Plastering is a widely used method in construction and home improvement. It provides a smooth finish to walls and ceilings. However, defects can arise due to poor materials or artistry.
Understanding common plaster defects and how to address them can prevent future issues and maintain the quality of your plastered surfaces. Let’s review some of these defects and practical ways to fix them.
Let’s get straight to the point.
Common plaster defects, such as blistering, de-bonding, cracks, efflorescence, flaking, popping, and bubbling, usually result from poor materials, improper mixing, or bad artistry.
To prevent these issues, clean and prepare surfaces well, use proper plaster mixes, allow adequate drying time, and address moisture sources.
Patch, re-plaster, or sand defects as needed, and always ensure professional craftsmanship and proper curing to maintain the quality of plastered surfaces.
Common Plaster Defects And Their Solution
1. Blistering Of The Plastered Surface
Blisters in plaster occur when lime particles in the mix expand beyond the plastered surface. This usually happens due to late slaking, which involves adding water to the lime at the wrong process stage.
Uneven mixing of the plaster is another common cause.
How to Prevent It:
Ensure that the plaster ingredients are thoroughly mixed to avoid blistering. Address any moisture issues that might exacerbate this problem.
How to Fix It:
If blisters appear, replacing the affected plaster with a patch is best. Then, a joint repair compound replicates the original surface texture, ensuring a seamless blend with the plaster.
2. De-Bonding Of Plaster
De-bonding occurs when the plaster separates from the wall. This defect often results from inadequate substrate preparation, dusty or greasy surfaces, or the application of a too-thick plaster layer.
How to Prevent It:
- Clean the substrate thoroughly before applying plaster.
- Ensure the substrate has the proper moisture level before plastering.
- If needed, use bonding agents to strengthen the plaster’s adhesion.
3. Cracks In Plaster
Cracking is one of the most common plaster defects and can occur for various reasons, such as foundation movement, shrinkage, or poor craftsmanship. Different types of cracks can appear:
- Crazing: A fine network of cracks resembling a spider web, typically caused by excessive fines in the sand or plaster applied to a dry surface.
- Separation Cracks: These occur where different materials meet, such as between concrete and brick.
- Hollowness Cracks: These are caused by poor plaster application or excessive water in the plaster mixture.
How to Prevent It:
- Only trained professionals are used to mix and apply plaster, ensuring the correct water-to-material ratio.
- Prevent cracks by curing the plaster properly, allowing it to dry appropriately.
- Focus on the quality of materials and craftsmanship to reduce the risk of cracking.
4. Efflorescence On The Plaster Surface
Efflorescence appears as a white crystalline deposit on the surface. It occurs when soluble salts from construction materials, such as bricks or cement, rise to the plaster’s surface.
Moisture often exacerbates efflorescence.
How to Prevent It:
- Avoid using building materials that contain soluble salts.
- Protect plastered surfaces from moisture during and after the drying process.
5. Flaking And Peeling Of Plaster
Flaking occurs when the plaster surface becomes loose, while peeling is when a section of plaster falls off entirely. Both defects are caused by poor adhesion between plaster layers.
How to Prevent It: Proper preparation of both the surface and materials is essential to avoid weak adhesion. This requires skilled craftsmanship and attention to the quality of the plaster mixture.
How to Fix It:
Remove the damaged plaster and reapply fresh layers, ensuring each layer is correctly mixed and bonded.
6. Popping Of Plaster
Popping refers to forming small holes, or cones, on the plastered surface. This happens when foreign particles like burned lime or organic materials in the mortar mix expand during drying.
How to Prevent It:
Make sure the plaster mixture is free from impurities. Screening materials before mixing can help avoid this issue.
How to Fix It:
Remove the popped sections and refill them with a suitable plaster mix.
7. Loose Plaster
Loose plaster can be dislodged due to external forces or improper application. This is often caused by incorrect mixing ratios or insufficient curing time.
How to Prevent It:
- Use the correct plaster mix ratio and allow ample curing time.
- Ensure skilled professionals carry out all work to avoid errors in the mixing or application process.
8. Uneven Plaster Surface
APoor craftsmanship typically results in uneven plaster surfaces. These can affect a wall’s or ceiling’s aesthetics, making it visually unappealing.
How to Fix It:
If the unevenness is minor, use a hand sander or an electric sander with fine-grit sandpaper. For larger imperfections, apply a thin layer of fresh plaster to even out the surface.
