H e m p c r e t e A u s t r a l i a M a n u a l 1

7.1 The hemp render

Hemp render is applied as both an interior and exterior wall coating. It can be applied to existing and new wall surfaces.

The hemp for insulating renders has, in general, a smaller particle size than the hemp used in the other compositions.

Hemp render can be ordered especially through Hempcrete Australia or Insulcore can be sieved to separate the smaller particles.

The binder INSULIME, or INSULIME white, is also used as a render and is conform to the European norms NF EN 459-1 and NF P 15-201-1.

7.1.1 Mix

This wall mix has the following properties:

Density: 800 - 1000kg/m3

40 - 50kg/m2 (50mm wall thickness)

Elasticity: 20 MPa after 90 days

Resistance to compression: >1 MPa after 90 days

R rating: 0.35

Thermal conductivity λ: 0.14

Thermal resistance: 0.71m2KW-1 per 100mm

Mechanical strength, sound and thermal insulation depend on the amount of binder and hemp in the mix.

7. Hempcrete Installation: Hemp Render

material For 1m3 For 1m2 (50mm)

Insulcore/Hemp wood 1000Ltr (100kg) 52.5Ltr

Insulime 500kg 26.2Kg

Water 550 - 650Ltr 28.8 - 34Ltr

Sharp Sand Variable Variable

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7: Hempcrete Installation: Hemp Render

7.2 preparaTion and general inFormaTion

A variety of surfaces such as brick, stone, timber, concrete and fibre cement sheet can be fitted with the insulating hempcrete render.

7.2.1 Surface conditions

■ Timber surfaces must be well cured or dried.

■ Surfaces must be dampened before render is applied, as per standard render applications.

■ Loose particles should be removed and repairs undertaken with the same binder as used in render i.e. Insulime.

■ Surfaces should be sound.

Openings such as windows and doors should be adapted to the new thickness of the finished wall.

For external walls, a second render coat should be applied no sooner than 48 hours after application of the initial render. Render is applied in 20-40mm coats wet on wet.

Colorant and/or colored sands can be added to the final lime and sand coat.

The final coat should be a weaker lime mix, or a lime render with less compression strength.

This coat will be applied in two passes as per render standards.

Interior surfaces can be finished with lime wash.

The render must be able to breathe in all situations and at least

one of its surfaces should be permeable.

Acrylic paint finishes are not applicable.

7.3 mixing The render

1 Introduce 55-65 litres of water

2 Add the INSULIME or chosen render.

3 Mix for 3-5 minutes to obtain a homogenous milky paste.

4 Add the hemp and mix for 5-10 minutes until obtaining a homogenous mix and uniform colour.

The final mix should be fatty and smooth.

Do not mix for too long as the mix can become fluffy and lose its strength.

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7: Hempcrete Installation: Hemp Render

7.4 insulaTing render on inTernal Walls

7.4.1 Apply one hemp render coat without a finishing coat.

Application:

1 Test the wall for water absorbency. If the wall absorbs water easily it should be wetted thoroughly before application of hemp render. If the wall is not absorbing water very well, less water should be used. Hemp render needs a damp surface to adhere well.

2 Apply a stipple coat of the following mix on a well-prepared dry background:

1 part NHL 5 : 2 volumes of coarse sharp sand.

Mix the hempcrete render to the following proportions;

Coverage of this hemp render mix per m2 at 50mm thickness (depending on the grip):

1m2 of 50mm thick render requires 1 bag of binder and 55 litres of hemp.

3 Apply the hempcrete render in 20-30mm thick layers at 20-90 minute intervals. Colour can be added to this mix.

4 The hemp/lime mortar can be applied wet on wet on the stipple coat after approximately 12 hours. It is best to render an entire wall surface in one day. If finishing is completed within 1-3 days, these last layers should be as thick as possible.

5 When continuing the render after 1-3 days, lightly scratch the previous coat for maximum adhesion.

6 Apply the final 20mm coat of finer hemp aggregate several days later.

7 Allow to dry for 60-90 days. This final coat can be finished in standard render finishes, i.e. polished, floated or sponged.

