How does it happen and what can you do to fix cracked and hollow render?
How does render become cracked and hollow?
The external walls of your house perform two vital functions. they hold up the building and keep elements such as water from entering the house. Carrying out repairs is essential to protect your walls and structure.
Dampness within a building usually occurs where the walls are of a solid construction. These walls are often constructed of stone or solid brickwork and finished externally with a sand cement render. This render can be smooth finished or dashed with small stones.
Moisture/rainwater enters the structure through cracks that have occurred over the passage of time. What happens is that rainwater enters the structure via the cracks and with capillary action water is pulled in further. The water soaks the structure and through gravity drops, to the lower sections of the wall. Where the render is not defective at the lower level it is unable to escape and evaporate and is therefore drawn inside the property.
Over time, the structure will become saturated and in winter the water can freeze. This expansion of the water will cause the render to be pushed off the wall and for the cracks to increase in size. Ultimately the render will become hollow and start falling off.
Other causes of dampness in walls can be where the rainwater gutters are leaking at the joints or have perished over time. Also, where the running outlet has come away from the downpipe or where a downpipe has broken along its length. This continual saturation of the wall will cause problems as above.
Damaged Render: What to look for?
Over time hairline cracks can start to appear in render. This can due to a number of reasons such as small movements of the structure, weather damage, physical damage and more. Traditional Lime render tends to be more flexible than the modern cement version.
Top Tip! Don’t apply cement render to old solid wall buildings!
Look out for those hairline cracks and make sure you seal them when they first develop. Otherwise, water will start to penetrate the wall and could result in even larger cracks. This also applies to any physical damage. Repair immediately!
How to Repair House Render?
In the past render was applied in three layers that got thinner — these layers were known as the render, float and set coats. Nowadays, it’s normally 2 coats of render.
So the first job is usually to hack off any hollow, loose or cracked render. Allow the wall to dry out before you apply new render. On small repairs you can normally carry these out yourself or by a trusted handyman.
Large areas is a skilled job and best left to your building team or specialist.
Top Tip! Don’t use cement render to patch lime render it will fail over time!
Render Repair Costs
Prices can vary, so check with your local company/builder, but for hacking off old render, raking out the joints, cleaning down the wall and then applying a new 22mm render in two coats will cost in the region of £67/m²
Still not sure? Get in touch.
If you have any questions about cracked or hollow render or other issues, please don’t hesitate to get in touch.
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Thanks for reading.
Mike Woods, MCIAT
