Rendering NHL with a Spraygun

St Astier Natural Hydraulic Limes (NHL)

This method is particularly suitable to ensure optimum bonding even on smooth surfaces.
Spraying is recognized as the best method of application allowing sharper sands and lower water content in the mortar mix. The speed of work is considerably increased and an average of 100 m2 per day per man is quite normal. The pressurized application also allows to build up the thickness of a layer to 25mm. The pressure should not exceed 3.5 Bar*. Two coat work is normally sufficient with the use of a spray gun

  20-25mm 25-35mm up to 40mm
      (for thickness above 40mm
please consult us)
Stipple coat 3-5mm 3-5mm 5-8mm
NHL 5 or NHL 3.5 @ 1: 1.5
Sands: well graded 5mm down to 0.075
Leave 24/48 hours as sprayed to provide good key
     
1st coat 10-15mm 15-20mm 20-25mm
NHL 3.5 @ 1:2 or NHL 5 @ 1:2.5
Sands: well graded 3mm down to 0.075
     
Leave for a minimum of 4 days depending on weather conditions, coat thickness and the plasterer's judgment.
Level using a straight edge and key with criss-cross pattern.
If this is also the finishing coat (20-25mm only), depending on the finish required, a finer sand can be used (2mm down to 0.075).
2nd coat (finishing coat) 5-8mm 5-10mm 5-10mm
NHL 3.5 @ 1: 2.5 or NHL 2 @ 1:2
Sands: 3mm down.
     
Finer sands for wooden float or smooth finishes (2mm or finer) can be used. In these cases the thickness should not be over 5mm.

Notes: background preparation as per good practice. Always dampen surface before each application. On high suction background ensure that this is thoroughly dampened (no standing water on surface), if necessary several times, to minimise shrinkage.
Cure work for few days with water mist. Protect against rain, frost, drying wind and direct sun for 2 to 7 days.
See "Protecting Lime Mortar".
If dubbing out is required the mortar ratio should be the same as the 1st coat. Leave dubbed out areas as sprayed to provide a key.

*Sablon S3 Hopper gun

  20-25mm** 25-35mm up to 40mm
      (for thickness above 40mm
please consult us)
On well keyed surfaces.
(raking joints not necessary)
10-15mm 10-15mm  
NHL 5 or NHL 3.5 @ 1: 1.5
Sands: well graded 5mm down to 0.075
Trowel off high spots and leave 3-4 days as sprayed to provide good key.
     
2nd coat 5-10mm 10-15mm 10-15mm
NHL 5 @ 1:2.5 or NHL 3.5 @ 1:2
Sands: well graded 3mm down to 0.075
     
This can be the finishing coat for a 20-25mm render. If a smooth finish is required apply a 3rd coat as below.
Level using a straight edge and key with criss-cross patterns.
Leave about 7 days depending on weather conditions and the plasterer's judgment.
3rd coat (finishing) 3-5mm 5-8mm 5-10mm
  Smooth finishes only
otherwise use 2nd coat
as finishing coat.
   
Finer sands for wooden float or smooth finishes (2mm or finer) can be used. In these cases the thickness should not be over 5mm.
NHL 3.5 @ 1: 2.5 or NHL 2 @ 1:2
Sands: depending on the finish required.
>Finer sands for wooden float or smooth finishes (2mm or finer) can be used. In these cases the thickness should not be over 5mm.
** This thickness can be achieved in one coat (several passes) with suitable aggregates. Please consult us.

Notes: background preparation as per good practice. Always dampen surface before each application. On high suction background ensure that this is thoroughly dampened (no standing water), if necessary several times, to minimise shrinkage.
Cure work for few days with water mist. Protect against rain, frost, drying wind and direct sun for 2 to 7 days.
See "Protecting Lime Mortar".
If dubbing out is required the mortar ratio should be the same as the 1st coat. Leave dubbed out areas as sprayed to provide a key.

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For further Guidance, contact your St Astier Distributor.
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