Plumbing problems

Damp problems commonly stem from shower cubicle leaks. You are probably more likely to find leaks from enclosures made up on site, rather than factory-made patent units.

Let us look at some recent examples of ‘shower damp’, covering key symptoms, methods of investigation, and pointers to improved design.

Typically, the first signs of shower damp are the damaged ceiling - first stains, then eventually plaster collapse. Water may drip down from the light fitting. Occupiers may have prodded plasters to release a deluge of water, and soggy ceiling board dropped to the floor.

Plasterboard can hold a great deal of water. In a recent test, a section of gypsum wallboard of weight 104.2 grams was found to increase in weight to 173 grams after a good soaking. The plasterboard was able to hold (conveniently for mathematicians) 66% of its dry weight as water. As well as becoming much heavier from the water, the white (decorating) paper face had started to delaminate from the gypsum core. So as well as becoming heavier, becoming wetter and delaminating, the board would not possibly recover when dry.

Plasterboard is, after all, a cheap but convenient substitute for more durable traditional ceiling finishes.

Figure 1: The damp damage.

It would be possible to cut back the hole to joist lines and tack on new plasterboarding to make good the hole. In this case it required two layers of board, fixed by long plasterboard nails. The new board is then plaster skimmed to marry up with adjacent finish.

Water damage in a ceiling often necessitates isolating electric circuits. In this case the lighting circuit was isolated for health and safety reasons until the dampness had been remediated.

The room suffering the ceiling damage is a bathroom. Let’s take a look upstairs in the utility room to discover the cause of the leak.

Because of the way trays such as that in the last picture in 'Bathrooms and showers good design practice', right hand detail, are fabricated, there is a flat ledge at the abutment of tray and tiling. Ledges allow water to collect and linger, and the water can track through imperfections in seals. Perhaps trays should be designed with a sloping perimeter kerb; the better trays available have an upstand. The tray (see figure 2) is also rather shallow. It would be difficult to lap the shower curtain properly into the tray, meaning that whilst showering, water could drip out down the tray and onto the floor along the two outer sides. You could imagine this curtain being pulled out from the tray as the user exits, dripping water onto the floor. Water dripping down the outside of the tray will find a way through any gaps or flaws in the tile grouting – which may be adhering directly to unprotected softwood bearers.

The tray has a standard edge profile, and when seals break down, water will trickle at will down behind the tray. Some tiles are missing, and in the corner we find an extremely common problem. See figure 3.

Figure 2: The tray is sited in the utility room corner. Only by careful tucking of the curtain within the tray will spray be contained. A careless user might allow spray to run down the curtain and onto the adjacent flooring.

Figure 3: Standard tile grouting is quite a rigid jointing material, and can fail when differential movement of two walls creates stresses. It is important that sufficient gaps are created between tiles – so sufficient grout can be firmly pressed in. Here, tiles are clearly butted up far too closely together. Consider applying a silicone seal at internal angles.

The tiles are fixed to solid walls, so the background is ideal. Standard plasterboard is unsuitable in a wet area – although moisture resistant boards might last longer. Note that the bottom cut course of tiles to the right side are white, i.e. there have been failures, requiring some tile replacement. The tray itself offers no opportunity to access the trap and waste connections underneath. We often have no early warning of developing damp problems, especially from very small but persistent drips that would wet up support timbers and create conditions of high air humidity under the tray – a home for mould and wood rot.

The tray will most probably be supported by a simple grid of softwood bearers spiked onto the floorboards (see figure 5).

If only we had X-ray specs – but we do have imagination, experience and sometimes even the viewing equipment to see into concealed spaces.

