So what you need to do is to buy a wall primer and stabiliser, and you can get one from somewhere like Wickes DIY.
Everything You Need To Know About Painting Render
Render is one of the most common exterior surfaces that homeowners want to paint, but with so many types of render it can often be difficult to know exactly how to go about it. That is why we’ve put together our complete guide to painting render that contains everything you need to know before you get started.
The exterior walls of properties can come in a wide range of forms, including natural brick, stone or concrete. One of the most popular forms of external finish especially in the UK however is external render. Render is a form of external wall plaster that is applied to the masonry of properties to provide added protection from weathering and to leave an attractive finish to the property.
Like all building materials, not all render is made the same and can vary widely in terms of look, composition and performance. The most common types of render in the UK are:
- Conventional render – conventional render, often known as sand and cement render, is the most common form of render you will come across. It is a relatively unexpensive render that can be applied easily, which is why it is a popular choice for rendering projects. On the negative side, a sand and cement mix is less advanced than other forms of render, as it can uptake moisture, has low breathability and is rigid which can cause cracking due to movement. Furthermore, sand and cement does not come pre-coloured, meaning it is almost always painted to leave an attractive finish.
- Silicone render – silicone render is a more advanced form of render which has higher breathability than standard sand and cement render, while also having water repellent properties due to added silicone. This provides silicone render with extremely high durability thanks to the fact it does not absorb or trap moisture within the render, which can lead to damage. While it comes pre-coloured, some silicone renders can suffer from staining and discolouration over-time however, which can often lead to them being painted further down to the line.
- Acrylic render – another newer form of render, acrylic render is less breathable that silicone render and is not water repellent, although it is more cost-effective and offers a pre-coloured finish unlike sand and cement render.
- Lime render – lime render is a traditional form of render that has been used for hundreds of years on older, heritage properties. It is highly breathable making it breathable, allowing it is help regulate moisture levels in these older properties, although it does not offer much resistance to weathering due to its high level of porosity.
- Pebbledash – pebbledash is a very popular form of render that was popularised in the 1970’s as a highly durable render system that provides excellent weather protection, which is why it is commonly used in coastal and rural areas. It involves applying a plaster to walls and then throwing various pebbles and stones to the surface. Roughcast is a similar form of render which also involves pebbles and stones, however these are added to the render mix itself rather than applied to the outside of the wall. Pebbledash is not a pre-coloured render and can leave a dated finish, which is why it is one of the most common forms of render to be painted.
Did you know? Rendering a standard semi-detached house can cost an estimated £6,000 in the UK.
Why Would You Paint Render?
While some renders come pre-finished or pre-coloured, painting render is something that many homeowners decide to do both to new and older render. Many renders also do not come pre-finished, meaning that they are often left bare, leaving it looking tired and unfinished.
There are a number of reasons you may decide that painting render is the right thing for you, both to improve the aesthetic of the render but also its performance.
The trust is, the link between aesthetic appeal and the performance of the render go hand-in-hand. All renders that are non-silicone renders will absorb some level of moisture over-time. This is the case both with highly porous renders like lime render and renders that are designed for long-term durability like pebbledash . When moisture absorbs into the render, it saturates the material and can undergo what is known as a ‘freeze-thaw cycle’. The moisture can freeze when temperatures drop causing it to expand as it becomes a solid. This expansion leads to movement within the render which can cause cracks and holes to open up. These defects allow more moisture to enter the wall, leading to further movement and resulting in a continuing cycle of damage.
This water entering the render can also lead to discolouration in the from organic growth such as mildew, lichens and algae that all require moisture in order to develop. Renders that have not been previously painted are particularly susceptible to this growth, although even painted renders can develop this if moisture is allowed to absorb into substrate.
Can Render Cause Damp Problems?
Here in the UK we are all too familiar with damp problems, due to both the level of rainfall we get and the way many properties are constructed. Damp can come in a range of forms including rising damp, penetrating damp & condensation. All of these forms can occur on rendered walls if the right conditions are present, which is why understanding them and how they can develop is crucial.
Rising damp is caused by an external source of moisture, where water from the ground is able to soak up through the bottom course of bricks and continues to rise up the walls of a property. This is why properties have what is known as a damp proof course (DPC) which creates a barrier on the bottom level of the property to prevent the bridging of moisture. Unfortunately if this DPC is not present, is failing or is bridged by render, rising damp can develop through the wall causing significant damage and highly saturated walls.
