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Guidesheets: Rebuilding |
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click on the links below to find other Guidesheets:
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| Rendering | Plastering | Pointing | Limewashing | Metastar | Cob | |
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The size of the job and whether its a listed property will affect the questions below, which should be checked with your local council.
The requirements for repairs to an existing wall will differ from a new wall separating your patio from the neighbour's! The type of stone or brick used will affect the strength of mortar in which to bed them. Prior to the 1900's most solid walls of traditional construction were bedded in lime putty mortars, often with earth (subsoil) mixed in as well. Rebuilding and repairing with lime mortars offers a number of advantages:
Preparation: Select stone from a local quarry to match the existing. Take a sample along to the quarry if you're not sure. You can usually get two size ranges; 4"-6" and 6" - 9". For the bedding mortar use a volume mix of 7 parts coarse sharp well graded sand ( from fine up to 8mm size) and 2 parts mature lime putty, mixed in advance for at least a week. Lime mortars gain strength from carbonation with carbon dioxode from the air. In damp, frost prone or very exposed situations it may be appropriate to add an extra ingredient to a lime mortar to increase its compressive strength and frost resistance. Traditionally volcanic ash or brick dust were added, these are forms of burnt clay called pozzolans after the Italian town of Pozzuoli where volcanic ash was used by the Romans. We use a calcined clay from Cornwall called metastar at a volume gauge of 10 -25% depending on the degree of exposure. It won't give an overnight set but will slowly begin to add extra compressive strength to the mortar after a couple of weeks. Building: If you're
a novice, position a stone dry first to make sure it looks right and you
got the best face showing. Stagger the vertical joints so there isn't
a vertical joint running continuously up the wall Safety: Limes
are caustic. Always wear eye protection and protective gloves and clothing
and follow the safety instructions on the labels.
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