Executing a public works contract in Spain

Execution does not begin with the signature but with the acta de comprobación del replanteo (setting-out verification report): within one month of contract signature, the supervising team and the contractor verify on site that the design is viable and the land is available. The date of that report starts the clock on the execution period, a decisive fact for everything that follows (works programme, penalties, extensions). If the setting-out reveals problems, recording them in the report is the contractor's first line of protection.

The contractor is paid through certificaciones de obra (progress certificates) issued by the supervising team, as a general rule monthly, for the works actually executed valued at contract prices. Certificates are payments on account, not partial settlements: the definitive measurement comes with the final certificate. The administration has thirty days to pay from the approval of each certificate, with late-payment interest accruing automatically. The full mechanics, from the valued measurement to payment, are developed in the article on certifications and acceptance in public works.

No design survives contact with the site intact. The LCSP allows contract modification, but under a strict regime (articles 203 to 207 and, for works, 242): only on the grounds listed in the law, within precise quantitative limits and through a formal procedure. New work items that do not appear in the contract price schedule are valued through precios contradictorios (new rates negotiated between the supervising team and the contractor). Executing modified works without prior approval is the most expensive mistake in Spanish public works: proceeding de facto creates no right to payment. The full legal regime is analysed in the article on contract modifications and new rates.

Price revision allows contract prices to be updated when costs vary, but since the de-indexation act (Ley 2/2015) its scope is restrictive: only through official polynomial formulas provided for in the tender documents, never before two years of execution and twenty per cent of the contract amount have elapsed, and generally excluding labour costs. For bidders, knowing whether the contract includes price revision is a pricing input: in long contracts without revision, inflation risk is carried in the bid price. The conditions and formulas are detailed in the article on price revision in works contracts.

The execution period is an essential obligation. If the contractor falls behind for reasons attributable to it, the administration may choose between terminating the contract or imposing daily penalties, with a default rule of 0.60 euros per 1,000 euros of contract price. If the delay stems from causes not attributable to the contractor (modifications under processing, suspensions, force majeure), the contractor is entitled to an extension of the period, which must be requested formally and in good time. Documenting the cause of each delay as it happens, rather than at the end, is what separates a granted extension from a confirmed penalty. The full regime is developed in the article on deadlines, penalties and extensions.

The closing milestones follow a regulated sequence:

Acceptance without reservations and a well-measured final certificate shape the definitive financial result; both milestones are covered in the article on certifications and acceptance in public works. Both are prepared throughout the works rather than in their last week.