Penetrating damp much like rising damp is caused by an external source of moisture, however it is caused from rainfall that soaks into the external walls of a property. Penetrating damp is a universal problem that can affect any external wall that is not water repellent, including brick, stone, concrete and the majority of external renders. It can particularly be a problem for renders that have poor breathability such as pebbledash as they can trap this moisture when it enters the render and allow the wall to hold the damp within the fabric of the building. When the moisture enters the external wall it can soak straight through into internal walls, damaging plaster, paintwork and causing black mould .
Condensation is an internal source of moisture caused by a natural build up of humidity from day-to-day living such as washing machines, dryers and cooking. If a property suffers from poor ventilation or has poor breathability, this condensation will continue to develop within the walls leading to black mould and damp. Like penetrating damp, poor breathability of external walls either from the render itself or a coating on the render will exacerbate these problems.
Damp, highly saturated walls will not only cause problems like mould but it can also be a precurser to heat loss. When exterior walls get wet, they transfer heat much quicker than dry walls.
Did you know? Damp content of 5% can lower the insulating properties of a material by 50%.
With 35% of heat loss in a property occuring from the walls, by having damp, wet walls you are likely to experience significant problems with heat loss, especially through the winter months.
How to paint a rendered exterior wall on a typical house
New render, and the painting of it, would at first seem a doddle.
After all, no repairs are needed and no prep work in the guide of mould or moss removal, scraping old paint off, or crack repairs, will be needed. But it’s not as simple as that.
One of the key things to consider about painting new render is the drying time, or hydration time of the rendering if it is newly applied.
Remember, when we apply render to a wall, water is added to the mix to consolidate the mortar ingredients and also to aid application.
That water in the mortar mix needs to evaporate first, or painting over it will either trap the water in, causing cracks or damp at a later stage, or it will dissipate out of the wall and eventually make the paint bubble.
So, it always best to leave new render a few days before painting is started, maybe longer in the colder and wetter months of the year.
Before painting starts, make sure you have all the right tools and equipment needed to paint.
Often on brand new render, depending on what sand is used in the mortar mix, there may be a light coating of dust across the wall. Whilst this may seem innocuous, if you try and pain tit like it is, the dust will get mixed into the paint and will look terrible.
In this case, a broom head or other stiff brush may be used to remove the dust from the wall. Be sure to wear a mask and eye protection when doing this task. It will take time and be boring, but this is all part of preparation, the most important aspect of any painting job.
The first thing you need to do is to inspect the wall as even the best plasterers sometimes miss bits. Go around the house and look closely at the wall to make sure no cracks have appeared whilst the render is drying, and no bits have been missed. Pay special attention to corners and around doors and windows
If you find anything, you need to attend to, use a fine exterior surface filler, such as Ronseal exterior ready mixed wall filler.
Also look for what a plasterer calls “snots” (no, nothing to do with your nose bogies) and this is small beads of render that may have been flicked on to the wall or dropped from the trowel during the laying up (applying) of the render.
These need to be scraped off the wall, along with any other defects or things that should not be there. It’s a simple common sense job anyone can do.
If you find any “proud” spots of render, bits that haven’t quite ended up as flat as the rest of the wall, take a plasterers float.
Wet it, and then vigorously scrub the area using circular motions, which will wear down the bulging area to flat. If this still doesn’t work and the area of render is much “prouder” than the rest of the wall, sorry to say you are going to have to hack that bit off and re-render the area to flat or it will stick out even more once a colour is added to the wall.
How to prepare to paint a dusty or friable wall
If the wall to be painted seems dusty or dirty, take a stiff brush or a broom head and brush over the entire wall, as mentioned earlier.
This will get rid of any dust or sand that has been left behind as you don’t want that coming out in the paint.
Sometimes a newly plastered external wall can have a surface which we call friable.
This means that a slightly incorrect mortar mix may have been used (with too much sand, not enough Portland cement, not enough water, or any variety of these common mistakes), resulting in an excessively “sandy” or dusty surface.
Now, it’s no good to get your outdoor wall paint and simply paint over, even if you take the steps above and brush the dust off.
The surface left won’t really be strong enough to hold the paint.
So what you need to do is to buy a wall primer and stabiliser, and you can get one from somewhere like Wickes DIY.
You need to paint that across the whole house and then allow to dry.
The resulting paint job on the outside walls will be much better and easier as a result, plus it’s going to last much longer before you need to repaint.
Once you are confident the wall is fully prepared, now is the time to start painting it.
Make sure you keep all your tools, paint and equipment in one place on site and make sure that kids and pets are kept well away.
If you are painting a wall from a ladder it is often good practice to have someone hold the ladder for you, especially if there is a breeze on that day. If that is impossible and no one is there to help you, simply drape a full, sealed bad of sand on the lowest rung.