9. Bubbled Plaster Walls
Bubbles in plaster usually appear due to significant water damage. The excess moisture causes the plaster to expand and lose its adherence to the surface.
How to Prevent It:
Find the source of the moisture and fix any leaks immediately. Ensure that the wall is dry before reapplying plaster.
How to Fix It:
Clean the area of any loose plaster, let it dry completely, and apply an oil-based primer before repainting or re-plastering.
10. Grinning In Plaster
Grinning refers to visible mortar joints showing through the plaster surface. This usually happens when there is a suction difference between the brick and mortar or when the mortar joints are weak.
How to Prevent It:
Always apply a spatter dash coat or an undercoat before plastering to prevent the materials from sliding or creating visible joint lines.
11. Softness Of The Plaster
Excess moisture or deliquescent salts in the finishing coat often cause soft plaster. Insufficient undercoat suction can also contribute to this defect.
How to Prevent It:
Ensure that plaster mixes are appropriately proportioned and dried. Avoid moisture build-up on the plastered surface.
12. Rust Stains On Plastered Surfaces
Rust stains can appear when plaster is applied over metal lath, corroding the metal and leaving marks on the surface.
How to Prevent It:
Use galvanised or stainless steel lath, or coat the metal with rust-inhibiting paint before applying plaster.
13. Improper Plaster Mixture
When touched, improperly mixed plaster breaks down easily, often turning into fine sand. This happens when the ratio of cementing materials is imbalanced.
How to Fix It:
Remove the crumbling section if the affected area is small and replace it with a well-mixed plaster patch. For larger areas, consult a professional to ensure the mixture meets the correct specifications.
14. Improper Base Coat
When the base coat is not done correctly, cracks may develop through all three layers of plaster. This is especially problematic when the plaster is applied to a surface that has yet to dry fully.
How to Prevent It:
Ensure that the base coat is applied evenly and allowed to dry completely before adding subsequent layers of plaster. If you notice issues with the base coat, it may be necessary to remove all three layers and start fresh.
15. Improper Plaster Thickness
Plaster thickness errors can lead to cracking and chipping, a defect commonly called alligator chipping.
How to Fix It:
Remove the damaged plaster layers, including any portions of the base coat. Reapply the plaster layers, ensuring each layer is the appropriate thickness.
16. Improper Curing
If plaster doesn’t cure correctly, the layers can chip and crack. This is often caused by rushing the drying process or applying too many layers too quickly.
How to Prevent It:
Allow each layer to dry and cure properly before applying the next one. Proper timing and attention to detail can prevent these issues from occurring.
Safety Measures When Plastering
To ensure a successful plastering process and avoid common defects, follow these safety measures:
- Clean the masonry surfaces and ensure proper adhesion before plastering.
- Remove loose debris from stonework and wet the areas to be plastered.
- Clean the mortar joints with wire brushes before plastering.
- Maintain consistent levels when filling spaces between screeds.
- Follow the recommended cement-to-sand ratio for mortar.
- Use wood floats to harden the mortar.
Conclusion
Plaster defects such as blistering, cracks, de-bonding, and flaking are common in construction. However, the right techniques and materials can prevent and fix these issues.
To maintain the quality and longevity of your walls and ceilings, always ensure that plaster is mixed, applied, and cured correctly.
FAQs About Plastering
What Measures Can I Take To Prevent Shrinkage In Plaster?
To prevent shrinkage, ensure proper plaster mixing with the correct water-to-plaster ratio, apply plaster in thin, even coats, and provide adequate curing time in a controlled environment to minimise moisture loss.
How Do I Address Mould Growth On Plaster Surfaces?
Mold growth is often caused by moisture buildup on the plaster surface. To cure it, remove the mould using water and detergent, improve ventilation to reduce humidity, and consider applying mould-resistant coatings or paints.
What Should I Do If I Encounter Hairline Cracks In Plaster?
Hairline cracks are common and can be cured by widening the crack, removing loose material, filling it with an appropriate filler or patching compound, and smoothing the surface to match the surrounding area.
How Can I Prevent Plaster Defects During Application?
To prevent plaster defects, ensure proper surface preparation, use high-quality materials, follow recommended application techniques, control environmental conditions, and address any issues promptly as they arise.
When Should I Seek Professional Help To Cure Plaster Defects?
Suppose you encounter severe plaster defects or are unsure how to address them effectively. In that case, it’s advisable to seek professional assistance from experienced plastering contractors or building inspectors to assess the situation and recommend appropriate remedies.
