Priced on Proof, Not on the Clock: Why Surface Preparation Should Be Sold as an Outcome

There is a familiar line in almost every blasting tender issued in Britain: so many pounds per hour, per rig, inclusive of operator, fuel and consumables, dayworks rates to follow. It is a convenient way to buy a service and an unreliable way to buy a result. The client is purchasing time; the contractor is being paid for time; and neither of them is buying a blasted surface to a stated standard until somebody starts arguing about it.

This is an argument for changing the unit of sale.

What the clock cannot tell you

Hourly pricing looks fair because it appears transparent. In practice it transfers almost every variable onto the party least able to manage it. Weather, access restrictions, unexpected coating thickness, friable substrate, an occupied building with a strict working window — all of these convert directly into invoiced hours that the client did not budget for and cannot readily challenge.

There is a second problem, quieter but more corrosive. Rig time rewards duration. No contractor sets out to spin a job out, but an hourly structure provides no positive incentive to work briskly, and no mechanism for the client to reward the crew that finishes a bay in nine hours rather than twelve. Efficiency improvements are invisible on an invoice that simply says hours used.

The dispute that follows

Main contractors working under JCT or NEC forms need to establish cause when a programme slips. If blasting was bought by the hour, the argument becomes one of attendance: how many shifts were lost, whose delay it was, whether the rig was standing idle through no fault of the client. Daywork sheets, gate logs and weather records become exhibits. Facilities managers caught in the middle find themselves explaining to a finance director why a package cost forty per cent more than the estimate when nobody can point to anything that failed.

By contrast, a dispute about whether a panel meets Sa 2½ is a technical question with a published answer. That is a far better argument to have.

Defining the outcome in measurable terms

An outcome-based contract is not vague language about a good finish. It is a schedule of measurable acceptance criteria, agreed before mobilisation. For steel substrates these typically draw on:

• Visual cleanliness to ISO 8501-1, commonly Sa 2½ for blast-cleaned steel prior to priming.
• Surface profile to ISO 8503-2, agreed by grade and comparator, for example medium G, with the method and frequency of check stated.
• Soluble salt contamination by Bresle extraction to ISO 8502-6 and 8502-9, with a threshold in milligrams per square metre.
• Dust assessment to ISO 8502-3 where a coating system is sensitive to it.
• Adhesion testing where a primer or coating is applied within the package, using cross-cut to ISO 2409 or pull-off to ASTM D4541, with the acceptance figure fixed in advance.

For masonry, concrete or timber the criteria differ, but the principle holds: the parties agree on a reference standard, a method of verification, a sampling frequency and a person competent to sign it off.

Structuring the agreement so it survives contact with site

An outcome price is only defensible if the assumptions behind it are written down. A workable structure usually contains the following.

A pre-tender survey and stated substrate assumptions. Existing coating type and thickness, substrate soundness, contamination, and any areas excluded from the price. Anything outside those assumptions becomes a variation.

A measurement basis tied to drawings, not hours. Measured areas, with a re-measurement rule for areas that differ from the drawn quantities by more than an agreed percentage.

A benchmark panel ratified jointly. The first defined area — often fifty to one hundred square metres — is inspected together and, once accepted, becomes the physical reference for the remainder of the works. Photographs of that panel sit in the contract file.

Hold points and joint inspection. Stated stages at which work pauses for sign-off. This protects both sides: the contractor is not asked to reblast work that was already acceptable, and the client is not handed a completed area that fails on inspection.

A weather and access provision. Rain, wind above safe working limits and condensation risk are British constants. The contract should state how downtime is treated, and reserve standing-time charges for delay caused by the client or by others under their control.

A variation mechanism for substrate condition. Two or three defined condition bands, each with an associated adjustment, allow a genuinely worse substrate to be priced without reopening the whole tender.

An evidence pack per area. Photographs, readings, instrument calibration records and a signed inspection sheet for each defined area. This is the deliverable that makes payment straightforward and later disputes short.

Payment milestones linked to those records. Money follows signed acceptance, not calendar months.

A named dispute route. An independent inspector, agreed before work starts, to adjudicate on contested areas. The existence of that clause prevents most of the arguments it was written for.

The commercial reality

Outcome pricing moves risk to the contractor, and it must be priced accordingly. A sensible bid carries a contingency, and a sensible contractor explains what that contingency covers rather than burying it. Open-book treatment of the allowance, with an agreed share of any underspend, is one way to keep the client comfortable without pretending the risk is free.

Two further points deserve attention. Cash flow becomes milestone-dependent, so the milestone schedule should be granular enough that a long bay does not starve the contractor of working capital. And wherever the contractor certifies a grade, professional indemnity cover should be checked against that activity, because a signed inspection sheet is a statement of professional opinion as much as a commercial one.

Why it is worth the effort

The practical benefit is fewer disputes, and shorter ones. Arguments shift from blame for elapsed time to evidence against a stated standard, which is a conversation two reasonable parties can finish in an afternoon.

For facilities managers, an outcome price is a number that can be defended in a capital submission, because it is attached to a defined asset condition rather than an estimate of effort. For main contractors, the programme reflects productivity rather than attendance, which makes sequencing with follow-on trades far more reliable. For the contractor, a reputation for certifying what it delivers is commercially valuable in a market where repeat work is won on trust.

The transition is best made deliberately rather than everywhere at once. Take one package, write the acceptance criteria properly, brief the supervisors on record-keeping, and run it. The paperwork is front-loaded and the arguments are not.