Cracking in Lime Rendered Walls Rendering Part 1

June 26, 2018




Patching and Rendering.

Patching the cracked walls is generally the first job in minor home restoration jobs. It can be one of the messiest (if you need a renderer) so it is wise to prepare the room first. If you have old carpet that you intend to replace, then remove it immediately. These will lift at the corners easily and you can cut it to manageable strips with your Stanley knife.

The floor area should be covered with a heavy-duty builders plastic that is taped to the skirting with grey ducting tape. The black plastic comes in twenty metre rolls and is 2 metres wide. Don’t tape it to the plaster or painted walls as the tape when removed can leave a nasty bikini line.

If you have cracks that run down both sides of a wall and you can see light through them then you need to treat them seriously. There is no failsafe way of totally eliminating them even major underpinning, often just moves the problem along the wall.

The method I have recently used involves removing the render along the crack to a width of 40 cm, approximately 20cm either side of the crack. In some cases I’ve seen this may involve a strip a metre and a half long. Often you’ll find the cracking is over windows or doors where timber or ash lintels have moved when the walls supporting them have been affected by reactive soils. Unless you absolutely have too, leave the architraves in position and remove the crumbling render around and up to them. As you follow the cracks you will find they close up, continue removing the render well into the good lime render. Any areas that are drummy should also be removed. Drummy is when you tap your knuckle on the plaster and it gives a hollow sound. Often drummy plaster will bubble like a small burn and falls off easily.

Once you have removed the plaster you need to tidy everything up. You want nice clean lines between the old and the new. The exposed bricks should be swept with a hand broom to remove all the excess sand. 

I then cut flexible builders mesh along the length of the exposed area. If you lap the mesh the renderer will have troubles with a proud surface so you need to measure carefully and cut one piece that runs the full length of the exposed surface. You can fix the mesh to the wall with Mickey pins and nail it to the bricks or drill and plug the bricks and screw it in place. This is time consuming but needs to be done effectively. You may need to run a straight edge between the two sides of the plasterwork to ensure the mesh is not proud. Obviously or not, the mesh needs to be fixed below the line of the render. After you have meshed the major cracks you can call in the renderer to patch the affected areas.

If you have the old lime set walls then you will need to hardset the walls after the rendering has dried to maintain that smooth finish.

In a recent case because hardsetting is messy, expensive and difficult to do on small areas after the rendering has been done we have finished the wall with a bucket of top coat Gyprocking cement. This is the final coat the gyprockers put on ceilings and walls. I don’t know how it rates in the purists’ books but it is certainly quick and effective gives you a smooth finish and can be placed on top of the render once it has dried to a reasonable level. Naturally it needs to be done by an experienced renderer. 

Good building and design!

Note: The views expressed in this article are of a broadly based nature and are in no way to be taken as the basis of an individual design. Should a reader wish to pursue the ideas expressed then at all times we recommend they consult with the appropriate professionals. 

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