Processing guidelines for façade bricks

Various processing methods are used for the processing of façade bricks of Caprice - B.V. Steenfabriek Huissenswaard. The most common are:

• Traditional masonry with masonry mortar and finished afterwards by filling the joints with joint mortar.
• Doorstrijk masonry with a doorstrijk mortar and finish the joints in the masonry process.

There are many different ways to provide traditional masonry with masonry mortar, with a joint. Important for the jointing is that the masonry mortar is scratched out far enough in the masonry process so that a good adhesion of the joint mortar can be established. The scratching should be done in such a way that a flat square cross-section is created at such a depth that a joint with a thickness equal to the 
height is guaranteed.

In traditional half-brick masonry of outer walls, it should be avoided that both sides are scratched out, because the adhesive surface of the masonry mortar would then be too small. In such cases, it is advisable to door te strijken the so-called dirty side with the mortar.

Façade masonry is increasingly being provided with jointing in the colour of the brick. To avoid mortar stains on the edge of the brick, it is important to also use a masonry mortar of the same colour.

Doorstrijken
For masonry with poor to moderate water absorbing bricks, it is advisable to perform the masonry using the doorstrijk technique. With masonry of these types of bricks, damage often occurs due to poor adhesion of the joint to the brick. This causes cracks along the attachment surface, resulting in detachment of the joint.

Another type of damage that may occur with masonry with poor to moderate water absorbing bricks is the leaching of lime from the mortar by straining the joints in the masonry. Experience shows that if this masonry is carried out using the doorstrijk technique this damage does not occur.

Important with doorstrijken is that a factory-made doorstrijk mortar is used, with the addition of trass.

Special masonry
In addition to the above-mentioned traditional and doorstrijk techniques, there are also processing techniques in which the vertical joints are not filled, the so-called vertical joint-free masonry.

With traditional masonry and doorstrijk techniques, the joint is about 20% of the façade surface. If the joint surface is reduced, the brick will have a different visual presentation, the brick will ‘speak’ more. This effect can be achieved by glueing façade masonry or laying bricks with thin joints.

Glued masonry
In this technique, the masonry joints have a thickness of 3–5 mm. Adhesive mortars are factory manufactured and often colour-matched. The adhesive mortar is applied mechanically using special processing techniques. The joint is usually recessed and is finished off in the process.

Masonry with thin joints
This method of bricklaying is also called thin bed masonry. A special mortar for these joints of 4-8 mm is used here. The mortar is factory manufactured and mixed with a special mixer. It is traditionally applied using a trowel. The mortar is usually colour-matched and the joints are finished immediately during the bricklaying process.

In both glued masonry and masonry with thin joints variants without vertical joints can be realised.

Work preparation and implementationWork preparation starts after choosing the façade bricks and the implementation method of the façade masonry.

For a proper preparation of the façade masonry, it is important to choose the right mortar.

Caprice - B.V. Steenfabriek Huissenswaard recommends using a prefabricated masonry mortar and joint mortar with KOMO product certificate for the laying of its bricks.

Choosing the right prefabricated mortar and joint mortar is primarily motivated by the voluntary water intake of the brick. It is therefore important that, prior to the start of the work, the brick specification is discussed with the manufacturer/supplier of the mortar, so as to choose the right mortar.

To ensure fair-faced masonry, the detailing, in addition to the proper and correct implementation, is of great importance.
Caprice - B.V. Steenfabriek Huissenswaard will provide you with advice, without any obligations, on the façade detailing and masonry expansion joints. This advice is in accordance with the publications issued by the KNB ‘Ontwerpen met dilataties’ (Designing with expansion joints) and ‘Schoon metselwerk’ (Fair-faced masonry).

An important point of attention in the execution of the masonry is the connection of the façade masonry from the foundation at ground level. Due to rising damp from the ground, moisture damage may occur by omitting several courses of damp-proof bricks.

The use of water features against the façade masonry will also lead to damage to the façade masonry if measures have not been taken to prevent the rising of moisture.

Applying a water barrier in the outer leaf of the masonry at ground level will prevent such damage.

