I have a walkout basement and have parging on my above grade exterior concrete block walls. In a small area I have dug out a several feet. The problem is that the area of the wall that used to be below grade is covered with waterproofing tar. I would like to continue the parging down over the tar to cover it up. Is it possible to put parging over the tar? Will it stick given that the moisture from the mortar mix won't be able to be absorbed into the concrete block since it is now covered by tar? Should I remove the tar? If so, how? Any other suggestions?

Thanks!

 

I need to do this as well. Did you ever get the tar pulled off? I plan on trying to pressure-wash the tar off the block foundation... if that doesn't work I intend on using a grinder with a wire bristle disc to brush it off.

Also, if you did the parging do you have any tips with application or creating the mix? I'm completely new to this and any tips would be helpful.

 

Well I have gotten a few quotes on the job. Some think the tar needs to be grinded off, others think they can paint some glue over it then parge. Costs almost double to grind off the tar first.

Would love a definitive answer too!!

 

Removing the tar (or shall we say, trying to remove it) will be a messy, time-consuming process. I've had a few, very brief experiences using an angle grinder--have a fire extinguisher handy, because the stuff will both melt and burn when hot enough.

Better solution would be to cover it with close-weave stucco or plaster mesh (nailed or screwed to the block wall underneath). Then apply your parging over the mesh, feathered down at the borders to the level of the adjacent parging.

 

I like the sounds of that better than removing the tar. Would chicken wire work? Also this is a solid concrete wall - what would be the easiest method to connect the wire to the wall? The thought of drilling 50 tapcons makes me scared, maybe just hammer some concrete nails in??

 

Unless Canadian chicken wire is a lot stiffer and has smaller openings than the stuff here in the U.S., no, I don't think it would work very well. Too many large open spaces of asphalt showing to get a good bond with the new material you'll be applying. Bite the bullet, and buy some wire mesh specifically made for plaster or stucco. You don't want to do things twice just to save a few bucks.

I'd be inclined to use a nail gun for fastening it. Either renting a decent Hilti or buying a cheap single charge hammer-style (Harbor Freight had one on sale recently for less than $20). And use the large plastic washers with your nails, to get enough "bite" on the mesh.