I find planters as an excellent opportunity to give colour and a pleasant dimension to the townscape.
Planters can be made from many materials, concrete included. Planters made from porous materials definitely need waterproofing.
In waterproofing terms and procedures we had better consider planters as basements because there is constant contact with moist soil.
Now, you will not find hydrostatic pressure in a planter &' except for rare occasions &' but you will
ertainly find capillary absorption and salt transportation to the external surfaces.
Effloresence wont bring the disaster but aesthetically speaking the depreciation of the planter could be significant.
WATERPROOFING OPTIONS
Waterproofing materials suitable for planters should combine the following characteristics:
1) flexibility: planters are continuously exposed to temperature variations.
2) withstand temporary hydrostatic pressure.
3) possess antiroot properties. Acids excreted from plant root systems are very powerful.
Waterproofing products to be excluded:
* conventional SBS and APP membranes
* asphalt emulsions and rubberized emulsions
* cementitious waterproofing products.
What we should use:
a) SBS membranes type garden. These products are used for big planters. They are the same products we use for conventional roof gardens with extensive vegetation.
b) SBS, self-adhesive membranes with antiroot properties . This is a very effective solution and could be a do-it-yourself one with proper care. Always use the appropriate,preparatory asphaltic primer
c) For small planters we could choose brushable,elastomeric,waterproofing products most ususally based on polyurethane resins. This is a simple, versatile and efficacious as well solution.
Termination of waterproofing on vertical walls should be 10-15 cm above soil surface. An additional, protective waterproofing stripe might be needed near soil surface if main waterproofing layer shouldnt stay exposed.
Before proceeding to planting, always execute a flood test.
DRAINAGE CONSIDERATIONS
Do cater for the easy drainage of excessive water. Big water quantities in the root zone will cause problems.
Traditionally we used gravel to form a drainage layer. Then one geotextile on the top and everything OK!
There are better ways nowadays! We have many light and flexible geocomposite products in our drainage weaponry.
Personally I prefer and use a dimpled (studded) HDPE membrane with 20mm dimples (studs) and slots for the water to pass freely. On top of this I place spubonded geotextile of min weight 200gr/m2.
It is of utmost importance to select a geotextile filter with no clogging properties!
Take care: geotextile should terminate a little above soil.
Dont ever forget to let 1 or 2 drain outlets!
We should see planters as small roof gardens. They give us an opportunity to bring nature &' or the least its illusion &' in the city environment. Victims as we are of a galloping urbanization, we should resist in every possible way!
Chris Strogilis
http://maconwaterproofing.blogspot.com
About the Author:
Civil engineer with postgraduate studies in MBA and Marketing
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