How to fix bubbling in Interior Plaster Wall? [PDF]

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The bubbling or bulging or blown plaster of the masonry wall is a severe condition of the building wall. Use this indication to find the cause of the problem before going for costly wall repairs. The major cause of plaster wall bubbling or bulging is dampness. The reason for dampness could be either because of the rainwater coming through the roof or moisture absorption from the ground or unexpected floods.

It is essential to find out the reason for dampness first and then choose an appropriate remedy. This article explains the top causes of moisture in the interior wall and the solution to fix the problem in detail.

Why Plaster Wall Bubbles?

Bubbling of plaster walls is caused due to the rise of dampness through the wall. Here, the plaster crumbles out, and the powdered mix falls down the adjacent floor. The rise of moisture through the wall is caused due to the absence of a damp-proof course or bad site drainage issues or inadequate sub-floor ventilation.

Fix the Causes of Bubbling of Plaster Walls

In this step, stop all the probable causes of the rise of dampness through the building walls. Some of the solutions are:

1. Improve the drainage system of the site. Always make sure that the surrounding slopes away from the building.
2. Always check for space under the floorboards to facilitate easy evaporation of moisture from the soil below. These vapors must pass through wall vents easily.
3. The next remedy is the application of a damp proof course. This is recommended when there is no solution to prevent waster rise through the walls. The damp proof course application is a work that is done best by the professionals.

How to repair a bubbled plaster wall?

After taking essential steps to fix the rise of dampness in plaster walls, the next step is to repair the plaster. Repairing the plaster without finding and solving the cause of plaster bubbling ends up with complete loss of work.

The step-by-step procedure to repair the damaged plaster are enlisted below:

Step 1: Remove the Damaged Wall Material

This step includes the removal of bubbling materials, the peeled paint, crumbling paint materials, and the bubbling plaster. 

• Remove the damaged material from the surface using a putty knife. 
• Liftoff the flaking paint and the bubbling plaster by utilizing a putty knife. Dig out all the soft and loose material from the wall surface. This is done with firm pressure and controlled digging. Follow the procedure also around the edges of the damaged area. 
• Continue digging until a hard and undamaged plaster layer is observed.
• Check whether the paint around the damaged area peels of easily or not. 
• Always start peeling off the paint from the center of the damaged area.

Step 2: Clean the Surface

The wall surface after conducting step-1 must be cleaned using a stiff nylon brush and a shop-vac.

Note: Shop-vac is a special vacuum unit with a high-powered motor that helps to suck the debris, dirt, and chunk materials from the building sites and wood workshops.

Wash the surrounding surfaces using a sponge and clean water. This process helps to remove any lime deposits. Once cleaned, allow the surface to dry before proceeding to the next step.

Step 3: Seal the Water Damage Surface

• Once the wall surface is cleaned and prepared, apply a coat of primer. The priming process blocks the residual contamination present on the wall surface. It helps to get a proper bond with the patching compound. Primer also prevents the bleeding of the stains while painting. The primer used can be either an oil-based primer or a quick-dry primer-sealer. 
• Shake the primer vigorously to mix the solution properly. Coat the affected surfaces and overlap on to the surrounding wall paint also. Allow the primer to dry. Oil paint takes 24 hours to dry, while quick-dry primers take an hour to dry.

Step 4: Repairing the Plaster

• Fill the missing plaster and level the wall, either using a jointing compound or patching plaster. The choice is dependent on the area of repair. For a small area, a jointing compound can be used. With an increase in the damage area, plaster is the best repair compound.
• The number of coats of plaster or jointing compound is dependent on the depth of repair from the exiting wall outer layer.

First Coat Application of Jointing Compound

• Apply the first coat of the jointing compound mixture using a jointing knife. Start by buttering the mixture on the wall at a thickness of 1/4th inch. Now go back over it to skim off the excess one side of repair to the other side of the defect.
• Always float the blade across the deeper damage to fill it and skim the surrounding walls so that they get a thin coat. Do not make thick layers around the perimeters of the damage, which demands more sanding at the final stage.
• Use a long thin board to apply the compound if the area of repair is large. Any ridges left can be sanded by a coarse to medium sandpaper. Do sanding only after the compound has dried off completely.
• After finishing the sanding process, brush off the dust and wipe the area with a clean damp sponge. Before the next coat, remove the scraping and the sanding dust present on the surface.

Second Coat Application of Jointing Compound

• During the second coat, apply the compound on the deepest parts of damage. Skim off excess mixture by taking parallel strokes. The buttering and skimming off is conducted in the perpendicular direction of what was followed in the first coat. 
• Do not bother about ridges formed while using the jointing knife. But remember to keep the compound thin as possible, to minimize the final sanding.
• Leave the second coat to dry. This is followed by scraping, sanding process. Wipe off dust and materials on the surface. If required, the number of coats can be increased.

Tip: For each coat, remember to reverse the direction of the application. Avoid building up the compound on the surrounding surfaces.

Instead of using jointing compound, plaster can be used.

Also Read: Work Procedure to Plaster Masonry Walls

Step 5: Sand and Touch Up

• Allow the last coat to set and dry thoroughly. 
• Sand the surface with 120 sandpaper to smooth the outer edges and the wall surfaces. 
• After sanding, clean off the sanding dust using a damp rag.
• Apply primer before painting. A solvent-based primer-sealer is best compared to latex paint because the former prevents residual water contamination with the new paint coat. 
• A latex primer is not good for applying on a water damaged wall surface. Always wait for the primer to dry before starting touching up and wall painting.

FAQs on Blown Plaster Wall Repairs

Read More:

1. How to Repair Plaster Walls?
2. Types of Plaster Finishes and External Rendering for Buildings