How to Choose the Right Plaster for Your Project

10th Jun 2024 -

Plaster is an essential material for home improvement and construction projects. Whether you are patching plaster walls or creating decorative plastering designs, choosing the right type is crucial. With many types available, it can be difficult to determine which is best suited for your needs. This guide outlines the key considerations for choosing the right plaster for your project. 

What are the different plaster types?

It is important to understand the properties of each type. From the versatile gypsum plaster to the durable and breathable lime-based varieties, there is a wide range of plaster options. Below, we detail the plaster types available.

1. Gypsum plaster

Gypsum plaster is one of the most easy-to-use options. It dries rapidly, can be easily sanded and accepts paint well. However, it is not recommended for exterior applications or areas with high moisture levels as it can deteriorate.

2. Venetian plaster

Venetian plaster is a decorative plaster made from slaked lime (calcium hydroxide), marble dust and pigments. It develops a polished look with unique layered colours and textures. Venetian plaster is an upscale interior finish with dramatic depth and shine on walls.

3. Lime plaster

This is a durable and breathable plaster, allowing moisture to pass through rather than getting trapped. It has excellent self-healing properties and re-crystallises to fill in minor crack areas. Lime plaster develops a hard, polished finish when properly cured.

4. Clay plaster

Clay plaster is a natural, environmentally-friendly option with excellent insulating and moisture-regulating properties. It helps moderate indoor humidity levels and temperature. Clay plasters can be tinted with natural pigments to create earthy, decorative finishes.

5. Ready mixed plaster

The convenience of premixed plaster makes it ideal for small patch jobs and repair tasks. It is typically gypsum-based and may contain lightweight additives for easier application. Premixed plaster saves time compared to dry mixes that require mixing on-site.

6. Bonding plaster

Bonding plaster creates exceptional adhesion and a rough surface for subsequent plaster coats to bind to. It is formulated with extended setting times for proper curing between coats. Creating a quality bond is crucial for a long-lasting plaster application.

7. Hardwall plaster

Hardwall plaster contains dense gypsum and is highly durable once set. It resists denting, cracking and deterioration from moisture better than regular gypsum plaster. The smooth, dense finish is ideal for high-traffic areas.

8. Finishing plaster

Also known as topping plaster, it has an ultra-fine consistency that allows for an exceptionally smooth final coat over plaster undercoats. Options like multi finish plaster are best for creating flat, level surfaces for wallpapering or painting. Careful application is required to avoid tool marks.

9. Browning plaster

Browning plaster gets its distinctive warm brown tone from special pigments in the mix. When properly aged, it develops an authentic look reminiscent of historic plasterwork. It is popular for achieving aged interior aesthetics.

10. Cement plaster

Cement plaster is extremely strong and weather-resistant, making it suitable for exterior stucco applications. It has a longer working time than gypsum but requires precise plaster mix ratios. Cement plaster can be pigmented or have aggregates like sand added for texture.

11. Dri-coat plaster

Dri-coat plaster incorporates unique water-resistant agents that prevent moisture penetration and dampness issues. This waterproof plaster option is recommended for damp interior spaces like bathrooms as well as for exterior plaster that may be exposed to precipitation.

How to choose the right plaster

Selecting the right plaster type involves evaluating several key factors. Understanding each factor and how it relates to the different plaster options will help you achieve the best possible results. Here, we explore these factors to help you make the right decision. 

Project location (interior vs exterior)

Whether interior or exterior, the project plays a role in choosing the appropriate plaster type. Interior plasters like gypsum, lime and clay are designed for projects like plastering a wall. Exterior applications require more durable options with weather resistance like cement plaster or specialised coatings like dri-coat.

Desired finish

Different plaster types achieve a wide range of finishes, from ultra-smooth and polished to highly textured and decorative. Consider the appearance you want to achieve, from a sleek finish or a historic aesthetic with Venetian or browning plasters.

Existing surface conditions

The condition of the surface you will be plastering over is a critical factor. For example, some options like bonding plaster are specifically formulated to adhere well to lath or concrete bases. Gypsum plasters can be applied over existing drywall or plaster. Evaluate the surface texture, porosity and any potential moisture issues to choose a compatible plaster.