Implementation Guidelines
The KNB ‘Design and implementation guidelines for Bricks in Outer Walls’, edition April 2006, reads as follows: "Masonry brick for outer walls"

1. Masonry brick should be specified according to NEN-EN 771-1 ‘Masonry brick’ and preferably be provided with a KOMO product certificate.
2. Check visually if colour, shape, the nature of the surface and damage of the bricks supplied comply with the KOMO specification form according to assessment guideline BRL1007 and with a coded delivery sample (at least 16 bricks).
3. The moisture content of the masonry brick upon delivery may not exceed what is allowed for the processing with a masonry mortar suited for the brick.
4. Preferably use separable brick packages (12 foot partial package or 6 foot pallet), so that the bricks can be delivered mechanically to the bricklayer.

Place the brick packages on a clean, dry and flat surface (such as scaffolding components), so that the bricks are stable and so that water and dirt cannot penetrate the bricks. 

Protect the packages from water penetration and contamination by covering them; aeration should be possible. Keep the packaging foil of the bricks open on the dry side during storage. It is recommended to deliver the bricks mechanically to the bricklayer. For transport on the construction site, use the appropriate tools available, such as the 6 foot tongs. It is recommended to place the bricks with the bricklayer at a height of 400 to 550 mm above the surface of the scaffolding.

In special cases, depending on a variation in colour in the individual brick packages, it may be necessary to take bricks from several packages and deliver them to the bricklayer in order to ensure that a uniform distribution of colour is produced in the masonry. In these cases, follow the instructions of the respective brick manufacturer.

Masonry mortar

1. Masonry mortar must be specified according to NEN-EN 998-2 ‘Mortars for masonry’.
2. For the masonry of outer walls, use at least mortar application type A in accordance with BRL 1905. Use mortar application type A modified with trass for quay walls and earth retaining walls. It is recommended to use prefabricated masonry mortar that comes with a KOMO product certificate. This ensures a constant quality level. Request a detailed masonry mortar advice from the manufacturer of the prefabricated masonry mortar regarding the conditions for processing the masonry mortar and the masonry brick. The masonry mortar quality according to NEN-EN 998-2 (M5 - M15) should be determined in consultation with the architect/ constructor.
3. A (prefabricated) masonry mortar with lime is preferred above a sand-cement mortar because of improved properties regarding curing behaviour, processability and sensitivity to efflorescence.
4. When the mortar is mixed on the construction site, the following composition ratio of the volume parts can be used for the laying of bricks with average properties during the summer period:

   Portland cement : lime : sand = 1 : 1 : 5 or 6.

   For the winter period, the composition ratio of the volume parts is 1 : 0.5 : 4.5. To achieve a good stackability and optimum speed of construction, for bricks with moderate water absorption

   (0.5-1.5 kg/m2/min), the coarse fraction C4-C5,6 may form up to 10-15% of the sand package.

5. Do not use additives in mortar that is compiled and mixed on the construction site.
6. The processing time for mortar is a maximum of two hours. For wet prefabricated mortar with setting retarder, a maximum storage time of twelve hours is recommended.

Joint mortar

1. Joint mortar must meet the requirements of CUR Recommendation 61 ‘Masonry joints”.
2. Preferably use a prefabricated joint mortar, whereby a constant level of quality is guaranteed. Request a detailed joint mortar advice from the manufacturer of the prefabricated joint mortar regarding the conditions for processing the joint mortar. The joint mortar quality according to CUR Recommendation 61 (VH15 - VH45) should be determined in consultation with the architect.
3. For joint mortar mixed on the construction site, apply a composition ratio in volume parts in accordance with CUR Recommendation 61. In connection with a high risk of ‘burning’, blast furnace cement is not recommended for jointing. The sand must comply with NEN-EN 998-2 and BRL1905, with the exception of the prescribed grain size distribution. In this respect the provisions in CUR Recommendation 61 apply.

