A formwork carpenter is a type of skilled worker who specializes in constructing formwork that acts as a mold in which concrete can be poured and supported until it sets. This type of carpenter will work with various types of formwork and falsework to create a usable mold before any concrete pouring processes begin. The formwork carpenter may or may not also help in the process of pouring the concrete and monitoring as it sets. Once the concrete has set fully, the carpenter will be responsible for removing the falsework and formwork.

https://www.practicaladultinsights.com/what-does-a-formwork-...

Een betontimmerman of bekister is een bouwvakker die bekistingen van hout of metaal maakt. In de (traditionele) bouw maakt hij de bekistingen volgens de aangeleverde vormtekeningen.

Samen met de ijzervlechter, die het betonstaal op de juiste plaats monteert, geeft de betontimmerman dus vorm aan de betonnen bouwelementen, voornamelijk funderingen en de hoofdconstructie (kolommen, vloeren, liftkokers, wanden, balken en lateien) van gebouwen.

https://nl.wikipedia.org/wiki/Betontimmerman

See: https://en.wiktionary.org/wiki/shutterer

"shutterer: (construction) A worker who constructs shuttering/formwork."

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Looking for: Shutterer / Carpenter

For one of our clients, we are immediately looking for Shutterers – Carpenters. In this position you work in a motivated team with professionals. You are mainly concerned with the making of formwork in which concrete is poured. You are responsible for the dimensions and the quality of the formwork and the associated work..

(https://www.europeatwork.nl/vacatures/shutterer-carpenter/?l... )

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Note added at 10 hrs (2022-03-09 10:28:03 GMT)
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see also: https://en.wiktionary.org/wiki/formworker

"formworker (plural formworkers):
A laborer or workman who makes formwork.

Synonyms:
– formwork carpenter
– form setter
– (UK) shuttering carpenter"

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Note added at 10 hrs (2022-03-09 10:29:27 GMT)
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Groot Woordenboek Duits-Nederlands (Van Dale):

betontimmerman (dem)
1. Einschaler (der)

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Note added at 13 hrs (2022-03-09 13:56:13 GMT)
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"What does it take to become a CONCRETE SHUTTERER?

A concrete shutterer’s job description includes fabricating and setting up the forms in which concrete is poured to create walkways, walls, pillars and other structures. Work alongside construction workers by erecting and setting forms for concrete structures, they build wooden moulds and clamp them using appropriate hand tools in fabricating concrete beams, columns and panels. They also introduce rebar or wire mesh to reinforce the material, use trowels and other tools to spread and smooth concrete, and mold expansion joins and edges. They interpret blueprints and read survey stakes with a view to establish appropriate grades, prepare worksites for concrete footings and assemble concrete forms on specified locations." (https://careerportal.nta.com.na/wp-content/uploads/2020/10/1... )

seems to be widely used in this context see reference