Your guide to rendering and bagging
Theres no doubting the value to your home that resurfacing can bring. But, do you render or bag? And is it worth doing on your style of home? We give you the answers.
The process of covering internal or external walls with a layer, or gradual layers, of cement-based render mixes is called cement rendering and is done by a plasterer. This is one of the quickest and easiest ways of updating a home and can greatly increase its market value.
Cement render on internal and external wall surfaces improves on the waterproofing, fire-rating and appearance of a home and can include pigments, admixtures and various textured finishes.
You can use materials such as:
- Portland cement—hydrated lime that will make the mix creamier and more workable and provide some elasticity to prevent cracking;
- clean, sharp sand thats free of clay or impurities;
- clean water;
- admixtures, however pigments should never exceed 10 per cent of the weight of the cement in the mix and additives. Bycol will slow the drying process. And bonding agents such as Bond Crete can be used diluted with water to increase the adherence of the render mix to brick walls.
Is it suitable for all homes?
In the early 20th century rendering was a popular covering for façades of terrace houses. From the60s to the 80s, there was a resurgence of rendered external brick walls for homes.
Today, homeowners who are renovating, choose render only if it is appropriate to their particular house style. If building a new home, owners will generally choose a rendered external façade for its clean looks.
Project home builders also tend to favour a standard rendered external finish for their homes. Many of them give their designs exotic Mediterranean or Tuscan names and simply add an external wall render that has been coloured. The original Mediterranean villas in Europe were rendered and painted white to help keep the home cool from the stifling heat of the summer sun.
Many owners also choose a rendered look for their new home simply because there is a considerable saving when buying bricks. Face bricks, which are laid and left as they are, tend to cost a lot more than bricks that are covered by a layer or layers of cement render.
Is render long-lasting?
A rendered finish should stay intact for 15-20 years if properly applied and painted to protect it from the elements. A plasterer carrying out rendering work should give a guarantee that his work will last for this period.
What are the potential problems?
There are many things to consider when rendering: it is important that the render mix is suitable for the background surface; it is applied in the correct number of coatings; and that appropriate time is given for it to cure or harden properly.
Rendered surfaces need to be cut and given control joints to minimise surface cracks. Minute surface cracks, called crazing, are usually due to render drying out too quickly, so it is important to allow for proper curing conditions, dampening the walls and protecting them from the harsh sun.
Poor substrate preparation can lead to render spalling off the wall, in a matter of days in some cases. These areas are easily located; they will sound hollow when tapped and rise off the surface, eventually falling off. They can be patched but ideally the problem should not occur.
It is a difficult exercise to keep correct proportions of colour additives in the render mix. If these are not exact, then youll get a patchy finish on the external walls. Also, if you get an even finish on an external façade, the colour oxides can sometimes fade quickly. They can show up in darker patches in some areas where, say, the wall beneath the render is affected by rising damp or there is a waterproofing problem. Ideally, the finished render should be painted to protect it from the elements.
Render will simply fall away if it has been applied to a wall or part of a wall affected by either rising damp or falling damp. If you apply waterproof render coatings to a damp wall it will simply push the dampness to another part of the wall and not fix the dampness. You must treat a wall for damp first before you start rendering.
Bagging versus render
A house that has been rendered and painted will have clean, smooth lines, precise corners and detailed finishes to window sills. A straight edge placed against it should not reveal any bumps or imperfections.
Bagging, on the other hand, highlights any imperfections rather than hiding them. A bagged wall gives a rustic appearance and the pigments used are similar to the ones used in Tuscany. It is usually applied to a wall without much precision and it allows for irregularities, bumps and a little calculated chaos.
Coarse-graded sands are used for bagging and finer ones for rendering.
You can buy coloured bagging render in various colours and all you do is add water to it. This is applied thinly to a thickness of about 5mm. Standard rendering, on the other hand, is applied in layers if required, each layer between 10-15mm depending on the substrate conditions or degree of smoothness.
Can you bag or render over old walls?
It is easy to bag or render over old walls. But old walls may have value in so far as their period of construction is concerned. It is better to keep the façade of a home in harmony to its period of construction than simply hide surface blemishes. If bricks are loose, crumbling away or damaged, these can be matched and replaced. If the mortar between the bricks is crumbling, you can get professionals to re-point the brick. They do this by scraping 25mm of the mortar joints and replacing them with new mortar that has an additive that prevents any further cracking or crumbling of mortar joints.
Before you start, the substrate (the bare brick wall) needs to be cleaned of any loose material, such as oil, paint and dust. Other things to consider include:
- the mortar joints must be free of any crumbling mortar;
- the wall is free of any loose or cracked bricks;
- there is no soil subsidence that gives rise to cracking of walls and may continue to do so after the render is applied;
- the walls are free of any dampness; and
the walls be free of any efflorescence—the white, salty discharge usually associated with dampness in walls.
To render or bag?
A rendered finish gives a more elegant, cleaner and sophisticated look to the external faces of a home than a bagged finish. You can paint a rendered wall to achieve a smooth surface finish whereas a bagged wall is more rustic in its appearance. Bagged walls can be left as they are or painted but, in both cases, the contours of the bricks and mortar joints will still be clearly visible.
If youre trying to re-create a rustic look or the distant cousin of the Tuscan farmhouse, then opt for a bagged finish. Colour can even be added to the bagging mix to give a total Tuscan look.
Anyone can bag a wall. All you need is hessian-sack material, a steel trowel and a wood float or a sponge. You dont need any formal training or experience. However, you should get professional plasterers to do any rendering work.
For a new home, where you would be liaising closely with the architect at the design stage, we would recommend a smooth rendered façade, then a painted finish.
In an existing home, if the brickwork of a façade is in a poor state, try to preserve it to keep it in harmony with the style of the home and in keeping with neighbouring homes. Your council may also have a say in what can or cant be done as far as altering the external appearance of a home.
If brick walls cant be fixed or repaired to bring them to their former glory, then consider rendering, followed by painting. If rendering were not possible, particularly if a home did not benefit from render, then consider bagging.