Historic Churches 2015

BCD SPECIAL REPORT ON

HISTORIC CHURCHES

ND ANNUAL EDITION

INTERIOR DECORATION

and PERMEABILITY

Mark Parsons

OST CHURCHES and chapels

constructed before the first

world war have solid masonry

walls. When first constructed, these

walls were breathable, inside and out,

because they were built using permeable

lime mortars and their interiors were

usually lime plastered and finished with

limewash. These simple lime-based

materials helped the walls to dry quickly.

Following the development of fast-

setting cements in the 19th century and

of cheaper more durable synthetic paint

systems in the 20th, routine repairs led

to the interior surfaces of many churches

being effectively sealed. As the long term

consequences of this were not widely

understood until late in the 20th century,

few churches have escaped.

Typical results include areas of

blistering and peeling paint, black

mildewed north easterly and westerly

corners, drip stains beneath wall-heads

and valley gutters, and mildewed and

stained stone window surrounds. Add to

this the glossy sheen of the walls and the

rusted-up window vents, and the church

surveyor is faced with a virtual Rubik’s

cube of related issues.

Today, when a churchwarden or

PCC asks for advice on redecorating

the church interior walls, the answer

to this apparently simple question

suddenly becomes extraordinarily

complex. You cannot ‘simply’ restore a

vapour permeable painted surface either

‘technically’ or in the case of more ancient

structures ‘conservatively’. The advice

given has to be based on an understanding

of the church’s interior environment,

whether damp, dry, airy or humid. The

external condition of the church would

require assessment before good advice

could be given or the specification process

begun. If this is a ‘one-off’ commission

or you are a newly appointed church

architect, an initial inspection of the

fabric is best followed by a study of past

quinquennial inspection reports or

possibly the church’s log book. These

documents should provide information

on any ‘progressive’ repairs that have

occurred and will help to identify longer

term problems.

The level of ‘dampness’ in a church

building is largely a result of the actions

(and inaction) of its managers and

occupants over time. This level is best

expressed in terms of relative humidity

(at 100% relative humidity or ‘RH’, air of a

given temperature cannot hold any more

moisture): churches typically average

80 to 100 per cent RH in the UK, with

average internal RH readings of around

90 per cent being considered high. Drying

rates are mainly affected by the amount

of sunlight entering into the building,

the movement of warmed air and the

permeability of its fabric.

If the floor is impermeable to water

vapour due to ground conditions or

modern interventions (such as a plastic

DPM and/or concrete slab, or impervious

coverings such as rubber backed carpets)

the result will, no doubt, be rising damp

at the base of the walls and columns and

the crystallisation of salts (efflorescence).

Poorly detailed and badly maintained roof

abutment and drainage, together with

general orientation and exposure, are

often the primary sources of the rainwater

penetration which causes internal peeling

paints, salting, and ‘black spot’ mildew

and plaster surface degradation.

Poor ventilation can lead to

condensation on painted wall surfaces,

usually at high level in northerly corners

and typically indicated by black spot

mildew growth. White mildew is a

powdery fungus which is more apparent

on damp timber surfaces and appears

on furnishings and ceiling boards. You

may also see evidence of high humidity

on window panes with wet surfaces

and extensive green algal growth. Stone

window surrounds will also be prone to

black spot mildew. Ventilation of church

interior spaces and suspended timber

floor structures must be understood

and action taken to maintain through-

ventilation.

Salting and surface paint loss can

also be caused by an interaction between

modern plasterwork and either open

external mortar joints or those closed

with hard cement mortars. Normally at

high or low levels and around windows

and door openings some re-plastering will

have taken place using modern moisture

absorbing plasters, which are generally

termed ‘Carlite’ or ‘pink’ or ‘browning’.

These have been used as a quick low-cost

solution to failing plasterwork at higher

level (particularly over the chancel arch)

or degrading and loosening plasters

at low level. They are quick and easy

to apply. Where wall plaster must be

Lime-washed permeable walls of St Nicholas Church, Compton, Surrey with a simple medieval decorative scheme