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HOW TO DESIGN THE PERFECT PLANTER

AND DECK DETAIL

By Geoffrey C. Thompson BE, AMI Chem. E. Technical Director

Wrimco Waterproofing Division of Laser Sonics Pty. Ltd.

Fig. 1 TYPICAL PLANTER & DECK DESIGNS

The drawing above shows a number of variations which are all based on a suitable waterproof

membrane; and in the case of planters, protection board to the base and side with 30mmdrainage cell and 1mm filter fabric in the base.

The various elements and design options are discussed below.

Membrane Selection

Since single layer Plasticised PVC hot air applied plastic sheet membrane is not really an

option for planters and arguably for decks, the choice of membrane boils down to:

Single layer SBSelastomeric torch applied sheet membrane using West Indian bitumenwith double detailing at the perimeters, corners and drains;

Two layer APP (wax)plastomeric torch applied sheet membrane;

Urethane liquid appliedelastomericmembrane, solvent based;

Urethane modified acrylicplastomeric membrane, water based; or

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Latex bitumen or pure SBR latex rubber membrane, also water based, and often usedwith cement as a waterproof tile adhesive (Screedbond).

The torch-on SBS is preferred because of its guaranteed thickness, longer life and excellent

adhesion, which is superior to APP because it contains no wax. The West Indian bitumen in

SBS gives longer life compared with the Middle East bitumen in APP membranes.

The urethanes, and especially the pure urethanes (ie. normally not black) which have a longer

life than the bitumen extended urethanes, are the optimum choice for planters that are less than600mm wide and for decks that are curved or have many small diameter drains.

The recently developed water based urethane/acrylics are essentially acrylics but with superiorelastic properties. Together with SBR latex, they are best used on less critical balconies rather

than over habitable rooms or planters with bases. The standard acrylics are good for external

walls and for sealing off mortar beds so white porous-type tiles do not discolour from dampcement.

Fillets

The 50x50mm sand/cement fillets are a carry over from the old hot bitumen days but are still

recommended for APP. With SBS however, the lower melting point enables it to be used as an

angle fillet or double detail. This is preferred because the sand/cement fillet can easily causeproblems such as loss of adhesion and cracking if not applied correctly.

For the liquid applied membranes 10x10mm fillets of urethane sealant are used. Althoughincorrectly referred to as bond breakers, the elastic properties help to provide a good sealwhere low movement is to be expected. A properly designed joint with closed cell

polyethylene (PE) foam backing should be used if there is likely to be medium to highmovement. (Fig. 2)

Fig. 2

Protection

There are essentially four types of protection board on the market:

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Fibre cement (FC) sheet is seldom used unless a rigid load bearing sheet is requiredbecause it is heavy, quite brittle, breaks under stress unless uniformly supported and ismore expensive than the alternatives.

Polypropylene (PP) corrugated sheet 1.2x1.8m is satisfactory for planter bases butbecause it is practically impossible to adhere to any membrane, it is undesirable to use

on a planter wall unless it can be held in place mechanically such as a Z section or by aflashing.

Extruded/laminated polystyrene board (EPXL) is supplied as a fan fold or concertinasheet that opens up to approximately 1.2x15m. It is easily adhered with styrene

compatible glue or simply adhered to an APP or SBS membrane by briefly heating themembrane with a propane torch and then pressing the EPXL to the molten bitumen

surface. It is more flexible than the PP so is preferred for curved walls and also acts as

an expansion joint. With an R-value of 0.2 (equivalent to 54mm concrete), it isfrequently used for thermal insulation and its impact sound deadening qualities

confirmed by the CSIRO make it very cost effective for external decks over habitable

rooms.

Expanded polystyrene board (EPS) is white in colour and quite brittle so normally mustbe at least 20mm thick.

Of the four, the dedicated EPXL (Wrimco PB4) has the best combination of properties and iscertainly the most versatile and easiest to apply.

Drainage Cells

The 30mm injection moulded PP drainage cell with 1mm filter fabric on top definitely requiresthe use of a protection board as the edges are quite sharp and can easily cut into the membrane

and particularly soft urethane rubbers. Since it comes in 360x360mm squares, it is difficult to

use for the sides of planters and provides no useful function in this configuration.

Heavy rain will never flood a properly designed planter unless the drain becomes blocked. In

this case water overflowing down the insides will simply exacerbate the problem. However, ifrequired for structural reasons such as a brick retaining wall, the injection moulded drainage

cell is wrapped in filter fabric.

For shallow landscaped areas with good falls, there is a 10mm dimpled PP drainage cell with

filter fabric factory applied on top(Delta)which may be used in conjunction with the 30mm

drainage cell over drains that are set down 20mm. A similar product has loose filter fabric on

both sides (Coredrain). Both are often used vertically but normally have to be nailed in placewhich naturally may cause problems with the membrane. Such applications may well be

counter productive as they will only make the problem worse if drains become partially

blocked.

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Drains

To prevent water forming a dam from double detailing or sealant fillets around PVC drains, the

surface should be set down 3mm as sketched so water does not pool around these critical

locations. (Fig. 3)

Fig. 3

Many proprietary drains make no allowance for waterproofing so care must be taken in

their selection.

To provide ready access to a planter drain, and to act as an emergency overflow, an extensionpipe with slots near the bottom to drain the water from the drainage cell is sometimes used. It is

probably unnecessary if 50mm of double-washed river sand is used to prevent the 1mm filter

fabric from blocking up.

