The short answer: work out both the weight and the surface area of every item, because finishing is priced on one or the other. Hot-dip galvanising is commonly charged by weight, while blasting, painting and powder coating are usually priced by surface area and the coating system. Then add preparation, freight, handling and turnaround time, and confirm the basis with your finisher.
Know which basis your finisher uses
Ask each of your coaters how they quote, and write it into your rates. As a general pattern:
| Finish | Usually priced by | Things that change the price |
|---|---|---|
| Hot-dip galvanising | Weight (for example per tonne) | Awkward or bulky items, venting and draining work, minimum charges, duplex coating |
| Blast and paint | Surface area and coating system | Blast standard, number of coats, film thickness, colour, masking |
| Powder coating | Surface area or per item | Size of the oven, pre-treatment, colour, masking, minimum batch |
Every finisher is different, so treat this as a starting point and confirm it with yours.
Calculate weight and surface area for every item
Weight comes from your take-off: mass per metre times length for sections, and length times width times thickness times density for plate. Surface area comes from section tables, which give the painted surface area per metre for each section. For plate, include both faces and the edges. On thick plate, the edges add up.
Light, detailed items such as handrail, stairs and grating have a lot of surface area for their weight. Heavy beams have relatively little. That's why a single "per tonne" finishing rate goes wrong on mixed jobs.
Read the coating specification
The specification should name the coating system. For galvanising in Australia, the reference standard is AS/NZS 4680, and AS/NZS 2312.2 guides selection for durability. For paint systems, look for the surface preparation standard, the number of coats and the dry film thickness. If the spec just says "paint", send an RFI. A one-coat primer and a three-coat industrial system are very different prices.
Don't forget the hidden costs
- Design for galvanising: vent and drain holes in hollow sections and closed assemblies, which add drilling time.
- Freight: to and from the coater, including loading and unloading time.
- Turnaround: days at the coater affect your program and your delivery date.
- Touch-up and repair: after erection or after site welding.
- Masking: faying surfaces, threads and areas to be site-welded.
- Minimum charges: small jobs can attract a minimum fee.
Show it clearly on the quote
List the coating system, the standard, and what's included and excluded, such as touch-up on site. If you've priced galvanising by weight, it's worth showing the weight you assumed, so a change to the steel can be priced fairly.
How we help
Factory Hub lets you pick a finish for each line on the quote and calculates it from the item's weight or surface area, including plate edges, so finishing is priced from the take-off rather than guessed.
This guide is a general summary. Always confirm pricing with your finisher and check the coating requirements in your project specification.
Common questions
Is galvanising priced by weight or surface area?
Hot-dip galvanising is commonly priced by weight, while painting and powder coating are usually priced by surface area and coating system. Always confirm the basis with your finisher.
Which Australian standard covers hot-dip galvanising?
AS/NZS 4680 covers hot-dip galvanized coatings on fabricated ferrous articles, and AS/NZS 2312.2 guides the selection of galvanized coatings for durability.
Why does a per-tonne finishing rate go wrong?
Light, detailed items such as handrail and stairs have much more surface area per tonne than heavy beams, so a single per-tonne rate under-prices area-based finishes on light work.