Plaster Surface Guide
This is the right guide for you if you want to learn how to:
- limewash standard plaster, gypsum or set coat plaster
- limewash traditional lime or clay plaster
- prepare your surface before limewashing
- apply limewash paint
- maintain the breathability of historic lime plaster or clay plaster
During construction or renovation, it is advisable to schedule Bauwerk painting as the final trade to prevent damage to the final finish caused by other trades or building equipment.
The coverage of Limewash Paint over Bauwerk Prep Coat on plaster walls is 10-15 m² per litre, per coat, with 2 coats required.
The coverage of Bauwerk Prep Coat over previously Painted/Sealed walls is 6 m² per litre, per coat, with 1 coat required.
*Recommendations for coverage are to be used as a guide only, variation in quantity needed will depend on the porosity of the surface to be painted. We always recommend the use of sample pots for an accurate colour representation and consumption for your particular surface and light conditions.
Step 1 : Prime
We recommend 2 coats of a water-based undercoat-sealer/primer –not a mist coat and non-diluted. You do not need to prime if your walls are either :
- already correctly primed and without patches and repairs, OR
- historic lime plaster or clay plaster that needs to remain breathable. See FAQs below.
If your wall is already painted or made of plaster, it's very important that your walls are correctly primed, as Limewash and Prep Coat won't mask what is on your wall. For example, inconsistent materials like join lines, may ghost through the final finish. Newly plastered walls can be very absorbent, which can make it a little tricky to achieve a consistent appearance. To achieve a uniform finish on raw plaster, we recommend sealing the surface. This ensures a consistent appearance, prevents the ghosting of micro-cracks, and helps minimise the absorbency.
Step 2: Prep Coat
Apply 1 coat of Bauwerk Prep Coat. We have specially developed our Prep Coat as a bridging layer to enhance the durability and ease of application of limewash. Bauwerk Prep Coat is not a primer; it’s a preparatory paint recommended for non-porous indoor surfaces to create the ideal conditions for applying limewash paint.
- Stir the limewash well and make sure all pigment is thoroughly mixed into the paint. Do not paint from a full bucket. Decant into a larger vessel and work with only around 8cm (3in) of paint in a bucket.
- Continue to stir paint regularly while painting. We recommend a machine stirrer, like a Bamix stick blender, or an egg whisk.
- Ensure you have the correct brush for the job. Our 4x14 limewash block brush is our most popular size, perfect for all applications.
Step 3: Limewash
Apply 2 coats of Bauwerk Limewash Paint
- Dip the brush into the bucket and flick off excess paint. The brush can hold a lot of paint, but should not be dripping.
- Start in a corner of the wall–holding the brush at a right angle to the wall. It may be best to hold the brush on the brush body, rather than the handle for more control.
- Using loose, free strokes stretch the paint as far as possible, varying the direction of strokes constantly. Let the bristles do the work. There is no need to apply too much pressure.
- Brush out the paint evenly in a thin coat, preventing runs or drips, while covering every part of the surface in the first coat. Maintain a wet edge at all times to prevent lines in your finished surface*. Finish each coat in one continuous application. Do not try and patch walls once the coat is finished, as missed areas can be covered in the next coat.
- When wet, the colour will appear darker and transparent. Do not compensate for this by applying more paint. As the paint dries, the colour will lighten to the chosen colour and become more opaque.
- Allow a minimum of 1-2 hours between coats. Apply a second coat faster, wet-in-wet and a lot looser. Missing spots is okay, as the first coat should have covered everything. Allow the paint to dry.
If you're painting with our 'whites', maintaining a wet edge is not required. These colours patch easily and are great for spot touchups.
- There is no need for a sealer or additional top coat over the limewash. A third coat of limewash can be applied, based on your colour and coverage preferences.
- All brushes, tools, and containers wash out quickly with minimal water and without harm to groundwater.
- Following these steps ensures a natural, dust-free surface with a fantastic texture, making it easy to repaint and maintain.
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I don't want to prime and prep my plaster wall, what do I need to know?
If you prefer not to prime and prep your plaster wall, or if you need to maintain the breathability of historic lime plaster or clay plaster, here are some considerations:
In some cases, it's possible to paint directly onto unprimed plaster walls, although this depends on the quality and type of plaster, as well as the importance of breathability. This works better with lime plaster or raw clay plaster, than with gypsum or hard set plaster, as these plasters can be very thirsty, making direct application to the wall a little more difficult. Typically, a primer is applied to address this issue, which also helps hide any micro-cracking that may occur with plasters. A simple technique to detect micro or hairline cracks is to brush a coat of water on the wall; the cracks will become immediately apparent.
If you prefer a foolproof method, follow the standard instructions for plaster walls, which involve using primer and Prep Coat. Otherwise, to preserve breathability and skip the primer, consider the three alternative solutions listed below.
Feel free to schedule an appointment with our technical team, who are heritage and building specialists: Email [email protected]
