Drying Out Walls After Damp Course Installation: What to Expect and How to Prepare

Once a new damp‑course has been installed, the most important step is allowing the treated walls to dry out properly. This drying phase takes several months and must be completed before any re‑plastering, re‑rendering, painting, tuck‑pointing, or re‑pointing begins. Rushing this stage can trap residual salts and moisture inside the wall, leading to ongoing dampness and failed surface finishes.

What Happens During the Drying Process

In the first few weeks, the minor component of the damp‑course evaporates from the wall. This may produce a noticeable sweet odour, which is normal. The silicone component remains inside the brickwork, where it reacts with moisture to form a durable, long‑lasting plastic damp‑course.

As the wall dries, salts from the rising damp zone migrate toward the surface. These salts accumulate in the existing render, plaster, or brick face above the new damp‑course. This is a natural part of the drying cycle.

Drying Times by Wall Type

Cement‑Rendered or Plasterboarded Walls

These walls typically require a minimum of 3 months of drying before re‑plastering or re‑rendering. Very salty walls may need up to 6 months.

During this period:

• Brush away salt crystals from plaster or exposed brickwork behind skirting boards.
• Prevent salts from falling into the wall–floor junction.
• Wipe away droplets of salty moisture with a slightly damp cloth—never a wet one, as this dissolves salts back into the wall.

Walls may appear wetter during this phase. This is normal. The salts drawn to the surface absorb atmospheric moisture, giving the wall a damp appearance.

Painted Brick or Bare Brick Walls

These walls require a much longer drying period—12 months or more—because there is no render layer to act as a poultice.

Every 2–3 weeks:

• Wipe away surface salts with a slightly damp cloth.
• Continue until no new salts appear.

Painted brickwork often needs to be stripped and cleaned before repainting or re‑plastering.

Re‑Rendering and Re‑Plastering Once the Wall Is Dry

To ensure long‑term success:

1. Remove all salt‑contaminated plaster/render to 350 mm above the last visible damp mark.
2. Rake out and replace salt‑affected mortar joints.
3. Clean exposed brickwork and remove residual salts.
4. Apply a 15 mm cement render (1:3 cement/sand) with a waterproofing admixture such as:
   • Tech‑Dry Salt Retarder (Tech‑Dry Mortar Additive)
   • Sealwall
   • Fosroc
5. Apply a base coat, then finish with hard plaster.
6. Do not extend render behind skirting boards—batten skirting so the top meets the plaster line.

Plasterboard is not recommended due to poor salt resistance. If used, it must be installed on treated pine battens or rubber‑based adhesives, never fixed directly to brickwork.

If you’re unsure about any stage of re‑rendering or re‑plastering, the Tech‑Dry team is always ready to help.