Concrete Retaining Wall Curing/Finishing Issue

[Murphy9190]

Gentlemen, this is more of a builder than engineering question but, if any of you can speak to the properties of concrete perhaps you can answer the question.

I am a geo-tech and builder in California for 40 years. I have done numerous projects that required retaining walls of varying heights and thicknesses, but have a residential project in the San Francisco bay area of California with retaining walls up to 7' high and the owner wants a "perfectly smooth" concrete finish. The issue is within the wall we have the rebar of course, but also two rows of conduit with light and electrical boxes. The vibrator has to be inserted and relocated gently (no ramming it down real quick) with some marked areas unable to vibrate.

For a clean wall, my preferred solution is perfect forms, built modularly for easy removal and, when necessary, I will even use a 1/4" melamine liner for a perfectly smooth non-stick surface. They concrete sub I am using "comes with the project," is primarily a structural steel guy, is young and I am not pleased with the wall form construction, joints etc. and have concerns about the final finish. The concrete contractor says not to worry as he will remove the forms after the walls have "setup" then float/finish them smooth. I asked him if he had ever pulled forms early on retaining walls to smooth finish them and he said "no." I asked how he knows when the concrete is set up enough to safely remove the forms and he said his finishers know.

I've been in this business and around people long enough to know when the risk factor starts climbing and have a number of concerns, 1. Lack of vibration in certain areas will likely result in air pockets on the finished walls that will require finishing 2. The walls are varying heights and thicknesses, so each should have its own "set-up" timing. 3. I don't trust this scenario and the potential for catastrophic disaster exists.

The concrete is 3,000 psi pea gravel for pumping. One wall is 13" thick x 12' W x 43" H. The second wall is 8.5" thick, 25' long and stepped to follow grade with varying pour heights from 40" to 84".

I'm thinking of not letting him remove the forms and deal with surface imperfections with a guy a know who is a great indoor (Venetian) and outdoor (Santa Barbara finish) plaster. If he can float them all smooth to look like concrete then great. If not we'll apply a texture.

Question is, is it possible (for the right experienced man) to remove retaining wall forms early enough in the game to finish them smooth or is there no way to do this safely?

I defer to your expertise.

 

[hokie66]

To achieve what the owner wants, you will have to rub them anyway, no matter when the forms are removed. It sounds like your plasterer is the go.

 

[JAE]

Two things I've done in the past:

ONE
At a large justice center in south Texas we had very high retaining walls that were about 12 ft to 14 ft tall as I recall.
The architect wanted a "marble-like" finish so we used white Portland cement (vs. gray) and the form liners were a type of smooth glossy vinyl (like a linoleum material) with silicone sealant used at all the form joints to ensure a smooth look.

The results came out wall - but as always - years later the concrete isn't "white" anymore or "marble-like" but stained a bit by the weathering.

TWO
What hokie66 suggests is what I thought of first - ACI has provisions - or descriptions - of a "rubbed finish" and this shows up in most MasterSpec concrete specifications - remove the forms - chip off any protruding fins etc. and then with a carborundum brick and water rub the concrete surface to generate a cementitious slurry that fills in bug holes and smooths out the surface to a uniform texture.
This will not be a "marble-llke" finish but more of a textured finish.