Roughcast or wet dash is a coarse plaster surface used on outside walls that consists of lime and sometimes cement mixed with sand, small gravel, and often pebbles or shells. Aggregates — objects such as pebbles, shells or gravel — are mixed with a binding medium like lime or cement. This is applied in handfuls to a wall, being flung against it to form an irregular, rough surface. This guide covers everything you need to know about what is roughcast, from how to apply this type of render to its benefits.

What is Roughcast Rendering?

Roughcast render, known alternatively as harling or pebble dash, grants walls a unique, coarse aesthetic. The rocks set into the render offer coarse texture and eye-catching detail. It had long been used as a roofing system, acting as a long-lasting and weatherproof shell for structures. Today, it’s selected for its protective factor and for show, too.

Composition and Application

Roughcast rendering is made up from:

Roughcast Render can be made up of several things – but typically it is made up from:

• Bond: Lime, cement, or lime and cement.
• Aggregates: Small pebbles, stones, shells, or gravel.
• Water: To thin the mixture down.
• Additives: Pigments to color it, polymers to help it adhere and become flexible (some don’t like the feel of the liquid when it dries).

It is applied by throwing the wet mix onto a wall with a trowel or a special machine. It is the throw that embeds the aggregate into the binder, mesmerizing for the textured surface. Effective use is critical to an even and consistent result.

Historical Significance

Roughcast render has been around for hundreds of years. It was especially prevalent in harsh environments because it was known for its texturized surface and the protection it offered the structure from the elements. Traditional techniques employed local materials and led to regional differences in morphology. Historical roughcast buildings are still evident now, a testament to the hardwearing nature of this finish.

Benefits of Roughcast Rendering

Roughcast rendering in many ways is extremely efficient as a rendering surface type.

The following are reasons as to why roughcast rendering has many advantages:

• Weather Resistance: It can withstand any weather conditions, protecting from the harsh weather.
• Resistance to Weather: Corrosion and frost resistant; repels water.
• Appearance: Has a distinctive and textured finish.
• Covers Flaws: Camouflages slight surface imperfections in the substrate.
• Low Maintenance: Little to no cleaning or repairs necessary.

Enhanced Weather Protection

The irregular texture of roughcast render protects against rain and wind. The lumps of whatever also prevent the water from entering the wall. This is useful in keeping the inside dry and avoiding moisture-related problems like dampness and mildew.

Aesthetic Versatility

Roughcast has a rather naturalistic look but is suitable for many types of architecture. The selection of aggregates, binder color, and application method can all impact the finished appearance. It also works wonderfully for older homes and even more contemporary dwellings to bring texture and visual interest.

Long Durable Life / Low Maintenance

Correctly applied roughcast render can be expected to last many years with little attention. The strong use of materials and the robust use method have a long life. Minimal cleaning, once in a while, white mark, lime scale, algae and major repairs are unlikely.

Types of Roughcast Render

There are several renditions of roughcast render, all of which have slightly different properties:

• Lime-Based Roughcast: Contains references to lime-rich surfaces.
• Cementitious Roughcast: Cement serves as the major binding agent.
• Pebble Dash: Dense pebbles incorporated in the top coat of the render.
• Spar Dash: Has spar (a mineral) as the aggregate, giving a glittering effect.

Lime-Based Roughcast

Lime-based roughcast has the benefits of breathability and flexibility. Lime lets the wall breathe and moisture can escape, so less chance of damp. It is also more flexible than cement, which helps it resist cracking. Lime-based render inherently has less strength and is more tensile compared to cement render.

Cement-Based Roughcast

Cement roughcast is stronger and more waterproof compared to lime render. It produces a tough, long-lasting finish that will stand up to all types of weather. Cement-based render isn’t as breathable as lime-based render, so we need to make sure that the wall underneath is well ventilated.

Pebble Dash Variations

Pebble dash is a decorative exterior wall finish generally thrown on a wet render base coat. The pebbles grip the surface, achieving texture. The size, color, and material of the pebbles may be larger or smaller and of different colors and materials for various aesthetic effects. This procedure is renowned for strength and weather resistance.

The Application Process – How To Roughcast Render

The process of roughcast rendering is done in the following stages:

1. Surface Treatment: Clean and prime the wall.
2. Blending the Render: Blending the bonding agent, ingredients, and water.
3. Base Coat: A coat of render on the wall.
4. Mouldering the Roughcast: Hurling the roughcast into position where required upon the base coat.
5. Curing: Drying and curing of the render.

Preparing the Surface

Ensuring that the surface to be worked on is properly prepared is an integral part of the roughcast process. This involves:

• Removing all loose or friable render.
• Washing down the wall, removing dirt, algae, and other residue.
• Filling any holes or cracks in the wall.
• Using primer to enhance adhesion.

Mixing the Roughcast

The stucco composition should be prepared in accordance with the manufacturer’s directions. The optimum proportioning of binder, aggregate(s), and water is critical to achieve the desired consistency and performance. Stir the ingredients together well until you get a smooth mixture. For solid plasterwork – don’t add too much water or the render will be weak.

