Building materials have changed hugely over the years. Modern walls are generally made of a mixture of softwood, bricks, blocks, damp-proof membranes and cement. They are designed to be as water-tight as possible.

Older walls tend to be made with lime mortars. Because until recently it wasn’t possible to exclude water totally, buildings were expected to ‘breathe’. Water might permeate into a wall, but lime mortar allowed the damp to escape.  

Both construction techniques work well, but it is a mistake to mix the two. Repairing a porous old stone wall cement can allow rain in, only to keep it there. We kept this very much in mind while restoring the building to something like its inter-war appearance.

Green oak framing

In the days before mechanical saws, our ancestors used fresh oak to construct sturdy wooden frames held together by pegs. The last are not rounded on a lathe, but whittled to produce a foot-long poly-sided wooden nail. Holes of a fractionally smaller diameter than the peg are drilled into each mortice and tenon joint from either side at slight angles to meet in the middle. This creates a hole which is effectively slightly curved. The peg is then greased with candle wax and hammered home. Once in, the peg’s ridges are squeezed tightly against the hole’s walls while the tension from being forced into a curve means the peg is held so tightly it can never be removed.

This type of construction is most apparent in the main living room of the old house, but you can also see it upstairs, in the roof of the dairy/parlour extension and in the front of the two store rooms to the west of the house. We have cut off peg ends below eye-level (to avoid accidents), but have deliberately left those higher up to show the method.

Lime mortar

This has been used since the 4th century BC and is created by roasting limestone (calcium carbonate – CaCO3) in a kiln. The heat drives off the carbon dioxide in the carbonate to create calcium oxide (quick lime, caustic soda or CaO). This is extremely alkaline and reactive, so it is ‘slaked’ with water to create the much milder calcium hydroxide (Ca(OH)2). The final product has the consistency of a stiff putty or clay.

This will keep for many months in a large bag, but when spread in a relatively thin layer (e.g. as a mortar between bricks or as a render on a wall’s surface), the lime absorbs carbon dioxide from the atmosphere to create a relatively soft, slightly crumbly, mortar. This allows a limited movement of water in – and critically out – of the wall. Importantly, in an era of concern about global warming, unlike modern cements, this is a relatively carbon neutral material. The raw material is limestone (calcium carbonate) which is heated in a kiln to break down into quick lime (calcium oxide) and carbon dioxide. When this is mixed with water this becomes calcium hydroxide, but as the mortar hardens it absorbs the same amount of atmospheric carbon dioxide which was driven off in its manufacture.

The main farmhouse and rear wall of the forge were constructed with lime mortar some 200 years ago. A thin ‘wash’ or render of the same was applied to the walls and this kept out the elements for some 150 years until a ‘modern’ pebble dash was applied in the 1960s. This kept out the driving rain, but unfortunately it also sealed in water seeping in from the roof and rising damp. As this rose to the surface, expanded with hard frosts, and generally snaked its way beneath the cement, it loosened the render and by the time we bought the house in 2013 most was barely attached to the walls.

We therefore removed all of the 1960s protective covering, leaving the dilemma of what next? Clearly some sort of coating had always been there for a reason, but what next? In the end we have come up with a variety of solutions. We have left the south and east walls exposed because these are relatively protected from the prevailing elements and the stonework is attractive. The northern wall has a lime render – a cross between paint and mortar - using the traditional binding agent of horsehair which was harvested from our own ponies, Spice and Penny. As modern constructions, the kitchen and east extensions have a Portland cement-based render, but we have deliberately roughened this to blend in with the older building.

Timber frame / breeze block

Modern building methods need less explanation. Foundations are dug and low walls built to create a shallow tank. Then a damp-proof membrane is laid and a modern concrete (Portland cement-based) is poured over a rigid welded wire mesh to make a reinforced concrete pad. Breeze block walls are built up and the inside lined with a light timber frame. This is infilled with the highest modern insulation material available and covered with board and finished with a ‘skim’ of conventional plaster.

 The advantage of this type of construction is that it is cheaper and much more thermally-efficient than ancient building techniques. On the other hand there can be a clash of styles with the older parts of a restoration project.

In the case of the two extensions and the kitchen, while not hiding the use of modern materials, we have tried to smooth out the contrasts between old and new. We have done this with the limited use of green oak and stone, while using deliberately roughened finishes on modern renders.

Slate

Houses along the coast are battered by frequent storms driving in from the west up St George’s Channel. Originally a lime render was the preferred protection (this was usually painted either with a white lime wash or lime mixed with ox blood to produce a characteristic pink effect).

As the Industrial Revolution developed and trains made it easier to transport heavy materials, so many Welsh houses started to hang exposed walls with slate. This began to fall out of fashion during the 1960s and 1970s however in favour of pebble-dash renders made with modern cements. These were applied to Glebe House in the late 1960s, but unfortunately the use of an impenetrable barrier on a potentially damp wall was very destructive in the long-run. As the roof deteriorated in the 1980s and ‘90s water seeped down into the walls causing major damage to the internal floors and joists and slowly detaching the render from the external walls. The last was so damaged that it had to be removed in 2013.  

The fact that previous owners had felt it necessary to apply an additional protective layer indicated something was probably sensible. We decided to revert to slate on the most exposed western walls. Unfortunately Welsh slate is now prohibitively expensive and we reluctantly decided to use modern synthetic slates to clad the west end of the house.