Part 4A: Replastering System No.1: Dryzone Express Replastering System
Plasterboard Damp-proofing Application Guidelines
1. Preparatory Work
Fully remove all contaminated plaster, exposing the underlying masonry. All loose material should be fully removed by brushing clean. Proceed with the application of Dryzone Damp-Proofing Cream or Dryrod Damp-Proofing Rods as per normal.
2. Dryshield Cream: Prime the Wall
Apply Dryshield to wall in a single coat using a large soft brush. Make sure any holes and cracks are filled with cream and that all areas are coated evenly. One 5 litre pack of Dryshield Cream covers up to 25 m2, depending upon the unevenness and porosity of the substrate. If there are any electrical sockets or light fittings in the wall, unscrew, remove back‐plates and apply cream to masonry. Ensure gloves, safety glasses and other appropriate clothing is worn.
3. Dryshield Cream: Absorption
Allow Dryshield Cream to soak into the substrate for at least 30 minutes. Do not leave for more than 24 hours before applying Drygrip Adhesive. Reinstate any removed fittings and socket fixtures before continuing.
4. Plasterboard: Trim and Fit
If required, prepare the plasterboard by measuring and trimming to size. Check fit by offering board up to wall. A gap of 12 mm should be remaining between the board base and the floor when installed. Also ensure to cut and trim around any electrical sockets and light fittings as needed.
5. Drygrip Adhesive: Prepare Applicator
Drygrip Adhesive can now be used to secure plasterboard to the wall. Prepare adhesive by inserting cartridge into Drygrip applicator gun and cutting it open. Screw nozzle cap into place. Trim nozzle to 10 mm diameter size hole. Tip: If leaving opened cartridge in gun, ensure nozzle is covered with tape or similar to prevent material drying in nozzle and gluing cap in place.
6. Drygrip Adhesive: Apply
Apply small dabs of Drygrip to reverse of plasterboard at regular intervals. Typical consumption should be 1 – 2 Drygrip tubes per sheet of standard size plasterboard. The thickness of Drygrip will allow for some adjustment, permitting the plasterboard to accommodate and cover uneven areas of the wall. Tip: When application is finished, remove nozzle cap and clean gun of all adhesive.
7. Plasterboard: Fit to Wall
Offer the board up to the wall and fit into place. Ensure sufficient contact with Drygrip Adhesive whilst allowing an air gap to remain so that the plasterboard is not in contact with the wall. Adjust sections of plasterboard to fit over uneven areas as necessary.
8. Plasterboard: Prop up
It is recommended to prop up the board. Use 12 mm plastic wedges for a precise fit. Alternatively, offcut pieces of plasterboard at 12 mm height or more can be used for the board to rest on. At normal temperatures Drygrip Adhesive should set adequately after 1½ hours. At colder temperatures (i.e. sub 10°C), leave for 2 – 3 hours and check adhesion by gently pressing board before further work.
9. Plasterboard: Fix and Set
Use Dryzone System Fixing Plugs to ensure an even flat surface across all boards. Use the provided Dryzone drill bit to drill holes at board corners no closer than 25 mm to edges. Tap in Fixing Plugs with a hammer, ensuring the final surface is even.
10. Finishing Tape and Plaster
Apply scrim tape to all board joins. A skim coat of plaster can now be applied. Proceed with additional replastering or decoration as required. For faster replastering: tape and joint boards using dry jointing method, then apply a coat of plasterboard sealer. This can be immediately painted onto once the sealer is touch‐dry.
Calculations show that the overall risk of condensation is reduced when using the Dryzone Express Replastering System compared with traditional sand:cement replastering systems. However, when using this type of product, due consideration must be given to the overall design to minimise risk of condensation and the recommendations contained in BS 5250:2011 should be followed. Where higher levels of relative humidity are anticipated other environmental controls should be considered, such as:
- Safeguard Humidistat Fan
- Safeguard Positive Pressure Unit
Use of Insulated Plasterboard
Most forms of insulated plasterboard can be used with the Dryzone Express Replastering System, provided that the normal precautions associated with the installation of internal insulation are adhered to. In particular, care should be taken to ensure that the insulation board is correctly fitted and all gaps filled to prevent moisture migrating from the warm air in the room to the colder solid wall behind the insulation as this will present a condensation risk.
The guidance given in BS 5250:2011 “Code of practice for control of condensation in buildings” should be followed with particular reference to sections G.3.1.4 “Solid masonry wall – Internal insulation” and G.3.2.4 “Masonry wall with cavity – Internal insulation”:
Internally applied thermal insulation isolates the heated interior from the masonry, which will therefore be cold, producing a risk of interstitial condensation behind the thermal insulation; to prevent that, an AVCL should be applied on the warm side of the thermal insulation.
BS 5250:2011 “Code of practice for control of condensation in buildings”
A suitable AVCL can usually be achieved by the application of a skim coat or by taping and jointing the tapered edges of the insulated plasterboards. However, where calculations indicate a risk of persistent condensation, a dedicated AVCL of suitably high vapour resistance should be used – see BS 5250:2011 section 4.5.6 for guidance.
It should also be noted that insulated plasterboard is not “breathable” and therefore its use will cause walls that have been treated for rising damp to take longer to dry out.