When a construction joint is required on a wall on wall or column on column pour the joint line can cause problems with deflection, grout loss and achieving a true straight edge to the joint.
Deflection is the biggest issue and should not be ‘feathered in’ to the concrete plane of the pour below. It may appear to be a solution but the concrete will always look worse if this is attempted. It will always appear to be ill considered and look funny to the eye. The only solution is to continue the plane of the concrete and form a true straight joint line. The joint line, even though it is not flush, will help the repair to be more accepted by the eye (see image).
Grout loss will also be present but this can be resolved but protect the pour below!
If the wall from the previous pour is not ‘struck off’ to a straight line with the formwork then this will also require the re-instatement of a new joint line as a wobbly line will prevail. Finishing the top face of a pour to flatness is important...
Grout loss occurs when the formwork is not completely sealed. Grout will find its way through the tiniest of gaps especially when the concrete is compacted. The issue of grout runs causing striations on a concrete surface is a common occurrence and a very frustrating one.
Grout will run down the face of a previously poured wall or column when the section or slab above is poured and the new formwork is not sealed properly. A grout check is normally detailed in this intersection to prevent this. However, if there is any deflection in the wall below (which is likely) a straight cut of new formwork board will not snugly fit. Sometimes a decent grout check is not enough. Proper protection should be in place for the concrete below the pour and it is wise to consider using silicone, tape and plastic sheeting sealing the older face from the new first then adding the grout check. The protection will serve the older pour and the grout check will prevent issues with the new pour. Even if the tape...
A focus of our work is concerned with Architectural concrete repair to fair faced concrete. For me this image is fascinating. Not just because I've never seen grout loss quite so honestly displayed before but also because this image clearly illustrates cause and effect.
The base of the column (steel shuttering) had a tiny band of hydration staining (dark line) and some very minor honeycombing (voids around larger aggregates). On the floor, in almost a mirror image was the grout that was lost, lying in place. Call me boring but THIS is my Friday night out.