Construction & Contractors/Repair Concrete Drain


Good day
With reference to a box drain which was built poorly by an inexperienced contractor. Some of the defects are:
1. drain walls are not uniform (some areas wider by between 1/2 to 1 inch)
2. drain outer surface not smooth (rough spots etc.) - how repair and make surface drain smooth to look uniform. Heard plastering the concrete drain does not hold. What other options, additives, techniques can be used to restore and smoothen the surface of the drain.
3. Where can I learn more about repairing and restoring concrete structures

What scale is the box drain?  might it be appropriate to consider just replacing it with a precast unit and be done with it?

I don't think there is much that can, or probably needs to be, done about nonuniform walls as long as they are not too thin, which can evidence inadequate reinforcement cover.  If they are too thin you are probably stuck with casting over the walls with new concrete, applying a bonding agent between the old and the new.

As for the outer walls, the drain types I am picturing are embedded in the ground so nobody cares what the outer finish looks like as long as the drain is structurally sound and doesn't leak.  Obviously there is something I don't understand here then because you are concerned about the appearance.  

If the problem with the drain exterior was improperly vibrated concrete or cold joints so that the aggregate is exposed, you are kind of stuck with that.  I would assume that when the exterior was plastered over, it was done after pressure-washing the area to remove all scale and dirt, an appropriate bonding agent was applied, and a high-strength cementitious product designed for thinset applications was thoroughly worked into the surface.  Even so, "plastering" the exterior may not hold if there is moisture penetration through the concrete walls.  Evidence of that would be moisture on the material flaking off,  discoloration or salt efflorescence.  I don't know of a thinset coating that will fix that situation without suffering the same scaling problem due to permeation.  What would have to happen in that case  is that the interior would need to be sealed.  There are epoxies used to repair concrete that can serve that purpose.  Just be sure that the product used is thick enough and durable enough that it cannot be worn away by sediment passing through the drain.

There are many many resources on concrete repair and restoration.  You might consider contacting Hanson Precast or the Portland Cement Association.

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Robert Cummings, P.E.


I can answer questions related to rock blasting, rock and soil excavation (such as tunnels and highway cuts), stability of such excavations, and foundations in rock and soil. I can also answer questions related to geology and mining.


30+ years as a geotechnical engineer and minerals engineer. Active consulting practice in rock blasting, geotechnical engineering, and rock mechanics for mining and heavy construction.

Society of Mining Engineers, Deep Foundations Institute, Association of Engineering Geologists, and International Society of Explosives Engineers.

Mining Engineering, AEG Bulletin.

BS and MS Geological Engineering

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