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I have a sub grade vertical stack of perforated brick (foundation) which I need to coat in a thick layer of mortar or concrete in order to fill gaps, creating a flat surface for subsequent painting/hydro isolation.

Besides cleaning the brick, what else should I do to prepare them as a substrate?

  • The brick should be plenty rough for the new mortar to get a good grip on it. – FreeMan Jul 6 at 13:07
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Make sure that they are neither bone-dry nor dripping wet, either of which interferes with getting a proper bond. Damp is good. Recall (or learn) that mortar and concrete do not, as commonly misnomered, "dry" to set, they hydrate to cure, in a chemical reaction where crystals grow throughout the mass, and that needs water to work. A common problem with casual brickwork is excessively dry bricks that suck the water out of the mortar and prevent it from curing properly.

There is also a matter of technique to get mortar to stick to a vertical surface - it wants to be thrown or slapped on and spread out, not applied in a tentative manner.

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