Technical Procedures Disclaimer
Prior to inclusion in GSA’s library of procedures, documents are reviewed by one or more qualified preservation specialists for general consistency with the Secretary of Interior Standards for rehabilitating historic buildings as understood at the time the procedure is added to the library. All specifications require project-specific editing and professional judgement regarding the applicability of a procedure to a particular building, project or location. References to products and suppliers are to serve as a general guideline and do not constitute a federal endorsement or determination that a product or method is the best or most current alternative, remains available, or is compliant with current environmental regulations and safety standards. The library of procedures is intended to serve as a resource, not a substitute, for specification development by a qualified preservation professional.
We’ve reviewed these procedures for general consistency with federal standards for rehabilitating historic buildings and provide them only as a reference. Specifications should only be applied under the guidance of a qualified preservation professional who can assess the applicability of a procedure to a particular building, project or location. References to products and suppliers serve as general guidelines and do not constitute a federal endorsement nor a determination that a product or method is the best alternative or compliant with current environmental regulations and safety standards.
DAMPPROOFING OF AN HISTORIC BUILDING IS CONSIDERED AS THE LAST RESORT BECAUSE SUCH WORK CAN CAUSE IRREVERSABLE DAMAGE TO THE BUILDING. BEFORE PROCEEDING WITH SUCH WORK TRY REGRADING AT THE BASE OF THE STRUCTURE, REPAIRING UNDERGROUND DRAINAGE SYSTEMS, OR ADDING OR INCREASING VENTILATION.
- This procedure includes guidance on treating rising damp in masonry walls by installing a chemical dampproof course.
- See 01100-07-S for general project guidelines to be reviewed along with this procedure. These guidelines cover the following sections:
- Safety Precautions
- Historic Structures Precautions
- Quality Assurance
- Delivery, Storage and Handling
- Project/Site Conditions
- Sequencing and Scheduling
- General Protection (Surface and Surrounding)
These guidelines should be reviewed prior to performing this procedure and should be followed, when applicable, along with recommendations from the Regional Historic Preservation Officer (RHPO).
- Rising damp - the upward capillary migration of ground moisture through porous masonry walls.
- Rising damp may result from the presence of below- grade membranes applied to vertical foundation surfaces which prevent moisture from leaving the masonry through the exterior wall surfaces, and forcing the moisture to migrate upward to heights of three or more feet above the grade line before evaporating.
- Rising damp can result in the development of numerous other problems, including damp patches on walls, unhealthy living conditions, fungal growth, increased heat losses, and staining and deterioration of interior finishes, the masonry surface and the basic structure of the building.
- Dampproof course - a physical barrier (traditional= ly high-fired brick, lead sheets, slate, or bitumen material) which is usually inserted approximately six inches above the natural ground level during construction to prevent the condition of rising damp.=
- These materials may eventually fail due to poor installation or deterioration over the years.
- Reinstallation of a mechanical dampproof course is an expensive and disruptive process. Such a solid horizontal barrier is difficult to achieve in rubble or cavity walls.
- Chemical dampproof course - A specially formulated water repellent designed for either low pressu re injection or gravity feed into holes drilled at regular intervals.
- The fluid impregnates the masonry, migrates through the capillaries, and forms a chemical water-repellent barrier by lining the pores of the masonry, and prevents the moisture from migrating.
- The barrier interrupts the migration of water through natural capillary action.
- Chemical dampproofing is less costly, quicker, and involves far less disturbance to the building than mechanical dampproofing.
- In Europe, siliconate resins have been used in chemical dampproofing and have proven effective in controlling rising damp for periods of 10 or more years, provided there are no unusual ground water conditions or contaminants and provided there are no highly alkaline mortars (as in repair work).
- ProSoCo, Inc. 755 Minnesota Avenue P.O. Box 1578 Kansas City, KS 66117 800/255-4255 or 913/281-2700 Request Tech Bulletin 683-1 and Conservare Dampcourse Fluid Product Data.
- Latex-siliconate, such as "Conservare Dampcourse Fluid" (ProSoCo, Inc.), or approved equal; or silicone solutions in organic solvent, or aluminum stearates.
- Infusion reservoir bottles and tubes.
- Low pressure injection equipment.
- Electric drill with 1/2" to 3/4" diameter diamond masonry bits
- Surface Preparation:
- Remove exterior and interior finishes only as required to expose masonry walls for treatment.
- Remove interior plaster damaged by hygroscopic salts to a height of 18" above the maximum level of rising damp.
- If recommended by chemical manufacturer and RHPO, grout large voids in cavity walls within damp zone.
3.02 ERECTION, INSTALLATION, APPLICATION
- Drill 1/2" - 3/4" diameter holes at six to eight inch intervals on one side of the wall only.
- The more porous the masonry, the further apart the holes may be placed.
- Holes should be placed within mortar joints as much as possible.
- Depth of holes shall be one-ha= lf to three-quarters the depth of the wall.
- For walls over 18" thick drill holes into both sides of the wall to ensure even penetration of dampproof chemical.
- Installation of dampproof liquid - Gravity Infusion Method:
- Fill infusion cups with liquid and allow liquid to flow into holes.
- A minimum of 2AB quarts of liquid will be required per 36 lineal inches of a 10-inch thick wall.
- Installation of dampproof liquid - Pressure Injection Method:
- Set pressure of injection equipment to provide 50 to 100 psi.
- Attach hoses to pump and inject dampproof course liquid in stages, or as recommended by manufacturer.
- Pump liquid in 4-inch to 6-inch stages, allowing each stage to cure according to manufacturer's instructions before pumping in next stage.
- Allow initial dry out period of approximately fourteen days before plugging injection holes with sand/cement mortar colored to match the existing wall surface. For guidance on repointing mortar joints see 04211-07-S and 04520-02-R.