Waterproofing Concrete Planter Boxes

The presence of concrete planter boxes can spruce up almost any garden or yard and is a great structure to house and contain your plants. How you are sealing or waterproofing concrete planter boxes will help to maximize the service life of the planter box.

Waterproofing your concrete planter box is highly recommended to ensure your plants remain healthy. Waterproofing avoids the leaching of highly alkaline salts into the soil in the planter. The alkalinity of the soil may stunt the growth of some plants. Also, some masonry blocks and bricks are very porous and the soil may dry out too quickly.

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Sloped Mortar bed under the waterproofing for drainage. For best practice always use protection board to protect your waterproofing membrane

How to waterproofing concrete planter boxes, masonry blocks, or brick planter boxes

Step 1

Vigorously clean your concrete plant planter box. Scrabble floor wall join in readiness for fillet of Drizoro Maxrest. Especially necessary if it is a highly troweled slab. Remove any efflorescence with Efflorescence Rid

Step 2

Dampen the area. Install Drizoro Maxrest fillet or coving to join floor wall joint. (minimum fillet 20 x 20 mm which will consume approximately 1 Kg of Maxrest per Lineal metre). Remove any loose material from the planter box.

Step 3

Install drainage points. Those required to remove excess water from the masonry planter box. Seal around the pipe using Drizoro Maxjoint Elastic

Step 4

Dampen the surface and apply a coating of Drizoro Maxseal Flex from top to bottom. Allow curing overnight. Dampen again before applying the second coat.

Step 5

Allow the coating to cure for 10 – 14 days. Then place protection Board.  Fill with appropriate fill / potting mix and plant install your plants.

Here you will find some Raised Garden Bed designs.

Pictures via Houzz

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Planter Boxes Attached to sidewall

Planter boxes, pictured above, should be waterproofed. Included in the building design plan. Planter boxes are often added as an afterthought creating some headaches for the waterproofing contractor.  One builder I worked with at one time had in fact rendered the external walls. Then someone decided that would look more upmarket if a fountain was put on the wall. So they just bricked up to the wall, rendered it, and partially installed the plumbing. Then asked the waterproofer to make it waterproof.

No problem right? 

4 Problems created for building and the waterproofer by adding a planter box or a fountain to your external wall are

  1. Water penetration through the exterior wall into the internal space
  2. Making the join between the planter box and the exterior wall watertight
  3. Will the bricks or masonry planter / fountain stay attached to the rendered wall.
  4. If it placed on an exterior slab (not part of the original construction). What will movement between house slab and planter slab cause movement and cracking.

At the time I completed 30 + planters and only had 2 issues –

a. fountain installer damaged the waterproofing – minor issue

b. where no room for expansion between 2 slabs caused the bottom of the fountain to crack severely. Major issue needed redesign fountain. Installation of an proper expansion joint.


Luckily Drizoro products were, in this instance, very effective even when the design was an afterthought. Only one out of 30 needed some redesigning before completion of waterproofing was even possible.

Waterproofing concrete planter boxes is necessary to prevent water from damaging the retaining structure


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