- In excessively cold conditions Damp proof courses should be stored in a warm environment for at least 24hours ahead of installation, this will make unrolling and handling easier in cold conditions.
It should not be assumed that because the ambient temperature is as required for laying masonry the DPC roll is at the same temperature, if left outside overnight.
- Care must be taken to follow the specification and details to ensure the continuity of the DPC at ground level with the Damp Proof Membrane.
- All joints between lengths of damp proof course must be by overlapping the DPC a minimum of 100mm and must be sealed using Xtra-Load DPC Jointing Tape.
- Joints between lengths of cavity trays must be by overlapping a minimum of 100mm and sealed using Xtra-Load DPC Jointing Tape. Xtra-Load DPC Joint Supports must be positioned behind each cavity tray joint. In the case of joints with preformed cavity tray units the joint support is an integral part of the pre-formed unit, thus an additional joint support is not required.
- All Damp proof courses at ground level must be maintained a minimum of 150mm above the finished ground level, including when stepping a damp proof course on a sloping site.
- All damp proof courses must be laid between an even, fresh bed of mortar in continuous lengths for the full width of the wall or leaf and preferably project beyond the finished external face of the external leaf. (including any externally applied render).
- Perforations in adjacent courses of brickwork must be completely filled with mortar.
- Where a separate damp proof course is laid on each leaf at the base of a wall it is essential that the DPC is not allowed to project into the cavity allowing mortar droppings to build up and cause possible bridging of the cavity and moisture penetration across the cavity to the inner leaf.
- Xtra-Load Pre-formed Cavity Tray Units must be used at all stop ends, corners and changes in level of cavity trays.
- Where the cavity tray passes columns and wind posts etc that project into the cavity special pre-formed cavity tray units should be designed and detailed.
- Cavity trays over cavity bridges, such as door and window lintels, ducts and horizontal cavity barriers and steel support angles, should be laid in continuous lengths. Where it is necessary to make a joint a 100mm overlap must be provided and sealed using Xtra-Load DPC Jointing Tape and the joint supported using the Xtra-Load DPC Joint Support System.
Intermittent cavity trays over door and window openings must be fitted to cover the full extent of the lintel or cavity bridge and be fitted with stop-ends to prevent water penetrating the cavity and direct water to weep-holes
- Cavity trays must be fixed diagonally across the cavity, stepping down towards the outer leaf a minimum of 150mm.
- Where partial fill cavity wall insulation is installed against the cavity face of the inner leaf any cavity tray must be fitted from the inner leaf across the insulation before stepping down across the cavity to the outer reaf, this will avoid any possible cold bridge above and below the cavity tray.
- Where a pitched roof abuts a horizontal cavity, a cavity tray should be installed above the roof level, maintaining a minimum of 150mm above the finished pitched roof level to ensure effective drainage of water through weep-holes in the external leaf.
- Where the junction between a pitched roof and a cavity wall forms a sloping abutment then a system of stepped cavity trays should be installed.
- When cavity insulation is stopped below the highest point of the wall; the top edge of the insulation should be protected by a cavity tray.
- Where a parapet wall is finished with a masonry coping a horizontal damp proof course must be installed and supported across the cavity immediately below the coping.
Damp Proof Course Jointing
- All surfaces to be joined must be clean and dry.
- All joints must overlap a minimum of 100mm and be sealed with Xtra-Load DPC jointing Tape.
- Release paper protecting the self adhesive tapes should not be removed until the joint is ready to be formed.
- When forming a joint in cavity trays the Xtra-Load Joint support must be used behind the joints. When making joints between linear cavity trays and pre-formed cavity tray units additional joint supports are not required as each sloping face of the cavity tray unit is fitted with an integral joint support.
Horizontal Damp Proof Course Joints
- When forming a lap joint between two horizontal lengths of DPC the surfaces to be joined should be brushed clean of any loose surfacing material and dried if wet.
- The overlap must be a minimum of 100mm.
- Apply a strip of Xtra-Load DPC Jointing Tape to one surface, leaving the silicone release film in place; rub the tape onto the surface to ensure a good bond. Pull off the release paper and apply the second piece of DPC applying an even pressure to secure a good bond to the tape. A rubber roller will prove useful in providing good even pressure.
