In Washington, crane-lifted forms must be securely attached to slings with a minimum safety factor of 5. If a sling fails, the form and everything under it moves with it. That makes the sling a specification item, and an estimator should settle it before the rigging line is priced. A low number built on the wrong slings is not a saving. It is a cost that turns up later, usually on a site with a crew waiting and a crane already booked.
Washington's construction safety rules address this situation in WAC 296-155-684. The same section also addresses makeshift lashing and hoisting equipment built in the field or in a shop, and both change what you price.
Material choice is a separate question. Many slings on formwork jobs are synthetic, and the Canadian Centre for Occupational Health and Safety explains how synthetic web slings behave under heat, sun, moisture, and contact with other materials in its guidance on synthetic web slings. That guidance is useful for the site-conditions part of the spec.
Work through the seven steps below in order, because each one narrows the choices in the next. Start with how the forms will move, then set the safety factor, choose the material, protect and attach the slings, price any custom gear, and finally assemble the rigging line. The advice stays with what to price and what to ask for.
If your job is outside Washington, check the rules where the work happens before you lock the spec. Treat the steps as the order of questions to ask, and let the rules that apply to your site fill in the answers.
Confirm the lift falls under the sling rule
Start with the lift method, not the price list. The sling requirement in WAC 296-155-684 depends on how the forms move. The rule covers forms that are "moved or raised by crane, cableway, A-frame, or similar mechanical device." If any part of the job uses one of those methods, the requirement applies to that part, whether the lift is a single panel going to a deck or a larger assembly moved to the next pour.
Write the lift method into the scope before you pull any rigging costs. A crane, a cableway, an A-frame, and a similar device each change what goes on the hook, so the sling spec follows from the method. An estimate that says "crane lift" on one line and "sling package" on another, with no link between them, is hard to check and easy to get wrong.
Ask the site superintendent or the form supplier how each form set will be handled. Forms are often moved by hand for one part of the job and by crane for another. Price the rigging for each lift type separately. Where a set is moved only by hand, the sling rule as quoted does not describe that work, and you should not carry sling costs for it without a stated reason from the site.
Ask about the sequence, too. A form raised once and left in place needs a different plan from a form that moves every day. The number of lifts, the distance moved, and whether forms are stripped or positioned all affect how many slings the crew needs and how often they are handled. Get those facts from the people who will run the crane, not from the drawings alone.
Walk the lift path with the crane operator if you can. The operator sees the radius, the swing, and the landing zone, and can tell you where a sling will rub, bend, or hang up. A short walk before the estimate is final is usually cheaper than a change order after the crane is on site.
Finally, record the lift list in the estimate file. Each lift should name the method, the form set, and the crew that will attach the slings. When the superintendent changes the plan, you can see which sling lines move with it.
Document the sling safety factor
You do not need to run the engineering calculation yourself to price the job. You do need the supplier to state the factor for each sling you are buying, at or above the minimum in the rule.
Put the spec in writing in every request for quote. Ask each rigging supplier to state the safety factor for the proposed slings and to confirm that it meets the requirement. A quote that does not state the factor cannot be checked against the rule. A lower-priced sling with an unstated factor is a risk you have not priced, not a saving.
Compare like with like when the quotes come back. Two slings can look alike in a catalog, have the same length and fitting, and still differ in the factor the supplier states. If one quote is missing the factor, send it back for the missing information rather than filling in the blank yourself.
Ask for the sling's identification as well as the factor. A supplier who can name the sling's rating, material, and serial or batch marking gives the crew something to match against the sling on the truck. A general claim does not travel well from the quote to the lift.
Keep the supplier's statement in the job file. When someone asks later why a given sling was chosen, the statement is the record that shows the spec was met for that lift. Without it, the estimate shows a price but not the basis for the price.
Choose the sling material for the site conditions
With the safety factor fixed, choose the material. The CCOHS guidance on synthetic web slings is the most direct source for this step. The page makes two points that matter for estimators.
The first is abrasion. CCOHS states that synthetic web slings are easily cut and have poor abrasion resistance when compared with chain and wire rope slings. Forms dragged over a rough deck edge, set against concrete corners, or wrapped around sharp steel will wear a synthetic sling faster than a metal one. That does not rule out synthetic slings, but the protection and replacement lines in your estimate have to reflect the path the sling takes.
The second is the environment. CCOHS states that "Sunlight, moisture, and temperatures above 90°C (194°F) or below -40°C (-40°F) damage both nylon and polyester slings." The same page says synthetic slings are typically not affected by grease, oil, moisture and certain chemicals. Those statements pull in different directions on moisture, so neither settles the question alone. The page also advises that you check with the manufacturer to determine which conditions apply to the exact material you are using.
Turn that into a request. Ask the supplier, in writing, which exposures the proposed sling tolerates: sun, rain or a wet deck, heat near the work, and contact with the oils, greases, and chemicals used on site. Form release agents are a good example, because they are common on formwork jobs, and the supplier's answer should name them.
Then match the price to the conditions. A sling for a shaded, dry staging area and a sling for an open deck through a hot summer may need different materials. If conditions differ between lifts, the estimate should say so line by line rather than averaging the lifts into one rate. A single blended rate hides the lift that will fail first.
