The application of the plaster must be performed only on dry surfaces. Avoid, therefore, application on walling wet from rain, frozen or with unset concrete. Do not apply the plaster with temperatures less than 4°C as this can delay significantly the hardening of the plaster and, consequently, the application of finishings.
The week before applying plaster, close any gaps caused by incorrect laying with mortar in order to avoid notable thicknesses of plaster which might result in areas of crazing. The walls should be adequately levelled and squared during installation as the application of thicknesses of plaster to straighten and square off walling is inconceivable and ineffective.
A thicknesses of plaster greater of 2 cm may lead to the formation of cracks and crazing. Where it is necessary to apply plaster thicker than 2 cm, it is essential that it is applied in two coats separated by at least 28 days.
With these important premises, the plaster can be applied, pre-mixed or traditionally prepared, considering the fact that it must protect the walling from weather and wear and that its thickness must be as uniform as possible at 15 mm, bearing in mind that a greater or lesser thickness can facilitate the formation of cracks.
Over the last few years, insulation is becoming ever more efficient which makes it all the more important to consider inserting a suitable netting, in alkali-resistant fibre glass with CE marking, positioned half way through the plaster; that being 7-8 mm from the support.
Finishings (e.g. fine mortar or other) should always be applied after a coat of adhesive of hardened plaster, generally at least 3-4 weeks beforehand, depending on climatic conditions.
Isotex Srl does not recommend the use of this type of finish (for exteriors), which in order to work well must have a fully hardened base coat of about 15 mm so as avoid the formation of shrinkage cracks, given the enormous difficulties in verifying that application and timing conditions are met.
From the experience gained since 1995 on various construction sites and considering that in recent years structural blocks have improved heat performance thus subjecting the plaster to greater stress, the solution we suggest consists in applying directly on the plaster base coat (15mm), levelled during application, a thick coloured finish after 4-6 weeks, thus obviating the need for fine mortar or other.
When applying the base coat and leveling with a straight edge it is important to maintain a uniform and consistent covering to avoid chalking the surface.
Isotex Srl can provide information on the characteristics of these products for external finishes and methods of application to ensure waterproofing yet breathability. For interiors we recommend an interval of 4-5 days between plaster foundation and fine mortar (or other finish) to ensure a good and thorough maturation of the plaster before applying the mortar.
Consider the particularities of the S 39 panelling, which for thermal reasons has joints but not concrete between the panels. In correspondence with these junctions micro-cracks may form and therefore, to avoid this, it is recommended to use a plasterboard finish. For intermediate floors (S20-S25-S30), if a plaster finish with a thickness of 15mm (no less) is chosen, the recommendation is to “embed” half way through the thickness, a reinforcing net in alkali-resistant fibre with CE marking. Then wait 4/5 days, depending on the season, before applying the finish and 4/6 weeks before painting.
Please note that, Isotex Srl, due to the fact that it is unable to physically monitor on a day to day basis compliance with these recommendations, the quality of materials used (plaster and coloured finishes) and timings between applications, disclaims any responsibility for issues that may occur in the future.
