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 mÂČ per litre, per coat, with 2 coats required.
The coverage of Bauwerk Prep Coat over previously Painted/Sealed walls is 6 mÂČ 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.Â
Step 1 : Prime
We recommend 2 coats of a water-based undercoat-sealer/primer ânot 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.
Why prime a new plaster wall?
If your walls are made of raw plaster, it's very important that they are correctly primed to achieve a consistent, even finish. For this reason we recommend sealing the surface with a water-based primer, before applying Bauwerk Prep Coat.
- Raw plaster can be composed of inconsistent materials with differing absorbency levels, the difference in materials may ghost through as patching in the final finish.
- Raw plaster can be prone to hairline cracking, occurring as the plaster contracts during drying. Priming the wall will seal over the plaster to help avoid ghosting of hairline cracks.
- Newly plastered walls can be very absorbent, which can make it a little tricky to achieve a consistent appearance. This is because the paint will be absorbed into the surface before it can be evenly spread over the wall. Priming will help to 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; itâs 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. You will need an absorbent bristle block brushâ our 4x14 limewash block brush is our most popular size, perfect for most 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 wallâholding 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.
- All brushes, tools, and containers wash out quickly with minimal water and without harm to groundwater.
- There is no need for a sealer or additional top coat over the limewash. To maintain your limewashed wall, we recommend simply applying another coat of limewash.
- More stubborn stains and damage to the wall can be patched. Refer to our Youtube video for instructions on patching your limewashed wall.
- Simply wipe the walls down with a damp cloth to cleanâdo not scrub the walls or use cleaning products or harsh chemicals.
- Following these steps ensures a natural, dust-free surface with a fantastic texture, making it easy to repaint and maintain.
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Q: I don't want to prime and prep my plaster wall, what do I need to know?
A: 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. To detect micro or hairline cracks, test your wall by brushing a light coat of water onto the wallâjust enough to wet the surface without soaking it. If the water is absorbed evenly and the surface looks smooth, you can expect Limewash to behave similarly. However, if the water doesn't spread easily or micro or hairline cracks appear, you'll need to prepare the wall with 1-2 coats of Bauwerk Transparent White. This will create a better base for the final limewash application.
- When sampling colours on lime plaster, it is best to apply it to a separate piece of the same material or a discreet, hidden area. Sampling directly on the surface may leave a visible patch.
- 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 sales@bauwerkcolour.com
