Plaster walls often develop small cracks that are too fine to patch but too large to cover with paint. A skim coat can restore a smooth, even surface.
Skim plastering involves applying multiple thin layers of joint compound to create a flawless finish. This guide will explain when skim plastering is necessary, how to prepare your walls, and the steps involved in applying a skim coat.
Let’s get straight to the point.
Skim plastering is a method for repairing cracked or uneven walls. It involves applying thin layers of joint compound to create a smooth surface. The process requires cleaning and priming the wall, mixing the plaster to a creamy consistency, and applying multiple coats with a trowel.
Focus on speed and consistency, especially around corners and edges. After drying, sand the surface for a flawless finish.
Skim plastering can be time-consuming, but with patience and practice, it offers professional-quality results ready for painting or wallpapering. Avoid common mistakes like over-mixing plaster or skipping primer.
Signs Your Wall Needs Skim Plastering
Knowing when your walls need some care is key to deciding if skim plastering is necessary. There are several signs to look for:
- Hairline Cracks are often too small to patch but too visible to paint over.
- Uneven Surfaces: Bumps or dips on the wall can make painting difficult and cause imperfections in the finish.
- Loose Plaster: If pressing on the wall causes it to move or depress, this indicates that the plaster is loose, and skim coating alone won’t be enough.
In such cases, you may need to replace the damaged sections with new drywall.
Skimming is an excellent way to bring your walls back to life. It provides a smooth finish that’s ready for painting or wallpapering.
Tools And Materials You Will Need
Before starting your skim plastering project, gather the necessary tools and materials:
- Trowel
- Drywall taping knife
- Ready-mix joint compound
- Plastic sheeting
- Water-based primer
- Ladder
- Mixing rod (if using quick set plaster)
- Hammer with a nail pry tool
- Sandpaper (180-220 grit)
- Large bucket
- Paint roller
- Drill (if using quick set plaster)
Step 1: Preparation
Check The Plasterboard
Before skimming, ensure the plasterboard is secure and free from obstacles. Remove any glue splotches or nails and ensure no tripping hazards, such as loose wires or furniture, are present.
Clean The Walls
The walls must be clean and dry for the skim coat to adhere properly. Use a dry cloth or brush to remove dust and loose particles.
Fill any cracks or holes with pre-mix joint compound, smoothing them out with a drywall knife. Allow the repairs to dry completely before proceeding to the next step.
Step 2: Mixing The Skim Plaster
Skim plaster is notoriously difficult to mix, especially for beginners. The goal is to achieve a thick, creamy consistency without any lumps. Follow these steps to mix the plaster:
- Fill a large bucket with about one-third clean, cold water.
- Slowly add the dry plaster to the water, stirring continuously. Do not add water to the powder, as this can cause clumping.
- Mix the plaster using a paddle blade attached to a variable-speed electric drill. Stir until it reaches a uniform, porridge-like texture.
Mix as much plaster as you can in one go, as it will start to harden while you work.
Step 3: Applying The Skim Coat
Priming The Wall
Before applying the skim coat, prime the walls with a water-based primer. This helps the joint compound adhere better and seal any loose surface material.
First Coat
Load the plaster onto a hawk and apply it to the wall with a trowel. Spread the plaster evenly, aiming for a 2-3 millimetres thickness.
At this stage, focus on speed and consistency rather than perfection. Cover as much of the wall as possible with the first coat, ensuring it is smooth but not necessarily flawless.
Corners And Edges
When applying plaster to interior corners, use a painter’s brush to smooth the plaster into the joint. Keep the brush slightly damp to avoid dragging the plaster.
For exterior corners, apply the plaster along the metal corner bead, ensuring the trowel stays flush with both the bead and the wall for a smooth finish.
Step 4: Applying The Second Coat
Once the first coat has dried, you can begin applying the second coat. This layer should be about 1.5 millimetres thick and serve to smooth out any imperfections from the first coat.
- Tip: Skim plaster dries quickly, so work efficiently to avoid trowel marks. After applying the plaster, smooth the surface with a wide drywall taping knife.
Step 5: Trowelling Up
After the second coat has been applied and is still slightly damp, begin “trowelling up.” This involves running a clean trowel over the surface to remove imperfections and create a smooth finish.
If needed, you can mist the surface with a spray bottle to keep it workable as you smooth it out.
Step 6: Sanding The Surface
After the plaster completely dries (usually 24 hours), it’s time to sand the surface. Use fine-grit sandpaper (180-220 grit) to remove any remaining lumps, bumps, or trowel marks.
Use coarser sandpaper (100-120 grit) to tackle more prominent imperfections if necessary.
- Tip: Always wipe down the wall after sanding to remove dust. A dusty surface can interfere with the adhesion of paint or wallpaper.
Step 7: Finishing Touches
After sanding:
- Inspect the surface for any remaining flaws.
- Apply a final, thin skim coat to cover any imperfections if necessary.
- Allow this coat to dry, then lightly sand it for a flawless finish. Your wall should now be perfectly smooth and ready for painting or wallpapering.
Common Mistakes To Avoid
- Mixing Too Much Plaster: If you’re new to skim plastering, only mix as much plaster as possible in 20-30 minutes. Plaster hardens quickly and will become unusable if it sets while you’re working.
- Skipping the Primer: Failure to apply a primer can cause the plaster not to adhere properly, leading to cracks and peeling later.
- Inconsistent Thickness: Ensure each coat is even. A consistent thickness will lead to an uneven surface, defeating the purpose of skim plastering.
Conclusion
Skim plastering is an effective way to repair cracked or uneven walls. While it can be time-consuming, with patience and practice, anyone can achieve professional-looking results.
Remember to work in thin, even layers, and allow plenty of drying time between coats. By following this guide and avoiding common mistakes, you’ll be well on your way to restoring your walls to a smooth, flawless finish.
Frequently Asked Questions About Plaster Wall
Can You Sand Old Plaster Walls?
You can sand plaster walls. Plaster walls were often used in early 20th century homes. While this surface is very hard and durable, it is not the easiest wall material to apply. However, if you have done your plasterwork or have patched a section and have found the surface isn’t even, you can fix it with a little work.
How Many Coats of Plaster Do You Need to Skim a Wall?
When the first coat (we always recommend two coats) is “laid on”, it is usually ready to be trowelled up and the second coat applied. Skimming is as much about timing as anything else, and trying to get a polished finish too quickly or too late, can result in a horrible job.
What Plaster Is Used for Skimming?
The multi finish is ideal for (indeed, is manufactured for) using as a finishing plaster when there are a variety of backing surfaces to be covered. Board Finish: Board finish plaster is used on surfaces with low – medium suction. Plasterboard and Dry-Coat plaster will accept Board Finish well.
Do I Need to Prime Walls Before Skim Coating?
Before skim coating:
Make sure the surface is clean. Repair any water stained surfaces and seal them with primer-sealer before skim coating. If the paint is peeling or plaster and joint compound are popping off, remove all the loose material, wipe away all dust, and coat with primer-sealer.
How Do You Hide Imperfections in Plaster Walls?
Pour a small amount of textured paint into a plastic bucket. Use a 2- to 3-inch paintbrush to apply paint around the edges of plaster surfaces. Apply textured paint to the remainder of the surfaces with a roller. Use a series of overlapping, random strokes.
