The best methods for repairing wall formwork
Have you purchased wall formwork (panels) and need to know how to maintain and repair them?
Looking for some tips to make them last as long as possible?
Let’s see what the most common and optimal steps to take care of your panels are!
Wall formwork panels are steel (or aluminum) components for concreting vertical walls. The steel frame is usually galvanized or painted.
Normally, this formwork is covered with a plywood panel coated with a special film (phenolic resin) to prevent the concrete from adhering. In exceptional cases, plastic or metal cladding can also be found, but in this article we will only talk about panels with plywood cladding, which is undoubtedly the most commonly used solution.
Why is it important to know how to repair and maintain wall formwork?
Durability and re-usability
Wall formwork panels are modular components that have a fairly long service life. You can use them for many years, depending on how well the material is cared for on site and the maintenance carried out over the years.
The weakest component of the formwork is the phenolic resin plywood sheathing, to which you have to pay more attention in installing it and in the maintenance/repair phase.
Since the purchase of these systems requires significant investments, it is very important to ensure ongoing maintenance in order to amortize the investment over a period of time as long as possible. Therefore, I recommend that you start maintenance from the same purchase, whether it is new or used material.
Cleaning the frame and phenolic resin
What actions are required to keep the formwork clean before, during, and after a job is done?
1.- The first action to take before using the material, is to check that it has the correct qualities for use (clean and greased). If not, this needs to be corrected.
2.- The second action, during the use in the work execution, is to clean/minimize the slurry in metallic and phenolic resin parts, as well as to grease the phenolic resin part on every concreting with release agent.
3.- The third action after use, when the formwork is returned from a construction site to be stored until further use, is to clean the frame and the phenolic resin. The panels ‘breathe’ concrete, and the concrete sticks to them, this is absolutely normal.
How can you clean the frame by removing the adhering concrete fragments?
There may be different degrees of concrete adherence on both sides of the panel, and depending on the number of concrete fragments, one methodology or another can be used for cleaning.
This classification could be divided into three categories:
1.- Extremely dirty panel: in this case there are three batches to perform:
- First phase of pneumatic hand hammering tool removing thick concrete on each side of the panel going deep into hard to reach places and through holes for plugged bolts.
- Second phase with a hydro-cleaner, cleaning debris and adhered grout (does not include phenolic resin part). It is a very high pressure water jet cleaning, using special hydrodynamic machines. This process allows the removal of concrete fragments with little effort, although it is slower on the inside face of the panel. The pressure to be used on the steel structure is 1,000 bar.
- If required for various reasons of adhesion, a third stage with abrasive grinding and removal of final residues may be required. The grinder works by ‘smoothing’ the frame and then removing the concrete debris. This process has the advantage of using a less expensive machine, less heavy and with no water consumption. On the other hand, it is a process with a greater impact in terms of airborne dust.
2.- Medium soiled panel: It would include the second phase indicated above, with some retouching in areas where bolts pass through with a first phase tool.
3.- Panel not very dirty: Only the second stage tool (hydro-cleaner) would be necessary.
It is important to note that these three classifications do not include oxidized material that must pass through a shot blasting room and then be recycled with paint.
Phenolic resin repair
The next step after cleaning the frame is to repair the phenolic resin plywood sheathing. The phenolic resin panel is the most delicate part of the formwork, and therefore the one that is subject to the most wear and tear. It usually consists of a plywood panel covered with a phenolic resin film with protective resin, which guarantees its waterproofing.
The use of the formwork on site frequently causes wear or abrasion of the phenolic resin sheet, which can tear, and can be replaced in case of serious breakage or excessive wear.
So it’s definitely the part of the formwork you need to pay attention to.
To operate in the repair of phenolic resin panel, there are mainly two methods:
- Putty polyester: it is an excellent solution for minor and/or irregularly shaped breaks. It enables fast and efficient repair in terms of adhesion to the panel, without leaving any trace that would be visible in the following concreting. It must be applied on a very clean and dry surface.
- Wood patch: for small/medium holes there are repair methods with wood veneer plugs of the same phenolic resin type, pre-cut to size. Using a special wood milling machine, the hole is given the correct shape and at the same time the appropriate size sealing plug is inserted. With this procedure, holes up to 6 cm in diameter can be closed, or breaks of even greater length (not recommended in conjunction with metal profile mainly in angular areas or longitudinal damage caused by dragging on the ground or touching parts of steel framework).
Phenolic resin replacement
If the phenolic resin panel is too damaged, it must be replaced. Before replacing it, the condition of the panel’s back side should be checked, as it is often in very good condition, so you can simply flip it over to use the side on the back. Make sure that it doesn’t have too much damage to be used, such as excessive drilling, splinters or burst parts perforating the usable face.
Whether replacing or rotating, the process entails removing the bolts that attach the plywood to the frame, placing the new plywood and replacing the screws in the frame (never change the number of screws indicated on the product design).
Finally, it is important to apply silicone to the entire perimeter edge of the panel at the connection with the frame, for sealing purposes and to prevent humidity in the wood.
The use of the panels on site inevitably involves wear and tear, which can cause dents, rust, holes, cuts and bending of the frame.
- Dents: Repairing frame dents is not always straightforward, but for damage that is not too large it is possible with ‘manual’ action and using a hammer or similar tools.
- Drillings: up to Ø50mm you can repair with welding.
- Cuts: depending on whether it is straight, oblique or missing part of the frame, decide whether to repair or discard to scrap.
- Rust: rust is a process due to the action of air, water and humidity on metals without protective coatings. Since the panels are continuously exposed to atmospheric agents, it is normal for rusty areas to form over time, even if they are galvanized. When a panel is rusted, the most effective process is sandblasting/blasting and re-galvanizing (and repainting), to bring it back to a protective condition against rusting agents. It is very important to exhaustively review possible perforation due to rust on any part of the metal frame that may cause sinking or deformation in the installation of the formwork on site. In this case, discard the panel for scrap.
- Frame bending: if the panel’s frame is bent so much that the verticality of the concreting is no longer guaranteed, it must be rectified. It is an important process to avoid ‘distortions’ when concreting the wall and therefore to ensure the minimum tolerances required in carpentry. Grinding can only be carried out in special centers with suitable machinery.
In case of frame bending or diagonal misalignment, it cannot be rectified and must be discarded for scrap.
I hope that you now have an idea of the different actions that can or should be carried out when maintaining wall formwork panels, although this topic would certainly require more exhaustive study.