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The process for the treatment of rising damp consists of two main phases;
This section of the booklet will cover both the treatment and replastering methods in a step‐by‐step guide.
In order to stop the progress of rising damp through a wall, it is necessary to create a new DPC. Installing a new physical DPC into an existing wall can be hazardous, expensive and impractical in many situations (e.g. party walls). Older pressure pump injection methods directly into the brick are also time consuming and often ineffective.
The most practical and effective way to create a new DPC in a wall is to make an existing mortar course into a waterproof barrier using high strength damp‐proofing creams or rods (see Figure 7).
Figure 7: Stop rising damp by creating a waterproof mortar course
Most types of traditionally built masonry walls can be treated using Dryzone Damp-Proofing Cream or Dryrod Damp-Proofing Rods. However, some walls should not or cannot be suitably treated. Special procedures may be required for certain types of masonry, e.g. perforated brick and some types of blockwork. Please contact our technical department on 01403 210204 or submit an enquiry for information on treating these types of wall.
Earth retaining walls can only be treated above external ground level. The area below ground must be suitably ‘tanked’ to prevent lateral moisture penetration. Information on waterproofing walls below ground can be found in our basement waterproofing section.
Important: before undertaking any work it is essential to check the following:
Read material safety datasheet for all Safeguard products and related materials before use and carry out a health and safety assessment of the procedures (e.g. drilling holes) necessary for the installation of Dryzone Damp-Proofing Cream or Dryrod Damp-Proofing Rods.
When appropriate ensure that the property owners have complied with the Party Wall Act 1996. Advise interested parties of possible inconvenience of noise and vibration especially neighbours living in an adjoining property which shares a party wall to be treated.
In order to install either Dryzone Damp-Proofing Cream or Dryrod Damp-Proofing Rods, it is necessary to drill holes in a continuous line along a horizontal mortar course. Care must be taken to ensure the correct position of the DPC is chosen and the proper technique is used for the type of wall that is being treated.
Where possible, the line of the DPC for external walls should be placed at least 150 mm above external ground level in order to minimise the risk of rain splash‐back from external hard surfaces bridging the DPC (see Figure 8).
The intended line for the DPC should be exposed and clearly defined, taking into consideration internal and external ground levels, party and abutting walls, and changes in ground levels.
Internally, where a solid floor is present, the DPC should be inserted as close as possible to floor level. In all cases there should be continuity between the injected DPC and any DPM of a solid floor, the latter being taken up the wall to overlap with the injected DPC as described in CP 102.
Where suspended timber floors are encountered the DPC should, if possible, be inserted below the timbers.
Positioning of the DPC in relation to timber joists should be in accordance with BS 6576:
Where possible, the proposed DPC should be installed below the level of the timber joists and a check made that the DPC line is not bridged by sleeper walls, etc… If a DPC has to be installed above a timber floor, the client should be informed (in writing) that the floor is at risk of fungal decay.
BS 6576 “Code of practice for diagnosis of rising damp in walls of buildings and installation of chemical damp-proof courses”
X = all timber should be preferably physically isolated from any damp masonry in the vicinity of the DPC. Where this is not possible, fully treat timbers with ProBor 50 in accordance with the directions given in the Safeguard publication, Dry Rot & its Control. Visit the dry rot page for further details.
Where adjoining / abutting walls are present which are not to be treated, a vertical DPC must be installed. This should not be less than 1200 mm high and extend not less than 500 mm above the last evidence of dampness / salt contamination.
Vertical isolations are not capable of withstanding hydrostatic pressures which may be encountered with stepped properties, raised external ground levels, etc.
Where joist ends / timber wall plates are embedded in damp masonry, these must be checked for the presence of fungal decay. Ideally, physically isolate the timbers from the masonry by a DPM or joist hangers.
Where this is not possible and where timbers are damp and not decayed or just embedded in masonry, the ends should be given a thorough application of Safeguard ProBor 20 and / or ProBor 50 as described in the Safeguard publication, Dry Rot & its Control. Any timber remaining damp will always be at risk to decay; proper treatment as described in the above publication will reduce the risk of rot.
