Shower Tray And Bath Seals

Leaks through the joint between the shower tray or bath ledge and adjacent walls still plague the domestic construction industry.

Leaks through the joint between the shower tray or bath ledge and adjacent walls still plague the domestic construction industry.

Aggravated clients are bad for business not to mention the financial impact of substantial cost claims that follow the path of leaking seals.

To date, property owners and contractors have borne the cost of repairing water damage caused by leaking seals.

That may be about to change with the introduction of The Sale and Supply of Goods to Consumer Regulations 2002 which came into force in the UK on 31st March 2003, wherein the 'reversed burden of proof' has direct implications for retailers.

Rarely are movement joint seals specified for a shower tray or bath in a typical domestic project, in spite of the fact that BS 5385 Part 4 (domestic showers) advises specifiers that movement joints should be considered at design stage, and special attention to be paid to sealing the gap between wall and base, particularly over suspended floors.

Perhaps this lack of technical direction from specifiers has in part contributed to an 'industry vacuum', wherein some sealing products promoted in the DIY sector are more focused on 'ease-n-speed' to attract a sale, rather than meeting the requirements of the British Standards or even basic 'fitness for purpose' obligations under The Sale of Goods Act 1979.

The environmental demands (and not selling at all costs) should dictate what is required of the seal and the seal dictates what is required of the installer.

A gifted installer is of little benefit if the seal is not 'fit for purpose' in the first place.

Let's look at three sealing products, Silicone, Trimlux and Pre-formed Strips, in the context of achieving a 'fit for purpose' watertight seal over a movement joint in the domestic shower environment.

It is clear from the BS 5385 that the joint between a shower tray or bath ledge and the adjacent walls in a typical domestic dwelling is a movement joint.

The joint is designed to relieve tension (not compression) created by contraction (drying shrinkage), deflection (weight) and structural movement (settlement).

Not only must the seal expand while remaining watertight, but it must do so in consideration of other factors such as fluctuating temperatures, chemical attack, wear, the passage of time, contamination and damage from the cleaning process.

In deciding how much this joint will expand, one could look to BS 4305 Part 1 wherein a maximum permissible deflection on the roll of an acrylic bath (with an integral support structure) after base loading is 2mm.

In new dwellings, post kiln joist shrinkage can account for another 2mm.

It is reasonable to assume that a 4mm expansion of the wall/ledge movement joint may occur in new dwellings wherein an acrylic bath is installed upstairs over a timber joist floor.

Silicone is the most frequently used sealing material today.

When installing silicone manufacturers will generally recommend adherence to BS 5385 which says that silicone has a Movement Accommodation Factor (MAF) of 25%.

BSI recommends that an internal back-up material is used to 'shutter' the silicone inside the joint, and that this back-up material is coated with a silicone bond breaker (adhesive tape) to avoid 3 side adhesion and allow 'a tensile release' of the silicone off the back up material to create a stretchable bridge of silicone across two surfaces.

If silicone is required to accommodate 4mm joint movement, a releasable movement zone of 16mm is required.

But the problem is that the gap between a typical shower tray or bath ledge and adjacent wall may only vary from 0mm - 10mm, it is seldom as much as 16mm.

To comply with BS 5385 one must surface mount the silicone over the joint to achieve the releasable 16mm movement zone required.

Assuming a further 5mm bond width is required to hold this movement zone between the wall and ledge (a right angle detail), the exposed face of silicone can exceed 20mm.

For contractors, the extra labor cost involved in fixing a triangular backing material firmly over this joint, then applying a bond breaking tape to create a 16mm long silicone movement zone, then tooling up a 20mm wide exposed silicone face is not exactly what competitors are pricing for, and not what the end user really wants to see! For most end users an exposed face of 20mm of silicone is just too unattractive.

Exposed silicone acts like a magnet for shower waste matter, it is unhygienic and needs regular cleaning.

Silicone may need replacement from time to time as the aggressive shower environment takes its toll.

While there is an appreciation of the unique benefits of silicone, there is a reluctance to meet BS 5385 'principals'.

In the cost/benefit shakeup, end users favor 'aesthetics' over 'technical merit'.

BS 5385 'principals' simply need to be aesthetically re-packaged for homes.

However, if our gifted installer fixes a silicone seal to BS 5385 recommendations, the seal will meet the criteria as being a 'fit for purpose' watertight seal over a movement joint in the normal shower environment.

Trimlux (www.trimlux.com) is a hybrid sealing system that combines silicone with a preformed strip.

The Trimlux strip acts as an external backing material inside which a silicone bond breaker leg prevents the silicone from bonding to the underside and restricting movement.

The installer slightly over fills the strip with silicone and plants it onto the ledge tight against the wall.

When joint movement occurs the semi-flexible profile bridges the ledge and adjacent wall.

The silicone bond width on the ledge is 12mm ensuring strong adhesion to counter joint tension.

The silicone remains concealed and protected inside the pre-formed strip, it will not attract gunge and requires little maintenance.

The benefits of Trimlux are that it packages the principal recommendations of BS 5385 (silicone, backing material, bond breakers) into a DIY friendly product that meets the technical and aesthetic requirements of domestic shower environments.

If our gifted installer fixes Trimlux in accordance with the manufacturers instructions, it will be a 'fit for purpose' watertight seal over a movement joint in the normal shower environment.

Preformed strips in the context of shower tray and bath seals are generically called sealing strips.

They rely on a flexible lip attached to the outer leg to form a 'pressure' critical seal with the ledge during installation.

They are promoted strongly in the DIY sector.

BS 5385 : Part 3 Section 3 19.4 states that pre-formed strips are suitable for use in stress-relieving or compression joints where a watertight seal is not critical - It is implied that if a watertight seal is critical, pre-formed strips are unsuitable.

Fixing a sealing strip to a wall and relying on the pressure of a outer flexible lip to maintain a constant seal with an offset ledge that is expected to drop away from the lip, leads to the one obvious conclusion - if the ledge drops down, lip pressure is reduced and the effectiveness of the seal (to say the least) is diminished.

If our gifted installer installs a pre-formed strip to the manufacturer's instructions, the weight of evidence suggests it is not 'fit for purpose' as a watertight seal over a movement joint in the normal shower environment.

On 31st March 2003 The Sale and Supply of Goods to Consumer Regulations 2002 came into force.

In the event of a dispute in the first six months after purchase over the 'fitness for purpose' of a seal, the 'reversed burden of proof' places the onus on the seller to prove to the customer, the seal was 'fit for purpose'.

There is no onus on the customer to prove otherwise.

If between six months and six years after the purchase (five years in Scotland), property damage has occurred and it was subsequently proven by the customer the seal was so poorly designed that break down was likely or certain to occur at some unreasonable future date, the consumer may seek damages from the seller as consequential losses.

In 2002, a self proclaimed 'world leader in seals' claimed their sealing strip was a 'highly effective, permanent, long-lasting, watertight seal' only later to admit they had 'no test data' and 'no records of the development trials' (wonder why!).

Two months later a spokesman for their new design center in Paris observed that many companies developing products for the mass market have not given the proper focus to product design and development in the past! Confused ? Retailers and Contractors are now in a precarious position if their suppliers cannot prove what they sell is 'fit for purpose'.

Best read about this now and at least be aware of the changing situation.

Back to top