Lath Plastering Introduction
Lath and plaster is a building technique used mainly for interior walls in period buildings. A lath is a narrow strip of wood approximately 2 inches wide which is nailed horizontally to each stud in the frame. Each lath is spaced approximately 1/4 ( Thickness of the average little finger ) away from the next leaving enough space for the mortar to push through and hook over the lath to form a key laths.
Preparation
The laths must be free from dirt, grease and vegetation. These elements should be removed before damaged laths are repaired. Spray a clean cold water mist on to the laths prior to applying the scratch coat.
First Coat
Using A ratio of 1 part Lime to 2 1/2 - 3 parts sharp washed sand with evenly distributed hair throughout the mortar and working to a layer of 10mm thick, push the plaster into and across the pre wet laths at a 45degree angle to the lathes.
The plaster should be left until set hard but tended to protect from heat and draughts.
Second Coat
The second coat also known as the intermediate or float coat will be applied similar to the first coat only without any hair being added to the mortar. You must ensure you wet down the first coat with a fine mist before spreading a 7mm coat , before scratching up and leaving in preparation of the finish coat.
Finish Coat
For the final top coat a fine mix of 1 lime putty to 2 parts well graded super fine sand. Remembering to wet down the surface before application with a fine mist spray. Allow time for the water to absorb into the plaster then apply a coat of approximately 5mm, then rule off and leave for a couple of hours. When ready rub up the finish coat using a plastic or wooden trowel to bring back the fat until the required finish has been reached in the case of any light crazing this can be rubbed up and trowelled out.
Health and Safety
Lime mortar by its nature of application carries a risk
factor, and therefore personnel should wear protective equipment,
particular attention to be given to eye and skin protection. Eye
wash should always be on hand. Gloves should be worn when working
with any mortars or plasters.
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