Waterproofing systems
Selecting waterproofing
| Criterion | Cavity drained | Multi-coat render | Cementitious coating |
|---|---|---|---|
| Defence against hydrostatic pressure | Good if drainage maintained. Cavity thwarts hydrostatic pressure | Good | Average. Improved on positive side |
| Ease of repair | Repair possible during and after installation | Defects can be located but reliable repair not easily achieved | Good |
| Requirement for sound substrate | Good fixings required at specific spacings | Sound substrate required | Base render coat needed if substrate unreliable. May be applied on a damp substrate |
| Running maintenance | Drain to be cleared and sumps/pumps serviced | Nil, but check render not compromised by fixings, hole drillings, etc | Nil. |
| Loss of internal space | Average for waterproofing | Average | Minimal if applied to substrate |
| Ease of application | Skilled operatives needed | Use pre-bagged materials, trained operative | Skilled operative needed |
| Cost | Average | Average | Average |
| Substrate preparation | Minimal substrate preparation needed. The substrate does not need to be dry | Good preparation essential to achieve good bond | Good preparation essential to achieve good bond |
| Provision for fixing | Some point fixings need pre-planning. Can be curtain-fixed from top | Mechanical fixings can cause problems; adhesives are preferred method | Mechanical fixings can cause problems; adhesives are preferred method |
| Decorative options | All available. Dry finishes can be used to produce fast installation times | Can be decorated directly. Use only vapour-permeable paints for at least 6 months | Can be decorated directly. Use only vapour-permeable paints for at least 6 months |
| Ease of application to complex shapes | Sheets fairly rigid, cannot be applied flat to soffits | Easily applied to complex shapes | Easily applied to complex shapes |
| Effect of building movement | Can cope with some movement/cracks to substrate | Affected by movement/cracking of substrate | Can cope with limited movement/cracks to substrate |
| Loading coat | Not required | Not required | Base render coat sometimes needed |
| Traditional mastic asphalt | Liquid applied membrane | Bonded sheet |
|---|---|---|
| Good with loading coats | Good with loading coats | Good with loading coats |
| Access to waterproofing | Access to waterproofing | Access to waterproofing |
| Substrate must be dry before application | Some liquid membranes | Substrate must be dry before application |
| N/A | N/A | N/A |
| Needs screed plus loading slab on floor, and loading wall on walls | Loading coats can cause loss of internal space | Loading coats can cause loss of internal space |
| Skilled operatives needed | Skilled operatives needed | Skilled operatives needed |
| High | High | High |
| Good preparation essential to achieve good bond | Good preparation essential of achieve good reliable thickness of waterproofing | Good preparation essential to achieve good bond |
| Fixings easily made as waterproofing behind a loading wall or slab | Fixings easily made as waterproofing behind a loading wall or slab | Fixings easily made as waterproofing behind a loading wall or slab |
|
Loading wall typically plastered and painted |
Loading wall typically plastered and painted |
Loading wall typically plastered and painted |
| Asphalt can negotiate complex shapes on any plane | Liquid waterproofing can negotiate complex shapes on any plane | Sheets need careful application to negotiate details |
| Can tolerate only limited building movement | Can tolerate only limited building movement | Can tolerate only limited building movement |
| Loading wall and slab needed | Loading wall and slab needed | Loading wall and slab needed |
The ‘Design Assessment Guide’ published in the BCA Design Guide Basement Waterproofing shows the suitability of the various waterproofing options under differing water table positions.
It is useful to note that Type C drained cavity waterproofing systems offer a low-risk waterproofing option for low and high water tables. Other options, such as Type A waterproofing, may not achieve a Grade 3 or 4 environment, even if drainage is incorporated. For a greater understanding of the guidance graphs, refer to ‘selection procedure’ in the BCA Guide.
The BCA advise that design of basement waterproofing can be determined from a systematic appraisal. You would first decide upon basement usage, then gather site information, decide upon a form of construction, and finally select the waterproofing most suited. In an existing basement, construction form would be there to inspect as found – and you would need to determine the materials used and thicknesses, etc. from site inspection.
Basement waterproofing should be carefully designed and implemented, and early contact with suitable specialist installers should be advised. There is merit to seeking advice from specialists, but the more knowledge you yourself acquire, the more able you will be to appraise the specialist's recommendation.