Installation shortcomings and defects of this shower tray installation No access to inspect under the shower tray. No access for maintenance of the shower tray. The shallow tray makes it difficult to tuck the shower curtain into the tray to limit leaks onto outside of tray and floor. Tiling below the tray liable to allow water penetration through to supporting timber bearers. Some tiling of the bottom coursing is missing. Half tiles along a bottom course may be more likely to detach and are indicative of poor setting out or alterations during the life of the tray – indicative of past problems. The tray has no upstand, relying on perfect tile/ tray sealing. Differential movement at the internal corner has opened up gaps in tile grouting. A deeper shower tray could have been directly floor mounted, eliminating the need for softwood bearers and vulnerable tile courses below the tray. Such a tray could be taken out and reinstalled as a maintenance operation. The tray installed cannot be easily removed for reinstallation, as tiling below it could be disturbed. It is difficult in any case to reliably fix ceramic tiles to timber substrates. Flexible sealants rather than rigid grouts should have been used at junction of top of plinth tiling and the tray, and at junction of plinth tiling and flooring. There is no provision for ventilation of the void under the tray. Regular maintenance, such as regrouting, resealing of tiles, etc., could have eliminated the water damage that has resulted. All silicone seals of baths and showers need to be maintained on a regular basis. Any shortcomings in a shower tray installation can result in serious damp damage.

How is the tray installed?

The tray in the first floor shower room has not been installed as in figure 62. We see the plinth is raised above floor level, with tiling below. But just imagine how difficult a waste trap would be to access in the shower installation method shown in figure 4. The trap is beautifully lost for good in the floor void.

Figure 4: Note there is not just reliance on the front silicone seal, but a second silicone seal between tray and wall. Sometimes self adhesive sealing tapes are used to achieve this. Typical installation sketches supplied with standard shower trays.

In such an installation waste pipework would need to be routed parallel to floor joists, otherwise notches would be required, of a depth likely to significantly weaken the floor joists.

But our shower tray was probably fitted on softwood joists as per figure 5, as we see a row of tiles forming its base plinth finish. Some trays are easily levelled by their own adjustable feet.

Figure 5: Timber support method for a tray on a solid floor. Typical installation sketches supplied with standard shower trays.

Trays on solid floors would more often be supported off timber bearers, as there is no floor void in which traps and pipework could be routed.

Any water seeping under the tray – from defective grouting of the tiled enclosure, defective perimeter tray seals, faulty plumbing or even water tracking under the tray from adjacent water splashed flooring – can sit on the solid floor and soak bearing timbers. An ideal environment for rots or moulds to flourish in!

Looking at figure 2, the tray is most probably raised on softwood bearers – a method more commonly used when a tray is supported off a solid floor. See figure 5. The support for the tray needs to be both level and as stable and rigid as possible. This tray does not benefit from an integral upstand, so failure of the edge seal will mean that shower water can penetrate through the edge of the tray down underneath to cause damp damage. Poor seals can also result in wetting and deterioration of the wall plasters.

So, what are the remedy options?

a) Reusing existing tray

If matching replacement tiles are available, replace the defective bottom course of tiles, reseal the tray perimeter and seal the vertical tile joint at the internal angle using silicone. In addition, check the waste fitting and trap, renewing if necessary. Make good the ceiling after testing and upgrading the ceiling light wiring and renewing the ceiling light fitting to current regulations. Check the adequacy of shower mixer and upgrade or renew.

b) Reusing existing tray

Consider erecting an additional side wall to form a three-sided enclosure.
Retile all three sides, and fit a front shower curtain and rail. Upgrade the shower waste and lighting electrics as necessary. Check the adequacy of shower mixer, and upgrade or renew.

c) New enclosure or tray

Consider installing a patent shower cubicle, tray and shower system. Carry out ceiling repair and upgrade of ceiling electrics below.

In addition to an upgrade of the shower cubicle, you may upgrade ventilation in the shower room, and make sure the shower room door provides good compartmentalisation, to keep moisture laden air in the shower room, where it should be swiftly extracted before it can migrate out into other parts of the dwelling.

Also check the surrounding flooring when the shower tray has been taken out, to assess its integrity. There may have been a seepage of water underneath the surrounding floor coverings, damaging base boarding such as hardboard, or breaking down adhesives. If this has happened, then it will usually be necessary to completely replace floor coverings.

Remember too that a shower tray is unique – in that water sprayed into it from the shower head can only drain away directly into the trap from the tray. There will not be an overflow. If the trap becomes blocked, the tray willl fill up to overflowing.