Understanding Waterproofing Tender Assumptions
Discover how a waterproofing tender may appear profitable yet still incur losses. Learn about the hidden scope gaps, detailing issues, and assumptions that can significantly impact your waterproofing margins.
EDUCATIONAL
Sumit Kumar
7/31/2026
There is a particular kind of job that looks great when you win it.
The drawings looked manageable.
The quantities seemed reasonable.
The client accepted your price.
You get the contract signed and think, good job - that's another one across the line.
Then the job starts.
A detail you didn't allow for appears.
The substrate isn't what you expected.
Another trade hasn't completed its work.
The builder wants something done differently.
There are more penetrations than you picked up.
A section of the drawing wasn't as clear as it looked during tender.
Suddenly, the margin you thought you had starts disappearing.
This is one of the biggest problems I see with waterproofing tenders.
The problem isn't always that the contractor priced too low. Sometimes the contractor priced exactly what they measured - but didn't price everything the project actually requires.
The square metres aren't usually the problem
A waterproofing takeoff can tell you that there are 850m² of membrane. That's useful. But 850m² doesn't tell you what it takes to deliver those 850m². You still need to understand what is happening around them.
Where are the penetrations?
How many upstands are there?
What happens at thresholds?
How are corners and junctions detailed?
Are there internal gutters?
What preparation does the substrate require?
What happens where the waterproofing meets another system?
Are there areas that will need multiple visits because of sequencing?
These details don't always make the headline quantity look much different. They can, however, make a significant difference to the cost of delivering the work.
The dangerous assumption is "I'll deal with it later"
This is where waterproofing contractors can get caught. A tender is often prepared under pressure. You have other jobs running. The builder wants the price back. The drawings aren't perfect. So you make a reasonable assumption and keep moving. One assumption isn't necessarily a problem.
The problem is when ten reasonable assumptions quietly become ten pieces of unpriced work.
By the time the issue appears on site, you're no longer negotiating from a strong position.
The builder sees it as part of the job.
You see it as additional work.
And now everyone is looking back through emails, drawings and conversations trying to work out who understood what.
That is not where you want your margin protected.
A better way to look at your tender
Before asking, "How much is this job worth?"
Ask: "What could make this job cost more than the number I'm about to submit?" That changes the review completely.
You start looking for:
Scope gaps
Drawing inconsistencies
Missing details
Trade interfaces
Unclear exclusions
Difficult access
Substrate assumptions
Protection requirements
Sequencing constraints
Material allowances
Areas requiring clarification
This is where a specialist QS can add real value to a waterproofing business. Not by simply taking a measurement and sending you a spreadsheet.
The value is in having another person deliberately trying to find where the tender can go wrong before you've committed your business to the price.
And this matters even when you win the job
A good tender review doesn't just help you decide what to charge. It gives you a record of what you actually priced. That becomes incredibly useful later. If the builder changes a detail, adds an area or asks you to undertake work outside the original scope, you have something to compare against. Your tender becomes more than a price. It becomes the commercial starting point for the project.
The best tender is not necessarily the highest one
And it isn't necessarily the lowest either. The best tender is one where you understand what you're committing your business to. That's the difference between pricing a project and understanding a project. For a waterproofing contractor, that difference can be worth far more than another decimal place in your rate.
How AQUOSYNC helps
AQUOSYNC provides specialist waterproofing QS support for contractors who want another set of experienced eyes over their tenders. We review drawings and specifications, complete takeoffs, identify scope and coordination issues, structure tender information and highlight risks before you submit your price. The goal is simple:
Know what you're pricing before you promise to deliver it.
If you're regularly pricing commercial, multi-unit or complex residential waterproofing work and want stronger commercial control around your tenders, AQUOSYNC can support you on a project-by-project basis.
Get in touch with AQUOSYNC to discuss your next waterproofing tender.
