Conservation or refurbishment?
03/01/2014 - By Paul Watts
As a nation we are fascinated by other people's attempts to improve their homes or developing them. We have an almost obsessive need to buy and then put our own mark on our home. How do we best achieve this without harming the property?
As a nation we are fascinated by other people's attempts to improve their homes or become millionaires through developing or modernising. We have an almost obsessive need to buy and then put our own mark on our own little castles. How else can we explain the proliferation of property programmes on the TV?
Many programmes are pure entertainment and should not be taken too seriously, others are designed to be more informative but can be misleading when dealing with period properties that form an important part of our heritage.
Far too often we get a presenter failing to comment on inappropriate use of cements and gypsums and even say that lime isn't needed because the building 'isn't listed'. This of course is patent nonsense and they should know better.
How many times have we seen budding developers ripping out perfectly good lath walls and ceilings to be replaced with plasterboard as this is cheaper? This is usually the only route the builder knows due to having little knowledge of the requirements of a traditional building and a lack of specialist skills. Plasterboard may be inappropriate in many cases and may even be a criminal offence if the building is listed. Unfortunately, with few notable exceptions, this TV vandalism is rarely commented upon as the history of a building is destroyed.
With the aid of some basic information it is possible to avoid some of the pitfalls that lead to unnecessary destruction of our valuable heritage. It isn't always necessary to embark on major removal of the fabric of a building to obtain an accurate diagnosis of problems the building may have. It is however, vital to gain as much detailed information about any building as is practicable before undertaking even minor work. On higher quality properties modern equipment may offer a cost effective way to determine the condition of a building.
Impulse Radar can locate voids and cracks in mass walls but requires an experienced technician to correctly interpret the readings. This can be a relatively expensive procedure.
Endoscopy can offer a way of accessing those hard to reach areas for minimal disruption requiring access points of just 2-12mm.
Ultrasonics can be particularly helpful in assessing timber decay and fractures but is also useful to diagnose the depth of surface cracks.
Micro-drilling is specifically used for assessment of timber by drilling a 1mm hole into timber
Moisture measurement is very helpful in finding potential problems and helping to deal with some existing ones. A simple electrical resistance meter is potentially misleading and can sometimes be used by unscrupulous or ignorant damp control specialists. This equipment only records resistance, and this can be effected not only by moisture but by salts, condensation or foil backed wall paper.
For more accurate results a carbide meter or a weighed sample that is then dried and re-weighed is required. It can also useful to record the relative humidity with a hygrometer.
Be sure to consult with your conservation officer before any work is considered if the building is listed or in a conservation area.
Sagging lath ceilings
The normal thickness of a lath and plaster ceiling is likely to be perhaps 30-35mm with the combined lath and lime or earth plaster. This is a lot of weight, perhaps 30-40kg per m2. If a crack or bulge appears in the ceiling it is prudent to investigate and address any issues promptly.
From beneath, one option is to gently push the plaster upwards to check for movement. Also it will be helpful to try and visually inspect above the lath by raising floorboards or accessing the loft void.
Try to establish if
1. the plaster has broken away from the lath
2. the laths fixings have failed
3. the joists are too flexible or rotten
It may be that a crack is historic and requires nothing more than filling with lime filler and redecoration with a breathable paint such as limewash.
If supporting walls have been removed resulting in too much flex, this needs to be addressed. Supporting walls may be replaced or an appropriate beam/RSJ fitted. The least visually disruptive way of strengthening is to put extra joists in alongside the existing. This can also be the best way to strengthen rotten flooring joists once the timbers have been treated.
This type of work may need reference to a structural engineer and of course the local authority building control department before deciding on the best course of action.
If the plaster has delaminated from the lath but the lath is still soundly fixed, there is a method that could save the plaster. Place a board with cushioning material flat against the underneath of the ceiling and prop until the plaster is held in it's current position. If accessible from above, 90 degree brackets are fixed against the vertical part of the joist with expanded metal lath (eml) laid on top of the protruding bracket. The area is then flooded with a wet mix of fine casting plaster. This quickly hardens and secures the plaster to the eml and brackets making a sound fix once again.
It is also possible to screw fixings with penny washers from below and patch repair to hide; this may be the only way to fix if access from above is not possible.
Delaminated plaster on walls is less of a problem than on a ceiling. Small patches of failed wall plaster can be left for many years without any problems as it can be held in place by surrounding plaster. So if a small patch does fail it is not so great a safety issue.
Some of the techniques suggested for ceiling repairs can be employed on the walls where action is required.
Significant damage or decay can require radical repairs to make the building sound. If major work is deemed necessary then reflect before going ahead with work. Why were certain materials previously used? It is for a very good reason that heritage specialists use the term 'like for like'. If a building was originally made using a particular material, it is normally a very good idea to use the same material again when undertaking repair or maintenance work.
When cement became widely used, it was thought to be an excellent alternative to lime. Cement hardens much quicker than lime, it is very much harder than lime and offers a greater certainty of timings for work. All of these qualities are good for the builder but can be disastrous for the building. The thermal expansion rates of cement are considerably different to that of lime, stone, cob or timber. Cement expands and contracts to a greater extent and will therefore always risk the possibility of cracking when in contact with traditional building materials. Cement based repairs may result in higher moisture levels in adjoining timbers and walls. Even use of modern paints can have serious adverse effects on a traditional building.
If a decision is made to use different materials to original, be sure that the full implications are understood, only then can an informed decision be made.
Anybody who owns or works on a traditionally constructed building needs to have a basic understanding of the way these buildings have stood for so many years and what is needed to keep them healthy and sound.
There are many courses available from specialist organisations or local authorities. The Society for the Protection of Ancient Buildings (SPAB) offer a number of short courses for builders and home owners throughout the country.
Paul Watts works for Mike Wye & Associates Ltd which are one of the country's leading building lime specialists and have conducted one day practical training courses for over 17 years. Over 3,000 people have been introduced to the wonderful qualities of lime and traditional repair techniques.
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