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Visit to Holterman Factory

A group of 6 people, all part of the Building Team for our new building, visited the STF Holterman factory where the prefab concrete part are being produced.

The group consisted of DuraVermeer (developer), Ector Hoogstad Architects and DuPont. During the visit, the plant manager gave a plant tour and explained more about the production process of these pre-fab parts.

After the architect had designed the building on paper, a team of people turned it, together with the architect, into a construction plan with details about each part of the concrete the building will be built with. For each individual part, the required strength was calculated, which in turn was translated into a design for the reinforced concrete part.

This brief report includes photos of the tour along with a short description, with the purpose of showing how much time and effort the preparation of the prefab parts for requires.

Visit to Holterman Factory

In the carpentry, the molds for the pre-fab parts are prepared. Highly skilled carpenters are required for this particular job. They have to think in “negative” as they create the mold that will shape the pre-fab part. Special recesses are made for places where later on, cables, connections and pipes will be placed.

All the prepared parts are labeled and transferred to the factory hall where the actual mold is being build. On average it takes the carpenters around 5 hours to make one relative simple mold.

Once the mold is finished, the inside is cleaned, oiled and special holders are placed inside. These round shaped holders are needed to make sure the metal enforcement that is going to be place inside the mold, is not touching the outside of the pre-fab part.

Visit to Holterman Factory

In a separate hall in the plant, the metal enforcements are made by welding the different parts together and cutting out pieces where openings are needed. The finished enforcement is transferred to the prepared mold and hoisted in place. Once all final parts have been added and fixed in place, the mold is ready to be filled with concrete.

In this way, all the “tables” in the hall are prepared with molds and filled with concrete every day. Most of the pre-fab parts need 1 day to harden and can be taken out of the mold the next day. Then the entire process starts over for the next pre-fab part.

Visit to Holterman Factory

During the visit, the largest part of our building was just finished and was taken out of the mold. The label below shows how each part is recorded so it can be tracked throughout the plant and transported to the building site. At this moment the plant is preparing pre-fab parts for six different projects - the new Leiden building being one of them. They will continue the production for around three months, after which all pre-fab should be completed.

Most likely, the large crane needed to put all the pre-fab concrete parts in place will be build in Oegstgeest on April 3rd. The week of April 9th, they will start “stacking” the prefab parts. The plan is to have one floor finished each month.