Portland stone has a variety of uses. The diagram below shows you the recommended uses for each bed of stone.
NOTE: It is recommended that in most locations, Portland Stone should be used on its natural bed. Although the stone is slightly stronger when used on its natural bed, this advice is given for aesthetical reasons. The only exceptions to this rule are paving, where we recommend using the stone edge bedded and cladding in Roach Stone, where we would suggest again for aesthetical reasons face bedding the stone will give a more consistent distribution of the shells.
The reason for edge bedding the paving is for aesthetical reasons as the larger oyster shells can appear as rather unsightly large round shells when cut horizontally.
A - All porous Limestones draw in moisture from surrounding media. Therefore, contact with soils without protection could cause slight staining, particularly during the first two years and if the soils are heavily contaminated with mineral salts these salts may crystallize on the surface of the stone causing accelerated weathering of the stone surface in the form of pitting. Portland Stone should never be used as a formwork for in situ concrete as alkali salts from the concrete may lead to discolouration.
B - Due to the open nature of this stone, the designer needs to be certain that this stone is suitable in the proposed location.
C - Roach is a hard stone and is, therefore, not easily carved or worked by a mason. More time and therefore more cost should be allowed for working this stone in comparison to other Portland Limestones.
D - Portland Basebeds, although physically stronger, are less durable than the other Portland Stones. The higher Saturation Coefficient and Salt Crystallisation results indicate that if these stones are continually saturated and salts become concentrated and the form crystals within the structure of the stone., then damage to the surface could occur. Although this damage would probably only occur in the first 1 to 2mm of the stone, the resulting pitting effect is likely to be unsightly. We therefore recommend that further advice is sought before using Basebed in these exposed areas, i.e. external treads not protected by a dpc etc.