How to manage subcontractors on your Gantt

Map every sub to one accountable name

Map every subcontractor on your Gantt to a single accountable person, not a company logo, so you always know who answers when a task slips. A crew name on a bar tells you nothing at 7am when the bar turns red. Put a real name and phone number on it instead. Say the tiling sub is Khun Wirat's team: his name sits on the tiling task, his number is one tap away in SiteBoard, and the owner sharing the view sees who owns the work. When the slab pour drifts two days, you call Wirat, not a switchboard, and the schedule conversation starts with the right person already on the line.

Sequence subs so trades never collide

Two subcontractors fighting for the same room on the same day is a schedule problem you can see before it happens. On the Gantt, the painter and the electrician both want the second-floor bedrooms on Tuesday, but only one can work cleanly while the other is cutting in conduit. Lay their bars side by side and the overlap is obvious days ahead. Pull the painter back two days, let Khun Somchai's electricians finish rough-in and clear out, then the finish coat goes on undisturbed. Sequencing on paper costs you a drag of the mouse; sequencing on site costs you a repaint and a sour crew.

Log every sub delay as it happens

Write down each subcontractor delay the day it occurs, with the reason, so the pattern is undeniable when payment day arrives. A red bar tells you something slipped; a one-line note tells you why and whose call it was. If the waterproofing sub lost three days because his material landed late, mark it the morning it happens, not from memory a month later. In SiteBoard the progress update and the date live together, so when the sub claims the whole job ran long, your timeline shows the rain delay was two days and his no-show was five. Honest records end arguments faster than a raised voice.

Why subcontractors fall off the plan

The main contractor controls the master schedule, but subcontractors often work from their own mental calendar — a rough agreement made weeks ago, adjusted by phone. When their work is not visible on your Gantt, you cannot see a conflict coming until the electrician turns up on Tuesday and the plasterers have not finished the wall yet. The gap between what you agreed and what actually happens is where most project delays are born.

Treat every subcontractor as a set of tasks, not a name

The most common mistake is adding a subcontractor as a single bar on the Gantt — "MEP: 3 weeks" — and leaving it at that. That tells you nothing useful. Break each sub's scope into concrete tasks: conduit rough-in first floor, conduit rough-in second floor, panel installation, final connections. When tasks are granular, you can see which one is blocking the next trade and exactly how much float you have before the delay cascades.

Link subcontractor start dates to predecessor tasks

Every subcontractor has a condition for starting: the slab must be cured, the framing must be inspected, the wall must be plastered. Set those conditions as dependencies in the plan. When the predecessor slips by two days, the sub's start date shifts automatically — and you have two days to call them and renegotiate, rather than discovering the conflict on the morning they arrive.

Define handoff points explicitly

A handoff point is the moment when one trade finishes and the next can begin. For example: tiler finishes wet areas → waterproofer can start → tiler returns for wall tiles. Each of these should be a distinct task with a specific completion criterion, not a vague overlap. When you define handoffs on the Gantt, the sequence becomes visible to everyone — including the subcontractors you share the schedule with.

Share a filtered view with each sub

You do not need to show the full 200-task Gantt to a subcontractor. Filter the plan to their tasks plus the predecessor tasks they depend on, and share that view. A subcontractor who can see "I start after task 14 — currently at 60%, estimated done Friday" will manage their own mobilisation without a weekly phone call from you. Fewer surprises, fewer holding costs.

Track sub progress the same way you track your own crew

Ask subcontractors to update their task percentages at the end of each day, or designate someone on your team to walk the sub's scope and update on their behalf. When sub progress appears in the same Gantt as your own crew's work, the plan-vs-actual picture is complete. A task stuck at 40% for three days tells you to call — before the delay ripples into the next trade's start.

Handle scope changes on paper before they happen on site

Subcontractors frequently ask for small scope additions: an extra circuit here, an additional drainage point there. Each addition is a negotiation and a potential schedule impact. When the request comes in, open the Gantt before you agree. How many days does it add? Does it push a handoff? If the impact is acceptable, add the task to the plan and note the change. If it pushes a milestone, price it accordingly and update the owner.

What to do when a sub goes silent

A subcontractor who stops updating and stops returning calls is usually in trouble — overcommitted on another site, short on labour, or waiting on materials they have not told you about. Do not wait for the weekly meeting. If a task has not moved in two days when it should be running, call the site supervisor directly, not the company owner. Get a realistic completion date and decide immediately: wait, find a parallel path, or bring in a replacement.

Build float into the handoff, not into the deadline

The instinct is to add buffer at the end of the project. A more effective approach is to build one to two days of float into each critical handoff between trades. If the plasterer finishes on Thursday and you need the painter to start Monday, the float is built in. When the plasterer finishes Friday instead, nothing cascades. Float at the end of the project disappears first; float at the handoffs protects the work sequence where it is most fragile.

The foreman briefing that keeps subs honest

At the Monday morning briefing, review not just your own crew's tasks but the subcontractors' tasks for the week. When a sub knows that their schedule is visible to the whole team — and that slippage will be discussed at Monday's meeting — they are far more likely to flag problems early. Visibility is the cheapest form of accountability. You do not need a penalty clause if the sub knows you will see the delay the same day it happens.