Stramit PrimeForm



This Stramit PrimeForm™ Left-in-place Formwork System Technical Manual includes product features as well as installation techniques and formwork design data. 

Features include:

  • Long spanning formwork that saves time by removing the need for propping joists.
  • Left-in-place formwork eliminates the need for removal, cleaning and storage.
  • Easy sheet locking for fast laying.
  • Convenient 500mm or 600mm wide location widths for easier setout.
  • 100mm rib spacing assists in reinforcement layout.
  • Grooved flat surface for safe and easy walking.
  • Stramit PrimeForm™ Shades™ has a low-reflective coating that improves worker safety and comfort. 

Stramit continues to collaborate closely with various academic and research organisations. Testing of Stramit®products is mainly performed by independent bodies.This interaction ensures that Stramit is at the forefront of metal deck system design for floor slabs. 


Stramit PrimeForm™ Left-in-place Formwork System is ideal for floor slab construction in residential, commercial and many industrial applications when used in conjunction with propping systems. It is suitable for use in both steel frame and concrete frame floor slab construction where conventional plywood is generally used. In addition Stramit PrimeForm™ Left-in-place Formwork System can be used in post-tensioned slabs. 


Stramit PrimeForm™ Left-in-place Formwork is manufactured from high-tensile (G550) steel with a Z350/Z450* galvanised coating, in full conformance with AS1397. Stramit PrimeForm™ Left-in-place Formwork End Cover accessory is manufactured from high-tensile (G550) or G300 steel with a Z275 galvanised coating.

* Z450 galvanised coating is not readily available and requires a special order 


Stramit PrimeForm™ Left-in-place Formwork has been tested for fire and structural performance by independent test authorities. 

  Stramit PrimeForm™ Left-in-place Formwork is supplied in 0.60mm bmt 0.75mm bmt. 



Stramit Product


Mass – Z350

Mass – Z450



per unit

per unit

per unit

per unit








*Base metal thickness (BMT) is used for structural design analysis, whilst total coated thickness (TCT) values are approximate and given for reference only.

Engineering Specification

Maintaining the correct specification of formwork is important to ensure that all design requirements are met.

The following specification is recommended: 

The formwork shall be Stramit PrimeForm™ Left-in-place Formwork with 27mm high ribs spaced at 100mm centres. Material shall be G550 high-tensile steel in accordance with AS1397, with a Z350/Z450 galvanised coating.  

Individual sheets shall be hinged into position in accordance with the manufacturer's instructions. Prior to placement, concrete pouring, foot traffic and other construction loads being applied, the left-in-place formwork shall be propped in accordance with the manufacturer's propping table. Reinforcement and concrete placement shall be as directed by the engineer. All work is to be completed in a workmanlike manner and all dirt, mud, debris, screws, rivets, cuttings, etc are to be removed prior to concrete pouring. Props are not to be removed until authorised by the site engineer.

Adverse Conditions

Stramit PrimeForm™ Left-in-place Formwork has excellent durability. However, in applications close to marine or severe industrial environments, or closer than 450mm to the ground, please contact Stramit for a more detailed assessment of your needs, and any precautions that may be required. Note however that in the event of decking corrosion there is no compromise to the slab strength or performance. 


Direct contact between galvanised steel and copper, or water run-off from copper onto galvanised steel must be avoided, as premature corrosion will result.



System Description

Floor slabs using Stramit PrimeForm™ Left-in-place Formwork are like any conventional reinforced concrete slab except that the formwork is left in place rather than removed. 


There are no changes to the design of a reinforced concrete slab when using Stramit PrimeForm™ Left-inplace Formwork. In detailing the only change is that the depth of the formwork (27mm) must be added to the slab depth (equivalent to 9mm of concrete). Placement heights for reinforcement must be taken from the top of the profile. 

Remember that the floor to slab clearance height must allow for the height (27mm) of the left-in-place formwork. 

The layout of Stramit PrimeForm™ Left-in-place Formwork must ensure that each sheet has at least two permanent supports.The sheet ends should be as close as practical to the permanent supports with a minimum contact width of 50mm at each support.The sheet ends are to be fixed to the permanent supports or embedded into the concrete beam by at least 25mm.


In service Stramit PrimeForm™ Left-in-place Formwork is nominally unloaded as the slab carries the load. However during placement and pouring the formwork will be subjected to construction loads. The accompanying tables assume construction loads as recommended in AS3610.

Deflection Limits

The span data shown incorporates a deflection allowance of L/240 and L/150. Overall slab deflection, including longterm deflection is a characteristic of the concrete slab design.