Environmental requirements

Certain environments demand plasters with specific properties. Areas with high humidity or moisture levels require breathable plasters like lime or clay that prevent moisture buildup. Exterior applications necessitate weather-resistant options like cement plaster or waterproof coatings.

Indoor air quality

With interior spaces for people with respiratory issues and chemical sensitivities, natural options like clay are preferable. They do not contain the synthetic additives found in some gypsum-based plasters that potentially off-gas volatile organic compounds (VOCs). Minimising airborne particulates is also important during plaster application for maintaining good indoor air quality.

Compatibility with other materials

How the plaster interacts with adjoining materials like wood framing, insulation, paints, and sealants is an important consideration. For example, gypsum plasters may not adhere well to extremely dense or flexible surfaces.

Lime and clay plasters are more breathable and can better accommodate minor structural movements without cracking. Using incompatible materials together increases the risk of separation, cracking or bonding issues.

Durability and maintenance

Durability and ongoing maintenance should also be a consideration. Hardwall and cement plasters are highly durable and resistant to damage such as cracks in ceiling plaster. Gypsum plasters may require more frequent repairs or touch-ups. Assess the expected wear and tear to choose a plaster that can withstand the conditions.

Insulation and soundproofing

Certain plaster types offer better thermal and acoustic insulative properties than others. Clay and lime plasters can help regulate temperatures and have inherent sound-dampening abilities. If enhanced insulation or soundproofing is a priority, factor those needs into your plaster selection. 

How to apply different plaster mixes

Achieving high-quality plaster finishes relies heavily on using the correct application methods for the specific plaster type. While some general techniques apply across different plasters, others have unique requirements. Here, we detail the ideal application approaches for several key plaster categories. 

Gypsum plaster 

• Typically applied in 2-3 coats over lath/drywall with a hawk and trowel.
• The scratch coat is scratched to create keys for the brown coat to bind.
• A brown coat is flattened and levelled before the final skim coat.
• Topping mixes may require adding a gauging plaster like lime putty.
• Each coat should be lightly misted with water between applications for proper curing.

Lime plaster 

• Applies in 3+ coats over lath or solid bases like brickwork.
• Coats consist of scratch, brown and finishing layers with time between.
• Can be applied with a hawk and trowel or thrown on with a rendering trowel.
• Each coat must be cross-raked and roughed to create a key and roughen the texture.
• Requires misting/damp curing over weeks to achieve hardness.

Clay plaster 

• Best applied in thin coats over built-up lath or drywall surfaces.
• A premixed terracotta base coat is applied and levelled.
• Finishing coats of clay plaster are troweled on in multiple thin layers.
• Each coat requires light misting but overhydration can cause cracking.
• Can create unique textures by troweling in free-form patterns.

Cement plaster 

• Requires solid masonry/concrete base for exterior application.
• Applied in 2-3 coats consisting of a scratch coat, brown coat and finish.
• A brown coat is applied with significant pressure and trowel marks.
• The finish coat can be troweled smooth or textured using various techniques.
• Requires misting during initial curing and proper control joints.

Venetian plaster

• Typically applied over special plaster bases or drywall in multiple thin coats.
• Layers of coloured lime putty or plaster are burnished with a metal trowel.
• Alternating matte and polished coats are applied using specialised techniques.
• Wax or sealer is applied overtop to deepen the tone. 

Premixed plaster

• Generally applied in a single, smooth coat over drywall or repair areas.
• A joint compound may be used for a first topping coat in some applications.
• Best applied using a flat trowel or broad putty knife and feathered out.
• Quick setting times and working in smaller sections are recommended.
• Some products may require very little water to be added. 

How long does plaster take to dry?

Drying times vary significantly depending on the plaster composition, number of coats, environmental conditions and thickness of application. Below is a comparison table analysing the typical drying periods for common plasters. 