Bricklaying

1. Perform a complete visual inspection of the surrounding (support) structure with regard to dimensions, flatness, anchoring, stability and carry out the building work in accordance with the KOMO process certification of Masonry Structures. The following guidelines apply:
   The moisture content of masonry bricks at the time of processing merits attention. The use of too dry or wet bricks, may lead to poor processability and/or poor adhesion of the masonry mortar. If a prefabricated masonry mortar is applied, follow the advice given by the mortar manufacturer regarding the conditions for the processing of the mortar and the masonry brick. Bricks that are too dry can be prepared for use by slightly wetting the brick packages one or two days before processing and by allowing them to dry, covering only the top, so that the bricks become wind-dry, which means that they look dry, yet the inside is still moist.Stenen met een lage initiële Bricks with a low initial rate of water absorption (< 0.5 kg/(m2.min)), should be processed dry.
   1. National Assessment Guideline for the Manufacture of Masonry and Adhesive Structures and/or Jointing
      IKOBBKB publicatie BRL 2826
   2. Implementation Guideline for Masonry Structures
      (Bricks, building blocks and stones made of 
      concrete, aerated concrete and calcium silicate)
      IKOB-BKB publication No. PBL 0357
   3. Implementation Guideline for jointing masonry
      IKOBBKB publicatie Nr. PBL 0359
   4. Implementation Guideline for Glueing Façade Bricks 
      IKOBBKB publicatie Nr. PBL 0475
2. Carry out the masonry in the specified brickwork bond according to the standards of good workmanship. To achieve a uniform adhesion between the brick and masonry mortar, it is important that a generous amount of mortar is applied.
3. If the doorstrijk technique is used, application of a generous amount of mortar is required.
4. Always place the best looking side of the brick in sight and the possibly sanded side facing upwards. With half brick masonry, mason the brick with a frog (hollow on the flat sanded side) in such a way that the frog faces upward.
5. An expansion joint plan according to the KNB publication ‘Designing with expansion joints’ is recommended to prevent cracking in the masonry. Expansion joints should be made with care.
6. A vertical expansion joint is understood to mean a vertical joint over the entire wall thickness of the masonry filled with a compression tape - rot resistant or not - with a width of 5 mm. Take note: a cut joint (joint width of 0 mm) is not considered an expansion joint. 
   With buildings higher than 15 meters, the expansion joints must be filled with a compression tape.
   A horizontal expansion joint (at a masonry lintel) is understood to mean an oil free sealant over back filling, over the full wall thickness of the horizontal joint in the masonry with a width of 10 mm between the bottom of the wall support and the top of the masonry below.
7. Expansion joints should be entirely free from masonry and joint mortar.
8. To ensure proper aeration and drainage of the air cavity, one joint in three to four stretcher faces must be left open at the site of all horizontal ends of the masonry, like under and above a frame, with the roof connection, just above the ground level and above built-in water barriers. For glazed and other, less water-absorbent bricks, an open vertical joint for every two or three stretcher faces must be assumed. For proper drainage of moisture that can get behind the outer leaf of the cavity wall, one vertical joint for every two stretcher faces must be left open near the connection of the masonry to the foundation.
9. Cavity anchors must be included in the fully applied masonry mortar of the longitudinal joint, such that the anchors are placed in the centre of the longitudinal joint after the next layer of bricks has been laid. Cavity anchors may not enable the transport of moisture to the inner leaf of the cavity wall.
10. Never anchor frames to the outer leaf of the cavity wall. Only apply sliding anchors in the expansion joints after consulting the constructor.
11. Masonry reinforcement must be placed in the centre of the mortar of the longitudinal joint. Method: first apply half of the required mortar, followed by the reinforcement and the remaining amount of mortar.
    There are various qualities of mortar reinforcements for indoor and outdoor use.
    For outdoor use, at least apply galvanised reinforcement with epoxy coating or stainless steel reinforcement.
12. The designed air cavity should at least have a free cavity of 40 mm. While laying bricks, it must be kept free of spilled mortar and bits of brick that may cause moisture bridges between the outer and the inner leaf. Avoid dripping mortar as much as possible on the air cavity side and pay attention to other protruding items such as chopped bricks. The implementation guideline Masonry Structures: IKOB-BKB Publication No. PBL 0357/98 indicates: "The design should include such a cavity width that after applying the insulation and after laying the bricks, the remaining width is at least 20 mm, considering burrs of mortar and other protruding parts (e.g. chopped bricks, etc). This means that, in the design phase, a design air cavity width of 40 mm + insulation thickness should be taken into account."
13. After laying the bricks, the mortar should be scratched out such that the joint depth is equal to the average vertical and longitudinal joint thickness (square cross-section). The scratched out masonry should be brushed out with a stiff broom.
14. Bricklaying should be carried out such that smudges on the bricks are avoided. If smudges are made, these should be removed prior to jointing. Processing glazed bricks requires special attention. It is important to take into account the etching effect of unslaked lime, which can cause dull spots on the glazed brick surface. Mortar stains on glazed bricks must be removed immediately.
15. Avoid contaminating the masonry. Protect the bottom of the masonry from splashing water if there is a risk of this. To protect masonry from splashing water from the scaffolding, it is recommended that the first part of the scaffolding is folded in. It is not advisable to work with a single scaffold system.
16. Prevent the occurrence of efflorescence, cement residue and loss of adhesion by protecting the fresh masonry from dehydration and water penetration for at least 48 hours, preferably even longer. It is recommended to work with a scaffolding provided with a mesh and canopy. If not, the use of a light weight plastic cover profile is recommended.
    Also refer to KNB publication "Fair-faced masonry".

