ᐅ How to Repair a Damp Basement Wall Made of Concrete Blocks?
Created on: 2 Nov 2025 23:42
H
Hajooo2025H
Hajooo20252 Nov 2025 23:42Hello everyone,
The basement of our house was built in 1966/67 using concrete blocks B160 with dimensions LxWxH: 30x36.5x23.8 cm (12x14.4x9.4 inches).
Not only that, back then all kinds of construction debris and waste were thrown into the excavation pit. My real favorite uncle—may he rest in peace—who was a mason by trade, built parts of it using mainly PM binder or very little cement.
Since the basement walls eventually became damp, we excavated and waterproofed the walls on the neighbor’s side to the left and the front along the street in the early 1990s, and then in the mid-2000s along the courtyard side and the rear under the terrace.
The two walls at the front courtyard side, forming an L-shape about 1.80 x 4.10 m (6 x 13.5 ft), where the landing and staircase to the house entrance are located, were left untouched.
Over the last 10–15 years, the plaster has noticeably bulged and loosened along the joints and across the surface. This week, I started working on the project and removed the plaster from the 4.10 m (13.5 ft) wall (hobby/ironing room).
As with the earlier waterproofing, I can partly scrape the joints out with my fingers—the mortar has become very soft and crumbly. I suspect this is due to the low cement content.
Now my questions regarding the renovation:
Part a)
Repointing and replastering:
I plan to repoint the joints. How deep should I scrape out the old joints in a reasonable way—30 cm (12 inches), or as wide as the block is?
Would it make sense to use a waterproof and hard mortar here?
What type of plaster should I use—pure cement plaster?
Part b)
Waterproofing the wall from the inside using an injection method.
According to the system, many holes are drilled, and some sealing material is injected. There is apparently also a solution involving capillary replacement.
For example, Tobolin focuses mainly on horizontal barriers, while Isofin seems applicable to larger areas as well.
What is generally applied for concrete block walls?
Who has experience with this?
Thank you and best regards.
The basement of our house was built in 1966/67 using concrete blocks B160 with dimensions LxWxH: 30x36.5x23.8 cm (12x14.4x9.4 inches).
Not only that, back then all kinds of construction debris and waste were thrown into the excavation pit. My real favorite uncle—may he rest in peace—who was a mason by trade, built parts of it using mainly PM binder or very little cement.
Since the basement walls eventually became damp, we excavated and waterproofed the walls on the neighbor’s side to the left and the front along the street in the early 1990s, and then in the mid-2000s along the courtyard side and the rear under the terrace.
The two walls at the front courtyard side, forming an L-shape about 1.80 x 4.10 m (6 x 13.5 ft), where the landing and staircase to the house entrance are located, were left untouched.
Over the last 10–15 years, the plaster has noticeably bulged and loosened along the joints and across the surface. This week, I started working on the project and removed the plaster from the 4.10 m (13.5 ft) wall (hobby/ironing room).
As with the earlier waterproofing, I can partly scrape the joints out with my fingers—the mortar has become very soft and crumbly. I suspect this is due to the low cement content.
Now my questions regarding the renovation:
Part a)
Repointing and replastering:
I plan to repoint the joints. How deep should I scrape out the old joints in a reasonable way—30 cm (12 inches), or as wide as the block is?
Would it make sense to use a waterproof and hard mortar here?
What type of plaster should I use—pure cement plaster?
Part b)
Waterproofing the wall from the inside using an injection method.
According to the system, many holes are drilled, and some sealing material is injected. There is apparently also a solution involving capillary replacement.
For example, Tobolin focuses mainly on horizontal barriers, while Isofin seems applicable to larger areas as well.
What is generally applied for concrete block walls?
Who has experience with this?
Thank you and best regards.
Chase out joints down to solid mortar and re-point with cement-sand mortar. Injections are only worthwhile for walls with low porosity. They are of little use on old porous concrete blocks. First ensure structural stability, then consider barriers/injections.
Best regards!
Best regards!
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