Plaster type	Set time (plaster hardening)	Dry to recoat (finishing plaster coat)	Full cure time (final curing period)	Drying factors
Gypsum	1-3 hours	24-48 hours	2-3 days	Thickness, temperature, humidity
Ready mix	1-2 hours	16-24 hours	2-3 days for thicker apps	Thickness, airflow, humidity
Lime	6-12 hours per coat	5-7 days	4-6 weeks	Temperature, humidity, CO2 levels
Clay	12-24 hours	6-12 hours	2-4 weeks	Humidity levels, thickness
Cement	1-24 hours per coat	24-48 hours	28 days	Temperature, humidity, misting
Venetian	3-6 hours per coat	24-48 hours	60 days	Humidity levels

Can you paint onto new plaster?

Once your project is complete, you may consider painting new plaster to achieve your desired finish. However, it is important to follow the right steps to ensure proper paint adhesion. Here are some key considerations when painting over newly plastered walls and ceilings. 

1. Plaster type

Certain plasters are more compatible with paint than others. Gypsum plaster and premixed plasters can typically be painted once fully cured and dried. Lime-based plasters may require extra preparation like an acrylic primer/sealer coat first. Clay plasters often accept paint well but may need a bonding primer.

2. Curing time

Allow the new plaster to fully cure and dry before attempting to paint, following the recommended cure times per the plaster manufacturer. Painting too soon leads to adhesion failure, bubbling or damage to the plaster surface. As outlined above, curing times vary from 24 hours to several weeks depending on plaster type.

3. Surface preparation

New plaster surfaces must be properly cleaned and prepared before painting. Lightly sand any protruding edges or trowel marks for a smooth appearance. Vacuum up any loose plaster dust. For very porous plaster, a mist coat of diluted drywall primer helps seal the surface.

4. Primer selection

Using the correct plastering primer is crucial for good paint and plaster bonding. Acrylic primers are generally recommended. They allow the plaster to breathe and are alkali-resistant to prevent issues with high-pH lime plasters. Oil-based primers may prevent proper curing.

5. Paint type

For excellent results, use high-quality acrylic latex paints formulated for use on plaster surfaces. The flexibility and breathability of latex paint work well as plaster expands and contracts slightly. Avoid vinyl or oil-based paints which can degrade prematurely.

6. Application technique

When painting new plaster, use consistent brush/roller strokes in one direction. Excessive working of the paint may cause it to pull away from the surface. Apply thin, even coats rather than one thick layer. Cutting in corners carefully is also advised.

How much maintenance does plaster need?

Maintenance frequency varies on the plaster type, location and the original quality of the installation. By exploring the maintenance demands of different types, you can plan accordingly and take the proper steps to protect plaster. Below, we look at the maintenance techniques to consider.

Gypsum plaster

Gypsum plaster requires repainting every 3-5 years for interior applications. It should be checked annually for hairline cracks, holes or other damage. Any cracks or damage should be patched and sanded promptly to prevent spreading. Areas with high moisture exposure may need more frequent repair than drier spaces.

Ready mix plaster

For premixed plaster, plan to repaint every 5-7 years. Inspect annually and quickly repair any cracks, holes or delamination. Occasionally misting may be required if applying plaster patching compounds. For exterior plaster, recoating every 3-5 years is recommended to maintain protection.

Lime plaster

Lime plaster requires minimal maintenance if properly installed and cured initially. It should still be inspected every 5 years and any repairs made using compatible lime-based plaster. To boost the finish, reapplying a fresh linseed oil coating every 7-10 years may be beneficial.

Clay plaster

Clay plaster has very low maintenance requirements as long as it is sealed properly after installation. Inspect for any cracking or damage every 5-7 years. Patching and refinishing can be done using compatible clay plasters as needed. Reapplying clay-based topcoats may be required every 10-15 years.

Cement/stucco plaster

​​For exterior cement stucco plaster, plan to repaint every 5-8 years. It should be inspected annually for any cracks, spalling or moisture damage. Cracks and holes need to be properly routed out and patched. Control joints will also require inspection and re-caulking.

Venetian plaster

Venetian plaster's signature polished look requires re-waxing every 2-3 years. Full resurfacing of Venetian plaster may be required every 10-15 years. Promptly repairing any cracks is essential to prevent further spreading.