Standard approach to getting stains out of porous masonry involves poulticing with a solvent (water is a solvent) which will dissolve the stain.

In the case of oil, you will almost certainly need to use a hydrocarbon based solvent to mobilise the oil.

I would be looking at a nice toxic degreaser in the first instance to get the surface material off.  This will be real difficult to dispose of, because it essentially emulsifies the oil to permit water to carry it away.

After 1-2 applications of the degreaser, I would then want to try and mobilise the oil in a solvent, using a poultice to pull it out of the wall. 

Standard poulticing practice is to mix up a poultice of attapulgite clay or whiting or even tissue/blotting/news paper with the solvent, then thoroughly wet the wall with the solvent, apply the paste / paper mixture in a thickness of at least 1/4 inch, and cover with plastic sheet to allow it to dry out slowly.  After drying, then remove and repeat.  This can require multiple applications (5, 10, 15 ..????) to mobilise very heavy and obstinate stains.

There are proprietary poultice products on the market, usually marketed by some of the stone cleaning product suppliers.  ProSoCo used to do one, and there are half a dozen other US based companies who might be in the market place.

Since bricks are clay, I would suspect that you will never remove all of the oil stains, especially given the timeframe.  Some of the oils will probably have bound into the clay matrix.

Hope this helps

david



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david west
Arup Facade Engineering
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