A wet joint is a connection between structural elements that is filled on site with concrete, mortar or grout. Once cured, the joint acts as one with the adjoining elements. Its counterpart is the dry joint, which is made purely mechanically with bolts, dowels or a bearing.
What such a joint looks like
In precast concrete construction, reinforcement bars, loops or anchors project from the elements. On site these are brought together in a pocket or a joint, supplemented if necessary with continuity reinforcement, and the void is filled with a low-shrinkage grout or concrete. Common applications:
- Column to foundation — the column is set in a pocket or anchor sleeve and grouted in
- Wall-to-wall connections — vertical joints between precast walls with loop connections
- Floor joints — the joints between hollow-core slabs, grouted to create diaphragm action
- Structural topping — an in-situ layer over precast planks that ties the units together
- Lattice girder (filigree) slabs — the precast plank acts as permanent formwork; the in-situ topping makes it structural
Advantages and drawbacks
A wet joint can transfer moments and shear and produces monolithic behaviour: the structure acts as a whole, which benefits stability, fire resistance and sound insulation. The drawbacks are curing time, sensitivity to frost, and difficult dismantling later — a wet joint is not a circular detail.
Points to watch
- Filling is skilled work. A partially filled joint is a hidden weak spot. Provide enough space, a vent path and a sensibly placed pouring opening
- Low-shrinkage grout. Ordinary mortar shrinks and debonds from the contact face; use a tested non-shrink grout in accordance with the manufacturer’s instructions
- Cover. Reinforcement cover has to be achieved inside the joint as well
- Temperature. Do not grout in frost without measures; fresh grout in a narrow joint cools rapidly
- Sequence and propping. Elements must stay aligned and propped until the joint has gained sufficient strength
- Records. Log which joints were filled and when — this is a standard check point in quality assurance
Related terms
- Dry joint
- Precast concrete
- Hollow-core slab
- Shrinkage
- Reinforcement
- In-situ concrete
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