Tar DPC in Stone Wall?

[Rawler]

Hello!

I have just come across what I think is a tar based Damp Proof Course.

I started off thinking I would improve the pointing around the base of my wall and then decided to take out the cement join where the stone flags meet the wall as I thought that may not be helping.

I have come across a tar line, hard to tell how far into the wall it penetrates, although I have also found it on the inside of the same wall. Perhaps it's just added to the face of each surface?

Not sure whether I should leave it exposed, fill with Gravel or lime mortar it up?

Anyone come across something similar? It's not creating a significant issue. There are some issues on the inside of the same area of the wall, but I think this is due to replacement tiles being laid on cement.

 

[Rawler]

This is the inside of the same wall. The quarry tiles laid square (as opposed to diagonal) have been laid as some retrofit on cement. The stone at the base of the wall was pretty damp and is drying now. There's been some strange work done below the revised (?) window sill hence the messy brickwork (laid in cement).

I think the original quarry tiles are laid on limeash type screed, it's firm, grey and solid, not soft like soil.

The wall has a cavity which is filled with soil. I think when they originally put gas in and modern sewerage they damaged the wall and this is the remnants of that.

I am thinking to remove a stone and clear the soil out of the cavity and then fill it back up (lime mortar and stone).

Any thoughts or observations? Again found tar on the inside surface of the stone wall below the quarry tile level. There was constant signs of damp along the base of this wall.

Appreciate any insight.

Many thanks

 

[Cubist]

Yes I'ver come across a similar DPC myself, or rather I did while in the company of my father. They can work really well provided they were thoroughly applied and have not been disturbed but they can be repaired if need be. The thing to remember is that the tar would have originally been 'poured' over the top surface of the stone/brick work whilst still hot from a pitch-boiler. The succeeding course of stone/brick would have been laid almost immediately over the freshly poured tar to create a good close fitting joint and to spread any excess tar. Typically it would not have been 'painted' on to the surface unless the guy handling the ladle was careless. It can be repaired, if damaged, using the black pitch like adhesive used to fix felt to wooden roofs. Can be a messy job though.

 

[Rawler]

Thank you Cubist. That's a helpful insight.

Any thoughts as to what I should do with the small channel between the flags and the wall? NHL mortar or Gravel seems to be my options?

 

[Cubist]

Assuming the flags are laid over earth and maybe a mortar bed I wouldn't worry to much about the channel by the wall - provided there is no easy route for pooling water to penetrate the structure. To be safe a fillet of lime mortar would help to prevent that while re-pointing the wall and to reduce the possibility of weeds taking root in the future.

 

[Rawler]

Many thanks! Sounds sensible. Will do that.