To prevent excessive heat loss to the outside, it is advisable to provide a rigid waterproof insulation between the perimeter duct and the outside wall. Air Supply and Exhaust for Heaters. Special types of packaged, or preassembled, units are available for heating that include a direct oil- or gas-fired heat exchanger complete with operating controls. These units must have a flue to convey the products of combustion to the outdoors. The flue pipe must be incombustible and capable of withstanding high temperatures without losing strength from corrosion. Corrosion is usually caused by sulfuric and sulfurous acids, which are formed during combustion and caused by the presence of sulfur in the fuel. Gas-fired heaters and boilers are usually provided with a draft hood approved by building officials. This should be installed in accordance with the manufacturers recommendations. Oil-fired heaters and boilers should be provided with an approved draft stabilizer in the vent pipe. The hoods and stabilizers are used to prevent snuffing out of the flame in extreme cases and pulling of excessive air through the combustion chamber when the chimney draft is above normal, as in extremely cold

Banding Whole sections of brickwork that differ in colour and stand out from the main body of work Example of banding in a brick wall Spot board A board made of durable material roughly 600mm x 600mm, on which mortar is placed Try checking the Brick Development Association website www.brick.org.uk to see if you can find out when and why changes were made to brick numbers. Spot board Stack of bricks Spot boards with mortar next to a wall of five courses Once the materials are safely moved to the work area and positioned for efficient working, we can begin the job of setting out the wall ready for building. Bricks are manufactured to dimensions and tolerances decided by official institutes. In the UK, the British Standards Institute (see Chapter 2, page 47) has in the past been the agency that produced official standards and gave numbers to components so that the details about them could be easily checked. Now the European Union has more control and the numbers have changed. For example, clay bricks used to have the number BS 3921. This has now changed to BS EN 7711.

Inspection of fabrication and placement is usually most conveniently performed in the field, where gross errors would require correction in any event. Under the ACI 318 Building Code, the bars should be free of oil, paint, form coatings, and mud when placed. Rust or mill scale sufficiently loose to damage the bond is normally dislodged in handling. If heavily rusted bars (which may result from improper storage for a long time exposed to rusting conditions) are discovered at the time of placing, a quick field test of suitability requires only scales, a wire brush, and calipers. In this test, a measured length of the bar is wire-brushed manually and weighed. If less than 94% of the nominal weight remains, or if the height of the deformations is deficient, the rust is deemed excessive. In either case, the material may then be rejected or penalized as structurally inadequate. Where space permits placing additional bars to make up the structural deficiency (in anchorage capacity or weight), as in walls and slabs, this solution is preferred, because construction delay then is avoided. Where project specifications impose requirements on rust more severe than the structural requirements of the ACI 318 Building Code, for example, for decorative surfaces exposed to weather, the inspection should employ the special criteria required.