17. 

18. If the doorstrijk technique is used, it is recommended that protective measures be taken against precipitation and dehydration to prevent colour differences in the jointing due to changing weather conditions. The risk of colour difference is further reduced by the use of colour matched doorstrijk mortar.
19. The use of an acid to remove efflorescence is strongly discouraged. Also refer to KNB publication "Fair-faced masonry".
20. It is advised to take protective measures at air temperatures less than 0 ºC. In that case, when using prefabricated masonry mortar, follow the directions of the masonry mortar producer.

Jointing

1. The masonry may not be too dry or too wet for jointing. Ideally, the masonry was first able to dry completely, then generously moistened (one day prior to jointing). With less water-absorbent bricks, wait as long as possible before jointing. This significantly reduces the risk of efflorescence formation. Between the bricklaying and jointing, it is recommended to wait for a period of at least two weeks.
2. Before jointing, all dust and masonry mortar residues must be removed.
3. The square cross section of the joint must be filled entirely and the joint mortar must be firmly pressed in. For standard jointing, this means that the joint should be approximately 10 or 12 mm deep.
4. Avoid filling the expansion joints and the open vertical joints during jointing, and check that all open expansion joints and all open vertical joints are entirely free of joint mortar upon completion of the jointing.
5. Take into account the occurrence of colour differences in the jointing 
   ("imperfections") as a result of changing weather conditions. To prevent this, it is advised to take protective measures.
6. Jointing should be carried out such that smudges on the bricks are avoided. Processing glazed bricks requires special attention. It is important to take into account the etching effect of unslaked lime, which may cause dull spots to appear on the glazed brick surface. Joint mortar stains on glazed bricks should be removed immediately.
7. Avoid contaminating the masonry. Protect the bottom of the masonry from splashing water if there is a risk of this. To protect masonry from splashing water from the scaffolding, it is recommended that the first part of the scaffolding is folded in. It is not advisable to work with a single scaffold system.
8. Prevent the occurrence of efflorescence, cement residue and loss of adhesion by protecting the fresh jointing from dehydration and water penetration for at least 48 hours, preferably even longer. Also refer to KNB publication ‘Fair-faced masonry’.
9. The use of an acid to remove efflorescence is strongly discouraged. Also refer to KNB publication "Fair-faced masonry".
10. It is recommended not to joint at daytime temperatures of less than 5 ºC. If jointing is performed nonetheless, protective measures should be taken. When using prefabricated joint mortar, follow the instructions of the joint mortar manufacturer."

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