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Plaster remains one of the best building materials available on the market. This material is used for ceilings, floors and walls and has the quality of curing to achieve a tight seal against elements such as fire or mold. Although the use in favor of wooden houses has declined, there are still many houses in which plaster is used before the 1950s. So you may want to know how to fix plaster walls and ceilings as they crack after so long.
Fortunately, we can take various measures to fix the various defects that the plaster can have. With glass fiber and gypsum panes, we can restore the material’s characteristic durability.
Reasons why a plaster wall is damaged
The first cause of wall plaster failure is that the material has been separated from the support structure, in this case wooden slats. If the structure is not reconnected to the plaster during the repair of the plaster wall, it will tear regardless of all repairs we have carried out.
Plaster breaks easily, although it is hard if it is not supported by anything. Over time, the elements that hold the plaster together with the wooden slats break, resulting in a weak wall. The wear process is much faster if the house is constantly moving due to earthquakes or sedimentation.
How can we repair plaster walls and ceilings with this defect? There are two options for our budget. It is most economical to reconnect the wall with plasterboard to the wooden structure, although this has the disadvantage that it does not work on all occasions. The second alternative, which is more expensive and requires trained personnel, is to remove the existing defects in the plaster and plaster the area again.
As with other building materials, we have to repair plaster walls if they are attacked by water. The leaks can be seen from the outside of the wall as they cause the plaster to discolour.
Finally, there is the human factor. The plaster is not indestructible. If you hit it with furniture, spill liquids on it, and other things, its durability can gradually deteriorate.
How to repair plaster walls – small cracks
Before we even start small crack repairs, we have to make sure that the plaster wall is attached to the rear support. Just press on the wall and make sure it bends freely (don’t use as much force as it can break if it is loose). If it has come off the wooden slats, we have to hire a specialist to repair the joints.
If the wall is in good condition, you should follow these steps to mend plaster walls.
Spread the crack
As ironic as it may sound, the first step is to enlarge the crack with a lever or a screwdriver. The crack should be at most 1/8 wide to be considered small. This is also the size that we have to reach to work on the plaster.
Clean damaged areas
Now you need to prepare the area for work and remove dirt and imperfections that arise around the crack. To remove the bumps, it is best to use a hammer or cold chisel, while you can use a spatula or scraper to cut off the excess.
Finally, remove the dust created by this work with water, trisodium phosphate and a brush to rub the wall.
Prepare the new mix
Once the cracks are cleaned, it is time to prepare the plaster mix. Simply mix the amount you need for maintenance, always following the manufacturer’s instructions.
A well-mixed plaster has a consistency similar to that of a cake and no lumps.
Apply the plaster
The plaster is applied in several layers. With a 10-inch wall knife, we apply a first layer that is no thicker than a quarter of an inch. After application, draw crossed lines (preferably with a spatula) before drying the plaster to create a surface for the next layer.
After drying, apply a second ¼ ”or 3/8” layer and draw the same cross line so that the next layer sticks.
Prepare the finish
When the second layer of plaster is dry, it is time to apply the grout on it. Follow the manufacturer’s instructions for preparation again and use the 10 inch wall knife to apply it.
Finish the job
After the grout has dried, the plaster must be firm and the crack sealed. All that remains is to sand the area with fine-grained sandpaper, clean the excess dust with a damp cloth and paint the area with the appropriate color.
How to repair plaster walls – large cracks
Protect the room
Unlike small cracks, larger holes require the use of heavy tools and techniques that make our environment very dirty. Therefore, it is best to cover the floor with towels or plastic blankets before starting.
In this way we can easily remove any gypsum or joint splashes. If you have ventilation slots for an HVAC system, cover them so that they do not absorb dust.
Expand the hole
To enlarge a large crack you need to use a drill bit as we have to drill a few holes around it. Drill a hole about 5 cm from the crack with 3/16 masonry until it touches the wooden slat.
Repeat this process several times by separating each hole 3 inches from each other and holding it 2 inches from the crack. Thanks to the masonry drill, we don’t accidentally drill wooden slats, so we should make sure that every hole we drill touches a slat.
Apply the conditioner
Use a sprayer to apply some acrylic conditioner to each hole you drilled. You should also apply the conditioner to the edges of the crack and remove any excess material. This should penetrate the wood and plaster in about 10 minutes.
It’s time to inject the glue
After the conditioner has done its job, we need to apply the glue that connects the plasterboard to the wood. It is best to do this with a cartridge gun so that we can control the amount of glue that gets into each hole.
Install the cleaning disks
Insert a 1 5/8 ”drywall screw with a 2” plastic washer into one of the holes filled with adhesive. In this way, the screw can exert sufficient pressure on the drywall during the drying of the adhesive.
Now place washers on both sides of the crack with a gap between 8 and 12 inches. After the adhesive has dried, remove the screws and plastic washers. If the washers stick to the wall, remove them with a spatula.
Finish repair
In some cases, the adhesive may leak out of the holes. After drying, remove this excess with a spatula.
When the wall is smooth, apply a layer of grout and let it dry overnight. Use a 120 grit sandpaper to remove imperfections and rough edges that are left on the wall.
Finally, apply a thinner layer of compound, apply the primer and paint the wall.
Alternatives for fixing plaster walls
If our plaster wall is perfectly connected to the structure but has large cracks, we have the option to install fiberglass panels to seal it.
The hardware stores have self-adhesive fiberglass panels, which we simply have to stick to the wall and cover with joint layers so that the installation is not noticed.
Another option that guarantees us the creation of a flexible protective layer to avoid future cracks is Nu-Wal. We apply a layer of latex to the crack in the plaster wall and then place a glass fiber plate so that the latex absorbs it.
How to repair plaster walls – repair the wooden slats beforehand
Before the repair of the plaster wall begins, the structural slats must be in perfect condition. Sometimes there are also cracks in the wood, so it needs to be repaired.
Replace wood with metal
The first is to remove the damaged piece of wood with a saw or chisel and a mallet. Find a piece of metal grille and insert a wire loop in the middle.
Place the net on the damaged part, pass the metal strip through the hole and tighten to ensure that the net is firmly on the wood.
Create a replacement with plaster
Roll the piece of wire over a wooden mandrel and fill it with a layer of plaster. It doesn’t matter that you exceed the amount of material you are using, as you will have to remove the excess anyway.
Apply the grout
With the dry plaster you can remove the damaged wooden strip. Cut off the excess wire with pliers and finish the job by applying a layer of grout and closing the holes between the wooden structure and the new plaster. Your new structure is ready after 24 hours of drying.
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