The Merry Month – Robert Merry
Robert Merry is an independent stone consultant and project manager who ran his own company for 17 years. He also acts as an expert witness.
Installing large format stones as internal flooring or wet room walling is a health & safety risk that designers and masons are ignoring.
I don’t think fitting large panels can be achieved without considerable risk to the operatives, even though most fixers like the idea of achieving the seemingly impossible and want to please. Rarely do they refuse to do it.
Designers like large format because it looks luxurious. They don’t understand the implications for the stone (usually at 20mm), the fixing, or the safety of the operatives. It is the stone industry’s problem and we don’t complain.
CDM covers health & safety but, of course, it is often ignored. It is the responsibility of the client / designer to ensure that risks are eliminated from the build process where possible. But as injuries caused by fitting large format slabs are rarely reported and long term physical effects are not monitored, fitting large format stones in bathrooms is rarely challenged.
I have often discussed with MDs of stone companies how there is little or no support machinery that can fit into a bathroom or a shower enclosure to assist in fitting large stone panels.
Though builders insist on method statements and risk assessments, these are never entirely accurate or honest and normally skirt round this risk. Most of the time the only way to fit a large, full height wall panel is with brute force, all-be-it skilled brute force.
It is difficult to think of any other trade or practice on a building site nowadays that relies so heavily on raw human strength.
If it’s difficult to fit because of its size and weight, it’s also difficult to butter the back, butter the wall or floor, and achieve sufficient coverage.
Mesh backed stones for floors require 75% of the mesh to be removed to allow a bond between the back of the stone and the adhesive – see BS EN 8000 Pt 11.
The Stone Federation Code of Practice for the design and installation of internal flooring and BS 5385-5, Part 5: Design and installation of natural and agglomerated stone and terrazzo tile and slab flooring in normal conditions, both describe the requirement to solid-bed stone when using cementitious adhesive. This is to avoid voids in the floor which are a potential weakness under load.
Internal walls in showers and wet rooms also require the stones to be fully bedded, not for loading issues but against moisture ingress. Unfilled voids are moisture traps that can turn to mould. 25% of the mesh needs to be removed and mechanical restraint fixings used.
I talked to some time-served masons about the issues with mould, voids and lifting heavy stones. These are some suggestions they had, although they are not all practical or guaranteed to comply with the current requirements:
- “Butter the back of the slab, the wall and use dabs, but make sure it’s a ‘sloppy’ mix, to increase the chance of full coverage.”
- “Trowel horizontally to form a barrier to moisture running down the back.”
- “Internal rain screen system – no adhesive but with weep holes or cavity tray system returning the water to the gully.”
- “Back filling – but impossible with full height slabs.”
- “Fix with silicone / mastic and mechanical restraints.”
There was a consensus that the choice of adhesive and understanding of the method was important and that there was a “lack of trained fixers” who understood how to install large panels.
I think it is impossible to achieve the adhesive coverage required to bed stones fully, either on the wall or the floor, using large formats slabs.
Floor stone sizes are limited, according to the Standards, but they give room for calculated increases. Yet we still witness large floor slabs bowing. Too large a format for too thin a stone and the material is simply not stable enough. It’s a similar principle to plywood: the thinner the sheet the less stable it is and the greater likelihood it will bow.
Where do you draw the line on the size of the stones for bathroom walls and showers? The Designers and building owners have obligations under CDM to avoid or design out dangerous practices. Stone companies have a duty of care to their employees or sub-contractors to ensure they have a safe environment to work in and they go home in no worse a physical shape than they started the day.
As an industry we need to look more closely at what we agree to do in the name of design instead of simply considering what is within the limits of the stone. Or someone will get seriously hurt.