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Background: I recently replaced my home heating system (an oil burning furnace) for a modern heat pump (air-water). There is a room in our basement (2.9m x 3.5m, or roughly 10ft x 13ft) where the 10'000 liter (~2500 gallons) tank used to be. The room was completely sealed off from the basement, save for a small window-sized opening through which you could enter to service the tank, should that be necessary.

I had a contractor cut out a door opening, and then a specialized firm came to clean the tank, cut it into smaller pieces, and recycle the steel chunks. I have now and empty room that reeks of oil, which I want to turn into a home gym. It's been some 4 weeks since we cut a door opening, and opened up the grilled vent to the outside, and although I've let enough air circulate, it still reeks as much as it did on the first day.

I assumed some oil may have leaked through the years onto the floor, which had a sort of epoxy coating, stained brown in some places. So I carefully removed it all. It took a lot of effort with a putty knife and paint scrapers. But even with a completely clean floor, it still smells. The lower half of the walls, which have the same paint/epoxy coating, have brown stains all over, which I imagine may have significant deposits of oil, perpetuating the lingering smell in the room. I read that spraying concentrated hydrogen peroxide helps eliminate all smells, so I carefully sprayed 12% hp on the walls (wearing a full body suit, goggles and a breating mask), which didn't have any significant effect overnight.

The question: is there any reasonable way (that doesn't involve overly expensive or extremely time-consuming efforts) to get rid of the smell, before I apply the decorative textured plaster on the walls? Would a controlled burn (e.g. with a small gas torch, with proper ventilation) help at all? Do you think applying plaster over the existing walls wouldn't do enough to cover the oil smell?

These pictures show the level of stains on the walls. Here you can see what I believe was pretty much the original color of the coating (first pic) vs the back wall. Wall coating, barely stained at all

Remarkable dark spots on the coating, probably from oil spray?

Edit / Update: on Friday I primed and then used self-levelling compound (about 750lb / 350kg) to raise and level the floor, which had over 1 ¼ / 30mm height difference. The smell is completely gone. So as several of you pointed out, the oil had somehow leaked and penetrated the floor, which is now completely covered by a non porous concrete layer. Thank you all for your kind participation !!!

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    That split oil could have penetrated very deep into the wall structure... I lived in a place which had an internal tank and fitted a small computer ventialtion fan from a power supply (4") which reduced the smell inside ie forced ventilation to outside. – Solar Mike Mar 20 at 10:48
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    Note that you'll want some good ventilation system anyway to avoid moisture problems, unless the new layout is wide open to the rest of the basement and your basement is dry – Carl Witthoft Mar 20 at 14:53
  • Thank you, @CarlWitthoft. The basement is quite dry, no humidity issues there. I'm also cutting a window opening in 3 weeks (should the COVID situation permit it), and installing a proper window. – FrK Mar 20 at 15:21
  • The part that smells isn't the part that burns. I would be careful playing "amateur hour" on this one: cleaning is fine, but applying any sort of a coating could foreclose a more competent cleanup in the future. I wouldn't do that until I'd had a few professionals through. – Harper - Reinstate Monica Mar 20 at 18:48
  • One approach might be to put an ozone generator in the room; but that's probably better done by a remediation company with experience and the right sort of industrial-scale ozone generator and experience choosing if that's the BEST option in your case than slapped on haphazardly if you can even find one to rent/buy that's not so low output as to do no good. – Ecnerwal Mar 21 at 2:03
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I wouldn't do a "controlled burn". If the oil penetrated deep into the wall structure. You could create more problems than you have already.

If you want to plaster the walls and protect the new plaster from the oil on the walls, for belt and braces I would use an oil based paint and cover the affected areas in the paint. If you are not sure how much of the wall is affected, paint the whole wall.

Don't immediately plaster over the dry paint though as the paint here needs additional time to set.

Once the paint has had enough additional time to set, you can jump right in and start applying the priming PVA which will help the plaster adhere firmly to the wall.

It is also advised that you select the correct plaster undercoat for painted walls, for example, see Table 1a (Plaster selection - PDF page 7) in https://www.british-gypsum.com/~/media/Files/British-Gypsum/White-Book/White-Book-C07-S02-Linings-Plaster-systems.pdf?la=en

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    Might be a good idea to prime with "Odor Blocking Primer" before painting. – Carl Witthoft Mar 20 at 14:50
  • Will paint adhere to an oil saturated surface? – Ack Mar 20 at 16:17
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    @Ack - Oil and water doesn't mix as everyone knows so water-based paints won't adhere to a wall which has any oily surface, but oil-based paint should adhere. A good primer is advised though. There is such a thing as "oil block primer". This seals in grease and oil and makes a good base for painting – Chris Rogers Mar 20 at 22:34
  • @ChrisRogers FWIW, if you completely de-aerate water (no dissolved air), it will mix with oil just fine. Of course that's only achievable under laboratory conditions. – Carl Witthoft Mar 23 at 18:48
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This is no time for "amateur hour"

The problem with drunk-stumbling around this job is that many actions are irreversible and will block more effective efforts at cleanup. That includes:

  • Application of any sort of sealer or barrier coating. Most of the time when people try this, it does little to improve the problem. However, it will "seal it" against better cleaning products, and force removal of that coating to make any more progress. That's practically a trope around here; we get lots of people who tried to seal in a smell with paint, and accomplished nothing, and now the paint is in the way of proper treatment.
  • Heat, as in the odd notion of "burning out the smell", will chemically alter the surface - concrete, in particular, does not play well with heat. This too could interfere with proper removal. What's more, heating oil is a mix of several compounds, and the part that smells isn't the part that burns.

