Concealed joints

Following a 2-year development programme, Abeo has introduced a “joint-free” solution for SL-decks making it possible to conceal the traditional ceiling joint between two precast slabs.

With the new solution, SL-decks are delivered with a 250mm recess in the underside ready to be spackled after the SL-decks have been lifted in place. The solution ensures that the final ceiling surface will appear even and homogenous without visible joints and thus makes it possible to improve the aesthetic quality in a very cost-efficient way – without the use of a dropped ceiling system.

Traditional precast ceiling

SL-decks with joint-free solution

Drag the arrow left or right to see the difference between a traditional precast slab ceiling and the SL-deck joint-free solution.

Installation

SL-decks are produced with a 5mm deep and 250mm wide recess in the edges of the underside, creating a 500mm wide recess across two slabs to even out camber differences.

Spackling paste is applied in the total length of the joint after which a fibre mesh is put into the wet paste. The joint is then spackled again, wet in wet.

After drying out, the recess is spackled for a second time and the recess is grinded and primed.

The underside of the SL-deck is – per standard – produced with a self-levelling mortar, which, against the steel bed, provides a very smooth surface. It is not necessary to apply spackling paste to the underside of SL-decks, however, spot filling might be necessary to repair potential transportation or installation damages.

Result in final apartment unit

Inspiration from the gypsum board industry

The SL-deck’s joint-free solution has been developed with inspiration from the gypsum board industry, where the standard method for concealing joints between gypsum boards on walls and ceilings has for decades been the use of a wider joint design.

By introducing a similar recess in the underside of the SL-deck, it is now possible to smoothen and visually hide camber differences between slabs.

Background

Prestressed precast slabs were introduced in the 1950’s and has since evolved into a dominant slab system in a number of countries, especially in Scandinavia and Benelux. Precast concrete has had an important role in the industrialization of the construction industry by moving a large of the construction process to factories and improving the construction flow. However, the introduction of precast concrete units has also come at the expense of certain aesthetical considerations, including the emergence of visible ceiling joints.

The reason for the visible ceiling joints is due to camber differences. Camber is a well-known phenomenon within precast concrete buildings and a natural consequence of the use of prestressed reinforcement. It is not possible to avoid camber differences between slabs all-together, why all prestressed slab systems have always been produced with chamfering in the sides. Such chamfering helps make sure that camber differences will not be noticed by the human eye.

In Scandinavia and Benelux, visible ceiling joints are generally accepted today, primarily due to the economic benefits of using precast concrete units. However, in Central- and Southern Europe, visible ceiling joints are to a much wider extent perceived as having an industrial and “ghetto-like” look and is one of the reasons prestressed slabs have found it difficult to penetrate the market for residential construction in these markets. Rather, cast-in place solutions or non-prestressed filigree slabs (half slabs) with a cast-in place topping are used with the economical and timely benefits of precast construction vanishing.

In Scandinavia and Benelux today, smooth and joint-free ceiling are primarily reserved for “luxury” projects. In such projects, this look is achieved using dropped ceilings systems (typically gypsum boards) underneath the slabs. Dropped ceiling are, however, both expensive to install while also increasing the height of the building.

With the SL-deck’s joint-free solution, it is now possible to achieve to high aesthetical quality from cast-in place construction with the speed and cost-efficiency of precast construction.

Full article from Concrete Plant International