Should the DPC have to be above the floor timbers then measures must be taken to ensure that the timbers are not vulnerable to fungal decay. Precautions should be taken as described above especially with reference to the application of ProBor 50.
It should be noted that Probor 50 and Probor 20 are approved for professional use only.
For treatment to be fully effective with either Dryzone Damp-Proofing Cream or Dryrod Damp-Proofing Rods, the system requires 12 mm diameter holes to be drilled at horizontal intervals no greater than 120 mm. The depth of hole required for various thicknesses of solid wall is shown in the table on the next page. For all other walls the depth of hole should be to within 40 mm of the opposite face. In all cases the most effective target site is to drill horizontally directly into the mortar course, preferably at the top of all perpends of the selected course (see Figures 9 and 10).
When drilling certain types of mortar, a large amount of debris can remain in the hole after drilling. This can inhibit the application of Dryzone and Dryrods. In these situations, this residue should be removed using a Dryzone System Hole Clearing Tool prior to the installation of Dryzone Damp-Proofing Cream or Dryrod Damp-Proofing Rods.
Measure the thickness of each wall to be treated. Set the depth gauge of the drill or apply tape to the drill bit in order to identify the correct drilling depth accordingly.
Cavity walls may be drilled / treated from one side in a single operation when using Dryzone Damp-Proofing Cream. If Dryrod Damp-Proofing Rods are being used, each leaf should be treated separately. When undertaking treatment from one side, drill completely through the selected mortar course, allow the drill bit to pass across the cavity (see Figure 11) and then drill the other leaf of brickwork to a depth of 90 mm. The viscosity of Dryzone Damp-Proofing Cream is such that it is possible to treat each leaf from a single drilling operation. Always ensure that the cavity is clear before treatment.
| Wall Thickness | 4½″ (115 mm) | 9″ (230 mm) | 13½″ (345 mm) | 18″ (460 mm) |
|---|---|---|---|---|
| Depth of Drill Hole | 95 mm | 210 mm | 325 mm | 440 mm |
| Hole Intervals | 120 mm | 120 mm | 120 mm | 120 mm |
In virtually all cases solid brick walls may be drilled / treated from one side only in a single operation (see Figures 12, 13, and 14). Drill the selected mortar course at the prescribed intervals to the appropriate depth in accordance with the table above.
It is not generally advisable to use Dryrod Damp-Proofing Rods on random stone or rubble infill walls because the lack of material consistency throughout the wall can make debris clearance difficult. The use of Dryzone Damp-Proofing Cream is recommended.
As far as practically possible, follow the mortar course at the appropriate selected level (see Figure 15). The variable thickness of stone walls and the possibility of rubble infill dropping and blocking injection holes cause difficulties for any damp‐proofing system. Should these difficulties occur it might be necessary to drill to 50% of the wall thickness, from both sides at a corresponding height. Alternatively drill additional holes, which do not become obstructed, adjacent to obstructed holes to ensure that an adequate volume of Dryzone Damp-Proofing Cream is introduced.
Where there is difficulty locating the mortar course, consideration should be given to reducing the drill hole spacing from 120 mm to 100 mm.
Pierce the end of the foil wrapped sausage and then insert it into the Dryzone application gun. Insert the nozzle of the gun into the full depth of the pre‐drilled hole. Gently squeeze the gun trigger and back‐fill each hole fully with Dryzone Damp-Proofing Cream to within one centimetre of the surface. Periodically wipe clean the outside of the nozzle.
Install the mastic cartridge into a standard mastic gun and then attach the supplied nozzle. Insert the nozzle of the gun into the full depth of the pre‐drilled hole. Gently squeeze the gun trigger and back‐fill each hole fully with Dryzone Damp-Proofing Cream to within one centimetre of the surface. Periodically wipe clean the outside of the nozzle.
In order to prevent wastage when treating a cavity wall from one side, it is advisable to mark the delivery tube using tape to indicate the depth of the concealed hole and the width of the cavity.
