Screed Fault Diagnosis
Hollow-Sounding Debonded Areas
A hollow sound when tapping a bonded screed usually indicates localised loss of adhesion to the substrate, often from poor preparation or contamination.
When a screed is designed to bond directly to a concrete substrate, adhesion depends heavily on substrate preparation: removal of laitance, dust and contaminants, and often the use of a bonding slurry or primer. Where preparation was inadequate, or where the substrate itself was weak, patches of the screed can fail to key in properly, leaving voids that sound hollow when tapped.
Debonding doesn't always appear immediately. Thermal or moisture movement in the weeks after laying can be enough to separate a marginally bonded area that seemed sound at handover, which is why a considered aftercare and inspection period matters.
The extent of debonding is not always visible from the surface, so a systematic survey is needed before deciding whether repair, or in severe cases replacement, is the right course.
Hollow-Sounding Debonded Areas — the points that decide it
- Hollow sounding indicates loss of adhesion between screed and substrate
- Common causes include laitance, dust, oil or curing membrane residue on the base
- A BRE screed tester or simple tapping survey maps the extent of debonded areas
- Debonding can develop after handover as the floor experiences movement
- Small isolated areas may be resin-injected; larger areas often need cutting out
- Bonded screeds rely on correct substrate preparation and primer/slurry application
- Floating and unbonded screeds are not diagnosed the same way — see curling
Surveying the extent of debonding
A methodical tap-survey across the floor, marking hollow versus solid areas, gives a plan of where debonding has occurred. On larger commercial areas a BRE screed tester provides a more consistent and repeatable reading than hand tapping alone.
It's important to check whether hollow areas are isolated or connected, as this affects whether resin injection is viable or whether the affected section needs to be broken out and re-screeded.
Repair options
Small, isolated pockets can sometimes be treated by resin injection through drilled access points, bonding the screed back to the substrate without disturbing the surface finish. This is only appropriate where the screed itself remains sound and the void is limited in size.
Larger or multiple debonded areas usually need to be cut back to sound substrate, the base re-prepared correctly, and a new screed section bonded in — matched carefully to the surrounding floor level.
Hollow-Sounding Debonded Areas — your questions
Need a hollow-sounding floor properly surveyed?
Contact Exeter Liquid Screeders on 07791 510849 for a clear, honest assessment of the extent and the realistic repair options.
Or call our landline on 01392 237700
In short
A hollow sound when tapping a bonded screed usually indicates localised loss of adhesion to the substrate, often from poor preparation or contamination.
Need a hollow-sounding floor properly surveyed?
Contact Exeter Liquid Screeders on 07791 510849 for a clear, honest assessment of the extent and the realistic repair options.