5 practical tips for mortaring walls

September 5, 2015

Making repairs to mortared walls usually means filling and patching. Here are five practical tips to keep in mind when mortaring.

  1. About 15 minutes after you've applied the top coat — just before it begins to set — draw a straight-edged piece of wood across the patch from bottom to top. If any hollows show after levelling off, fill them quickly and level again. As the mortar starts to set, smooth the surface gently with a damp sponge or a damp wooden trowel.
  2. In cold climates, the bond between mortar and the wall can fail when moisture seeps between the two and freezes. To map the damage, tap the wall with the handle of a screwdriver. Wherever the sound comes out hollow you'll need to strip and replace the mortar.
  3. New mortar will bond better if the underlying surface has a key. Before you begin, coat the wall with a mixture made up of one part cement to one part coarse sand mixed into PVA sealer, diluted with two parts water. To apply the mixture stab it onto the masonry with a stiff brush. When it dries, the surface of the wall should feel like coarse sandpaper.
  4. For a good mortar, mix one part cement and one part hydrated lime then blend in four parts plastering sand (or builders' sand). Dilute with water to get the right consistency. If you need an alternative for the hydrate lime, use a liquid plasticiser; add it according to the manufacturer's directions.
  5. Don't let the weather ruin your mortar job. If you're mortaring in hot weather, try using a slow dry medium or keep a spray bottle full of water on hand to regularly wet what you've mortared. If there's a risk of freezing, add a frost-proofing additive to the mix. The mortar has to dry slowly to be strong. In hot weather, regularly mist the patch with water for a couple of days after application.

Keep these five practical tips in mind and you'll be ready to patch and to mortar your walls like a pro.

5 practical tips for mortaring walls
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