Applying the Base Coat

A coat of render is applied to create an even and smooth surface over which the roughcast is then fixed. Spread the base coat over the base with a trowel so that it is even and the desired height. Let the base coat dry a bit before applying the roughcast.

Casting the Coarse Mixture

The roughcast compound is splashed up on the basecoat. This can be accomplished by hand with a trowel or with a special machine. The throw is made such that the aggregates are forced into the base coat and produce the eroded texture. Try to get a uniform spread of the aggregates into the wall.

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Curing and Finishing

Once you have applied the roughcast then it should be cured properly. This entails keeping the surface damp for a period of days to help the render to cure and set. The render is to be shaded from the sun and strong wind during drying (curing). The render can be left as is, or painted as required for additional protection and aesthetics once the render reaches full cure.

What Determines the Cost of a Roughcast Render?

There are a number of things that influence the roughcast render cost:

• Size of build: The larger the space, the more it will cost in materials and labor.
• Category of Render: Render types have varying material costs.
• Surface prep: A lot of prep work ups the cost.
• Cost of labor: Depends where and who you hire.
• Accessibility: Labour costs can be high if access is poor.

Material Expenses

The cost of materials will vary and depend on what type of binder and aggregate you are using. Lime-based renders are higher in price than cement-based renders. Most expensive are “rare or exotic” stones and “deco” stones, such as the kinds of river rocks or polished pebbles used in VCT.

Labor Costs

Labor costs can be more or less depending on the experience of the contractor and complexity of the work. A trained applicator may bill at a higher rate but would be able to guarantee a superior finish. Obtain quotes from a few different contractors so you can compare prices.

Preparation Work

The requirements for upfront preparation work can also influence the cost of resealing your asphalt paved area. If the wall is in bad shape and you have to do significant repair work, expenses will be greater. Good prep work is critical for a finish that will last.

Maintaining Roughcast Render

Roughcast render does not require regular maintenance, although some cleaning may be required from time to time. Algae may grow in moist environments, and it should be cleaned up right away. Use mild detergent and a soft brush to keep the surface clean. Don’t use high-pressure washers as they can damage the render.

Cleaning Procedures

Roughcast render will be looking great with a good cleaning. Clean using brightener-cleaner or a fresh coat of paint and mild detergent. Hose down and wash the area with fresh water. For heavy staining, you may want to use a dedicated render cleaner.

Repairing Damage

Small chips and cracks can also be repaired with a patching compound. Clean the damaged area, and using the patching compound per the manufacturer directions. With larger damage, it is better to hire a professional renderer.

Preventing Problems

Just by some good design, some issues with roughcast render can be avoided. Part of this is to make sure that water does not pool against the wall. Hooded eaves are used in a weatherboard lapped application. Regular checkups will allow you to catch problems early.

Common Problems and Faults with Roughcast Rendering

A number of problems can crop up with roughcast render:

• Cracks: From the movement of the building or the curing of the render.
• Moisture: The render has let in water.
• Development Of Algae: On damp walls, shaded areas.
• Wear: Wear of the render surface.

Crack Detection and Repair

Conditions leading to cracks in roughcast render include movement within the building – this is the primary cause of cracks in the roughcast render on residing buildings. Tiny holes can usually be patched with a pliable sealer. More serious cracking might need the damaged render to be taken off and replaced.

Control of Dampness and Moisture

Damp is often an issue associated with roughcast render which can cause mold growth, and structural damage. To avoid damp, make sure that the render is well sealed, with no leaks or holes for water vapor to get in. Drain more water away from the building so that it does not pool on the walls. This is vital to the life of your roughcast render.

Preventing and Removing Algae

Algae is a frequent problem with roughcast render, particularly when it is in a damp and shaded area. To avoid the problem of green algae, the render must be kept clean and dry. You can use a fungicide to help kill algae. Seal the render to prevent further growth.

Tools and Equipment Needed

What tools do you need to roughcast render?

• Trowels: For green coat and dashing the roughcast.
• Mixing Equipment: To mix the render with.
• Pails and Cans: To contain the render.
• Scaffolding: The method to get to the high points.
• Safety Gear: Gloves, protective goggles and a dust mask.

Essential Hand Tools

A base coat is laid and the roughcast is thrown with a trowel. A plastering trowel is suitable for the base coat, and a roughcasting trowel is used for throwing the roughcast mix. Contamination of the binder, the aggregates, and the water are mixed by mixing tools, for example, shovels or mixing drill. Render is placed in buckets and tubs and left open for easy access.

Safety Equipment

Safety is of the utmost importance when working with roughcast render application. Make sure you have gloves for handling the render as the chemicals can be harsh on sensitive skin. Wear goggles to shield your eyes from splashes and dust. The dusty mask prevents dust from being inhaled. A scaffold or a ladder is required when working overhead. Check that the scaffolding is securely assembled and is stable. Observe all safety information and wear PPE.

