Rising Damp Post Wall Treatment

POST WALL TREATMENT 

DRYING OUT OF THE WALL

After damp-course installation, it is very important that the treated walls are left to dry for a period of several months before any re-plastering / re-rendering, painting, tuck-pointing and /or re-pointing is done. The solvent component of the damp-course material will evaporate out of the wall in the next few weeks, leaving a silicone component in the brickwork where it reacts with the moisture in the bricks forming a new durable plastic damp-course. During this drying out period, the rising damp salts in the brickwork (above the new damp-course) begin to migrate to the surface where they have accumulated in the existing wall surface.

The period of drying varies depending on the type of wall surface present.

1. Cement rendered or plaster boarded walls

Generally, it may take about a minimum of 3 months of drying before any re-plastering / re-rendering can be done.

Very salty walls should be left to dry for a minimum of 6 months. During drying, the following should be followed:

• Remove any salts crystals that may appear on the plaster or on the brickwork behind the loose skirting boards. DO NOT allow these salts to fall between the wall and the floor. Use a brush or dry cloth.

• Remove any droplets of salty water that may appear on the water repellent bricks behind the skirting boards by wiping with a dry cloth. DO NOT use a damp cloth as this will re-dissolve the salt back into the brickwork.

After treatment, the walls may appear worse, that is, seems damper. This should not cause alarm, as this is normal. The rising damp salts have migrated from the bricks on to the existing render / plaster, and it is these residual salts which absorb atmospheric moisture giving the wall a damp look and feel.

2. Painted brick or bare brick walls

The drying out period is much longer as there is no poultice on the brick surface to draw out the rising damp salts. This period can be in the order of 12 months plus. After treatment, salts will begin to migrate and appear on the surface. These should be immediately wiped away with a dry cloth or stiff bristled brush. This process should be performed once every 2-3 weeks until no more salts appears. If not removed, the wall will display damp patches particularly during wet and humid climate conditions. In case of painted brickwork, it is generally necessary to strip off the old paint to fully expose the original brickwork, clean the wall and allow sufficient drying time before painting or plastering is to commence.

RE-RENDERING AND RE-PLASTERING AFTER THE WALL HAS DRIED

All plaster and render contaminated with rising damp salts must be removed back to the bare bricks to a height of 350mm above the last visible signs of dampness. This refers to the removal of plaster and render above where the damp-course installation was carried out. Failure to do so will result in continual dampness in the wall, thus surface decorations will not be successful and paintwork will continue to peel off the salt contaminated surface.

Specification for re-plastering after the wall is dry:

These specifications should be given to a qualified hard plaster.

• Remove the old plaster and render to reveal the bare bricks to a height of 350mm (14 inches) above the last visible signs of damp. DO NOT allow this material to fall between the wall and the floor.
• Rake out and replace any salt contaminated mortar joints and remove any salts present on any exposed brickwork. Replace any badly contaminated bricks. Wipe exposed brickwork with a dry cloth or stiff bristled brush to remove any residual salts. This process may be repeated several times if any residual salts continue to emerge as the wall dries. Do Not allow these salts to fall between the wall and the floor.
• Apply a cement render finish approximately 15mm thick (preferred cement/sand ratio 1:3) containing a waterproofing admixture. The inclusion of this admixture inhibits the migration of residual salts through the new render. Suitable admixtures include:

Tech-Dry RENDER GUARD

Apply a base coat of render. When set, finish surface with a hard plaster. DO NOT extend this render/plaster, behind the skirting board, right to the floor. The skirting board should be battened away from the wall using either treated pine or stainless steel battens. The bottom of the render/plaster should extend down and finish either at the very top or just behind the top part of the skirting board.

PLEASE NOTE:

A cheaper alternative to cement render is plasterboard. The use of this material is not encouraged as it has very little resistance to residual salts in the wall. Plasterboard should NEVER be attached directly to the brickwork. Again, treated pine or stainless steel battens should be used. A reputable rubber-based adhesive can also be used as an alternate to the battens.

IF YOU HAVE ANY QUESTIONS AS TO WHAT TO DO IN RESPECT TO RE-RENDERING AND / OR RE-PLASTERING, PLEASE CONTACT Tech-Dry.