External Plastering (Rendering) On Concrete Masonry
To obtain the highest vapor permeability a block construction should
be built with an NHL mortar.
Sands: always use well graded coarse sand (#5 to #200) unless indicated.
NHL mortar will not alter the color of the sand. See also Sands
for NHL Mortar.
Main recommendations: make sure that the application
surface is dampened before first coat (stipple coat) application. On smooth
surfaces or surfaces with poor suction an SBR resin can be added to the
first coat (max. 3% of the weight of the lime). Mix mortar well making
sure that it is not over saturated with water.
Note:Volumetric mix ratios have been adjusted, when
necessary, to the nearest round or practical figure.
hot weather or windy conditions, dampen surface at least once a day with a fine
spray (first 2-3 days). Protect from frost and adverse weather for min. 72 hours.
Dampen before applying finishing coat.
|Scratch Coat (3/16" MAX):
coat should be cast on (or sprayed on) fairly evenly and left as cast to provide
good keying. Scrape off high spots.|
||Mixing Ratio: 1: 1.5 using NHL 5
WAIT at least 2 DAYS. Dampen well before applying 2nd coat. (3/8"
(3/8" to 1/2")
|Mixing Ratio: 1:2 using NHL 3.5, troweled or
Level with straight edge. After sufficient hardening, key with a devil
|WAIT 5-7 days in accordance
with performance related to weather conditions).|
|A - Fine wooden float finishes
-max. 3/16" thickness -use finer sands (#12-down) Mixing
|B - Coarse/Textured finishes - 3/16" - 5/16"
thickness with #6 sands. Mixing Ratio: 1:2.5
|Two coat work on concrete blocks is achievable. In this case
using a spray gun is highly recommended.
|See also Rendering with
a spray gun and NHL
renders general guidelines.
above information is given as general indication only. Dosages may vary in accordance
to materials and aggregates used and site conditions. Please liaise with your
St. Astier distributor to finalise mortars mixes. Good building practice is assumed
at all times.|