usually, the elimination of the wire mesh allows a contractor to do a quick and easy pour, put all the concrete quality responsibility on the supplier and allow him (the contractor) to walk away quickly. Any problems can be addressed later.

************


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## tripower (Nov 16, 2006)

concretemasonry said:


> Are you doing a structural slab "foundation" or a floating slab inside a footing/stem wall?
> 
> I love the "name" of confib - con as in convince and fib as in lie.
> 
> ...


 
floating slab inside a footing/stem wall.
Thanks. What is I put an epoxy coating on the floor after construction is complete? I am assuming this would negate any isses with stray fibers?


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## tripower (Nov 16, 2006)

joasis said:


> Old school versus new school thought: I pour a lot of mud, and we lay steel in the footings, whether it needs it or not (some local building codes still rquire it). I leave it to the customer on the issue of steel rebars or remesh in the floor, or adding fibers.
> 
> Now the truth (in my opinion) is concrete is going to crack, it is the nature of the material...sometimes it doesn't crack for years, but it will crack. If fiberglass reinforcement is blended well in the truck, I think it is as good as remesh, and according to engineering, it will have greater strength then rebar in flat work (floors). It is tougher to finish, since as you machine or hand trowel concrete, you will float cement up, and the fibers with them. I have found it is almost impossible to burn a finish with a trowel when fiber is used, but you can still get a nice finish. Some guys say the floor is "hairy" with fibers, and uncomfortable to lay on....truth is the fibers that are exposed will wear away in no time, and I know of a contractor that uses a propane torch to "lightly" burn the floor after it is set. So there you have it.
> 
> In my own home that I am building, it is getting steel in the footings, and fiber in the floor.


No other steel or mesh in the fiber floor?


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## 747 (Feb 11, 2005)

tripower said:


> floating slab inside a footing/stem wall.
> Thanks. What is I put an epoxy coating on the floor after construction is complete? I am assuming this would negate any isses with stray fibers?


sounds like that could be a problem according to joasis. You might have to burn them off before coating with epoxy. But im not sure. But after reading him when finishing the fibers will come to the top during floating. So its logical to assume this could affect painting the floor so you would need to get rid of those before painting with epoxy like burning them.


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## joasis (May 28, 2006)

In my new home, there is no load on the slab, other then it's own weight, due to the design of the home. I will do fibers, and then cut grout lines and acid stain for a beautiful finish. But my tastes are not for everyone. 

I get rid of fiber float by firing up a trowel after the finish is done...wet it down, and trowel high speed...kind of a modified burn, but not really changing the finish. This works for me, and I don't advise others to do it....but that is what a forum is for..the sharing of ideas and information.


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## ckrd23315 (Apr 9, 2009)

*Joasis - how did your slab turn out?*

I read that you intended to stain your concrete with fibermesh in the mix. How did it turn out? My concrete contractor wants to use fibermesh, but I want to stain and seal the concrete. I've seen some jobs with fibermesh where it is clearly visible on the surface. I'm concerned about the look of the finish. Any ideas?


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## wildcat (Oct 24, 2008)

I think its perfectly fine to use the fiberglass admixture. I've seen a warehouse (about 400,000 sq ft) built with an "unreinforced" 8" slab. The resistance to cracking was obtained with admixtures and at the joints diamond dowels were use instead of the traditional dowel baskets (old school and sloppy in my opinion).









Given the scale and use of a typical garage your slab will do just as good as a slab reinforced with rebar.

The only problem that I am aware of the warehouse slab having was due to and error in crane movement. A skid was not placed correctly and the weight of the crane cause a crack at one of the joints...it was easily fixed.


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## jomama45 (Nov 13, 2008)

CKRD, I believe your question has more to do with the asthetics of fibers & acid staining. In my experience, I would skip the fibers when doing acid staining. We have only stained once with fibers on a troweled floor, as it was an afterthought by the homeowner to stain, & I can tell you the fibers were deffinatly visable thru the stain. Non-fibered concrete is a far better choice for acid staining IMO.


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## Tscarborough (Mar 31, 2006)

When the fibers were glass, furry slabs were more of an issue. With the newer synthetic fibers, they tend to lay down and are not a problem.

Also, fiber products are used as secondary reinforcement (shrinkage crack reduction, increase in tensile strength) for concrete, not structural reinforcement.


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## concretemasonry (Oct 10, 2006)

Now, fibermesh is a generic term. The properties can vary widelu, depending on whether it is steel fibers, glass fibers or plastic/propalene fibers.

None are a substitute for structural reinforcement and proper controls joints and spacing.

Dick


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## yesitsconcrete (May 11, 2008)

dick, we've stopp'd using fiber ( f/g, polyesther, OR polypropylene ), welded wire mesh, or steel rebar,,, w/the latter, we will place it IF the slab's going to be 'load'd' & we need more flexural strength,,, steel fiber, as you know, acts differently in a slab & we would use them as rqd for a 'masterplate' floor.

some may ask why - largely, its the expense vs benefit,,, if the slab's properly design'd, jnt pattern's correct, & install'd at the right time, there'll be no random cracks,,, since the fiber reinforcement/mesh ONLY acts to add a little strength while the slab's in tension & nothing after the slab cures, why spend the addl $$$ ? ? ? ooops - forgot, steel mesh does hold the broken pieces together after it cracks :laughing:


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