Slate oil

[MikeG.]

Does anyone know what is in slate oil? Obviously I have a cupboard full of various different oils and would rather use those than go out and buy another, if any of them will do the same job. Can anyone think of a reason why any of the standard woodworking oils wouldn't do the same job?

 

[Cheshirechappie]

Honest answer - don't know.

However, clicking on the 'safety data' link on the attached description gives some chemical data under 'composition'. If we're lucky, someone with better knowledge of organic chemistry than I might be kind enough to translate it into plain English.

https://www.extensive.co.uk/slate-oil-1l.html

 

[MikeG.]

"spirit based wax and resin" makes it sound like Danish oil.

 

[samhay]

No, not chemically like Danish oil. It's closer to a mix of white spirits and wax and I don't think it would behave like a 'drying oil'.
What do you have in the cupboard to play with?

 

[MikeG.]

Any and every finishing oil known to man, lots of paste wax (and access to unlimited amounts of natural bees wax), plenty of varnishes....

Oil and wax are chemically all but identical.

 

[samhay]

The difference between a wax and an oil is the melting point of the constituent chemical(s). Waxes have compounds with melting points > room temperture(ish). Chemically this is due to them having different molecular weights, extent of saturation (double bonds) and/or other differences in molecular structure.
A simple example is something like octane (petrol) and hexadecane, which is effectively two octane molecules joined together and is a solid below 18 degrees. These may be all but identical to you, but quite different to myself (a chemist).

 

[samhay]

Do you want to mix something up to use on slate?

 

[MikeG.]

Yes, probably, if I can achieve something that would do the job. I haven't bought the slate yet, so I may be getting ahead of myself.

 

[samhay]

I haven't come across slate oil, so just did some more reading. Some do mention they also contain resins. Again, this can be quite a broad term, but I wonder if some of them are essentially a thinned varnish that penetrates slate nicely. Danish oil would then seem to be a reasonable choice. Similarly, a coat of BLO and then a paste wax might do the trick, but I'm guessing. Better to wait for someone to chip in with some real world experience.

 

[whiskywill]

When I installed a slate hearth many years ago, it was recommended that I apply a coat or two of boiled linseed oil. I did and it still looks good.

 

[MikeG.]

Cheers, WW. I'm not short of a gallon or two of linseed oil!

 

[Sheffield Tony]

I have a bottle of Stovax slate oil. It is definitely not the same as the above. No wiff of xylene or other VOC's, it is more (very) like liquid paraffin. There is no sign of dried remains around the bottle top so I believe it is a mineral oil. If I picked up the wrong bottle and used Chestnut food grade finishing oil, I doubt there would be any detectable difference. It does soak in and dry out, needs repeated applications to keep it looking dark satin black. Wood ash of course soaks it up and saponifies the oil.

 

[tomatwark]

A worktop supplier I used to deal with, used Johnston's baby oil

 

[MikeG.]

A worktop supplier I used to deal with, used Johnston's baby oil

Really? That is interesting. You can see why it might work well with slate, being pretty thin.

 

[RogerS]

Mike, is this for roofing slates or a hearth ?

 

[MikeG.]

A hearth.

 

[lurker]

A worktop supplier I used to deal with, used Johnston's baby oil

If you read the label, you will see it's just liquid paraffin with added smell.

 

[RogerS]

A hearth.

Now that's very interesting as we've got a slate hearth and I'd never heard of applying slate oil. What's the reason behind it? Am watching with interest.

 

[MikeG.]

It just darkens it down a bit, Roger, and puts a bit of a sheen on it. It will also help prevent ash dust making it grubby quite so quickly.

Are there any down sides to using slate for a hearth?

 

[RogerS]

....
Are there any down sides to using slate for a hearth?

None that I'm aware of. Heavy !