Installation

Head & Cill Installation

CAST STONE DECORATIVE HEAD WITH STEEL SUPPORTING LINTEL

Decorative heads are not load bearing therefore suitable support will be required. The supporting lintel will be visible on the soffit. It is important to maintain the free movement of the head by separating it from the supporting steel and surrounding brickwork. Decorative heads over 1500mm will generally be supplied in pieces.

Laying the lintel

Follow the lintel manufacturers installation advice.

1. Lintels should be installed with a minimum end bearing of 150mm, bedded on mortar and levelled along its length and across its width.

2. Raise the inner and outer leaves simultaneously to avoid excessive end loading, the masonry should be laid on a mortar bed and all perpendicular joints should be filled.

3. The external lintel flange must project beyond the window/door frame and it is recommended that a flexible sealing compound is used between the underside of the lintel flange and the frame.

DPC’s

4. In accordance with BS EN 1996-2 and NHBC requirements all external wall lintels must be installed with a flexible DPC (with the exception of those adequately protected by an eaves overhang or similar form of protection). Stop ends should be provided to avoid moisture entering the cavity near the reveals.

5. Form an integral stop end at the end of the head or incorporate proprietary stop ends. Provide weep holes at each end and at joints in the head if supplied in pieces. Place DPC slip plane along full length.

Laying the decorative head and secondary DPC

1. Mortar the head onto the slip plane on a full bed of mortar but leave the ends clear.

2. Lay DPC slip plane then the second cavity tray with stop ends extending to a suitable mortar perpendicular joint to suit the brickwork course above.

3. The DPC cavity tray should extend a minimum 150mm up toward the inner leaf.

4. Ensure weep holes are positioned at each end and at additional recommended spacings when required.

5. Lay surrounding brickwork on a full bed of mortar on top of the slip plane as normal ensuring it is in line and plumb.

6. To maintain free movement at the end of the head insert backing cord above weep vent and apply flexible sealant to match.

Generally, when laying cast stone products mortar strength should not exceed designation (iii), 1:1:5/6 cement : lime : sand proportional mix.

The use of lime is desirable to accommodate movement. Mortar no stronger than strength class M4 can be specified however movement may be restricted if lime is not a constituent element. Cracking can occur if mortar of a higher strength than recommended is used or if movement of the cill is restricted by mortar pointing.

 

CAST STONE STOOLED CILL DETAIL

Cast stone stooled cills are designed so each end of the cill appears to be supporting the masonry at each side of a window opening. They are available as one piece units up to 1500mm (dependent on unit height). Standard stooled cills are usually fitted as the build proceeds and protected from follow on trades, however some cills can be retro fitted.

To avoid stresses from differential movement the cill should be installed to the following guidance.

For one piece cills up to 1500mm.

1. At the window opening sit the cavity tray 20mm wider than cill (with stop ends), on a 4mm mortar bed. (The window aperture will be narrower than the cill unit).

2. Weep vents should be positioned at each end of the cavity tray.

3. Place a shorter section of low bond DPC material on top of the outer leaf surface of the cavity tray to act as a slip plane. Place at each end under the stooled profile positions only.

4. On top of the second DPC layer place a further 4mm mortar bed under the stool end only and carefully place the cill in position.

5. When forming the masonry reveal above the cill ensure free movement is maintained. Form a slip plane here by placing a 4mm mortar bed on top of the stool and smooth off. After hardening, place a square of low bond DPC cut to cover the mortared stool bed and side of the cill. Mortar on top of the DPC bed surface only and continue with construction of the masonry reveals ensuring bed joints remain in line and plumb.

6. At the end of construction insert a compressible backing cord into the gap between the bedded stool ends under the cill, and at the ends of the cill above the weep vents.

7. When considering an appropriate pointing solution, movement of different materials can be accommodated more effectively with a mastic or flexible joint sealant which would also prevent water penetration caused by mortar shrinkage.
 

Stooled cills exceeding 1500mm (dependent on height) will be supplied in sections.

1. For installation follow the general guidance for the one piece unit, however where the jointed sections meet a further section of low bond DPC should be placed on the external leaf of the cavity tray, enough to sit under 150mm of each bearing end and the mortared cill joint/s.

2. Place supporting mortar of a stiff consistency.

3. Apply a thin layer of mortar on one central end of the unit and lay. Carefully insert the second section ensuring the cill is level along the full length.

4. Ensure joint/s where the cill units meet are fully filled with mortar.

5. Place additional weep vents at intervals no greater than 1000mm before inserting the backing cord.

6. When considering an appropriate pointing solution, movement of different materials can be accommodated more effectively with a mastic or flexible joint sealant which would also prevent water penetration caused by mortar shrinkage.

 

Download our Heads & Cills Installation Guide

Heads & Cills Instalation Guide

For further help and advice please contact the sales office on 01993 842391