Composite slab design

Stramit PrimeForm™ Left-in-place Formwork has not been verified for composite performance.Therefore no composite action can be considered between the metal deck and the concrete. 

Design Principles

In the formwork mode design checks are made for positive and negative moments, deflection and reaction, and critical interactions of these.

Fire Design

Stramit PrimeForm™ Left-in-place Formwork is not taken into account in the slab strength design so there are no additional design requirements associated with fire. In fact tests have shown that, where other design constraints such as strength or deflection are not governing, there is a benefit in fire resistance. For a 2-hour fire rating an overall system depth of 120mm (i.e. full concrete slabs of 93mm plus profile depth of 27mm) is sufficient.

Span Table

STRAMIT PRIMEFORMä - Deck Section Properties (per metre width)





range* of
I values

 (104 mm4)

properties for strength limit state












6.16 – 8.8









9.15 – 10.8






* Value varies with span lenghts

Please refer to the Stramit PrimeForm™ brochure for the Deflection Limit Span Tables on pages 6 and 7.


The sub-headings within this Installation section are indicative of the sequence of installation. 

Good Practice

Stramit recommends that good trade practice be followed when using these products, such as found in CCAA/Standards Australia handbook HB67 ‘Concrete practice on building sites’. 

Site Induction

Consideration should be given to handling and installation issues as part of site induction safety procedures. Specific consideration should be given to pack handling, avoidance of cuts, trips, slips and falls, long sheet handling particularly in windy conditions, sheet cutting procedures and surface temperature on sunny days. Personal Protection Equipment (PPE) should always be used.

Sheet Handling

Cut resistant or leather gloves should be worn when handling product. Foot protection should be warn when handling and transporting product.


It is imperative that permanent supports (steel or concrete beams, or walls) be stable and of adequate strength to withstand loadings prior to the placement of the formwork. In the case of masonry walls, a dampcourse strip should be installed between the masonry and the decking. 


Take care when walking on Stramit PrimeForm™ Left-inplace Formwork System, particularly if the surface has become wet. Avoid walking on the sheet edge.


Stramit PrimeForm™ Left-in-place Formwork System is supplied cut to length so that cutting is generally only required around projections and cut-outs. Use a power saw fitted with an abrasive disc or metal cutting blade. It is recommended that cuts be started with the decking laid upside down (ribs down).Then turn the sheet and, necessary, complete the cutting of the ribs.This method should provide the neatest finish, and minimise the risk burred edges being exposed on the finished slab. 


Stramit PrimeForm™ Left-in-place Formwork will generally be propped unless spans are short. Spans given in this manual assume that props or propping frames will be used with propping bearers. Propping joists are generally not required but may be used to suit a particular propping frame arrangement. All propping should meet the requirements of AS3610, including bracing. 

Decking Placement

Stramit PrimeForm™ Left-in-place Formwork is easily placed by hinging the overlap edge of one sheet over the underlap edge of the previous sheet. Designated propping must be positioned first. The sheets can be laid to provide either 600 cover or 500 cover to minimize onsite cutting requirements. 


Once decking panels are laid they should immediately be secured against possible wind uplift. Typically use two fixings per sheet at end supports and one fixing per sheet at permanent internal supports. Self-drilling and tapping screws or powder actuated drive pins are commonly used. These fixings should be in the decking troughs. In exposed conditions additional fixing may be required. Puddle welds will also provide wind uplift resistance. 

Side-Lap Fastening

Side-lap fastening is only required if stacked construction materials are to be laid on the decking.Where required, side-lap fasteners should be at least No.10x16 self-drilling and tapping screws.These should be fixed through the trough in the sheet overlap, and positioned at mid span. As the screws will protrude below the deck surface consideration should be given to removing them prior to the concrete pour. 

Slab Edges

The edge of Stramit PrimeForm™ Left-in-place Formwork System may be addressed in a number of different ways.

Edges of metal deck slabs exposed to direct or indirect rainfall should have a continuous drip feature to prevent water running to the underside of the decking. This is typically achieved by incorporating a formed notch in an all-concrete edge strip overhanging the supports. 

Slab Penetrations

Any shape and size of penetration can be cut through Stramit PrimeForm™ Left-in-place Formwork decking.  Provide adequate supports around the decking cut-out prior to concrete pouring as for conventional plywood.

Stramit PrimeForm™ End Capping

End capping is available to provide a neat finish to the ends of Stramit PrimeForm™ Left-in-place Formwork decking.  Its use is particularly recommended for cases where the decking ends protrude into a band beam or similar opening where the capping provides a safer contact edge. 

