bossed render example

If you decide to have your house rendered, or you buy a house that has been rendered, you can be rest assured that your home will be protected from the elements, will be well-insulated, and will be able to breathe. Rendering can also give your house a stylish and sophisticated finish. But rendering can also be prone to problems that not only will make the exterior of your house look messy but can also even cause structural damage if left unrepaired.

What is render?

Render is a form of plastering that is used on the outside of walls. It can be in the form of cement, lime, acrylic, silicone or other materials, but its purpose is to protect the exterior walls from the elements and to protect the stone or brickwork from cracking or damage. It also provides a smooth finish that can either be pre-coloured or that can be painted.

Some types of render, such as acrylic ones, can be applied in one coat but other types such as sand and cement render, need to be applied in two coats (a scratch coat underneath and then a topcoat). In both cases, a smooth finish is created, in a similar way to a plaster screed.

What is bossed render?

Cracks appearing in your render is fairly common. Your house will move over time, expanding and contracting in the heat, and this can cause hairline cracks to appear in your render (this is less common with lime rendering, which is more flexible). Normally, these cracks aren't a problem and are nothing more than a cosmetic issue.

Cracks are especially common in render mortar with sand and cement when a too high ratio of cement is used. They are also common around the edges of old patch repairs, where the new render isn't an exact match for the old render.

Sometimes, however, water can seep into the mortar through these cracks and get behind the render. The water then freezes in cold weather and expands in warmer weather which can make the render come loose from the wall it has been applied to. This loose render will sound hollow if you tap on it, and this loose and hollow render is known as bossed render.

As well as cracking, bulging plaster can be a sign that the render has become bossed. You may even see that chunks of it has fallen off. If you're worried about the damage to your wall boss rendering can do, then you are right to be.

What damage can bossed render do?

Of course, bossed render doesn't look very nice. If your home has been rendered in part to give it a nice finish, bossed render can make it look messy and untidy. Beyond that, however, bossed render can also cause structural damage to the walls underneath.

Moisture that has become trapped between the render and the stonework can penetrate through the walls, also known as penetrating damp, and this can cause timber decay throughout the home. This problem gets worse the longer it is left, so it is important to address loose, cracked, and hollow rendering as quickly as possible.

Can cracks in old render be repaired?

Cracks in old render can be repaired to a similar level of texture and look to match the original render. However, colour matching an old shade may be a bit tricky, so if the physical colour appearance of the crack and render is too much, you may wish to repaint the full area depending on the type of render you have.

How to repair bossed render

Thankfully, an area of bossed render doesn't necessarily mean that your entire house needs to be re-rendered. In most cases, localised patch repair will be enough, as long as the bossed render is contained to one small area.

The hollow and loose bossed render will need to be taken off, leaving bare patches of the wall underneath. Once this wall has dried out, new rendering can be applied. It is almost impossible to make this repair work invisible. The patch of the new render will usually be quite obvious next to the rest of the rendering. This is less of a problem with cement or lime because it can be painted over, but acrylic render sometimes is made to not be painted so it will be more difficult to cover up the repairs.

How much would it cost to re-render a house?

Inevitably, the property size will dramatically change the cost of repair as well as other factors such as difficulty and method used. Prices can start at £2000 and cost anything up to £8000, and generally last between 5-14 days to complete the job.

On top of that, don't forget that you will require scaffolding when rendering, so between £500-£800 should be reserved for scaffolding costs. You can either directly contact a scaffolding company yourself, or let the plasterer source one for you.

How long does render last?

If the job has been done by a professional, it will generally last longer, ranging between 20-40 years on modern acrylic or plastic-based renders. Depending on the smoothness of the job, and if the walls were cleaned prior to it being applied, the lifespan will vary.

In the more common cement-based renders, the lifespan is is significantly reduced due to the cracks or shrinkage. Cracks could form anywhere between 7-15 years.

How do you stop render from cracking?

Cracking can be eliminated by carefully choosing the type of render, i.e lime-based render is known for it's longevity.

A cement-based render will work best when the brick underneath was built with a cement-based mortar. However, cement-based render doesn't cope well on soft lime-based mortar as it has to deal with more movement and the rigidness of it makes it more difficult, resulting in more cracks, bumps and hollow spots.

Is rendering a good idea?

Rendering the property walls can help protect the building against the weather and prevent heat from escaping through the external walls. On average, around 30% of heat is lost through the external walls.

Other than the practical purposes, rendering is a good idea for aesthetical purposes too. It can make an old and tired building improve it's appearance. The surface will instantly be transformed, enhancing the overall appearance, possibly increasing the value of a property.

Can I render my house myself?

It is possible to do it on your own, but it can be difficult if you don't have the appropriate tools or training. It can also be quite time-consuming and cost more in the long run if you do not have the sufficient skills and correct technique.

Be careful when considering this though, as poorly rendered walls can look out of place and even devalue the property altogether.

Can you render straight onto brick?

In short, yes you can but a few factors may need to be considered before committing to the job and the standard of the wall will need to be assessed. This can easily affect the amount of materials you need for the job or the equipment needed.

Do you need permission to render your house?

No, you do not require planning permission to render, repair or maintain the appearance of your building as long as the materials used on the surface match the appearance of the main construction.

Does rendering insulate a house?

Yes, as mentioned above, approximately 30% of energy used to heat a home is lost through the external walls. With this extra layer, it will help keep heat in the building.

The bottom line

Bossed render is render that has come away from the wall underneath and that sounds hollow when it is tapped. It is a fairly common problem that occurs when water seeps in through hairline cracks and gets behind the rendering, which contracts and expands due to frost. Hairline cracks itself is not a major issue, but it is important to fix bossed rendering as soon as possible as it can lead to penetrating damp, therefore causing structural damage to your home.

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