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Damp proofing in
construction
Construction is a general term meaning the art and science to form objects, systems, or organizations,"Construction" def. 1.a. 1.b. and 1.c. ''Oxford English Dictionary'' Second Edition on CD-ROM (v. 4.0) Oxford University Press 2009 and com ...
is a type of moisture control applied to building walls and floors to prevent
moisture
Moisture is the presence of a liquid, especially water, often in trace amounts. Small amounts of water may be found, for example, in the air (humidity), in foods, and in some commercial products. Moisture also refers to the amount of water vapo ...
from passing into the interior spaces. Dampness problems are among the most frequent problems encountered in residences.
![FlexibleRainPipe](https://upload.wikimedia.org/wikipedia/commons/8/8f/FlexibleRainPipe.JPG)
''Damp proofing'' is defined by the
American Society for Testing and Materials
ASTM International, formerly known as American Society for Testing and Materials, is an international standards organization that develops and publishes voluntary consensus technical standards for a wide range of materials, products, systems, an ...
(ASTM) as a material that resists the passage of water with no
hydrostatic pressure
Fluid statics or hydrostatics is the branch of fluid mechanics that studies the condition of the equilibrium of a floating body and submerged body "fluids at hydrostatic equilibrium and the pressure in a fluid, or exerted by a fluid, on an imme ...
.
''Waterproof'' is defined by the ASTM as a treatment that resists the passage of water under pressure.
[Greenlaw, Bruce. "Moisture-Proofing New Basements", ''Foundations and concrete work''. Newtown, Connecticut: Taunton Press, 2003. 93. Print.] Generally, damp proofing keeps moisture out of a building, where
vapor barrier
A vapor barrier (or vapour barrier) is any material used for damp proofing, typically a plastic or foil sheet, that resists diffusion of moisture through the wall, floor, ceiling, or roof assemblies of buildings and of packaging to prevent inter ...
s keep interior moisture from getting into walls. Moisture resistance is not necessarily absolute; it is usually defined by a specific
test method
A test method is a method for a test in science or engineering, such as a physical test, chemical test, or statistical test. It is a definitive procedure that produces a test result. In order to ensure accurate and relevant test results, a test met ...
, limits, and
engineering tolerance
Engineering tolerance is the permissible limit or limits of variation in:
# a physical dimension;
# a measured value or physical property of a material, manufactured object, system, or service;
# other measured values (such as temperature, hum ...
s.
Methods
Damp proofing is accomplished several ways including all :
* A damp-proof course (DPC) is a barrier through the structure designed to prevent moisture rising by
capillary action
Capillary action (sometimes called capillarity, capillary motion, capillary rise, capillary effect, or wicking) is the process of a liquid flowing in a narrow space without the assistance of, or even in opposition to, any external forces li ...
such as through a phenomenon known as
rising damp
Structural dampness is the presence of unwanted moisture in the structure of a building, either the result of intrusion from outside or condensation from within the structure.
A high proportion of damp problems in buildings are caused by ambient ...
. Rising damp is the effect of water rising from the ground into property. The damp proof course may be horizontal or vertical.
[Punmia, B. C., A. K. Jain, and Arun Kumar Jain. ''Building construction''. 10th ed. New Delhi: Laxmi Pub., 2008. 631. Print.] A DPC layer is usually laid below all masonry walls, regardless if the wall is a
load bearing wall or a
partition wall
A wall is a structure and a surface that defines an area; carries a load; provides security, shelter, or soundproofing; or, is decorative. There are many kinds of walls, including:
* Walls in buildings that form a fundamental part of the super ...
.
* A damp-proof membrane (DPM) is a
membrane
A membrane is a selective barrier; it allows some things to pass through but stops others. Such things may be molecules, ions, or other small particles. Membranes can be generally classified into synthetic membranes and biological membranes. B ...
material applied to prevent moisture transmission. A common example is
polyethylene
Polyethylene or polythene (abbreviated PE; IUPAC name polyethene or poly(methylene)) is the most commonly produced plastic. It is a polymer, primarily used for packaging ( plastic bags, plastic films, geomembranes and containers including bo ...
sheeting laid under a concrete slab to prevent the
concrete
Concrete is a composite material composed of fine and coarse aggregate bonded together with a fluid cement (cement paste) that hardens (cures) over time. Concrete is the second-most-used substance in the world after water, and is the most wi ...
from gaining moisture through capillary action. A DPM may be used for the DPC.
* Integral damp proofing in concrete involves adding materials to the concrete mix to make the concrete itself impermeable.