Machine Application

Roughcast rendering can be done through machines made for this function. The machines have a number of benefits over hand application, such as faster application, more even coverage and reduced labour costs. These options are nice if you want a professional roughcast rendering.

Design Aspects of Roughcast

Roughcast is applicable in a variety of architectural designs:

• Colour: Go for colors which can be appropriate to the environment.
• Texture: Texture adds visual interest, so mix it up.
• Aggregates: For various effects, alternate between types of aggregate.

Color Selection

The color of roughcast render can play an important role in a building’s appearance. Select colors that are a good fit for the surroundings in terms of architectural design of the building and landscaping. Lighter exteriors can make the exterior appear larger and brighter, while darker colors can produce a more dramatic effect. Think also about how the light will affect your color; some colors may fade or shift over time.

Texture Variations

Random small stones and the like, thrown or placed onto a wet first coat make up the texture of rough-casting and it can be varied with different aggregates and applications. Coarse aggregates give this texture a rougher appearance, fine aggregates make it smoother. Texture may also be influenced by the application technique. I.e., if you chuck the render at the wall more, it will be rougher.

Aggregate Choices

The selection of aggregates will greatly influence the character of roughcast render. Your gravel will determine the look and feel, and alternating between various aggregates (pebbles, shells, spar) will produce different effects. Try to incorporate aggregates from local sources so that it looks like it belongs where it was cast.

Legal and Compliance Concerns

Before roughcast rendering, ensure you check local building regs first. There may also be limitations in some regions as to what the materials can look like. Get your necessary permits before you begin your work. This makes the work regulation-compliant.

Planning Permission

Sometimes, approval may be required to apply roughcast render. This is particularly the case if the building is listed or in a conservation area. Consult your local planning authority to see if planning permission is necessary. Apply for planning, get approval and then get it built.

Professional Essentials of Roughcast Rendering and How to Hire One

Several benefits to using a professional renderer:

• Skill: Skilled plasterers know how to roughcast render as it should be done.
• Quality: Experts use top-notch materials and methods that will leave you with a finish that is durable and long-lasting.
• Saves Time: Employing an expert can earn you some relaxation, you save in time.
• Guarantee: Most professional renderers guarantee their work.

Locating Skilled Contractors

Find skilled contractors by:

• Receiving recommendations from friends, family or neighbors.
• Using Online Directories and Review Sites.
• Reaching out to nearby building centers.

Requesting Quotes

Obtain quotes from a few contractors, in order to compare costs and services. Give the contractors as much info as possible about the job, such as the area you want rendered, what sort of render you want to use and whether you have any other special requirements. Request a written bid from each contractor which contains the cost of materials, labor, and other associated costs. Pay close attention to quotes and select the contractor providing the best value for your requirements.

Checking References

Before signing on the dotted line, check references of a contractor. Ask to speak to prior customers to check references to gauge former clients their satisfaction with the contractor. How about that contractor, did he finish on time and on budget? How was the quality of the work? Would they refer the contractor to someone else? This is an ideal consideration to take on roughcast render projects.

Negotiating Contracts

Sign a contract with the contractor before you start working. Details about the scope of work, the timeline, the payment schedule and any warranties should be outlined in the contract. Get the contract looked over by a lawyer before you sign it. Look out for yourself and make sure you are being treated fairly.

Exterior Wall Coverings Other Than Roughcast

There are also a number of alternatives to roughcast rendering:

• Smooth Render: An even/smooth finish.
• Brick Cladding: Single skin of brick veneer and a timeless appearance that lasts the distance.
• Stone Cladding: Natural and aesthetic, a soft finish to the stone.
• Wood Siding: Warm and homey.

Smooth Render

Medium texture smooth render offers durability for sustained use. It is less difficult to lay than roughcast, and calls for less skill. Smooth render generally does not last as long as roughcast render and is not as weather resistant. Use smooth render if you are after a contemporary, minimalist style.

Brick Cladding

Traditional and hard-wearing brick cladding. It is fire, bug and weather resistant. It is costly to install brick cladding. Opt for brick cladding for a timeless and time-honored look.

Stone Cladding

Natural finish with Stone cladding for aesthetic appeal. It is made to be durable and weather resistant. The laying of stone cladding can be costly as well. If you are looking for a lavish, high-end appearance, think about stone cladding.

Wood Siding

A wood facade creates a warm, welcoming finish. It’s easy enough to set up. Wood siding needs constant care — paint or stain. If you prefer a rustic, homey appearance, go with wood siding.

What is roughcast rendering exactly?

Roughcast or pebbledash is a coarse plaster surface used on outside walls that consists of lime and sometimes cement mixed with sand, small gravel, and often pebbles or shells.

How do you render roughcast?

Roughcast Render Application involves: surface preparation, mixing the render, applying the base coat, casting the roughcast, and curing the finish.

What are the benefits of roughcast rendering?

The unique benefits of this type of finish are durability, weather resistance, decorative effect, and ability to hide imperfections.

How much does roughcast render cost?

The roughcast render price will vary depending on the size of the project, the kind of render being used, the surface condition and the labor required.