damp proofing
A definition of dampproofing is inherently plagued by comparisons to waterproofing in which many areas it falls short except for it’s typical economical advantage. The primary purpose of dampproofing is to keep out soil moisture from passing through a structure to the opposite side. Dampproofing is unlike waterproofing in that it isn’t meant to keep out liquid water (hydrostatic pressure). Almost all current building codes now require that any concrete or masonry foundation wall that retains earth and encloses an inside space below grade should be dampproofed. Dampproofing is placed continuously from the top of the footing to the finish grade elevation. A situation where waterproofing would be required in lieu of dampproofing (according to most building codes) are: high-moisture soil types (perching water; silts and clays), areas where soil is known to consistently contain high moisture, or areas with high water tables or known seasonal water table fluctuations. Waterproofing is also commonly utilized in lieu of dampproofing in new residential or commercial construction where basements or below grade areas will be habitable spaces.
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Dampproofing is considered more susceptible to moisture infiltration through form tie-holes, shrinkage/structural cracks, bug holes, and careless backfilling damage. An active and properly installed drainage system (coarse grained backfill material, footer drains, and sump pump diversion) will make a dampproofed wall system much more effective and resistant to moisture penetration. If there is doubt as to the long-term performance of dampproofing based on the project conditions, most contractors and owners will choose waterproofing as worth the additional costs. An important engineering aspect to also consider in terms of the wicking and capillary action of water passing through a concrete wall is the water-cement ratio. A lower water-cement ratio (0.3 – 0.44 vs 0.45 – 0.6) will be more resistant to water passage. In new concrete foundation wall construction, this can be a challenge as many contractors prefer to use a higher slump mix which often yields a higher water-cement ratio. Plasticizing admixtures and water-reducers in the concrete can increase slump and flowability while helping maintain the low water-cement.
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Dampproofing coats the wall and is most commonly sprayed, trowel applied, or roll-applied. The most common thickness range is less than 10 mils thick. In low temperature, dampproofing materials can be more brittle in comparison to waterproofing. There are two major types of dampproofing, unmodified bituminous coatings and acrylic-modified cements:
Bituminous Dampproofing
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Bituminous Dampproofing can be:
Solvent based (petroleum products)
Water Based
Characteristics are:
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-cold-applied or hot applied
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-fibrated or non-fibrated
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-spray-applied (air or hydraulic), brush-applied, or trowel-applied.
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5-gallon pails are the most commonly used container for many dampproofing products.
A parge coat (1/4″ – 1/2″) cementious or polymeric mortar) may be required or useful to smooth and refine the surface prior to dampproofing application.
Not only will this add thickness to the dampproofing system, it will provide a better substrate for uniform and effective application. Note that many dampproofing products have substrate maximum moisture requirements before application. Note this amount of time both before planning the product sequence/schedule and placement dampproofing product. Specialized products, though often more expensive, are often available which can be applied to ‘green’ concrete. Firstly, assure safe clearances, benching, and shoring conditions before going below-grade to start application process.
Surface prep includes clearing/stripping/removal of dirt, oil, laitence, and water-repellents. For most mild substrate conditions this can be done by hand, with wire-brushes, mechanical/powered grinders, power-washers, compressed-air, etc.
When being sprayed on, a mastic spray gun is commonly used, with a 0.04-0.06 ” orifice with reversible tip and a 1/2 – 3/4″ inside diameter hose
If the substrate is dense (smooth concrete) 1 coat is commonly suitable. For uneven surfaces like concrete block, a primer product and two coats will commonly be more effective. For very uneven surfaces, a membrane system may be used which utilizes a fabric membrane (often fiberglass) in between damproofing coatings.
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Most products should not be applied below 40 degrees fahrenheit, but special products, though often more expensive, may be available for lower temperatures. Coating should be carried slightly onto footer horizontally and also slightly above the top of expected finish grade. Many bituminous dampproofing products require 24-48 hours cure time before backfilling will be acceptable without damaging the material. Paint thinner, mineral spirits, or kerosene is often effective at removing fresh product from tools and other unwanted surfaces. Dried/cured bituminous product can be more stubborn to remove. For trowel-application, 1/16 – 1/8″ thick coats are most common.
Cementious Damproofing
Cementious Damproofing is commonly composed of a dry, often pre-mixed, of portland cement, and sand masonry coating with acrylic fortifying agents either integral or added with the mix. It is used to dampproof, seal, and improve aesthetics on exposed concrete, block, brick, stucco, and stone walls. If used on exposed concrete, cementious dampproofing typically comes in gray or white colors and some products also offer liquid or powder coloring agents. It often comes in 20 lb pails or 40 lb bags. A typical recommended thickness for a flat concrete wall is 1/32″ – 1/16″. A minimum of 2 coats is typically recommended for dampproofing applications. Typical substrate preparation is recommended similar to bituminous dampproofing prep and the wall should be dampened with water prior to aplication. Application is commonly done by brush or spray. During hot weather the applied material should be mist dampened with water every fcouple hours to resist rapid moistre loss and drying shrinkage cracks. Water mixing quantity, mixing times, and curing conditions should remain consistent for exposed concrete to maintain color uniformity.