Plaster on old brick and new joints.

[Javadvetjadå]

I am going to fill in a hole I have made in the chimney and wonder what I need to consider when building up the wall of the hole and what I need to consider when plastering the old brick wall and the newly built hole.

1. Do I need to treat the old stones/joints with anything before plastering?
2. Do I need to treat the old stones with anything before building?
3. Is it possible to plaster directly on the newly built joints in the hole that are built with old stones?

Thinking about whether it should be watered or primed or something like that.

 

[Javadvetjadå]

Came up with another question while I have uploaded this picture. Do the bricks need to be cleaned from the white layer before new plastering/masonry? I heard something about some acid wash.

 

[MaxPax]

1. Yes, pre-wet to bind dust and prevent too rapid drying of the new masonry. A large element brush is your friend.
2. see 1
3. applying a thin layer as a primer is okay, but it is advisable to wait until this has cured before finishing the plastering. This is to prevent cracks. Also, water during curing, both the thin primer layer and after finishing the plastering, for the same reason. Brick absorbs water from the mortar very quickly.

The stones do not need to be cleaned of the white layer first.

 

[Javadvetjadå]

1. Yes, pre-watering to bind dust and prevent too fast drying of the new masonry. A large element brush is your friend.
2. see 1
3. applying a thin layer as priming is okay, but it's advisable to wait until it has cured before finishing the plastering. This is to prevent cracks. Also water during the curing, both the thin layer of priming and after completing plastering, for the same reasons. Bricks absorb water from the mortar very quickly.

The stones do not need to be cleaned from the white layer first.

Thanks for the clear advice!

 

[roland53]

To get better adhesion, you can mix a thin slurry of cement, some sand, and water, and sprinkle it on the existing surface. Let it dry. You will then have a base that the plaster adheres better to.