Dispose of used cartridges in a plastic bag in accordance with local waste disposal regulations.
| Wall Thickness | ||||
| Wall Length | 4½″ (115 mm) | 9″ (230 mm) | 13½″ (345 mm) | 18″ (460 mm) |
|---|---|---|---|---|
| 10 m | 1.5 | 3.3 | 5.1 | 6.9 |
| 20 m | 3.0 | 6.6 | 10.2 | 13.8 |
| 30 m | 4.5 | 9.9 | 15.3 | 20.7 |
Table 4: Number of 600 ml Dryzone cartridges required to treat walls of various length and thickness.
| Wall Thickness | ||||
| Wall Length | 4½″ (115 mm) | 9″ (230 mm) | 13½″ (345 mm) | 18″ (460 mm) |
|---|---|---|---|---|
| 10m | 2.9 | 6.4 | 9.9 | 13.4 |
| 20m | 5.8 | 12.8 | 19.8 | 26.8 |
| 30m | 8.7 | 19.2 | 29.6 | 40.1 |
Table 5: Number of 310 ml Dryzone cartridges required to treat walls of various length and thickness.
In the event of any accidental spillage of Dryzone Damp-Proofing Cream, the spilt material should be wiped up immediately and the wipes placed in a plastic bag and disposed appropriately. Contaminated surfaces should be washed immediately with warm soapy water.
Clear any drilled holes with the Dryzone System Hole Clearing Tool to remove any debris that may impede rod insertion. Wearing suitable gloves, remove the rods one by one from the packet, inserting a single rod into each hole. Ensure the rods are recessed approximately 5 mm from the brick face while trying not to force the rod into the hole.
When installing internally, performance of the rods will not be affected if the rods protrude slightly where mortar has eroded from the surface, as the rods will be covered during redecoration.
Dryrod Damp-Proofing Rods come in sealed foil packs of 10 rods. Each rod is designed to treat a 120 mm length of 9 inch double skin brick wall, giving a coverage rate of 1.2 m per foil pack of 10 rods.
For walls less than 9 inches thick, the rods can be cut to the appropriate size using the Dryzone System Rod Cutting Tool. For walls thicker than 9 inches, it is possible to combine up to 2 rods per hole, cutting the second rod to fill any excess space left over by the first. The following tables can be used as a coverage guide for various wall thicknesses:
| Wall Thickness | ||||
| 4½″ (115 mm) | 9″ (230 mm) | 13½″ (345 mm) | 18″ (460 mm) | |
|---|---|---|---|---|
| Depth of Drill Hole | 95 mm | 210 mm | 325 mm | 440 mm |
| Length of Dryrod | 90 mm | 180 mm | 270 mm | 360 mm |
Table 6: Dryrod lengths and drill hole depths for walls of various thicknesses.
| Wall Thickness | ||||
| Wall Length | 4½″ (115 mm) | 9″ (230 mm) | 13½″ (345 mm) | 18″ (460 mm) |
| 10 m | 42 | 84 | 125 | 167 |
Table 7: Number of Dryrods required to treat a 10 m long wall of various thicknesses.
It is advisable to keep the rods inside the foil packs until the time of insertion. If placed on a porous surface, the rod may start to spread water repellent material.
Any equipment that has come into prolonged contact with the rods should be cleaned regularly using warm water.
Important: Once Dryzone or Dryrods have been installed, the dampness that was already present in the wall will need to dry out through evaporation.
Therefore, if possible, it is beneficial to delay the attendant works for as long as is feasible to facilitate the maximum possible period for drying.
A damp wall takes time to dry out. As a general guide, the drying rate is given as 1 month for every 25 mm of wall thickness (BRE Digest 163 ‘Drying out buildings’). Thus 230 mm will take approximately 9 months to dry. However, the drying processes depend on environmental conditions, ventilation and the type of masonry, so drying may take considerably longer.
It is possible to redecorate within 24 hours of treatment if the Dryzone Express Replastering System is used. It allows for the immediate application of plasterboard and, when dry jointing is used, the immediate application of a skim coat. As the wall dries out, it is important to consider the following:
If replastering is not necesary or it is not possible to use the Dryzone Express Replastering System (in which case Dryzone Damp-Resistant Plaster should be used) the following points should be considered:
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