Parging and Tar 2

[PierreS]

I don't know if this is the place or the group I should be asking.
But here goes, my problem is the outer wall of my foundation (blocks)is covered with tar. I would like to apply a finish to it. I don't think the tar would be stable enough to hold the parging.
I have been given a number of solutions given by people,mainly doit yourselfers.
Apply directly on top of the tar and hope for the best.
Remove the tar using solvent(?)and scraping.
Fasten a mesh to the foundation and then apply the parging.
Maybe sandblasting will remove it.

Does anyone have any ideas?

Thanx

Pierre

 

[Ron]

I wouldn't remove the "tar". It is there for waterproofing.

You may apply a layer of lath (mesh), fastening with one fastener for every 2 square feet of area, then apply your portland cement plaster (stucco) in at least two layers...the first layer being the one to embed the lath, the second being a finish layer. Heavily score the first layer to provide a good bond between the first and second layers.

Ideally, a third layer would be applied, but since this is a retro-coat on a foundation block, you can get by with only the second layer. I would suggest a rough texture finish, as this will hide the finishing flaws if you are not a pro at finishing stucco.

 

How do you properly mix parging? What is the ratio? Can I tar over parging? Can I place Styrofoam SM insulation directly on this tar or does it have to be held on by some mechanical means? If I want to properly parge a stone wall, after repointing (below grade) do I hammer into it a wire mesh and then put two coats of parging over it then tar then sytrofoam?