Fibermesh concrete

I am planning to order a concrete slab for a 13,000 pound motor home. It will be approximately 10 x 20 feet, perhaps a bit larger. One potential contractor is touting fibermesh concrete and says a pad just 4 inches thick would be adequate. Another says he would prefer six inches with wire reinforcement. Four inches seems a bit thin to me for a pad or a driveway which I might also consider.

Could you advise me as to the advantages and disadvantages of fiber reinforced concrete and what you think would be the best route for me to take in planning this slab (and driveway) bearing in mind the load it would be handling.
I agree with your observation that 4" fibermesh slab may not be enough for load carrying purpose. In my experience, even residential slabs that carry no load failed to perform with fibermesh when not jointed properly.

The main problems were excessive cracks that opened up to 1/2" wide due to shrinkage alone.

The key here, however, is the fact that neither fibermesh nor wiremesh are considered reinforcement for concrete. Both serve only to control and minimize shrinkage cracking of the fresh concrete.

Concrete with both will require contraction joints spaced about 10' apart in order to perform. The joints are actually more important than the mesh.

Another critical factor is the type of soil and base preparation since the slab is fully supported on the ground. When the base is compacted properly it will carry most of the load without stressing the slab. In that case a 4" slab may be adequate. In every case, however, a 6" slab will outperform a 4" slab

The last critical issue is curing of the concrete. 7 days wet curing will almost always result in crack free slab if the joints are provided and the design strength is achieved.

My recommendation:

Ask your contractor to show you a similar slab that he placed at least 6 months ago under similar conditions. If it looks good, and he will back his work, then you may go with it. If not, then I would stay with the traditional wire-mesh or rebars.

Always ensure that base compaction, joints, and curing are done correctly.
I got your name from a a section of an internet site called "Ask the Doctor." I had entered "concrete" in a search engine, came up with 260 entries, scrolled through them and found your site.

My thanks for your detailed answer. I was only able to find one other reference that touched on my information, a short explanation of fiber mesh concrete and what it should and should not be used for.

I think I am going to go with the 6" slab. I also asked a friend of mine who is a contractor but cannot do my job and he says that he has had some problems with fiber reinforced concrete. He says if it cracks there is nothing to hold it together and the pieces can often come loose and separate if there is any movement or shifting of the ground for any reason. He also says it is "hairy" because of the fibers. He was hesitant to recommend its use to me.

I live in South Florida, quite close to Jupiter and West Palm Beach in an unincorporated section of Palm Beach County. My ground is pure sandy soil.