Damp in Traditional Buildings

7/25/2019 Damp in Traditional Buildings

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DAMP IN TRADITIONAL BUILDINGS

Prepared for discussion with students

Dr.Phani Sree Vagvala


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Diagnosis

Causes of damp

There are four main causes of damp in historic buildings:

Penetration of water.

. Condensation.

Hygroscopic salts (usually resulting from rising

damp).


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Diagnosis

Locating the source

The source may be remote from the symptom. A case of damp may have more than one cause.

A long term assessment may be necessary as.

Leaks from concealed plumbing can be mistaken forwater penetration.

The source of damp must be located before considering

specific treatment. Building defects are the most common source and

professional advice is recommended.


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Diagnosis and investigation

Visual inspection of the fabric A systematic

inspection of the roof, roof space, walls andrainwater system should be carried out.

Ground levels around the buildin should be

checked.

Visually assess the extent and properties of the

damp and its effect on materials.

Dampness due to rainwater penetration differs from

rising damp


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Treatment of damp

Keep up regular maintenance of external fabric.

Defects must be remedied using compatible

materials.

.

Maintain or increase levels of ventilation to aid

evaporation.

Reduce water vapor and increase surfacetemperatures.


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Rainwater Penetration

1. Debris, leaves and moss in parapet and centre

gutters.

2. Damaged lead or asphalt gutters.

3. Mortar joints in ridge tiles.

4. Displaced or damaged slates.

5. Lea as ings at a utments, c imney stac s an

parapets.

6. Mortar joints on top surfaces of coping stones and

parapets.

7. Open joints in brickwork.

8. Structural movement e.g. opening of mortar joints.9. Damaged rainwater gutters and downpipes.

10. Hairline cracks in render.

11. Missing render.

12. Vegetable growth and debris ingulleys.13. High ground level.


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Rainwater Penetration - walls

External Conditions

Some walls can be more susceptible to waterpenetration. The degree of penetration will depend

artl on the followin :

Thickness of wall.

Degree of exposure.

Porosity of material. Type of construction.


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Rainwater PenetrationRoof and wall defects are the most common source of

rainwater penetration. Lack of routine maintenance is a major cause of

building faults resulting in rain penetration.

enera a ure o ma er a s o e ex erna a r c walso cause water penetration, for instance:

Structural movement eg opening of mortar joints.

.Decay or failure of materials.

Incorrect earlier repairs such as impervious externalcoatings and cement rich mortar pointing.


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Rainwater Penetration - Roof level

Roof leaks not attended when the fault is hidden, remote or

inaccessible causing dampness and sometimes structuraldecay.

Tile and similar roof finishes

Re-fix displaced tiles and renew those broken in a

matching tile.

Renew mortar joints in ridge tiles where damaged, and

rebed any found to be loose. Ensure correct weathering

details


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Rainwater Penetration - Roof level Abutments and parapets

Renew fractured or missing lead flashings and soakersat abutments, and parapets

Renew cracked or missing mortar fillet at chimneys ac s. ep ac ng e e w ea as ng spreferred where possible.

Re-point mortar joints on top surfaces of coping stonesat parapets.

A lead DPC below the coping may be required if waterpenetration is serious.


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Rainwater Penetration - Roof level

Parapet gutters

Remove debris, leaves and moss and clearoverflows.

gutters. Do not line lead gutters with asphalt or

bitumen.


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Rainwater Penetration - wallsDefects in rainwater systems and external wall finishes can cause

damp in solid walls.

Defective rainwater goods

Leaks from damaged rainwater gutters and downpipes are normally apparenton the surface of the adjacent wall. (Evidence may be obscured where for instance square downpipesare flush with the wall surface or where exposed gutters are recessed into elaborate fascias.)

Replace cracked or damaged cast iron gutter and downpipe sections. Usethe identical section and material as the original.

Dismantle gutters and downpipes where joints have failed and reassemblewith a yam and red lead joint.

Repair cast iron hopper heads and all lead rainwater goods if defective,

do not replace them. Splits in lead downpipes should be patched notsoldered.

Remove all vegetable growth and debris from the discharge point ofdownpipes at gulley's.

Realign gutters if necessary to falls.


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Rainwater Penetration - walls Defective external wall Rainwater will penetrate walls

more readily where mortar joints have been washed out orwhere original render has cracked or blown.

Re-point open joints in brickwork in a mortar to match theoriginal pointing where the mortar is absent or extremely

.

Specialist advice should be sought where joints haveopened due to movement in the wall.

Hairline cracks in render should be widened sufficiently torepair. Render for the repair should be of a similar mix to

the original. DO NOT use waterproof membranes such as bitumen,

silicone water repellants or oil paint to remedy.


