What is water glass injection?
Water glass injection is a technique in which a solution of water glass (sodium or potassium silicate) is introduced into a row of holes drilled low in a wall to create a retrofit horizontal damp-proof course. It is used to stop rising damp in walls that have no damp-proof course or a failed one, as in much older masonry.
How does it work?
The water glass is drawn into the capillary pores of brick and mortar. There it reacts with lime and carbon dioxide to form a silica gel that narrows and blocks the pores. This creates a band through which moisture can no longer rise by capillary action. Today, silane and siloxane injection creams are also widely used; they make the pores water-repellent rather than filling them.
Method
- Drill a row of holes just above ground or floor level, usually in the bed joint and angled downwards.
- Blow out the drilling dust.
- Inject the product without pressure or at low pressure until the wall has taken the quantity specified by the manufacturer.
- Fill the holes with mortar.
Limitations and common mistakes
- Diagnose first. Much of what looks like rising damp is condensation, a leaking gutter or downpipe, or ground levels too high against the wall. Injection will not fix those.
- Very wet walls: if the pores are already full of water, the product penetrates poorly. Follow the manufacturer’s moisture limits.
- Salts stay in the plaster. Plaster above the new barrier is often salt-contaminated and keeps attracting moisture. Remove it and use a salt-resistant replastering system.
- Be patient: thick walls need months to dry out.
- Cavity walls: injection only works in the leaf you inject.
Related terms
- Capillarity
- Damp-proof course
- Concrete injection
- Injection hose
- Hydrophobizing
- Waterproofing
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