* Surface suppressant coating with thin water proof materials such as epoxy resin for resistance to non-pressurized moisture such as rain water or a coating of cement sprayed on such as
shotcrete
Shotcrete, gunite (), or sprayed concrete is concrete or mortar conveyed through a hose and pneumatically projected at high velocity onto a surface, as a construction technique, first used in 1907 invented by Carl Akeley. It is typically r ...
which can resist water under pressure.
* Cavity wall construction, such as
rainscreen
A rainscreen is an exterior wall detail where the siding (wall cladding) stands off from the moisture- resistant surface of an air/water barrier applied to the sheathing to create a capillary break and to allow drainage and evaporation. The ''ra ...
construction, is where the interior walls are separated from the exterior walls by a cavity.
*
Pressure grouting
Pressure grouting or jet grouting involves injecting a grout material into otherwise inaccessible but interconnected pore or void space of which neither the configuration or volume are known, and is often referred to simply as ''grouting''. The g ...
cracks and joints in masonry materials.
Materials
Materials widely used for damp proofing include:
* Flexible materials like
butyl rubber
Butyl rubber, sometimes just called "butyl", is a synthetic rubber, a copolymer of isobutylene with isoprene. The abbreviation IIR stands for isobutylene isoprene rubber. Polyisobutylene, also known as "PIB" or polyisobutene, (C4H8)n, is the ho ...
, hot bitumen (
asphalt
Asphalt, also known as bitumen (, ), is a sticky, black, highly viscous liquid or semi-solid form of petroleum. It may be found in natural deposits or may be a refined product, and is classed as a pitch. Before the 20th century, the term a ...
), plastic sheets,
bituminous felts, sheets of
lead
Lead is a chemical element with the symbol Pb (from the Latin ) and atomic number 82. It is a heavy metal that is denser than most common materials. Lead is soft and malleable, and also has a relatively low melting point. When freshly cu ...
,
copper
Copper is a chemical element with the symbol Cu (from la, cuprum) and atomic number 29. It is a soft, malleable, and ductile metal with very high thermal and electrical conductivity. A freshly exposed surface of pure copper has a pinkis ...
, etc.
* Semi-rigid materials like
mastic asphalt
Asphalt concrete (commonly called asphalt, blacktop, or pavement in North America, and tarmac, bitumen macadam, or rolled asphalt in the United Kingdom and the Republic of Ireland) is a composite material commonly used to surface roads, parkin ...
* Rigid materials, like impervious
brick
A brick is a type of block used to build walls, pavements and other elements in masonry construction. Properly, the term ''brick'' denotes a block composed of dried clay, but is now also used informally to denote other chemically cured cons ...
,
stone
In geology, rock (or stone) is any naturally occurring solid mass or aggregate of minerals or mineraloid matter. It is categorized by the minerals included, its Chemical compound, chemical composition, and the way in which it is formed. Rocks ...
,
slate
Slate is a fine-grained, foliated, homogeneous metamorphic rock derived from an original shale-type sedimentary rock composed of clay or volcanic ash through low-grade regional metamorphism. It is the finest grained foliated metamorphic rock. ...
,
cement mortar, or cement concrete painted with bitumen, etc.
* Stones
*
Mortar with waterproofing compounds
* Coarse
sand
Sand is a granular material composed of finely divided mineral particles. Sand has various compositions but is defined by its grain size. Sand grains are smaller than gravel and coarser than silt. Sand can also refer to a textural class of s ...
layers under floors
* Continuous plastic sheets under floors
Masonry construction
A DPC is a durable, impermeable material such as slate,
felt paper
Bituminous waterproofing systems are designed to protect residential and commercial buildings. Bitumen (asphalt or coal-tar pitch) is a mixed substance made up of organic liquids that are highly sticky, viscous, and waterproof. These systems ar ...
, metal, plastic or special engineered bricks bedded into the mortar between two courses of bricks or blocks. It can often be seen as a thin line in the mortar near ground level. To create a continuous barrier, pieces of DPC or DPM may be sealed together. In addition, the DPC may be sealed to the DPM around the outside edges of the ground floor, completely sealing the inside of the building from the damp ground around it.
In a masonry
cavity wall
A cavity wall is a type of wall that has a hollow center. They can be described as consisting of two "skins" separated by a hollow space (cavity). The skins typically are masonry, such as brick or cinder block. Masonry is an absorbent material ...
