Part 4B: Replastering System No.2: Dryzone Damp-Resistant Plaster
Renovation Plaster Application Guidelines
1. Preparatory Work
Remove all skirtings and architraves as outlined in the survey report. Remove plaster back to masonry to the height specified in the survey report, but this should not be less than 300 mm above the maximum level of the visual rising dampness and/or salt contaminated plaster. Remove any timber fixing grounds that are present in the masonry, then proceed with the application of Dryzone Damp-Proofing Cream or Dryrod Damp-Proofing Rods as per normal.
Dryzone Damp-Resistant Plaster should be mixed with a drill mixer. Pour 5 litres of water into a container, then slowly add a 25 kg bag of Dryzone Damp-Resistant Plaster to the mix. Once all of the ingredients have been added, start mixing the product at a slow speed to minimise dust generation. As the paste begins to form, the mixing speed may be increased.
3. Rough coat
Dryzone Damp-Resistant Plaster is applied in two layers. The first layer is a rough coat of 5 mm thickness. This will act as an anchoring layer for the second layer, which should not be applied until the rough coat has become sufficiently firm.
4. Plaster Coat
Apply the second layer of plaster to a minimum thickness of 15 mm giving a total plaster thickness of ≥20 mm , levelling it with a simple straight edge or adjusters to maintain the thickness. Dryzone Damp-Resistant Plaster working time is 30 – 60 minutes depending on temperature and humidity. If the product starts to stiffen, do not attempt to rework or remix.
Dryzone Damp-Resistant Plaster can be left as a decorative finish. Any other finishing (e.g. application of a skim coat) is carried out once the curing process is complete, after at least 14 days. Dryzone Mould-Resistant Emulsion Paint can also be used as a finish.
 Thinner thicknesses may be used (e.g. when matching in with existing plasterwork) but maximum moisture and salt resistance is achieved when the plaster thickness is at least 20 mm.
Important Points to Note
Please ensure that you read the section ‘Making good after treatment’ earlier within this manual.
Where walls are known to be excessively contaminated with hygroscopic salts (e.g. old barns, old kitchens, chimney flues, stables) then consideration should be given to tanking the walls using Vandex BB75 tanking slurry prior to replastering as added protection for the decorative surface. Alternatively the use of the Dryzone Express Replastering System should be considered.
Where masonry is unstable, this must be made good prior to the application of the plaster. Where it is not possible to obtain a proper bond between the wall fabric and the plaster, as in the case of cob walling for example, the plaster must be applied direct to the wall face but over expanded metal lath, previously fixed to the wall surface.
Drybase Liquid-Applied DPM should be used to prevent bridging of the DPC where the plaster meets a solid floor (see Figure 18).
It should be remembered that the walls will take a considerable time to dry out and it is possible that sufficient moisture could be absorbed by the new joinery to cause fungal decay.
It is important that the replastering specification is strictly adhered to and not varied in any way. No other additives must be added to the mix.
Read material safety datasheet for Dryzone Damp-Resistant Plaster and related materials before use and carry out a health and safety assessment of the procedures (e.g. mixing, and application) necessary for the use of the replastering system.