Sometimes an overflow spitter, which is situated flush with the base, is used to provide

drainage, but this must have a diameter of at least 60mm to facilitate SBS membrane

application and should preferably be positioned 3mm below the base as sketched so there is nodam effect and have 1% fall. (Fig. 4)

Fig. 4

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Conduits and Pipes

Electrical conduits should always be rigid PVC (not corrugated Plasticised PVC) and should

never pierce the wall so near to the base that they become impossible to waterproof. If they

must come out of the base, then they should be protected so they do not break when the soil is

dumped into the planter. The end of the conduit should be turned down and the cable sealedwith a ring of 6mm closed cell PE backing rod and sealant. (Fig. 5)

Fig. 5

Copper irrigation tubing as well as conduit should always be installed before the membrane isapplied to ensure proper sealing.

Topping before or after

Most planters end up with poor falls and the question often asked is whether it is preferable to

correct before or after applying membranes. Provided a sound topping is properly applied

(eg.Screedbond to enhance adhesion of new to old, 3:1 mix), the latter is normally preferred,despite the general advantage of waterproofing structural elements rather than applied finishes.

The ideal solution is to provide good falls to the drains in the first place but often this is

difficult to achieve in practice.

One advantage of topping after is that there is then no need for protection in the base. To guard

against any damage to the main membrane when the topping is applied, a liquid appliedmembrane such as latex bitumen could be applied over the topping. In this case protection

would be required.

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Terminating MembranesPlanters

Various ways of terminating membranes and combining with supplementary waterproofing are

shown in Fig. 1.

With so many planters being constructed from reinforced blockwork, which is so much moreporous than concrete, the challenge is to prevent water bypassing the system. The other

requirement is to mechanically hold the protection board in place and to facilitate maintenance.

Both these requirements can be met by sealing and rawlplugging a 20x10x20mm aluminium Z

section normally 100mm below the top and rendering down onto it, with the render thenwaterproofed with acrylic membrane. The Z section may also be advantageously used to

support an internal face stone.

Where there is a complex of planters and possibly pools, it may be best to membrane the deckbefore the blockwork walls are built. It is preferable to install the rebar after the membrane and

then seal it, especially if torch-on SBS membrane is used, but it can be done before. APPswould not be suitable here because of poor adhesion due to the wax and higher melting point.With membrane under the walls of the planter, there is no need to waterproof the render but it

is still worthwhile to prevent efflorescence due to the presence of lime (CaO) and dampness in

the external wall.

Where there is a capping stone or flashing, this should project at least 10mm inside the planter

so the protection board is not proud but is sheltered at the top. This enables the membrane and

protection board (preferably the PB4 because of its excellent ability to be adhered) to go to thetop with the membrane turned over to waterproof the top. (Fig. 1 RHS)

If waterproofing before rendering is preferred, take the membrane down onto the Z section asshown using the factory applied granular SBS to provide a good surface for the render to

adhere. (Fig. 6)

Fig. 6

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Safety First

Wherever possible, the cautious designer should avoid a planter wall abutting a habitable room

and it should certainly not form part of the main structure. (Fig. 7) The architect should aim for

a fail safe design so if, for example, a flashing is missed or is defective, water will escape

externally rather than penetrate internally.

Fig. 7

Since it is always preferable to avoid applying the main membrane to a topping or applied

finish and particularly render because of its porosity, if rendering is done before waterproofing,

then it must be cut straight 100mm down from the top. After curing it should be sealed withacrylic before applying the membrane.

If a whole wall has been rendered and it is not practical to remove it, the 20x10x20mm Zsection can be sealed and rawlplugged into a 20mm slot cut out of the render and subsequently

filled with sealant or render. This effectively brings the main membrane onto the structural

wall.

Terminating MembraneDecks

Since mortar shrinks, it is preferable to separate it from the membrane with an expansion joint

such as Abelflex closed cell polyethylenearound the perimeter. If it remains exposed, such

as for a concrete wall, then the membrane should stop 10mm below finished tile height so the

tiler can caulk after removing the 10x10mm pre-slit section. Acrylic membrane or solventbased acrylic sealer should then be applied 50mm above to prevent wind driven rain bypassing

the membrane.

When the wall has already been rendered and cut off 100mm from the bottom, then apply the

membrane to full height. The tiler lays against Abelflexcut to finished tile height and the gapis filled in with render and often a face tile used to cover the joint. Some tilers prefer to use6mm EPS cut and fitted 6mm below finished tile height and use silicone sealant to fill the joint

thus formed.

Where terminating under a sliding door, the membrane should finish on the upturn to under aflashing. Particularly with torch-on SBS, the membrane itself can be used as a hidden

additional flashing, as shown. (Fig. 8)

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Fig. 8

Since designers often prefer the outside tiled surface to be flush with the inside, thus creating a

problem with wind driven rain. The answer is to fix an angle behind where the window/door

frame is to be installed and apply the membrane onto it as illustrated. (Fig. 9) This effectivelyraises the height of the step. Since the membrane is being turned over a 90 edge, it should

have a radius of 5mm.

Fig. 9

Reglets are seldom used nowadays except for Plasticised PVC since they are installed by aformworker and thus involve another trade and add to the cost. They are also difficult to align

properly. Where a positive termination of the membrane is required for an exposed concrete

wall, a convenient and inexpensive solution is to saw-cut the wall 2mm and seal 20x25x1.6mmaluminium angle as a flashing/pressure seal. (Fig. 10) Another method is to rawl plug a 30mm

aluminium strip over the membrane and caulk with silicone or urethane sealant.

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Fig. 10

Specification

Visit our site (www.lasersonics.com.au) for comprehensive NATSPEC specifications thatincorporates the design and selection principles outlined above. These specifications not only

encompass planter design, but also tanking (essentially the same as for planter walls) and

roofing. Roofing may incorporate either protection/insulation board and pebbles (IRMA); orgranular surfaced SBS exposed or under seated pavers; or UV resistant urethane membrane.