Roundtower Natural Hydraulic Limes

NHL-2

Whether you are repairing historic masonry or constructing an environmentally conscious building, Roundtower offers many benefits to architects, contractors, quantity surveyors, conservationists and homeowners.

NHL 2 is recommended for use on internal plastering and for pointing masonry that has very low compressive strengths.

Features and Benefits:
* Low Compressive Strength
* High Vapor Permeability
* High Sulphate Resistance
* High Rates of Carbonation

Application Procedures - Pointing:

Surface Preparation:
Cut out any existing mortar and open the joints to a minimum depth of 2½ times the width of the mortar joint or 1" deep. Brush the debris from the wall and use light water pressure to rinse the joints clean. Always start at the top and work down the wall. Wet the clean wall to a point where it can’t absorb anymore, but there is no standing water on the surface.

Mixing (see Lime Mixing chart for actual ratios)
Only use the sands provided by Boston Restoration Supply with your NHL order to blend with the lime. A conventional cement mixer can be used, but for larger projects a roller-pan or paddle-mixer is preferable. It is very important to measure all of the ingredients by volume. A gauging box or bucket will be necessary for this task and due to inconsistencies, do not use a shovel for measuring. The following steps are for optimal mixing conditions (based on a 1:3 mix ratio):

1. Add 1 part sand to an empty mixer.
2. Followed by 1 part lime.
3. Followed by 2 parts sand.
4. Mix dry for at least 5 minutes.
5. Slowly add water until the desired consistency is reached. Be careful not to add too much water.
6. When desired consistency is reached, mix for another 20 minutes.

At first, the mix will appear dry, but as mixing time increases the mortar will become much ‘fatter’. If too much water is added the risk of shrinkage will increase and the final strength will be reduced. Do not use any plasticisers.

Application:
Before applying the mortar, spray the joint with water so that it is damp. The new mortar should be applied using pointing tools and should be well packed into the joint. Deep joints must be built up a minimum of ½" in consecutive layers with at least four days between coats.

When pointing stonework with wide joints, pack stone pinnings (small stone chips) into the new mortar. This will help avoid overly large joints, which may result in shrinkage. Pinnings may also support weak areas of masonry.

The finish style should match the style of the original pointing work and not any later remedial work. Joints that are flush or slightly recessed will blend with the masonry and should be finished by beating the wall with a stiff churn brush once the mortar is fairly stiff. This process also compacts the mortar and leaves an open texture, which will aid evaporation of moisture.

Protection and Curing:
New pointing work should be protected from direct sunlight, wind, frost, rapid drying and direct rain for a minimum period of seven days. New work should be cured for a minimum of ten days after completion and longer if possible. The curing should be more of a dampening as opposed to saturating the work.

Do not apply the NHL if the temperature is not above 40°F unless it is protected.

Surface Preparation

Clean the masonry so that it is free from biological growth and containments and reasonably dry throughout the wall. The wall should be structurally sound and the masonry and bedding mortars in good condition. The replacement of any damaged or missing masonry or open joints should be repaired before any plastering or dubbing out coats are applied. To present a reasonably flat background for plastering all hollow or unevenness needs to be corrected by use of mortar and stone or brick slips bedded into the mortar.

Check the absorption rate of the substrate by applying water and observing the rate at which the water is absorbed. Highly absorptive substrates will need to be wetted down before application while dense or near impervious substrates may require a slurry coat painted onto the background to act as a mechanical key.

Mixing:
Same as pointing (see above).

Application
To minimize shrinkage and rapid drying, apply the NHL in three coats. The first coat, known as the scratch or render coat, is applied in a coat of approximately .4" (10mm) thickness and is applied with a steel trowel or thrown onto the wall by use of a harling trowel and then flattened with the steel trowel. When this coat is firm, but not hard, it needs to be keyed or scratched using a lath scratcher or similar toothed instrument. Care should be taken not to cut through the plaster coat back to the background. The keying is usually in the shape of diamonds with approximately 1.18” (30mm) spacing. Allow this coat to harden for 72 hours, check for shrinkage cracks, fill any cracks with plaster and brush the surface to remove any dust or debris. Make the surface damp, but not wet before applying the second coat, known as the floating coat. To ensure a flat and even surface the floating coat is straightened and then is scoured up with a timber or polyurethane float (rubbing up with a float similar to finning up render). The scouring is usually required to be done twice during which time any small holes should be filled. Allow the floating coat to harden for 72 hours. Dampen the wall before applying the final coat known as the setting coat. This coat is applied in two layers with a trowel similar to skimming. After application, it is scoured in a similar manor as floating and can then be left with a rubbed up rendered type finish or polished smooth with a steel trowel.

Protection and Curing:
New plaster work should be protected from direct sunlight, wind, frost, rapid drying and direct rain for a minimum period of seven days. New work should be cured for a minimum of ten days after completion and longer if possible. The curing should be more of a dampening as opposed to saturating the work.

Do not apply the NHL if the temperature is not above 40°F unless it is protected.

Clean Up:

Remove uncured mortar from the perimeter of the repair before it dries using clean water and a rubber sponge. Repeat several times with clean water to prevent a halo effect (staining of adjacent masonry).

Storage and Shelf Life:

The NHL and the aggregate should be stored in a dry location. Moisture can cause irreversible damage to the NHL and the aggregate. Also, once opened the exposure to air will start to weaken the hydraulic set. Any opened bags should be carefully folded over at the top and put into dry storage at the end of each day. These bags will remain usable for another two or three days, but should be discarded if not used in this time frame.

Technical Data

Physical Properties	Units	Medium Characteristics
Whiteness	Y	73.7
Fineness to 90µ	%	4.7
Fineness to 200µ	%	0.7
Expansion	mm	1.4
Bulk Density	kg/dm³	0.610
Real Density	g/cm³	2.57
Compressive Strength*	PSI	530

 

Physical Properties	Units	Medium Characteristics
Free Water	%	0.25
Setting Times	mn	820
Penetration Test	mm	12.8
SO3	%	2.54
Free Lime	%	29.1
Blaine Value	cm ²/g	9107

*at 28 days

Warning:

Not for internal consumption. Keep out of reach of children and animals. Consult Material Safety Data Sheet (MSDS) for specific information. 

06/2006