skim plastering

Quick Answer: Skim coating (also called skim plastering) involves applying a thin 2-3mm layer of finishing plaster over plasterboard or existing walls to create a smooth, paint-ready surface. For beginners, expect the process to take 4-6 hours for a typical 3m x 2.4m wall, plus 24-48 hours drying time. The total material cost is approximately £15-25 per wall using multi-finish plaster from British Gypsum. While achievable as a DIY project, mastering the trowel technique requires patience and practice. What is Skim Coating and Why Does Your Wall Need It? Skim coating is the process of applying a thin, smooth layer of finishing plaster over plasterboard, old plaster, or previously painted surfaces. It’s the final stage that transforms rough or uneven walls into perfectly smooth surfaces ready for painting and decorating. Most newly built homes in the UK use plasterboard (also called drywall or gypsum board) for internal walls. While plasterboard provides a flat base, the joints between sheets, screw indentations, and slight imperfections need covering. That’s where skim coating comes in. You’ll need to skim coat when: Installing new plasterboard walls or ceilings Repairing damaged plaster that’s been patched Covering artex or textured finishes Refreshing old walls with minor imperfections Creating a smooth base after removing wallpaper Preparing walls for high-quality paint finishes According to British Gypsum’s technical guidance, a properly applied skim coat should be between 2mm and 3mm thick when finished. Any thicker and you’re wasting material; any thinner and you won’t adequately cover imperfections. Essential Tools and Materials You’ll Need Success with skim coating starts with having the right kit. Don’t try to cut corners here — professional tools make an enormous difference to your results. Core Plastering Tools Tool Size/Specification Approximate Cost Plastering trowel 14″ (356mm) stainless steel £25-45 Bucket/mixing tub 25-litre flexible plastic £8-15 Paddle mixer drill 1600W with mixing paddle £45-80 Hawk (hand board) 330mm aluminium £15-25 Spray bottle 500ml-1L capacity £3-6 Spot board/mixing board 600mm x 600mm £12-20 You can find all of these at Screwfix, Wickes, or Travis Perkins. For a complete breakdown of what professionals use, see our essential plastering tools guide. Materials and Consumables Plaster: For skim coating, you want finishing plaster. The industry standard is Thistle Multi-Finish from British Gypsum, which works on most substrates. A 25kg bag costs £8-12 and covers approximately 9-10m² at 2mm thickness. Primer/PVA: If you’re skimming over plasterboard, you’ll need a specialist primer like British Gypsum Thistle Bond-It or a diluted PVA solution (3-4 parts water to 1 part PVA). For more on this debate, check our guide on PVA for plastering. Other essentials: Scrim tape for plasterboard joints (£2-4 per roll) Dust sheets or heavy-duty plastic sheeting Protective workwear and dust mask Clean water supply Pro Tip: Buy one extra bag of plaster than you think you need. Multi-finish has a shelf life of 3-4 months when stored properly, and running out mid-job is a nightmare. Once you start mixing, you’ve got about 40 minutes before it begins to set. Preparing Your Wall Before Skim Coating Preparation accounts for 60% of a successful skim coat. Rush this stage and you’ll see the consequences for years to come. Step 1: Assess the Wall Condition For new plasterboard: Check all screw heads are countersunk below the surface (they should sit 1-2mm below the paper). Any proud screws will catch your trowel and tear the skim coat. For existing plaster: Tap the wall with your knuckles. Hollow sounds indicate blown plaster that needs removing. Check for cracks wider than 2mm — these need filling first. For painted surfaces: The paint must be sound and well-adhered. Flaking or gloss paint won’t accept plaster. Either remove it or apply a bonding agent like SBR (Styrene Butadiene Rubber). Step 2: Joint Treatment (Plasterboard Only) Every plasterboard joint needs reinforcing before skim coating: Apply a thin layer of finishing plaster along the joint Embed scrim tape into the wet plaster Smooth over with your trowel, ensuring the tape is fully covered Fill all screw indentations with a dab of plaster Allow 30-40 minutes to dry before priming Step 3: Prime the Surface Priming controls suction and prevents the wall from sucking moisture out of your plaster too quickly. Different surfaces need different approaches: Surface Type Primer Application New plasterboard PVA (4:1 water to PVA) Two coats, allow tacky (not dry) Old sound plaster PVA (3:1 water to PVA) One generous coat, skim when tacky High-suction substrate Thistle Bond-It (neat) One coat, allow to dry completely Painted surfaces SBR bonding agent Mix with water per manufacturer specs ⚠️ Warning: Never skim over completely dry PVA. The PVA should be tacky to the touch — this typically takes 15-30 minutes after application. Dry PVA creates a barrier that prevents proper adhesion, and your skim coat will crack or blow. Step 4: Protect the Area Plastering is messy. Cover floors with heavy-duty dust sheets (not thin plastic, which becomes dangerously slippery when wet). Mask off skirting boards, door frames, and window sills with decorator’s tape. Remove or cover electrical sockets. Mixing Plaster: Getting the Consistency Right The consistency of your plaster mix is critical. Too wet and it’ll slump off the wall; too dry and you can’t work it smooth. Proper mixing procedure: Fill your bucket with clean, cold water — approximately 11-12 litres for a 25kg bag Add the plaster powder gradually while mixing with your paddle drill on medium speed Mix for 2-3 minutes until you achieve a thick, creamy consistency (like thick custard or yoghurt) Let the mix stand for 2 minutes, then give it a final 30-second stir The Health and Safety Executive recommends wearing a dust mask during mixing. Plaster dust contains crystalline silica, which can cause respiratory issues with prolonged exposure. Pro Tip: Always add plaster to water, never water to plaster. This prevents lumps and ensures even consistency. If you see lumps forming, they won’t disappear — you’ll need to start again. Professional plasterers can tell mix consistency by how it falls off the paddle: