Steel trowel finished concrete slab - Is this good practice?

[Ted]

I am about to commence laying a slab in a warehouse.

The warehouse is for mending large crawler cranes and an engineer has specified the slab to be 30cm thick with two layers of reinforcement in it.

The client has now specified that it wants the concrete to have a very smooth finish.

Now here is the problem... here in Angola when builders do a steel trowel finished slab they lay the slab and then get it really smooth by mixing a bit of cement and sand into a very wet mix and troweling this in to the surface.

I am of the opinion that his technique may mean that the surface of the slab is somewhat weaker, even though this sand cement mix is trowled in when the slab is still soft.

However, on the other hand, the colour hardeners that PIC installers use are, as far as I know, just sand and cement (as well as pigment and maybe a little of a few other things).

So my question is if you were laying a slab would you just trowel it or do you think it is OK to add a bit of wet sand and cement mix to the surface when troweling it?

Thanks

[Tony McC]

There was some research paper published years ago (more than a decade, I think) by the then Concrete and Cement Association which showed that steel trowelled concrete had a much harder, abrasion-resistant surface than tamped or rough-floated concrete.

All the factory floors we used to install were power-floated as this was the only effective way to get a dead smooth, hard-as-diamond finish on larger areas. The ride-on power floats are great tools....for the first ten minutes, and then the vibration stops being a somewhat pleasant thrill and starts making your arse go numb!

[lutonlagerlout]

when you trowel summat ted you are pushing the larger aggregate away from the surface and the finer stuff (cement and fat) comes up,power floating is the best i reckon
LLL

[seanandruby]

It seems a long way around an easy job. Concrete needs to be placed with the minimum of fuss, to me levelling then trowelling more gear on top is a waste of time and money. get the right specified concrete get it level and then begin the finish....powerfloat.