- At changes in direction a full overlap must be allowed for and the joint sealed as described above.
- At all times the manufacturer’s instructions and those on any packaging must be followed.
Cavity Tray Joints
When making joints in cavity trays it is essential to use the Xtra-Load Joint Support System.
- Position the joint support behind the first length of cavity tray to be joined, turning the top and bottom of the support membrane onto the inner and outer leaves respectively by between 25 and 40mm, the back of the polystyrene wedge should be pressed against the cavity face of the inner leaf or insulation and the integral drip positioned down the cavity face of the external leaf.
- Bond a strip of Xtra-Load DPC Jointing Tape to the surface of the Joint support, leaving the release paper in place. When ready remove the release paper from the tape and bond the first length of the linear cavity tray to the joint support. Apply a good even pressure to the membrane to ensure a good bond.
- Apply a strip of Xtra-Load DPC Jointing Tape to the surface of the first linear cavity tray, leaving the release paper in place, position the second length of linear cavity tray over the joint, ensuring a minimum overlap of 100mm remove the release paper and secure the joint, applying even pressure to secure a good bond. Rolling with a rubber roller will make this easier.
- The above procedure should be followed for all joints in cavity trays.
Joints between linear cavity trays and Xtra-Load Pre-formed Cavity Tray Units
When making a joint between linear cavity trays and pre-formed cavity tray units it is not necessary to use the Xtra-Load Joint Support System as all sloping faces of Pre-Formed Cavity Tray Units are fitted with an integral joint support.
- Position the pre-formed cavity tray unit around the detail.
- Apply a strip of Xtra-Load DPC Jointing Tape to the sloping face of the Pre-formed cavity tray unit, leaving the release paper in place.
- When the linear cavity tray has been cut to the required length and positioned remove the release paper from the jointing tape and bond the linear cavity tray to the pre-formed unit applying even pressure to secure a seal.
When it is necessary to surface fix cavity trays to the cavity face of the inner leaf or to a concrete ring beam etc the substrate must be cleaned of any loose laitance, oils and grease. The substrate must be primed with Xtra-Seal QD Bitumen Primer following the coverage rates and instructions on the tin. The primer must be allowed to dry thoroughly. Typically between 3 and 4 hours depending on ambient conditions.
- Align the cavity tray to the substrate marking the position of the top edge of the cavity tray onto the primed substrate.
- Apply a continuous strip of Xtra-Load Jointing Tape below the mark leaving the release paper in place.
- Locate the cavity tray, remove the release paper from the jointing tape and bond the upper section of the cavity tray to the substrate, applying even pressure to ensure a full seal is achieved.
- The surface fixed detail must be permanently secured by mechanical fixing. Position a length of Xtra-Load DPC Fixing Strip aligning it with the top edge of the cavity tray and mark for drilling through the pre-drilled strip.
- Secure the strip by using a standard hammer screw fixing at 150mm centres.
- At joints the Xtra-Load Joint Support System is used as described above, making the joints before securing with mechanical fixing.
With all DPC materials damage can occur when cleaning mortar droppings from the cavity unless care is taken. The following recommendations should prevent damage occurring;
- Cavity battens should be used to prevent excessive mortar droppings reaching the DPC.
- Mortar droppings should be removed before they have time to harden.
- Implements such as steel rods should never be used to clean cavities.
- All Damp proof courses should be checked for damage as work proceeds and repaired as required to the satisfaction of both the contractor and the manufacturer.
Weepholes are required in the outer leaf of cavity construction immediately above a cavity tray. These are formed by leaving open perpendicular joints at a maximum of 900mm centres (every 4th. brick). A minimum of 2 weepholes is required over each window/ door opening.
Drainage from the weepholes may cause staining of the masonry below, as a result of cementitious wash out. Furthermore weepholes can allow the ingress of insects and wind driven rain and snow. Incorporation of a proprietary weephole filter system will reduce the risk of staining and prevent ingress into the cavity of insects etc as well as reducing the visual impact of weepholes.