▽ +09.00Technical article · Below grade
Crystalline waterproofing: admixture or surface-applied coating?
Crystalline technology waterproofs concrete from within: chemicals react with water and the products of cement hydration to grow crystals in the pores. It comes in two forms — mixed into new concrete, or applied to existing concrete — and each has its place.
02minutes read
- Topic
- Below grade
- Sections
- 06
- References
- 03
- Published
- Publisher
- Prime Shield — engineering content
How it works
The active ingredients travel through the concrete’s capillaries with water and react with calcium hydroxide and other hydration products, forming insoluble crystals that fill pores and fine shrinkage cracks, so the water paths shrink. Because the reaction needs water, it can restart when new moisture arrives through fine cracks — within the limits the manufacturer states.
Admixture: throughout the section
Coating: from the surface inward
- Crystals throughout the concrete (admixture)
- Crystalline coat on the surface
- Crystal growth zone near the surface
- Concrete
Crystalline admixtures
Added at the batching plant, the admixture is distributed through the whole concrete section, so the structure — with suitable joint details — becomes integral (Type B) protection in BS 8102 terms. It saves an application step on site and cannot be damaged during backfilling, but it is decided at design stage, needs mix trials, and does nothing for joints, ties and penetrations, which still need waterstops and details. ACI 212.3R groups such products among permeability-reducing admixtures for hydrostatic conditions.
Surface-applied crystalline coatings
Applied as a slurry by brush or spray to existing concrete — often from the negative side — the active chemicals penetrate from the surface. The surface must be open: laitance, form oil, paint and curing compounds removed, usually by water jetting or grinding, the concrete saturated before application, and moist curing afterwards. It is used in existing basements, tanks, lift pits and remedial work.
Side by side
| Aspect | Admixture | Coating |
|---|---|---|
| When it is decided | At design and mix-design stage | Any time, on existing concrete |
| Where it acts | Throughout the section | From the treated surface inward |
| Site work | Batching control, dosage, mix trials | Surface preparation, application, moist curing |
| Vulnerability | No surface layer to damage | The coat is protected until cured |
| Joints and cracks | Need waterstops, injection or joint systems | The same |
| Typical use | New basements, tanks, foundations | Existing basements, tanks, lift pits; the negative side |
What it does not do
- It takes no movement: moving cracks and joints are treated separately.
- It needs moisture to react, so very dry structures react slowly.
- It does not repair weak or honeycombed concrete — that comes first.
- It is not for non-cementitious substrates: blockwork, plaster or paint.
Checking the result
For an admixture: mix and dosage records, and permeability testing of the concrete where specified — for example water penetration under pressure to EN 12390-8. For a coating: surface-preparation records, the application rate per the TDS, curing records, then observing the treated area under wet conditions.
References
Standards and guides on the subject — named to show what they cover, not to claim that any product complies.
- ACI 212.3RReport on chemical admixtures for concrete, including permeability-reducing admixtures.
- EN 12390-8Testing hardened concrete: depth of penetration of water under pressure.
- BS 8102Protection types for below-ground structures, including integral protection.
General educational content; final values and requirements follow the manufacturer’s TDS and the approved project specification.
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