8 An optional decorative finish of tinted lime wash, EcoMortar, clay etc. can then be applied.

material For 1m3 specification

Insulcore/Hemp wood 100Ltr (11kg) Normal or Fine Core

Insulime WHITE 50kg 2 bags

Water 55 - 65Ltr

proportion Binder Content % by Weight compared to Total dry Weight

hemp Wood Content % by Weight compared to Total dry Weight

density dry (indicative)

Minimal Aggregate

(strong mixture)

90% 10% 1000Kg/m3

Maximum Aggregate

(weak mixture)

50% 50% 200Kg/m3

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7: Hempcrete Installation: Hemp Render

The final finish can be achieved using standard render techniques such as rubbed, plastic, steel trowel, brushed or textured.

The installation of skirting boards is good when using internal renders to avoid damage from furniture, brooms etc.

7.5 insulaTing render on exTernal Walls

7.5.1 Apply one hemp render coat with a finishing coat. See Figures 1 and 2.

Application:

Proceed as for Internal Walls (on previous page) from step 1 through to step 6.

7 Allow the final coat to dry for 60-90 days. It is essential that the wall has the optimum time to dry prior to rendering the finish coats.

8 Apply a finishing coat of EcoMortar at least 5mm thick. This is the waterproofing coat that will remain hygroscopic. It has good hydrophobic properties (capabilities to move vapor outwards). This coat can be coloured.

Consumption of EcoMortar:

■ 5mm thickness - 1m2 of render requires 1/8 bag of EcoMortar; or

■ 5mm thickness - 4.4m2 of render requires 1 bag of EcoMortar

Rendered surfaces exceeding 15m2 should have expansion joints.

All walls should be fitted with damp proof courses where the lower surfaces are joined with the slab and footings, to avoid moisture transfer by capillary action. See Chapter 4, Figure 7.

Figure 1:

Existing concrete wall with hempcrete render.

Timber ties or keys fitted to the wall to provide maximum adhesion.

Ties can be fitted with steel brackets or by creating perforations for the timber tie.

First Coat

Hempcrete

ConcreteTimber Tie

Render Finish Coat

EXTERIOR

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7: Hempcrete Installation: Hemp Render

Caution

■ All external walls should have a finishing coat.

■ Ventilation should be in place to adequately dry the hemp render.

■ Do not force dry. If shielding against rain leave a reasonable distance between the cover and hempcrete wall to allow for ventilation. Drying can then be properly monitored and renders may be able to be applied earlier than the 90 day period.

■ In all cases wall surfaces should not exceed 15m2 without movement joints.

■ Walls should have a damp proof course in place at the base to avoid moisture transfer by capillary action.

■ If adequate ventilation is not possible, dehumidifiers should be placed to distract the humidity in the hemp mortars.

■ Hemp render on outside walls need to be finished with a final render coat that does not contain hemp particles.

■ The information supplied in this document is for general guidance only.

Contact Hempcrete Australia for further information.

Figure 2:

Existing brick wall with hempcrete render.

Timber ties or keys fitted to the wall to provide maximum adhesion.

Existing Brick Wall

Hempcrete

First Coat

Render Finish Coat

Timber Ties

EXTERIOR

DisclaimerThis document is intended to give general guidelines and practical information to the builder. It does not constitute a specification. Neither Hempcrete Australia Pty Ltd or St. Astier Limes can accept any responsibility or liability on the use and application of their products, errors or omissions in this document, loss, damage, injury or adverse outcome of any kind resulting from the use of the information contained in this document or reliance upon it.

Readers are advised to seek specific professional advice from Hempcrete Australia relating to their construction project and circumstances before embarking on any construction work.

All care has been taken to guarantee the accuracy of the information.

Drawings and models representing technical details are indicative and suggestions only.

All diagrams and pictures are the property of Hempcrete Australia, and are subject to Copyright 2012 ©. No part of this book may be reproduced without prior written permission of Hempcrete Australia Pty. Ltd.

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Hempcrete Australia Pty Ltd

Director: Johan Tijssen

ABN: 76 155 685 859

Web: www.hempcrete.com.au

Email: info@hempcrete.com.au

Office: 07 4529 6634 International: +61 7 4529 6634

Mobile: 0416 331 008 +61 4 16 331 008

Fax: 07 4529 6635 +61 7 4529 6635

Technical support

Please get in touch with us if you require further information - contacts below.

The Hempcrete Australia website installers’ login is a rich source of information.

Street address:

8 Thynne Court,

Maleny Qld 4552 AUSTRALIA

Postal address:

P.O. Box 1229

Maleny Qld 4552 AUSTRALIA