Primitive slab finishing technique 1

[hinckley]

I am working in Latin America on a fairly large building. We are planning on installing a 4" floor slab which will be treated with an acid stain imported from the US. (If anyone has experience with acid staining, also, advice is very welcome) However, our contractor is accustomed to using a "mortar" of cement and very fine sand applied to the fresh slab, trowelled in and then dusted with cement powder in order to produce a very smooth surface. Power trowels, any power concrete finishing tools, in fact, are unheard of in this country. I want to produce the smoothest surface possible as it will remain the finish floor surface, but I am concerned with the negative impacts of the contractor's methods. Crazing of the concrete surface is not a concern as small cracks or craze marks would be considered a part of the "variegated" look of the acid stained finish. However, what is the risk for other more serious cracking problems or weakening of the slab finish from these finishing techniques?
The slab itself will be constructed as much as possible to "US standards", on a vapor barrier over a well compacted sub-base and gravel base, with standard size welded wire temperature reinforcement. We will also be pouring the slab in sections about 10'x20' and placing control joints at this interval. However, I have yet to find a contractor in this country that can finish concrete to anything like "US standards", so I am left with either finishing the slab with the local method or a rougher finish that is the best they can do without adding cement to the surface. In your experience, what is the danger of creating a thin finish layer on the slab that will later chip off? Are there other major concerns?

 

[jheidt2543]

Dusting the slab surface with sand and cement at the time of finishing used to be a "standard" practice in the US fifty or more years ago. Its main function was to "soak up" the excess mix water that would migrate to the surface just after pouring. That method has pretty much been discredited for a number of reasons.

Pouring a floor slab without power tools is pretty labor intensive and was one of the main reasons to add extra water at the site, to make the concrete flow.

The best floor slab results come from a 4,000 psi mix and pouring the concrete as stiff as possible, use a water reducer if available, keep the vapor barrier under the slab, but also be sure to wet cure the slab for at least seven days.

Finish the slab to screeds set to grade shot by a level. Hand finishing can be done on the smaller pour sizes you are using, but crew size if very important. On a hot day, the slab can sometimes "quick set" and get away from a smaller crew, so its important to have enough finishers to get the slab level before the initial set.