Inspect before choosing a coating
Record where water appears, its timing after rain and the condition of the roof, drains, outlets and junctions. The interior stain does not necessarily locate the entry point. Ask a competent person to distinguish a failed coating from drainage, plumbing or structural issues. This independent CDMX example concerns an accessible concrete roof; structural repair, roof replacement, tank relocation and hazardous-material removal are excluded.
Identify the existing layers and whether they can remain under the proposed system. A branded bucket alone is not a specification. Sika México’s product information illustrates how substrate condition, junction treatment and application conditions belong to a system. Obtain the current sheet for the product actually offered; its rules do not transfer automatically to a different acrylic, asphaltic or sheet membrane.
Separate measured area from material consumption
For arithmetic only, assume a 7 m by 8 m horizontal area plus a measured 0.30 m-high perimeter treatment. The 0.30 m is an example dimension, not a prescribed upstand height. The perimeter is 30 m, so its area is 9 m² and the total measured treatment area is 65 m². Actual details and deductions need their own drawing.
| Item | Quantity |
|---|---|
| Horizontal area, m² | 56 |
| Measured perimeter, m | 30 |
| Example perimeter treatment height, m | 0.30 |
| Perimeter treatment area, m² | 9 |
| Total treatment area, m² | 65 |
| Assumed total membrane consumption, L/m² | 1.60 |
| Membrane before example waste allowance, L | 104 |
| Quantity with 10% allowance, L | 114.40 |
| Assumed bucket size, L | 19 |
| Whole buckets required | 7 |
| Purchased volume, L | 133 |
Six buckets contain 114 L, just below the exercise’s 114.40 L target, so it requires seven. The assumed 1.60 L/m² is a total for all membrane coats together, not a per-coat quantity, and excludes primer and detail materials priced separately. It is invented for this exercise, unrelated to the cited Sika product. A real order must use the selected system’s verified coverage and the measured substrate.
Specify preparation, details and weather conditions
Ask the contractor to identify removal of incompatible layers, sound-substrate preparation, local nonstructural repairs, drain interfaces and penetrations. Map each detail so it is not reduced to a vague “two coats” promise. Access, edge protection and safe handling are part of the work plan, especially around roof-mounted equipment.
Obtain the selected system’s permitted substrate condition, application weather and curing requirements. Arrange temporary protection and a weather-dependent start decision. Touch-dry, rain-resistant and ready for service are different milestones. Do not improvise a roof flood test: the professional should specify a suitable verification method, considering structure, drainage and the system.
Price the complete defined package
These are invented MXN amounts. The example expressly assumes every line in the contractor subtotal is standard-taxable at 16%; the independent technical fee is already final. The seven fictional buckets cost MXN 1,250 each before IVA. Preparation and repairs are separate agreed tasks, not an unlimited promise to correct structural problems.
| Line | Amount |
|---|---|
| Seven membrane buckets | 8 750 |
| Primer materials | 1 800 |
| Reinforcement and detail materials | 2 400 |
| Removal and preparation | 6 000 |
| Defined nonstructural repairs | 3 500 |
| Application labour | 7 000 |
| Access and protection | 1 800 |
| Waste removal | 900 |
| Agreed verification | 1 200 |
| Contractor subtotal before IVA | 33 350 |
| Assumed IVA at 16% | 5 336 |
| Contractor final amount | 38 686 |
| Independent technical fee, final | 1 400 |
| Planning reserve: 10% of contractor final amount | 3 868.60 |
| Funding provision | 43 954.60 |
Control changed quantities and written promises
If one additional fictional bucket is genuinely required and accepted at the same net price, its assumed final cost is MXN 1,450. Keeping the reserve raises the provision to MXN 45,404.60. First ask why the quantity changed: a larger measured area, greater consumption on the actual substrate and avoidable waste are different explanations.
Keep the budget’s validity, the product’s storage life, its advertised durability and the contractor’s written guarantee distinct. Ask what the guarantee covers, who responds, what maintenance it requires and what evidence is needed. “Several years” on a package does not by itself establish the terms of a workmanship guarantee.
Keep a roof completion record
- Approve the surveyed condition and selected system.
- Confirm areas, details and supply responsibilities.
- Record preparation and covered details with dated photographs.
- Keep product identification and actual quantities.
- Complete the agreed professional verification.
- Record defects, maintenance instructions and the final account.
Plan later inspections and drain maintenance according to the property and system. Keep this roof file with the project costs so a future leak can be investigated against what was actually done, rather than simply ordering another layer over an unknown surface.
Sources, date and scope
Checked on 19 October 2026. Local examples concern Mexico City unless stated otherwise. All MXN amounts are invented calculation examples, not market prices or quotations. Each article describes an independent project. VAT is applied only under the example’s explicit assumptions; final amounts already include the applicable tax. Check diagnosis, design, procedures and contract conditions for the individual property with competent professionals.