I have several holes in concrete block walls in varying sizes ranges from the size of a fist to the size of a football that I want to patch and repair. They were broken open for plumbing and electrical installations.

Problem is these are 8" wide concrete blocks that are hollow, and anything you put inside these holes drops down into the rows below. What is the best way to patch them without using too much concrete?

I heard using old newspaper to stuff into the holes until the last 2 inches or so then patch with new concrete to flush.

I also heard of using chicken wire meshes.

Or use expansion foam to fill the void, then patch with concrete.

Is there a consensus on what is the best way?

Also, what is a good concrete to use for patches like this? Mortar mix? Topping Mix? Sand Mix?

 

IS this inside or outside?

 

These are exterior concrete block walls but the holes are facing the interior, they will eventually be covered with furring, insulation and sheetrock or Durock.

I know I don't have to patch it but I'd like to.

 

Big holes you will need some kind of backing. Many cases people will use newspaper or fiberglass but I would be concerned with mold. I would think you could use spray foam in a can. Use big gap filler, but go easy since it can get away from you.
If you want then you can follow up with some mortar mix of sand mix. Heck you might even be able you use some Quickcrete if your not looking for pretty.

 

What I found worked well is:

1. For the bridging material, just go to your local dump and liberate some cushions from an old sofa. Pull the foam rubber out of the seat cushions and cut it oversize to fit into the cavities.

2. When I did this (many times) I'd paint everything I wanted the cement mix to stick to with diluted white wood glue. Dilute the glue with enough water to make it into a paintable consistancy and allow it to dry on the concrete block. The moisture from the cement mix will re-activate the glue and cause the cement mix to bond well to the concrete blocks. (Concrete bonding agent works the same way, only concrete bonding agent will provide a "window of time" before a chemical change occurs in the glue so that it's unaffected by moisture. You have to get the new cement slurry in place during that time for the bonding agent to be reactivated by the moisture, or else you'll have to reapply new concrete bonding agent. White wood glue will always re-emulsify in water no matter how long it's been dry. If moisture penetration into this wall is a problem, use concrete bonding agent (available from most suppliers of construction materials) instead of white wood glue.)

3. In my case I was filling in the holes left behind when removing "inset" soap dishes from concrete block walls. I'd use Tapcon screws to fasten a piece of plywood over the hole so that only about 3/4 inch at the top of the hole was exposed.

4. Mix portland cement, hydrated lime and PEARLITE (available at any garden center) to make a bulky lightweight cement mix. Scoop that stuff onto a flat plastering trowel, rest the trowel edge on the top edge of the plywood and scoop the pearlite/cement mix into the opening with a square pointing trowel (for square mortar joints).



If you opt to use a heavier cement mix, like brick mortar, then best to just scoop in enough to bridge the bottom of the hole first, and then fill it up once the bridge has cured.

5. If you're gonna buy some portland cement and hydrated lime, you can also make brick mortar to patch smaller holes. The mixing ratio is:

1 part portland cement to 1 to 2 parts hydrated lime
whatever volume that gives you, mix with 2 1/2 times that volume of sand.
Mix the result with water.

(The more lime you use, the longer the brick mortar will remain "plastic" or workable. If your brick mortar starts to turn "crumbly" on you, it's only because the cement in it is starting to gel. Avoid the temptation to mix in more water. Simply mix the crumbly mortar aggressively and it should return to a workable state.)

Hope this helps.