(1) Mortars: classification.-Except where gypsum is required by section 36, or where another mortar is permitted under subsection (8) , mortar shall be one of the classes specified in Table III to subsection (7), and shall otherwise comply with the requirements of this section relating to its class. The requirements of this section relating to its class. The use of “artificial plasticisers” may be employees as an additive to cement mortars with the approval of the local authority.

(2) Composition: class A.- Class A mortar shall be composed of Portland cement together with fine aggregate in the proportions specified in subsection (7) . Plastic hydrated lime to the extent of no
more than 25 per centum of the dry cement by volume may be added to increase the workability, Such mortar shall be used within 60 minutes of the time when the cement was added to the mix.

(3) Composition: classes B and C.- Classes B and C mortars shall be composed of Portland cement together with fine aggregate in the proportions specified in subsection (7), and may include either lime-putty or hydrated lime.

(4) If normal lime is used in class B or class C mortar-

a) the mortar shall not be used as before it has been allowed to mature for at least 24 hours after the lime has been mixed with the fine aggregate; and

b) the mortar shall be used within 60 minutes of the time when the cement was added to the mix.

(5) Composition: class D.- Class D mortar shall be composed of lime-putty or hydrated lime and fine aggregate in the proportions specified in subsection (7), and Portland cement to the extent of not more than 25 per centum by volume of the dry lime may be added to increase the strength.

(6) If normal lime is used in class D mortar, the mortar shall be allowed to mature before being used for at least 24 hours after the lime has been mixed with the fine aggregate.

(7) Proportions and required strength mortars.- When tested in accordance with the Third Schedule, mortars of the classes specified in Table III shall have the minimum compressive strength shown in that Table.

TABLE III

MIXING PROPORTIONS AND STRENGTHS OF MORTARS

(8) Special mortars.- Mortars other than those specified in subsection (1), such as hydraulic lime mortar, may be used where tests have shown them to be satisfactory with regard to strength, soundness and consistency, to the satisfaction of the local authority.

(9) Permitted use of mortars.- Except where the provisions of this Chapter require otherwise, mortars shall be used only as specified in subsections (10) to (13):

Provided that mortar classes of a higher required compressive strength may be used for the purposes permitted for a class of lower required strength, but not vice versa.

(10)Class D mortar may be used-

a) in a bearing-wall or pier in a single storey building, or in the topmost storey of a building:

Provided that-

i) such wall shall not be a cavity-wall or a rubble stone wall; and

ii) such mortar shall not be used in a portion of the wall which is either above the surface of the roof or below the damp-proof course near ground-level or which is exposed to continual dampness;

b) in a partition-wall or a curtain-wall or a panel-wall, but not in a retaining-wall or a balustrade-wall or a free-standing wall.

(11) Class C mortar may be used-

a) in a bearing-wall pier:

Provided that such mortar shall not be used in a portion of the wall which is either above the surface of the roof or below the damp-roof course near ground-level, or which is exposed to severe conditions of continual dampness;

b) in a partition-wall or curtain-wall or a panel-wall, but not in a retaining wall or a balustrade-wall.

(12) Class B mortar may be used in bearing-walls, piers and columns, and in partition-walls, curtain-walls, panel-walls, free-standing walls and wing-walls.

(13) Class A mortar may be used in any masonry construction.

(14) Gypsum mortar.- Gypsum mortar shall composed of gypsum and fine aggregate, the volume of which shall not exceed twice that of the gypsum.

(15) In no case shall gypsum be mixed with Portland cement, or be allowed to come into contact with Portland cement or the products thereof within seven days of the time when Portland cement was mixed with water.

(16) Gypsum mortar shall not be used as mortar with building-units other than gypsum or glass blocks:

Provided that it may be used as internal plaster with any mature building units.