Using ordinary cleaning supplies, such as various detergents and soaps, is safe, and can be done without risk of setting yourself back. Remember, you must physically remove the offensive material. Sulfur is elemental, for instance, you can't turn it into something less smelly without a nuclear reactor or 7 years at Hogwarts. So I would be careful what you do with the rinsate (soap, water and the crud that came up). If you simply wash it out into the yard, you'll just move the smell there. I would suck it up in a Shop-Vac, and and dispose of that properly.

Honestly, rather than throwing stuff at the wall to see what sticks, it may be best to bring in professionals.

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  • I guess I should have tried detergent and water before, it never ocurred to me. The walls do NOT feel oily or tacky to the touch. My guess is that the difference in color is oil being ejected from the tank walls while the crew cut the tank with acetylene, and being burnt on the walls. See, the "offending" wall is opposite the entrance to the room, so my guess is that the crew first empited the tank and "cleaned" it a bit, then cut the top off, and lastly proceeded to "enter" the tank and cut it from the inside-out. That's how oil on the inner surface of the tank got on the walls. – FrK Mar 21 at 12:01
  • Oh, well that staining may not be oil at all, it may be weld spatter. But if they were torching from the inside of the tank, they must have been very confident of its cleanliness. I rather suspect your oil smell is coming from under the tank, areas that have been exposed to oil for 20+++ years, and are now uncovered. Did this room smell like lilacs before? Or did it smell like oil? – Harper - Reinstate Monica Mar 21 at 18:00
  • Because of legislation, the tank room must be completely water-proof, therefore there was no door or window into it, except for a small 3ftx3ft opening, from the basement. I only opened it a few times, and I'd say it's always smelled a bit. I think it's worse now. By now, I removed the entire floor coating, and applied a primer. Next week I'll level the floor with self-levelling compound. That will completely seal any smell coming off the floor. But I still think there must be something coming off the walls. I'll update next week. – FrK Mar 21 at 18:39
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Since you were able to remove the sealant with a putty knife I would believe it failed and allowed some of the fuel oil to penetrate into the concrete. I use hydrogen peroxide for mold and mildew and as a sanitizer but have not heard of this use.

when cleaning concrete I use muriatic acid and water, the muriatic acid etched the surface of the concrete , if the muriatic did not take the Oder out the surface would be prepped for a 2 part epoxy paint. I have good luck sealing basement floors for moisture reasons and have used in garages this may be your only choice if the oil has soaked into the concrete. After cleaning an oil spotted floor with muriatic rinsing and allowing to dry the 2 part epoxy pains did cure and held up fine in a garage. If you want a finished wall I would use sheetrock over plaster, it can be glued directly to a dry concrete surface with construction adhesive, I usually frame it in so I can run electrical but have found many places where it was glued in place.

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    I missed to mention that I plan to pour self-levelling screen on the floor, and given the sketchy state of the floor coating, it still made sense to remove it all. I'm quite confident the screed will completely block any odour coming off the floor. – FrK Mar 20 at 15:20
  • I would still acid etch, it or effective at preparing garage floors for additional coatings if you are sire your self leveling compound will seal the floor that is a start what about the walls where the contamination may be in the surface. – Ed Beal Mar 21 at 23:17
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The smell comes from the volatile compounds in the oil getting into the air (the smeller) and making it to the nose (the smellee). Addressing this in some way will address the issue and these solutions fall into two main categories noted below. You might want to choose a combination from these two groups as your solution

  1. Fool or protect the nose (stuff still in the air, we just don't want to be aware of them)
  2. Reduce or remove the volatile compounds from the air (remove the stuff in the air)

Fooling the nose includes such things air fresheners. Protecting the nose could include things like a mask or nose plugs. Upsides include it's usually the easiest and fast solution. Downsides include it usually is short term and requires somewhat continuous effort over time.

Removing and reducing the compounds in the air can then be broken into two subgroups

  1. not removing the source (stop or reduce the amount of compounds in the air)
  2. removing the source (compounds no longer exist)

If the source of the compounds is not removed then the task is to reduce the amount of the compounds that are in the air or reduce the amount that get into the air. Once the compounds are in the air then can be reduced by ventilation or filtration. Lowering the amount of compounds that make it into the air from the source requires a barrier such as plastic, paint, or other coating or sealer. These options have various upsides and downsides.

Ideally, the source of the compounds is removed. Upside are that it is a permanent solution that requires no future effort. Downsides include that it is often the most difficult and expensive solution.

The answers already provided here to your question all involve a barrier of some sort and leaving (not removing) the source because it is too difficult to get at it directly.

My answer is to NOT block the compounds from entering the air but rather use time a tool. Use time instead of effort and money. When the compounds get into the air they are also being removed from the source. Literally, the source will eventually be gone. With the bonus that over this time the amount of compounds in the air will be reducing and therefore will the smell will be less and less of an issue during the process (things will always be improving). In the meantime, use a combination of ventilation and air fresheners. Protip: using a fan to blow air over the surface of the source will significantly speed up the process.

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    Not a good idea, seeing as they not only smell bad but are rather toxic when inhaled. – Carl Witthoft Mar 20 at 17:22
  • Most of the smell is going to be sulfur. It's so overwhelming that I doubt you'd smell much else. Maybe a summer would help, but I would expect volatiles to have boiled off by now. – Harper - Reinstate Monica Mar 20 at 19:18
  • It takes time and how long it takes depends on several things such as how much oil was leaked and how well you ventilate the room. If the room isn't ventilated the compounds have no place to go... Most of the above is information to help you choose a plan of attack + my suggestion of how to approach it. It is definitely not for everyone. Also, any suggestion of how long is pure conjecture at this point – Ack Mar 20 at 19:35

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