Protect the slings from heat, cuts, and welding
Heat and sparks get less attention in estimates than they deserve. CCOHS advises: "Protect slings from heat sources such as steam pipes, open flame and welding splatter." Formwork jobs can have welding, cutting, or torch work close to the lift path, for embeds, bracing, or repairs. Sling routing should keep the slings clear of that work. Where that cannot be done, the slings need protection, or the hot work needs to move.
Price protection as its own line. Edge protectors or sleeves where a sling crosses a sharp corner are a small cost next to a damaged sling or a dropped form. Ask the crew to show where those protectors will go before the lift, so the protection is in place when the load first bears on the sling.
Build in an inspection allowance. Each sling should be checked before it goes on the hook, for cuts, abrasion, heat damage, and wear at the fittings. Ask the supplier and the site safety team to confirm the inspection schedule before you price the allowance. A sling with heat or cut damage is not one to patch and reuse to save money, so include a replacement allowance in the estimate.
Keep a simple sling log for the job. Record each sling's identification, the date it was inspected, what was found, and who did the check. The log turns a damaged-sling question into a matter of record rather than memory. It also gives the replacement allowance a basis, because damage found on earlier lifts is the best guide to how many slings a later job is likely to lose.
Storage matters too. Slings kept in the sun, on a wet pad, or beside a welding station will wear before the first lift. Include secure storage in the job setup, or confirm that the supplier's yard handles it. If slings sit on site for weeks between pours, the inspection before each lift matters even more than the original purchase check.
Last, decide who owns the slings during the job. If the crane company supplies them, replacement and inspection responsibilities may sit with that company. If your company supplies them, the estimate should carry the cost. Settle that in the subcontract or purchase order, not in the middle of a lift.
Attach the forms with proper hardware, not makeshift lashing
Under WAC 296-155-684, "tie wire, fiber rope, and similar makeshift lashing is prohibited."
For an estimator, that rules out a common shortcut. Crews sometimes reach for tie wire or fiber rope because it is on hand, and a rigging line that assumes it will do the job is not a compliant rigging line. The cost of doing it properly is the sling and its attachment hardware, not a roll of wire from the job box.
Confirm with the form supplier which attachment points or fittings the forms have, and whether the slings will fit them. A mismatch between a sling's fitting and the form's attachment point is easy to miss in an estimate and costly to find under the hook. If the fitting is wrong, the crew has to stop, change the hardware, and re-rig, so that time belongs in the estimate from the start.
Ask the superintendent how the forms will be attached in practice, from the first sling to the moment the load leaves the ground. If the answer includes any method other than the attachment hardware in your scope, correct the estimate before the crew arrives. A written sequence also gives the crew a set of checks anyone can follow, instead of a vague instruction to "rig it."
Give the attachment check an owner. Someone on the crew should be named as responsible for looking at each attachment before the lift, and that person's time belongs in the rigging line. An unnamed check is usually not done, even when everyone assumes it was.
Price engineering for field-built or shop-built gear
Some lifts need more than catalog slings. A lifting frame, a spreader, or a custom hook built on site or in a shop is hoisting equipment, and the rule covers it. WAC 296-155-684 states: "Field-fabricated or shop-fabricated hoisting equipment must be designed or approved by a registered professional engineer, incorporating a minimum safety factor of 5 in its design."
Price the engineering work and ask for the calculations with the design or approval, before the frame is welded and painted.
If the frame is bought from a supplier, ask for the engineer's approval and the stated safety factor in writing before you accept the price. If the crew plans to build it from stock steel on site, the design and approval work should be in the estimate before any cutting starts. A frame built on a guess cannot show that the design was approved, and the rework lands on the job budget.
Ask one question early: who is the engineer, and when are they engaged? An approval that arrives after the gear is built does not help the lift. Price the time for the review, not only the fee. The schedule should allow for a revision or two, because a first design returned for changes is a normal outcome.
Keep the drawings, the calculations, and the approval together in the job file. An estimate that cannot show engineering approval for each custom piece of gear has a gap in it, and the gap is most likely to show up on the day of the lift.
Also decide whether the gear is one-off or reusable. A frame built for a single pour needs its engineering priced once. For a frame reused across several pours or jobs, ask the engineer whether the approval covers the intended uses, and reflect any review costs in each estimate.
Assemble the rigging line and check it against the spec
Pull the pieces into one rigging line, and make every row trace back to a section above. Build the line from these parts:
- Sling count and type, with the supplier's stated safety factor
- Sling material chosen for the site exposures, with the manufacturer's confirmation
- Edge protection, inspection time, and a replacement allowance for damaged slings
- Attachment hardware that matches the form attachment points
- Engineering and approval for any field-built or shop-built lifting gear
- Crew time to attach the slings and check them before each lift
Once the line is built, check it before it goes to the client or the general contractor. Ask five questions. Does every sling's documentation meet the spec? Does the sling material match the conditions for each lift? Have you excluded prohibited lashing methods? Is there engineering in the scope for each custom piece of gear? Does every lift on the lift list have its own sling line?
Read the line once as the crew would. A foreman should be able to tell which sling goes on which lift, which attachment point it uses, and who checks it before the load moves. If any row leaves the foreman guessing, the row needs more detail. Clear rows also protect the estimate, because a client who approves a specific rigging package is less likely to dispute the cost when the lift goes ahead as written.
If the answer to any of these questions is no, the rigging line is not ready to send. Fix the gap, then check again. It is quicker to correct a line in the estimate than to correct a sling package after the crane is booked and the forms are stacked.
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