In brief
- A low waterproofing bid often omits surface preparation, lap widths, protection layers and repairs, not the membrane itself.
- Below ground leakage usually shows at construction joints, pipe entries and cold joints rather than sheet failure.
- Ask for a measured bill of quantities, product data sheets and a site quality plan before comparing waterproofing prices.
Contents
The visible sheet or coating price stays, the work around it disappears. The omission stays hidden until the first wet season, or until groundwater reaches the wall. By then the concrete is poured and access is gone.
What gets left out of a cheap foundation waterproofing bid?
The cheapest bill of quantities normally prices the membrane at the wall face and nothing else. Surface preparation, primer, detailing at corners, lap sealing, protection boards, backfill care, waterstops at construction joints, and repairs after backfill all cost labour and material. A bidder who wants the job cuts those lines first because the client cannot see them in a drawing.
Check the scope against a measured bill of quantities. Ask for square metres of membrane, linear metres of waterstop, number of pipe penetrations, and a separate line for surface preparation. If those items are missing or lumped into "waterproofing works", treat the price as incomplete. Ask the relevant local authority or the project designer whether any groundwater or ground-history records exist for the plot, because unknown obstructions and old masonry can push preparation cost up. Ask each bidder to name a reference project from its own records and to describe how the membrane was protected there before backfill. If the bidder cannot show that protection detail, the same omission can repeat here.
Why does below ground leakage show up after handover?
Water finds the joints, not the middle of the sheet. Construction joints, cold joints between pours, pipe entries, tie holes and the base slab to wall junction are where most below ground leakage starts. A bid that prices only the flat wall area cannot cover that detail work. The membrane also gets damaged when a machine drops backfill or a rebar end scrapes the face.
Detailing is slow work. Each penetration needs a collar, each corner needs a fillet and a reinforcement strip, and each lap needs the width the product data sheet states. General practice is that laps, surface preparation and protection must follow the manufacturer's written instructions, so confirm the exact figures against the project specification and the product data. If the contractor's method statement does not name a lap width or a protection layer, the site team will guess. A supervisor who checks only that the roll was laid will pass a job that leaks at the first rain.
How do you compare waterproofing prices fairly?
Compare scopes, not totals. Put every bidder on the same measured list, name the product and thickness, and require a method statement for preparation, laps, joints and backfill. Ask two suppliers for written quotes for the same product so you can see whether the bidder priced the material actually specified. Then check the site quality plan.
A realistic price includes preparation, primer, membrane, laps, collars, waterstops, protection and repairs. A price that covers only the membrane field is a variation waiting to happen. Check what the contract allows before you sign, because the client usually pays for omitted work later through a variation or through a leak. Ask whether the contract fixes the waterproofing scope by drawing, by specification or by performance, and read the clause before awarding.
What to do next
Send every bidder the same measured waterproofing schedule and ask them to price preparation, waterstops, penetrations, protection and repairs as separate lines. Request product data sheets and a method statement with lap widths and joint details, plus a reference project from the bidder's own records. Then ask the relevant local authority or the project designer what, if anything, it can share about the plot, and compare the returned schedules before you shortlist anyone.
Frequently asked questions
Is a low waterproofing bid always a bad sign?
Not always. A bidder with a nearby site, its own crew and a clear method statement can price lower. The warning sign is a bid that cannot show preparation, laps, waterstops, protection and repairs as separate lines. Ask for those lines before judging the total.
What is the most common source of below ground leakage?
Joints and penetrations. Construction joints, cold joints, pipe entries and the wall to base junction are harder to seal than a flat wall. A scope that only prices flat membrane area leaves that detail work unpaid.
How do I check the membrane product is the one specified?
Ask the supplier for a written quote and a product data sheet for the exact grade, then match the delivered roll labels against the submittal. Confirm lap and preparation requirements in the data sheet against the project specification.
Local reporting: this article is written for building work in Borama and Somaliland. Ground conditions, prices and rules differ between places; confirm the details for your own site.