Subcontractor Payment Certs: Use Your Gantt to Stay Fair

Why do subcontractor payment disputes happen on Thai building sites?

A subcontractor submits a monthly progress claim and the main contractor signs off, then disagreements emerge later about what was actually complete on that date. This cycle repeats on Thai construction sites every month, typically because the claim is measured in percentage words rather than verified against physical evidence on the ground. A plastering subcontractor who has finished three of six rooms may claim sixty percent complete, while the Gantt shows forty percent based on the foreman's last on-site progress update. Neither number is necessarily dishonest — they may reflect a genuine difference in how each party is counting — but without a shared reference, the dispute cannot be resolved cleanly. The main contractor who can point to a timestamped Gantt entry, a photo from the on-site progress update, and a task-level breakdown of what is and is not done has a factual foundation that a verbal disagreement cannot provide.

What should you check before signing a subcontractor progress claim?

Before approving any progress payment, verify four things. First, which tasks on the Gantt planning view does the claim relate to — does the claimed percentage match the task breakdown? Second, what does the most recent on-site progress update show for those tasks — is the photo evidence consistent with the percentage claimed? Third, are there tasks the sub lists as complete that are not yet visible in any update? Fourth, are there tasks included in the claim that were not in the original agreed scope? For a project running two or three concurrent trade subcontractors, this review takes fifteen to twenty minutes per sub per month when the Gantt and on-site progress updates are current. If updates have slipped, the review becomes a negotiation rather than a verification, which costs more time and goodwill than the update discipline would have.

How do you use the Gantt planning view as the reference for payment?

Open the Gantt planning view in SiteBoard and look at the tasks associated with the subcontractor in question. The percentage bar on each task reflects the most recent on-site progress update submitted by the foreman. Compare the weighted average completion across those tasks with the overall percentage in the sub's claim. For a straightforward scope — all tiling, all painting, all electrical rough-in — the comparison is direct. For mixed scopes that span tasks of different values, weight the percentage by the task duration or sub-scope value to produce a fair comparison. Document the agreed percentage in a note on the Gantt milestone that corresponds to that payment period. This creates a signed-off record attached to the same tool everyone is looking at, rather than a standalone note that diverges from the live schedule over time.

A real example: a plastering sub in Nonthaburi claiming 80% at week six

A main contractor managing a two-storey residential project in Nonthaburi had a plastering subcontractor submit a claim for eighty percent completion at the end of week six of a ten-week scope, invoiced at 128,000 baht against a 160,000-baht contract. The foreman's on-site progress updates for the eight plastering tasks in SiteBoard showed a weighted average of sixty-three percent. The contractor opened the Gantt at the payment meeting: ground-floor internal walls one hundred percent, ground-floor ceilings seventy percent, first-floor internal walls forty percent, first-floor ceilings zero percent. The sub had included first-floor ceiling work in the eighty-percent claim based on materials delivered rather than work done. Both sides agreed on sixty-five percent as the certified amount — 104,000 baht — with the remainder due when first-floor ceiling plaster was photographically documented in a progress update. The meeting took twenty-five minutes with no lasting dispute because both sides were reading the same Gantt.

Should the owner see subcontractor payment disputes through the sharing link?

No. The owner sharing link in SiteBoard gives the project owner a read-only view of overall Gantt progress and on-site updates — it is designed for owner communication, not for internal payment administration. Keep subcontractor payment reviews within the site management team. The owner does not need to know that the plastering sub claimed eighty percent when the Gantt showed sixty-three. What the owner sees through the sharing link is that plastering is progressing on plan, which protects their confidence in the project without burdening them with commercial detail that is not their concern. The discipline of keeping on-site progress updates current for owner reporting has the secondary benefit of producing accurate task-level data precisely when it is needed for payment certification.

How do you handle a case where the sub is right and the Gantt is behind?

Sometimes a subcontractor's claim is accurate and the Gantt has simply not been updated. If the foreman missed an on-site progress update for a week, the task percentage may be stale. The right response in that case is not to refuse the sub's claim but to update the Gantt first: ask the foreman to submit the missing progress updates with current photos, then verify against the sub's claim. If the updates confirm the work is done, approve the claim and use the event as a reminder to reinforce update discipline with the foreman. A Gantt that is consistently one or two weeks behind actual site conditions is a management issue. The value of on-site progress updates is that they create a habit of real-time recording — a habit that pays off every month at payment time and also protects the contractor in any future variation or extension-of-time discussion.

How often should you check subcontractor progress against the Gantt?

Check sub progress against the Gantt weekly, not only when an invoice arrives. A brief ten-minute weekly review of the Gantt planning view — looking at which sub tasks moved since last week, which are stalled, and whether any task has been marked complete without a supporting photo in the on-site progress update — catches discrepancies when they are small. When the only review happens at monthly invoice time, a four-week gap between the real site condition and the Gantt record means the payment discussion is trying to reconstruct a month of history. Weekly check-ins also give the main contractor time to ask the subcontractor to document completed work before the invoice date, rather than fighting about it on the day the money is supposed to move.

FAQ: Can a main contractor legally hold a subcontractor payment in Thailand?

Under Thai contract law, a main contractor can withhold part of a progress payment when they have a documented basis for disputing the claimed percentage. The contract typically requires payment of the undisputed amount while the disputed portion is resolved. The key word is documented: a Gantt task showing forty percent complete with a timestamped progress photo is documentation; a verbal statement that the work does not look finished is not. The safest practice is to pay the certified amount promptly — the percentage verified through the Gantt and progress photos — and notify the sub in writing, a LINE message is sufficient, that the remainder is held pending documentation of the additional work claimed. This keeps cash flowing on the undisputed portion and creates a clear written record of the basis for the hold.

FAQ: What if the subcontractor refuses to accept the Gantt as the reference?

A subcontractor who disputes the Gantt needs to provide their own evidence of the work done. Ask them to bring photos taken by their team on the relevant dates. If their photos show a higher percentage than the foreman's on-site progress updates, a joint site walk to count completed units — tiles laid, ceiling panels fixed, circuit runs pulled — is the most direct resolution. Most Thai subcontractors are pragmatic about this: if the work is done, it can be seen. Having a Gantt with dated photos on your side is the strongest possible position from which to request an independent count. Document the outcome of any site walk in a note on the relevant Gantt milestone, and file it with the payment record for that period.

FAQ: How should you record agreed payment certifications in the Gantt?

After each payment certification, add a note to the milestone task in SiteBoard that corresponds to the payment period. The note should record the sub's claimed percentage, the certified percentage, the invoiced amount, the certified payment amount, and the date both parties agreed. This takes two minutes to enter and creates a running record attached to the Gantt rather than buried in a separate folder of invoices. If a dispute arises later about what was certified at month three, the note is timestamped inside the same tool that shows the task progress at that date. For projects with three or more active trade subcontractors, this discipline also makes it straightforward to produce a quick progress summary for the project owner showing spend against plan — grounded in actual verified site conditions rather than claimed percentages.