Steel Mesh or Fibres in Concrete Screed

tedimc

I'm looking for some advice on screed options.

I'm renovating and the floor levels differ from room to room due to different floor make ups. I'm planning to go with one of the self levelling screeds for the rooms where I have 70mm or less.

However, my hallway, bedrooms & dining room have a T beam floor with insulated block infill, where I have 100 to 120mm for screed.

My original plan was to put in steel mesh and then a 10mm concrete to ensure good strength. However, some concrete layers I have talked to say that mesh is a waste of time and that the fibres through the concrete are just as good. I appreciate that the mesh makes their job harder, but to me I can't see fibre strands adding much to the mix strength wise. I know they help prevent cracking.

Any concrete experts think I am foolish to push for the mesh? My main concern is the strength of the floor over the beams - not worried about the floor structurally - it's really that there is no bounce and vibration.

Metric Tensor

120mm of screed is pretty heavy. Circa 290kg per square metre. Are you sure the T beam floor can handle the extra weight?

tedimc

It's a good point, I hadn't considered the additional weight of the screed. I'll check with the manufactures and see.

Thanks.

Tom Hagen

My take on fibers,

most concrete providers will provide Poly-Fiber concrete which is to prevent cracking. 8€ for a bag of fibers and 1 bag goes into every 1m3 of concrete you use.

but poly-fiber is NOT a reinforcing substitute, only crack prevention.

If you are not using steel mesh , then you need to use Steel-Fiber concrete. These are steel wire fibers added to concrete same as the poly-fibers are added. its added into the mix at the concrete plant when its going into the truck.

But these steel fibers need to be calculated for tensile strength, etc. by an engineer or specialist at the concrete plant. you will need to consult your concrete rep about this.

(might be just easier stick in sheets of mesh)

I think this is about the size of it, if anybody could shed more light it would be interesting to hear.

Dudda

As Tom said above poly-fibres they aren't structural and are only really used to stop cracking where you're going to leave the concrete exposed. For example if it was a store, warehouse or garage where the concrete floor is painted or sealed you could use the poly-fibers to reduce cracking. They're also used where you have a polished concrete floor and are exposing agerate, etc.

tedimc

Thanks guys for the feedback.

So I've checked with the supplier of the T Beams and they are happy with 120mm of concrete screed, but not much more.

I've talked to a few concrete installers and one or two are happy enough to work with the mesh in place. So I took the plunge and put it in at the weekend. Not much faith in the poly fibres to be honest. The steel ones are probably better than nothing but I can't see how they would be more effective than steel mesh.

Safehands

tedimc wrote: »

Thanks guys for the feedback.

So I've checked with the supplier of the T Beams and they are happy with 120mm of concrete screed, but not much more.

I've talked to a few concrete installers and one or two are happy enough to work with the mesh in place. So I took the plunge and put it in at the weekend. Not much faith in the poly fibres to be honest. The steel ones are probably better than nothing but I can't see how they would be more effective than steel mesh.

I know that the job is completed now but for your information, PP (poly) fibres help to prevent initial cracking when the concrete is in its plastic state. Once it is set they really don't do much. Steel fibres, applied at the correct dosage rate, help to provide ductility to the concrete. They allow supported concrete to be laid in thinner sections, while maintaining support for point loading. They probably would have allowed your floor to be poured in a thinner section thickness, while maintaining the strength required. That is one of their great benefits. They are not structural though. For that you require steel reinforcing. You were worried about 120mm, so perhaps you could have placed 100mm by adding steel fibres. The Fibre supplier could do a design calculation for you to see if that was possible.

tedimc

Thanks Safehands.

In conclusion - I went with the mesh in all the high risk areas and 10mm chip concrete pumped in (30 to 35N).

Happy enough with the job - seems very solid in the areas I was worried about. Have noticed 1 or 2 small cracks - but in areas I was half expecting them - one at an internal corner, only about 50mm depth.