How to remove bitumen of granite exterior wall?

[Suusmulligan]

Hi, I wonder if anyone has some advice on the topic of removing bitumen of the gable end of my stone cottage. It was built in 1780's using granite and soft mortar. It has had various abuse thrown at it over the past centuries which I am now hoping to reverse. The gable wall is very damp on the inside. I have removed all 5 layers of wallpaper including polystyrene layers! I am hoping the wall will be able to gently start to dry out naturally but there is still the sticky issue of bitumen on the wall. I would be grateful for any advise of how to deal with this.

 

[MatthewC]

Hi there, welcome to the forum

It's a bit quiet on here right now, but I'm sure someone will have some experience of that problem. This recent thread http://www.periodproperty.co.uk/forum/viewtopic.php?f=1&t=15334 (about moving the same sort of stuff from a floor) might help you.

Photos are always welcome!

Matthew

 

[Lime]

I'd use a sharp scrapper to get the worst off then some paraffin on a rag to rub and wipe it off the granite.
Change the rag regularly. Avoid drips.
Try not to wipe any pointing/mortar with the cloth.

 

[Roger H]

Hi. I'm guessing the issue is bitumen on the outside of the exterior wall? Normally you might be wary of 'abrasive' cleaning (i.e. grit blasting or similar) but with granite it might be an option. It will rip out the mortar but the granite should be unscathed.

 

[Suusmulligan]

Thank you, actually the current pointing is done in rock hard cement which I am planning to replace with lime based pointing. So I guess if the sandblasting removes the cement pointing that would be a happy side effect?
I will take a picture next time I am there.

 

[a twig]

Heat and scrape has worked well for me in the past...

 

[Toby Newell]

Hi

Seeing as you are removing the cement mortar (which normally is a criminal sin but next to granite not so bad as granite is so hard) you can do anything!

Scraping will leave marks in the granite which will need to be removed later by fine soda blasting, so you may as well apply that technique first.

You will need a strong solvent like xylene or a methyl chloride stripper to remove bitumen. Neither of these will damage your granite.

A hot alkaline solution like sodium or potassium hydroxide will work too but I am unsure whether this may attack the rock and the run off will be more damaging to the local flora and fauna.

Maybe a hot detergent pressure washer like they use on large commercial vehicles? Whilst it would work on the flats I am not sure whether using anything high pressure would be a sensible idea on old stonework because of the risk of forcing water through any gaps in the mortar, but I suspect it might work well in removing bitumen.

I (unfortunately) have plenty of experience of removing bitumen so know the substance well but (unfortunately) my experience only extends to interior woodwork.

Best of luck.