Lime Plastering on to Lath in 3 easy steps!
By Abode Renovation, Mar 12 2015 12:21PM
As with all lime putty based materials the best outcome requires patience and careful control of drying and suction, the reward being a good looking and long lasting plaster.
Before starting any work, always check that the building is not listed, if it is contact the local authority conservation officer to discuss the project.
Any existing plaster and paint should be removed. If there are sound lime mortars these should ideally be left to help preserve the buildings history and it clearly reduces material costs. Care must be taken to ensure that the structure isn't damaged. Look out for very thick patches of plaster that are effectively load bearing. It may be necessary to plaster on top rather than risk rebuilding an area.
It is very important to control suction from the background material (substrate) by damping with water before applying each coat of plaster, especially onto cob or porous brick. Although control of suction is important, so is surface tension so any damping down must be allowed to soak in and not be sitting on the surface when the plaster is applied.
Generally, lime putty mortars and plasters benefit from being pre-mixed for a minimum of a couple of weeks and then "knocked up" again prior to use to plasticise them - this reduces shrinkage in the plaster. The pre-mixed and ready to use materials can be purchased from us.
Example Specification on to lath walls
Dampen the lath before application.
1. Apply one coat of haired lime putty mortar, 3/1 haired lime putty mortar and press firmly onto the laths. This is known as a scratch coat. Make sure to press firmly so that the hair will act as a bonding agent and the mortar putty will grip firmly to the contours of the lath. Leave to cure for at least 24 hours.
2. Spray dampen the first coat of plaster before applying a second coat of unhaired 3/1 putty mortar. This is known as a float coat. We recommend a second coat of unhaired putty mortar as there will be no chance of hair coming through the top coat. Leave to cure for at least 24 hours.
3. Spray dampen the plaster before you apply a top coat of our lime-rich, 3/2 lime putty plaster, based on a very fine sand and lime putty in either one or two applications. For the very smoothest of textures, the second coat should be a 1mm skim of our lime putty plaster.
Our 3/2 fine lime plaster is ideal for a thin skim over a wide variety of backgrounds such as plasterboard, blocks and mixtures of old and new plaster, old paint etc. For plasterboard it will be necessary to apply a special bonding coat DG27. For bare plasterboard, it is always necessary to scrim the joints as is usual practice, normally this would be applied with a very thin coat of gypsum although lime wall finish smooth could be used. Failure to carry this out may result in cracking at the joints. Our lime plaster 3/2 can then be applied in one or two very thin coats or Regency plaster for the second coat for the very finest of finishes.
for an Example Specification per square metre on to a rough undulating surface
Scratch coat 3/1 haired lime putty mortar, 30kg per m2 (15mm)
Float coat 3/1 unhaired lime putty mortar, 20kg per m2 (10mm)
Two top coats of 3/2 lime putty plaster, totalling 6kg per m2 (3mm)
Limes are caustic. Always wear eye protection and protective gloves and clothing and follow the safety instructions on the labels.
Our advice and information are given in good faith. It's important that users satisfy themselves that they've chosen an appropriate product and have a suitably skilled workforce.
Why not come along to one of our training days and learn practical new skills in Lime plastering, repointing, brickwork and repair and maintenance of old buildings.
Call Eve on 01795 530503 or click here to find out more.