Resources
Frequently Asked Questions
The questions engineers and site teams ask most. We state the limits too — we are not claiming this suits every situation.
Will plastic formwork withstand the lateral pressure of fresh concrete?
Yes — provided the stated rate of placement and lift height limits are observed.
The lateral pressure fresh concrete exerts on formwork is not constant; it varies with pour rate, lift height, concrete temperature and consistency. This is the same physics for steel and plastic alike — every formwork system is designed to a defined pressure.
The design pressure, maximum rate of placement and maximum lift height for MenfeX panels are stated in the installation guide and on the panel label. Exceeding these limits can deform the panel — a rule that applies to every formwork system.
Does leaving the formwork in place cause a structural problem?
No. The plastic is excluded from the structural section and carries no load.
The structural approach is the same as for the stay-in-place formwork systems already in wide use: the formwork is not a load-bearing element. Capacity is provided entirely by the reinforced concrete section, exactly as in a culvert cast with steel formwork. The design ignores the plastic.
Reinforcement layout and 50 mm cover follow the project's structural design — MenfeX changes neither.
Will the client's engineer approve stay-in-place formwork?
Stay-in-place formwork is a recognised method, but its use in culverts depends on the project specification and the client's engineer.
Be sceptical of any supplier who tells you it is unconditionally permitted. On public contracts, a change of forming method goes through the supervising engineer and is confirmed in writing.
Raise it during the construction programme, not after award. The technical file to submit and the steps to follow are set out on the Specification & Approval page. We support witnessed trial installations on site where required.
Will it withstand vibration?
Yes, with normal internal vibration practice.
Concrete is compacted with a vibrator as in any formwork system. The one precaution is not to hold the poker against a panel face for a prolonged period — a rule that applies to steel formwork for surface quality, and here for both surface and panel.
Recommended poker diameter and immersion spacing are given in the installation guide.
Does it deform in hot or cold weather?
Not within the stated service temperature range.
The service temperature range is given in the product data sheet and covers the conditions in which concrete is normally placed.
Note that where temperature becomes critical, concreting itself is restricted — curing in extreme heat, setting in extreme cold. The limit is set by the concrete, not the formwork. Storage guidance for panels left in prolonged sunlight is in the installation guide.
Does the top slab form need propping?
It depends on the clear span. Small spans may need none; larger spans do.
The deck form carries the weight of wet concrete plus construction loads, and that load rises quickly with span. Above a given span, propping is installed beneath the form. Prop spacing by span is tabulated in the technical documentation.
This is not specific to MenfeX — steel systems are propped too. The difference is that here what gets struck afterwards is the props, not the formwork.
Does the plastic surface improve hydraulic capacity?
Do not expect a meaningful increase — but surface quality becomes consistent.
We would rather be straight about this. For hydraulically smooth sections — concrete, PVC or polyethylene alike — Manning's n is generally taken as 0.012–0.013. Against well-finished concrete, plastic offers no material hydraulic advantage.
The real difference is elsewhere: in cast-in-place culverts the inner surface varies with formwork and workmanship, and honeycombing raises flow resistance. A factory-formed surface removes that variability — a gain in predictability, not in capacity. Continue to use the coefficient specified in your design.
How does it behave in aggressive or sulphate-bearing ground?
The plastic surface does not corrode, but the concrete mix still follows the specification.
Sulphate-bearing soils are common in irrigation areas and the specification then requires sulphate-resisting cement. MenfeX does not remove that requirement — the plastic is there to form the concrete, not to protect it. Concrete class and cement type always follow the project specification.
The plastic itself does not rust or rot.
How does the cost compare with steel formwork?
Compare total cost per culvert, not the price of the formwork.
MenfeX is a consumable; steel formwork is an investment. Placing the two purchase prices side by side is meaningless. The right benchmark is what it costs to finish one culvert: the per-culvert items that recur with steel — crane, erection, stripping, release agent, cleaning, freight, storage, patching — are absent or much reduced here. Against that, MenfeX is bought for every culvert.
An honest note: if you are casting hundreds of identical culverts in one location with a crane already on site, steel is probably more economical. The calculator will not hide that from you.
How many culverts fit in a truck or container?
Substantially more than a steel set — the panels are light and stack densely.
Units per truck and per 40' container are given in the product data sheet. This is a decisive line item on dispersed sites and in export: a heavy steel set usually needs specialised transport and lifting equipment at both ends, whereas MenfeX ships on standard vehicles and is unloaded by hand.
What is its behaviour in fire?
The culvert itself is reinforced concrete; the plastic is a thin surface layer.
In watercourse culverts there is effectively no fire load. On large-section culverts used as underpasses the client's engineer may raise the question; the material's fire behaviour is stated in the product data sheet.
Where a project requires it, the inner surface can be rendered or lined.
What happens to the plastic over the culvert's service life?
The plastic does not rust or rot and is chemically stable in soil and water.
Because it contributes nothing to structural capacity, its degradation over time cannot reduce capacity either — the reinforced concrete section carries the load. Even in the worst case you are left with an ordinary reinforced-concrete box culvert.
For long-term abrasion behaviour in fast-flowing watercourses carrying abrasive material, see the product data sheet.
Is it recyclable?
The material is a recyclable polymer, though in a culvert it is used permanently.
A note on comparison: steel formwork is reused, but every cycle consumes release agent, wash water and transport fuel. A total environmental comparison needs measured data, and we make no unverified claim here.
How many people and how long does installation take?
No crane is required; panels are carried and erected by hand.
Crew size and installation time for a typical culvert are given in the product data sheet. No specialist trade is needed — the system is designed to be installed by any crew that can put up formwork.
We provide on-site support for the first installation.
What do I use to form the wing walls?
Wing walls and headwalls are formed at the inlet and outlet once the culvert barrel is complete.
Talk to our sales team about the forming solution for these — we advise based on the wing wall geometry in your project.
Question not answered here?
Ask your project-specific technical questions directly — our engineers will answer.