painting garden and boundry walls

Painting garden and boundary walls.In the last IT article we looked at painting exterior walls of the house itself. Garden and boundary walls need a extra care when initially painting or re-painting, otherwise flaking of paint and green staining will soon re-appear. Some years ago, stone walling was relatively cheap and hence common in Spain, later to save on materials costs, stone cladding became popular and now the average home owner will only stretch to low level stone cladding or simply painted render. Developers will, for obvious reasons, also favour the cheap but high maintenance rendered option. If you are lucky enough to have stone garden and boundary walls, you are likely to enjoy far more  leisure time than the less fortunate people that need to repaint their walls every other year. Rising damp, damp from retained earth, splash back staining and general settlement all play havoc with painted wall surfaces such that they soon look unsightly. Fortunately there are ways to improve the longevity of the painted surface.

New surfaces

If you can afford it, forget painted render and go for a stone finish. If you have to opt for render, at least try to allow for stone cladding the first half meter of wall, which will ensure that the wall looks smart for a much longer period between repaints (e.g. 5 years instead of two or less). As for external walls of the house itself (dealt with in last article), a textured surface provides a much better key than a smooth one, so wherever possible choose a textured finish, or simply ask your builder to brush the render (before dry) to give it a rougher rustic look and most importantly, a better key. (While a texture will take longer to paint, it won’t need painting so often).Large retaining walls should feature drain holes to reduce the length of time the wall is saturated after rain and most importantly to reduce the risk of collapse e.g. in a flash flood (many such walls in Spain are not proper retaining structures and hence the risk of collapse is very real). Ultimately, if you want to reduce maintenance to a minimum the  wall should be ‘tanked’ (waterproofed) from behind such that any water pressure pushes the rear tanking system onto the wall (a front surface system is likely to be pushed off the wall). Use a continuous membrane e.g. ‘Sika Lam SP-8’, and run a perforated land drain pipe along the full length of the wall base, falling to drain holes which penetrate to the outer surface of the wall (either plastic pipe or a more rustic look using two curved tiles). Alternatively paint the rear surface of the wall with a liquid membrane e.g. ‘Sika Bitusol’ and include the land drain and drain holes.
All raised borders (Jardineras) e.g. where a block or brick above ground planting area has been created, should be tanked on the inside with ‘Sika Igoflex Jardineras’ (available from good builders merchants). A drain hole should be created (about 100mm from the planter base) to allow for excess water to escape e.g during and after very heavy rainfall. The impermeable surface will protect the wall from saturation and hence the outer surface (often painted white), will be far less likely to flake or suffer algae / moss growth. The planter will also hold moisture for longer requiring less irrigation. Igoflex will not harm plant roots and is flexible to cope with minor settlement.
The exterior surface of raised planters, retaining walls and boundary walls will suffer quickly if normal exterior paints are used. Instead they can be painted with a white ‘slurry coat’ mortar ‘Sika Seal 101A’, which comes like cement for mixing with water into a thick paint like consistency, which can then be brushed on. The product is resistant to both negative and positive water pressure but allows the wall to breath.
In simple terms you are trying to encourage water to drain away quickly and protect the rear of the wall from saturation. Protection of the rear of the wall combined with the correct external surface finish should ensure a much longer surface life.

Existing surfaces

Unfortunately once a poor system is failing, it is very difficult to achieve a good key with the substrate, unless all old paint is fully removed (e.g. sand blasted off). For friable and porous failed systems a stabiliser (e.g. ‘Weber Ibodur’), can be applied before painting (which is designed to soak through the failed paint and bond into the underlying substrate), however this is not always achieved successfully as the wall may have been painted several times with different paint types and the surface must be porous.The best solution is to ensure a good paint key from day one i.e. when the substrate is new, but unfortunately for many home owners (even new ones) it’s too late, as a poor system has been applied.
Green stained surfaces can be treated with ‘Sikagard 715-W’, which is designed to kill algae and lichens (this can be rolled or sprayed on). All loose substrate and flaking paint must be scraped off and preferably sand blasted back to the render. A slurry coat of ‘Sika Seal 101A’ can then be applied.
Once Sika Seal has been applied and is fully dry, an optional conventional exterior paint system can be applied e.g. 100% Acrylic paint or Acrylic skim coat mortar (e.g. ‘Weber plastene extra’:-
-Buy good paint (preferably 100% Acrylic)
-Water the paint down according to manufacturer’s instructions
-Apply in at least two coats allowing for drying time between each one.
Remember, even when using the above products, it is still advisable to stone clad the first 0.5m of wall, which is most likely to show signs of damp and splash back staining. 300mm width of gravel adjacent to the wall base will also assist drainage and reduce splash back staining.
Garden and boundary walls are often the last part of any house build project, when money is running out. You will however save significant maintenance time if you allow to prepare these walls properly.

NB:- Information for advice purposes only. Proper safety precautions should be taken  and legal procedures followed when carrying out all works.

Information provided by Mark Paddon BSc Hons Building Surveying. ICIOB, property purchase advisor in the Valencia region.  962807247

ã Mark Paddon 2006


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