Frequently asked questions

• When can I decorate my walls after they've been plastered?
• How do I decorate new plaster?
• Is there any special paint that I should use on new plaster?
• Can you make-good distemper-coated ceilings?
• Why use lime in old buildings?
• What is wrong with cement mortar?
• What is haired lime mortar?
• What is lime plaster?
• What is Limewash?
• What is lath?
• What are cob blocks and cob bricks?
• What is render?
• What is plaster?
• Can you tile directly onto floor boards?
• What is the best way to seal around showers and baths?

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  When can I decorate my walls after they've been plastered?

  Recently plastered walls all tend to dry out at different rates depending on thickness of undercoat, time of year and masonary background. Typically, skimmed plasterboard can be decorated after two weeks (see how to decorate new plaster). Walls which have had undercoat plaster applied should not be decorated with standard emulsion or wallcoverings for at least six months, however a watered-down, breathable emulsion or Dulux Super-Matt may be used earlier.

  How do I decorate new plaster?

  New plaster and new artex are very porous indeed. If you apply any kind of ordinary paint directly onto either of these surfaces, moisture will immediately be sucked out of that paint. In simple terms this leaves the paint going dry on the surface only and because the moisture has been sucked out so quickly, it has no "roots" or "key". The surface paint may soon start to blister and flake off.

  It is therefore necessary to "prime" or "seal" the surface first. Sealing means applying a coating which is diluted enough to enter the pours of the material with the emulsion or liquid with which its mixed.

  To seal a newly plastered or artexed surface on which you intend to put water based paint, e.g. matt emulsion, mix some of that emulsion paint with water at a ratio of 4 parts paint to 1 part water and stir thoroughly. Apply this to the surface. If the plaster does not seem to be sucking up the liquid quickly, more water can be added to a maximum of 1 part water to 1 part paint.

  Its rarely necessary to apply two coats of sealer, but it will not harm the surface either. When the surface is sealed and dry, you can continue to paint as normal.

  As an alternative you can buy special, breathable emulsion for new plaster, i.e. Dulux Super-Matt. It's a more expensive way of doing it,but it's straight-forward to apply direct from the tin.
  
  

  Is there any special paint that I should use on new plaster?

  Dulux Super-Matt or a watered-down, water-based paint (e.g. matt emulsion).

  Can you make-good distemper-coated ceilings?

  Distemper is a traditional finish made from powdered chalk mixed with gelatine and water and is present in many older houses. It is not possible to decorate over distemper, depending on it's thickness it either needs to be removed or sealed, prior to being re-plastered or painted as required.
  
  

  Why use lime in old buildings?

  Before this century building techniques and materials were very different from those employed today. Traditional properties need to "breathe" to allow moisture inherent in a solid wall construction without a damp proof course to evaporate from the external stonework or render. Many old buildings are constructed from materials such as brick, cob and stone which are relatively porous and often of lower strength. Lime mortars were normally used for bedding and plastering. Lime mortar is a relatively softer mortar and therefore it is able to withstand a certain amount of movement (without cracking) that comes with settlement and seasonal changes in ground conditions. Lime mortar is porous and allows moisture to evaporate, helping to keep a building free of damp.
  
  

  What is wrong with cement mortar?

  Apart from the adverse effect it has on the environment in general, cement mortar is usually hard, brittle and less porous than lime mortar. It often contains additives to make it sometimes completely waterproof and is damaging to traditional buildings for several reasons. Cement mortar is often harder than old bricks, cob or some types of stone, therefore when movement occurs it may damage these softer traditional construction materials. Hard cement mortar can trap moisture behind it causing damage to the structure and encourages ground water to rise up a solid wall by capillary action. Trapped water in the wall can cause poor insulation, decay and crumbling. In severe cases a cob wall can fail. The brick, cob or stone can also be subject to frost damage if moisture levels are to high.
  
  

  What is haired lime mortar?

  Animal hair, usually horse, cow or goat, is added to the backing coats of lime mortar used for external rendering or internal plastering onto stone, cob, brick or timber lath. Adding hair gives extra strength and minimises shrinking and cracking. It allows thicker coats to be applied to uneven walls and holds the plaster keys in place when plastering onto lath.
  
  

  What is lime plaster?

  This is a finishing plaster used as a final skim internally.
  
  

  What is Limewash?

  Limewash is a traditional, breathable paint made from lime putty which is thinned with water. Our limewash is approximately 1 part mature lime putty to 1 part water. Other suppliers make much more watery limewash. Limewashes are coloured with pigments and can be used internally or externally on lime plaster, lime render, stone or brick. It works best on porous surfaces and hardens as it absorbs carbon dioxide from the atmosphere to form calcite crystals, giving it its unique appearance. Typically four coats are needed on new external render and three coats on new lime plaster.
  
  

  What is lath?

  These are thin strips of wood used as a key for the lime plaster. Chestnut, oak and larch are popular choices of timber for the lath. Riven lath is hand split along the grain using traditional tools and provides extra key on the surface of the lath so it is best for repairing lathed ceilings. Sawn lath is straighter with a less textured surface than riven is best for repairing lathed walls. In traditional buildings the lath would be lime plastered and limewashed. Lath can deteriorate over the years due to insect infestation or rot, especially if modern less breathable plasters or paints have been applied.
  
  

  What are cob blocks and cob bricks?

  These are made from a clay-based sub-soil with straw. The cob blocks are about the same size as a concrete block, the cob bricks are a little smaller than a modern brick. They are used for repairing holes and damage to cob walls as they are already dried and hence will not shrink in use. They are bedded in place with a 4/1 lime mortar or sieved sub-soil.
  
  

  What is render?

  A coating of lime (or cement) mortar, usually referring to the outside of a structure.
  
  

  What is plaster?

  A coating of lime (or cement or gypsum) mortar, usually referring to the inside of a structure.
  
  

  Can you tile directly onto floor boards?

  Floor boards should be secured as best as possible. Hard board covering fitted if necessary. Flexible adhesive and grout should be used.
  
  

  What is the best way to seal around showers and baths?

  For the best seal use a telescopic action strip, such as Teleseal. This provides a strong, flexible seal that moves as weight is placed in the bath or shower, which can be fitted before or after tiling.