Fiber Mesh or Wire Mesh/Rebar?

[UnionMan]

Hi All.

I've done some searches and looked around but couldn't find all the info I was looking for. I'm in the process of bidding out a pole building to build a wood workshop/Garage for my home in Virginia. the building will be 40x60x12 and pole building type construction. It will house a large area for wood working tools as well as have a small closed in office area with a full bath and on the far side I would like to put in a two post lift to make servicing my vehicles and equipment easier on me. I've been also getting bids for the concrete portion of the building. I've been basing bids off a recommendation I got from a friend to get 4" of gravel, 5" of 4000psi concrete. It seems that every bid I get from companies they recommend a fiber mesh concrete over a wire mesh. There reasoning is that it has the same strength as metal wire mesh but less labor which means cheaper overall cost.

What are everyone's thoughts on concrete pads?


UnionMan

 

[theoldwizard1]

Mesh does not add a lot of strength. I was told, when I had my driveway replaced 20 years ago, that wire mesh would help prevent the slabs from moving around if (when?) they cracked either at an expansion joint or other places.

No cracks, very little if any movement.

 

[Shadowdog500]

I was in the same dilemma five years ago. I was told that Fiber mesh is easy to do so it is attractive to the installer, but it really isn't as good as a wire mesh. I wound up using the belt and suspenders approach and got both. If you know what lift you plan to get, make sure your pad meets the requiremens required by the lift manufacturer. I went with a Mohawk lift so I used this guideline.

http://www.mohawklifts.com/library/manuals/Slab_Require_Recommend_11_07.pdf

I needed some fill to make my shop high and dry and had the concrete guy do it so there was only one guy to point at if things went wrong later. He used crushed concrete as the fill and really tamped it down it was almost as firm as a concrete floor when the base was done. I'm sure you know to get a good vapor barrier, but I'm mentioning it because I've seen people I know and here miss that step before.

Chris

 

[383 240z]

I doubled up as well. The mesh and the fiber. A few small cracks, but they are hairlines, no gaping. I plan on doing it again with the pads I'm should be pouring soon for the mill and the lathe. Keith

 

[MagKarl]

There is no clear answer. Well prepped base is very important. My concrete finisher told me he normally does fiber in the mix and rebar around the perimeter. I was not comfortable with that so I ran #4 rebar on 4 foot centers in addition to the fiber. Unfortunately you just have to go with your gut as opinions and experience vary so much. It's your money, get what you want.

 

[ConCretin]

Fibermesh is designed to resist plastic shrinkage cracks in the concrete very early in it's strength development but doesn't do much after that.

WWF and rebar (if properly positioned) are intended to hold cracks, including the ones at the bottom of control joints, from opening up. Contrary to popular opinion, neither bars nor mesh do much to prevent cracks.

I prefer rebar over mesh simply because it doesn't sag between supports and end up laying on the ground.

If you want to prevent cracks, you need to avoid re-entrant corners, increase aggregate size , minimize water content, cure the concrete properly, etc. Most people just opt to hide the cracks in the bottom of control joints.

As has been said, the most important consideration is a well compacted, granular base. The ground under the slab is going to support the weight placed on the slab. A 4, 5 or 6" slab just isn't going to span very far no matter how much bar you put in it.

So, to answer your question. If you have an excellent base and just want to prevent cracks long enough to cut some control joints, fiber is fine.

If there is any question that the base or loads placed on the slab might cause cracks or control joints to open up excessively, I'd skip over the WWF and go right to rebar. #4 bars at 24" centers is a good starting point. Hope that helps.