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Rainwater Penetration - Roofs and walls


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Condensation Condensation

Condensation results from a complex relationship between the moisturecontent and temperature of the air and that of the structure. It cannotbe satisfactorily controlled whilst other problems of damp remainuntreated

S m toms

Cool porous surfaces: Condensation will be absorbed. Moulds, normally black in color will occur on the surface of paint or

wallpaper (fig 10). Rising damp however may cause similar growth.

Moisture readings will be uniformly high, unlike those for rising

damp which decrease with height. Cool impervious surfaces: Condensation appears as tiny droplets of water

on cool non-porous surfaces. In extreme cases it forms vertical streamlets.

It can occur for instance on oil paint, metal surfaces and wall tiles.


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Condensation-RemediesThe following measures will help reduce condensation:

Reducing water vapor:

Maintain high levels of ventilation to the building, especially inkitchens, bathrooms, stores, cellars and roof voids.

Treat damp in external walls and solid floors caused by rising

Reduce human activities which raise the moisture content of air (eg:clothes drying, cooking etc).

Increasing surface temperatures: Surfaces warmer than dew-pointwill not attract condensation.

Provide continuous low level radiant heating to maintain warmsurfaces. Intermittent heating in old buildings can actually aggravatecondensation.

Insulate roof voids and install a continuous vapor barrier.


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Condensation


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Ventilation Ventilation is the key to a healthy historic building. It

reduces dampness, combats condensation and preventstimber decay.

The need for ventilation :A well maintained historicbuilding will gradually suffer the problems associated

wit amp w en starve o a venti ation. Natural ventilation is vital:

In vacant buildings. Continuous low-level heating mayalso be required.

To all areas and rooms, especially those with highhumidity.


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Ventilation

In cellars and roof spaces. Extra ventilation is necessary

where felt has been installed. Behind timber paneling or dry lining to walls where

there may be a risk of damp.

c mney ues w en ey ave een oc e up.

In stores adjacent to external walls.

Below raised ground floors.

Behind furniture where it is close to the wall in areas ofhigh humidity.

Provide an air gap.


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Ventilation


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Rising damp

Ground water rises by capillary action and affects mainly masonrywalls and solid floors. Its extent depends on the amount of water in

the ground, the wall's capacity to absorb it, and evaporation levels.Its symptoms differ from those of penetrating rain.

Dampness is always present, even during dry weather but notalways easily detectable. Damp will retreat in prolonged drywea er.

Symptoms

A characteristic 'tide mark' of crystalline salts is often apparent atthe top of the damp.

Salts expand forcing plaster to exfoliate and spall.

When measured dampness reduces with height.


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Rising damp

Causes for worsening of rising damp

The effects of rising damp may have worsened as conditionsin and around the building have changed.

External ground levels may have risen, pushing dampnessfurther up the wall.

An impervious floor, floor finish or damp proof membranemay have been installed. This increases rising damp in wallslacking a dpc.

Ventilation may have been restricted to avoid heat loss.

Non-porous surfaces may have been applied or pointingcarried out in cement rich mortar, driving moisture up thewall.


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Rising damp -Remedy

Reduce the moisture content of the structure and excessive groundwater, and increase internal evaporation:

Examine underground drains for leaks and repair. Remedy all faults causing penetration of rainwater.

Take measures to reduce condensation.

ncrease eve s o na ura ven a on roug ou e u ng

Use vapor permeable emulsion rather than impervious paints orother impervious finishes.

Timber such as skirting and door linings in contact with the remainingdamp wall must be isolated to prevent fungal attack.

Treat any salts which appear on the surface after drying out.


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Rising damp Remedy for Solid floors

Rising damp may affect some valuable historic floors. The type oftreatment should be tailored to avoid disruption of the floor finish.

Porous floor finishes such as stone, brick and some clay tiles whichhave been laid directly onto ground may suffer from rising damp.

Remedy rising dampness mild

Do not apply waterproof sealers. A beeswax and turpentine polishmay be suitable.

Open the joints in a brick or stone floor by removing hard pointing.Create a dry area (see next page)or batter the external ground toa channel to direct water away from the building.


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Rising damp Remedy for Solid floors

Remedy Dising Dampness Severe

Relaying the floor on hardcoreWater levels will be lowered by relaying the floor on

sand blinding overhand packed hardcore. The

treatment may however cause movement in thestructure.

Relaying the floor on a damp proof membrane

This concentrates more ground water in the walls. It istherefore only effective if used in conjunction with adpc

Documents

Damp in Traditional Buildings