Make sure the ground you place the ladder on is not full of leaves or moss or even in icy ground, as the ladder could slip away from you.
You should always start painting at the top of the wall.
Work down using confident strokes with your brush or roller.
Top tip: “Do all the cutting in around windows and corners with a small brush before you paint the rest of the wall.”
Then once the house is painted, you need to repeat the process (yes, you have to do it twice) and you should eventually end up with a nice looking painted rendered wall!
Note: Do you see from what I have written that most of the job is taken up by preparation?
Planning ahead and having all the tools you need is key to a good job.
Can You Paint Render?
In simple terms, yes, you can paint render. Having said this, there are paints that are more suitable than others. For example, silicone-based masonry paints are better suited for use on silicone renders as the whole point of silicone render is that it is water resistant and highly breathable. By applying a standard masonry paint to silicone render, you remove the benefits of that render.
Similarly using a low breathability masonry paint on lime render will create a barrier on the wall that will seal the moisture within the absorbent lime render, causing major issues. Sealing moisture in any building will cause significant damage, both aesthetically and structurally. When moisture cannot escape from the external wall, it will continue to build up as the moisture enters the render through cracks or soaks through the render if it is not water resistant. This moisture will then cause paint applied to the render to peel, causes penetrating damp through into the internal wall and can even cause damaged brickwork underneath the render.
When painting any render, we recommend you always opt for a highly breathable masonry paint as it will allow the moisture of a building to be freely regulated. We especially recommend only opting for a breathable masonry paint if you have a silicone rendered property or a lime rendered property which is likely to be an older, traditional property that is more susceptible to damp problems. If an acrylic-based masonry paint is used on a silicone or lime rendered property, it would prevent the high breathability of the render.
Why Paint Render?
There are a number of reasons why you may decide to paint render:
1. A Change Of Colour
While some renders come pre-coloured, sometimes a change of colour can be desired. Conventional renders can often come without a coloured finish, meaning they must be painted once dry.
2. Discolouring
Some renders can be particularly prone to discolouration and algae growth, which can be a huge eye-sore on external renders. While the discolouration of the render itself is caused by UV rays, algae and other green growth can grow on exterior renders due to moisture. Many homeowners opt to paint the render once clean to give it a new lease of life.
3. Damage
When moisture causes render to crack, the render can either be patched up using more render or repaired using an exterior filler and then painted over. This is often used as a chance to update the property with a fresh, attractive new colour.
The Best Paint For Render
The longevity of masonry paint & it’s weatherproof abilities go hand in hand. Moisture is the single biggest cause of paint failure, which is why silicone masonry paints have been designed. These paints create a water repellent surface on rendered walls that prevents any water being absorbed by the external wall.
While creating this water repellent surface, they maintain full breathability, allowing water vapour to freely escape from the render. This one-way transfer of moisture keeps buildings dry, warm and free from damp. The lifespan of the paint is also significantly higher than standard acrylic masonry paints as the moisture cannot cause paint failure.
The Best Silicone Masonry Paint
When it comes to a silicone-based masonry paint, the most advanced available today in the UK today is Emperor Masonry Paint, which is a completely waterproof masonry paint that creates a super hydrophobic surface on all external renders that prevents 96% of water absorption. It does this while being highly breathable. In an independent test conducted by UKAS accredited laboratory Lucideon, Emperor Masonry Paint was found to have an SD value of 0.60, while the same wall left untreated had an SD value of 0.57. Any surface that has an SD of under 1 is considered breathable, which demonstrated the lack of change in breathability once an external wall was treated using the paint.
In the same independent testing, Emperor Masonry Paint was found to have no change in appearance of performance after a 25-year accelerated weathering period. Due to this, Emperor Paint offer a lifetime guarantee on their masonry paint, ensuring it’s performance when applied to render for decades.
One of the most common reasons Emperor Masonry Paint is used on render is to prevent discolouration. While being resistant to UV rays, which prevents any colour fading, the masonry paint is also self-cleaning, meaning any green growth cannot attach itself to the render. It achieves this thanks to it’s water repellent technology, that results in any rain water cleaning the render down, leaving it clean and attractive with almost no maintenance.
Emperor Masonry Paint comes in 12 standard colours but can also be mixed in a range of light and pastel shades.
Pros:
- Waterproof
- Highly breathable
- Self-cleaning
- Proven to keep painted walls up to 6°C warmer on average
- Verified by the Energy Saving Trust
- Lifetime guarantee
- Prevents penetrating damp
- Ideal for preventing cracked render
Cons:
- Only available in 12 standard colours
- Is more expensive than other masonry paints on the market