Stacked Materials

Care must be taken during construction to avoid damage from stacked materials. The formwork span data given in this manual is based on a maximum stacked material load of 4.0kPa.  Refer to the engineer or the design drawings for the stacked material allowance used in design, as this is often varied.  If in doubt either do not stack materials onto the decking, or contact your Stramit Technical Representative.


Stramit PrimeForm™ Left-in-place Formwork provides good resistance to leakage during concrete pouring.  For most applications where the concrete slump is not excessive and the end capping is used no sealing is required. To prevent slurry leakage (if required) just tape over the recesses at each sheet end. 

Mesh Placement

Place mesh and reinforcement as you would for conventional plywood formwork.  Ensure that bottom cover distances are taken from the upper surface of the formwork decking. 

Concrete Pouring

Finally, the concrete must be poured evenly to the panel ends on the prepared clean deck, in the direction of span of the decking. Heaping of wet concrete must be avoided.  The concrete should be placed in accordance with the requirements of AS3600 and have a minimum 28 day compressive strength f’c = 25MPa and slump satisfying the engineer’s requirements.  As a guide, the slump should be 60mm – 80mm for vibrator compaction.  Hand compaction is not recommended. 

Concrete Curing

Stramit PrimeForm™ Left-in-place Formwork System slabs require the same degree of curing as a conventional reinforced concrete slab.  Follow the guidelines within AS3610. 

Prop Removal

Temporary propping must not be removed until the slab has cured sufficiently.  Prop removal procedure should be in accordance with AS3610 at the direction of the engineer. 

Suspension Hangers

Use shot-fired support pins/hangers through the upper surfaces in the recesses of the decking profile.  Do not rely on attachments to the under-hanging ribs.  



Obtaining Prices

Prices of Stramit PrimeForm™ Left-in-place Formwork System and accessories can be obtained from your nearest Stramit location, or distributor of Stramit products.


The Stramit PrimeForm™ Left-in-place Formwork System comprises:- 

Stramit PrimeForm™ Left-in-place Formwork decking – 0.60mm OR 0.75mm thick 
Stramit PrimeForm™ - End Capping – 0.55mm 
Stramit Edgeforma™ Slab Edging – 1.00mm (for slabs up to 140mm) OR 1.60mm (for slabs up to 200mm)


Stramit PrimeForm™ Left-in-place Formwork System can be supplied in any length up to the limit of the local Transport Authority regulations.Where practical nominated lengths should be site measurements rather than plan dimensions.The tolerance on lengths supplied is +/- 5mm.  Ensure that the lengths specified are the actual required sheet length, and not the spans used in design. Sheets must take into account the design requirements for permanent supports at each end of every sheet. 


Stramit PrimeForm™ Left-in-place Formwork System and accessories can be ordered directly from Stramit, or through distributors. 

Lead Times

Stramit PrimeForm™ Left-in-place Formwork System is normally supplied within 2 to 3 days of placement of order in Victoria. Please talk to Stramit about current lead time for other locations, particularly for large or non-standard orders. 

Related Products

Stramit also offers Stramit CondeckHP®metal formwork, a long-spanning composite permanent formwork decking used for slabs. 


Lead times are subject to location and quantity. Please talk to Stramit about delivery scheduling for large projects. Ensure that suitable arrangements have been made for truck unloading, as this is the responsibility of the receiver. Pack mass may be up to one tonne.

Site Storage

It is recommended that sheets be placed as soon as possible after delivery. If site storage is necessary packs should be kept dry and above ground. If sheets do become wet they should be separated, wiped and placed in the open to promote drying.



Technical Assistance

Stramit has experienced engineers and technical staff in each region. For assistance with design issues, decking applications and practical advice, contact your regional Technical Services Manager. Alternatively, ring your nearest Stramit location and say you have a technical enquiry regarding Stramit PrimeForm™ Left-in-place Formwork System. 

Further Information

As well as our standard range of Technical Manuals, Installation Leaflets, Case Studies and other promotional literature Stramit has a series of Guides to aid design. 

  • Concealed Fixed Decking
  • Roof Slope Guide
  • Foot Traffic Guide
  • Bullnosing, Curving and Crimping
  • Acoustic Panels
  • Cyclonic Areas
  • Spring Curving Guide

Please contact your nearest Stramit location for any of these guides, other literature. 

Other Products

Stramit offers a wide range of building products, including:

  • CondeckHP® composite decking
  • Purlins and girts
  • Roof and wall sheeting
  • Lightweight structural sections
  • Truss components
  • Gutters and downpipes
  • Fascias
  • Custom flashings
  • Insulating products
  • Fasteners