Roundtower NHL 3.5 Coarse (Premix)

Roundtower's premix range of lime mortars are a multi-purpose lime mortar. They are made with Natural Hydraulic Lime and selected sands to make a fully breathable lime mortar, which is suitable for restoration and conservation work as well as new builds.

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Through the controlled addition of work aids, the Roundtower premix range has been formulated to give improved work ability, reduced risk of shrinkage and reduced water requirements.

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Roundtower's premix range of lime mortars are batch blended for consistency, are naturally coloured with no pigment addition and are available in a range of sand (fine & coarse) and binder strengths (NHL 2 & NHL 3.5) to give the desired finish, natural colour and mortar properties.

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Finsh: Roundtower's premix range of lime mortars are available in two finishes. Coarse mortars are made with a coarse 5mm down sand, most commonly used for base coats and stone pointing. Fine mortars are made with a fine 2mm down sand which can be applied thinner and are most commonly chosen for their fine finishes.

Binder: Roundtower's premix range of lime mortars are held in stock in two binder strengths, NHL2 and NHL3.5. NHL5 mortars are available upon request. NHL2 is a weaker binder appropriate for softer stones and more heavily weathered surfaces; NHL3.5 is a moderate strength binder for more robust stonework.

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Factory blended mortar using a coarse kiln dried sand and NHL, combined with carefully selected additives to improve the mortar’s physical and mechanical properties, whilst maintaining all of the virtues of a pure Natural Hydraulic Lime mortar.

Binder Strength - NHL 3.5

Mix Ratio - 2:5

Aggregate - 5mm down

Usage:

Roundtower NHL 2 Coarse is a multi-purpose mortar designed for bedding, building and pointing applications, as well as weaker render coats.

Coverage:

After mixing, a 25kg bag will produce approximately 13.5 litres of mortar.

For render applications, a 25kg bag will cover approximately 1.35m2 at 10mm thickness.

For building applications, a 25kg bag will lay approximately 25 bricks.

Colours:

Roundtower NHL 3.5 Coarse is entirely natural in colour. No pigments or colourants are added.

For applications where colour is important (pointing, unpainted render finish), we strongly advise that sufficient quantities of mortar are purchased and all bags from the same batch to ensure consistency. However, please note that colour variation is still possible due to the use of natural sands.

Preparation:

In general, this will be determined by the purpose and application of the mortar.

We would expect appropriate preparation in accordance with best practice; where the surface is clean, free of dust and other debris.

Where necessary the background should be adequately dampened to promote adhesion/bond with the host surface.

Dense impervious backgrounds/materials are unlikely to be very absorbent and require little to no dampening, whereas more absorbent backgrounds/materials require adequate dampening in order to prevent rapid drying.

Mixing:

A 25kg bag of Roundtower NHL 3.5 Coarse will require 4 to 5 litres of clean potable water. The water addition will vary according to the application and desired consistency/workability of the mortar. Always avoid making the mortar too wet, as this can promote shrinkage issues, especially when used as a render.

For drum type mixers, it is essential not to overfill the mixer.

As a dry mixed material, it is possible that some settlement or separation may occur in the bag during transit; when mixing part bags, it is especially important that the dry contents are thoroughly blended prior to mixing with water.

Best Practice/Advised Mixing - First add 60 to 70% water of the total water into the mixer, followed by the Roundtower NHL 3.5 Coarse and turn the mixer on. Allow the mortar to mix until the water is thoroughly distributed, then add additional water to achieve desired consistency.

Mixing time - Mix for a minimum of 5 minutes, but for no longer than 10 minutes.

Other mix methods - We accept that it is generally site practice to add the water to the mortar, providing the mortar is well mixed and not too wet, this method will be sufficient.

Quenching - Like most lime mortars Roundtower NHL 3.5 Coarse will benefit from Quenching; allow the mortar to stand for 10 to 20 minutes after mixing, before use.

Should additional water be needed after quenching to maintain workability, this can be added and mixed thoroughly through the mortar.

All Roundtower products are CE marked and manufactured under an ISO9001:2015 accredited Factory Production Control System.

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