, there is usually a DPC in both the outer and inner wall. In the outer wall it is normally to above ground level (the height of 2-3 brick courses). This allows rain to form puddles and splash up off the ground, without saturating the wall above DPC level. The wall below the DPC may become saturated in rainy weather. The DPC in the inner wall is usually below floor level, (under a suspended timber floor structure), or, with a solid concrete floor, it is usually found immediately above the floor slab so that it can be linked to the DPM under the floor slab. This enables installation of skirting boards above floor level without fear of puncturing it. Alternatively, instead of fitting separate inner and outer DPCs, it is common in commercial housebuilding to use a one-piece length of rigid plastic (with an angled section) that fits neatly across the cavity and slots into both walls (a cavity tray). This method requires weep vents to enable water to drain from the cavity, otherwise dampness could rise from above the DPC.
Concrete walls and floors
Concrete
Concrete is a composite material composed of fine and coarse aggregate bonded together with a fluid cement (cement paste) that hardens (cures) over time. Concrete is the second-most-used substance in the world after water, and is the most wi ...
normally allows moisture to pass through so a vertical
vapor barrier
A vapor barrier (or vapour barrier) is any material used for damp proofing, typically a plastic or foil sheet, that resists diffusion of moisture through the wall, floor, ceiling, or roof assemblies of buildings and of packaging to prevent inter ...
is needed. Barriers may be a coating or membrane applied to the exterior of the concrete. The coating may be
asphalt
Asphalt, also known as bitumen (, ), is a sticky, black, highly viscous liquid or semi-solid form of petroleum. It may be found in natural deposits or may be a refined product, and is classed as a pitch. Before the 20th century, the term a ...
, asphalt emulsion, a thinned asphalt called cutback asphalt, or an
elastomer
An elastomer is a polymer with viscoelasticity (i.e. both viscosity and elasticity) and with weak intermolecular forces, generally low Young's modulus and high failure strain compared with other materials. The term, a portmanteau of ''elastic p ...
. Membranes are
rubberized asphalt
Rubberized asphalt concrete (RAC), also known as asphalt rubber or just rubberized asphalt, is noise reducing pavement material that consists of regular asphalt concrete mixed with crumb rubber made from recycled tires. Asphalt rubber is the la ...
or
EPDM rubber. Rubberized products perform better because concrete sometimes develops cracks and the barrier does not crack with the concrete.
Remedial damp proofing
Until the 20th century, masonry buildings in Europe and North America were generally constructed from highly permeable materials such as stone and
lime
Lime commonly refers to:
* Lime (fruit), a green citrus fruit
* Lime (material), inorganic materials containing calcium, usually calcium oxide or calcium hydroxide
* Lime (color), a color between yellow and green
Lime may also refer to:
Botany ...
-based mortars and renders covered with soft water-based paints which all allowed any damp to diffuse into the air without damage. The later application of impermeable materials which prevent the natural dispersion of damp, such as
tile
Tiles are usually thin, square or rectangular coverings manufactured from hard-wearing material such as ceramic, stone, metal, baked clay, or even glass. They are generally fixed in place in an array to cover roofs, floors, walls, edges, or o ...
,
linoleum
Linoleum, sometimes shortened to lino, is a floor covering made from materials such as solidified linseed oil (linoxyn), Pine Resin, pine resin, ground Cork (material), cork dust, sawdust, and mineral fillers such as calcium carbonate, most com ...
, cement and
gypsum
Gypsum is a soft sulfate mineral composed of calcium sulfate dihydrate, with the chemical formula . It is widely mined and is used as a fertilizer and as the main constituent in many forms of plaster, blackboard or sidewalk chalk, and drywall. ...
-based materials and synthetic paints is thought by some to be the most significant cause of damp problems in older buildings.
There are many solutions for dealing with dampness in existing buildings, the choice of which will largely be determined by the types of dampness that are affecting the building, ''e.g.'', rising damp, hygroscopic damp, condensation,
penetrating damp, etc.
In older buildings, damp stains on internal walls are usually due to external factors such as:
1. Leaking rainwater gutters
2. Misdirected rainwater downpipes
3. Insufficient external drainage
4. Poor drip details to cills and other protrusions
5. Bridging of the damp proof course
Health and safety
Some DPC materials may contain
asbestos
Asbestos () is a naturally occurring fibrous silicate mineral. There are six types, all of which are composed of long and thin fibrous crystals, each fibre being composed of many microscopic "fibrils" that can be released into the atmosphere b ...
fibres. This was more commonly found in the older, grey sealants as well as flexible tar boards.
References
External links
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Building engineering
Moisture protection
Masonry
Horticulture
Landscape architecture