A water repellent additive and salt inhibitor is to be mixed in the sand/cement
rendering coat prior to replastering after the insertion of a Damp Proof
The water must be clean, free from oil, dirt or other injurious chemicals
(water suitable for drinking, if available).
- MIXING - FIRST COAT:
- Prepare three parts salt free clean sharp sand (BS 1199) to
one part O.P.C.
- Use mix as per 1 in place of gauging water, use minimum of water
to ensure a dense coat, not more than 1.75 gallons (8 litres) per
110lbs. (50 kilos of dry mix (i.e. sand and cement 3-1)). Compact
mix into joints and render to give overall thickness of 12mm (.50").
When the cement obtains its first set, scratch to form a key.
- SECOND COAT: Apply a further 12mm (.50") coat of rendering
as above to give an overall finished thickness of25mm (1"). This coat
to be applied before first coat has finally set in order to obtain
satisfactory adhesion between the rendering coats, scratch surface
to form key as before.
- THIRD COAT: 3mm (1/8") mix of multi-finish or similar finish.
Other finishes are acceptable provided they are porous. Do not polish.
IMPORTANT POINTS TO NOTE
- Where masonry is unstable, this must be made good prior to the application
of the renderings. Where it is not possible to obtain a proper bond
between the wall fabric and rendering, as in the case of cob walling
for example, the renderings must not be applied direct to the wall
face but over expanded metal lath, previously fixed to the wall surface.
- All timberwork must be treated with wood preservatives with a minimum
of three brush coats. We do not recommend timber fixing grounds to
be used, the use of masonry nails or plastics is recommended. In cases
where internal floor levels are below external ground level, we do
not recommend skirtings are of timber. These should be formed of solid,
as rendering coat above.
- Solid floors, which are not watertight - plasterwork should not extend
behind skirtings but should be cut short of finished floor level in
order to prevent any damp within the solid floor from being transferred
into the soft setting coat.
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