Replies

1. 
   Zorrohood | Jul 09, 2009 08:39pm | #1

   Boiled will polymerize a lot faster, I.E. DRY.

   Raw stays wetter for quite awhile.

   I'd not use either on house siding, it gets black after a time.

1. 
   Piffin | Jul 10, 2009 01:48pm | #6

   The house I grew up in had one exterior feature wall of knotty pine. Dad loved the look there.But I had the job of sanding and scraping and re-applying his boiled linseed oil every year or two. 

    

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2. 
   Danno | Jul 10, 2009 12:13am | #2

   So called "boiled" linseed oil (BLO) is raw linseed oil with metallic dryers added to help it cure and harden (somewhat). The oil oxidizes as it ages and that hardens it--when they used to make linoleum (linseed oil and wood flour), I recall they bubled air through the linseed oil and then hung the sheets in a tower and blew air through to help harden them. Not for a long time has "boiled" linseed oil actually been boiled.

   I would think that saw linseed oil would not be as good to use for your prupose than "boiled" and as another poster said, both can darken and if I recall correctly, both can mold and mildew. Neither are very good protection in exterior use.

1. 
   DaveRicheson | Jul 10, 2009 01:20pm | #4

    both can mold and mildew. Neither are very good protection in exterior use.

   Huh?

   Linseed oil use to be used  in most "oil" based exterior paints years ago. The oxidation process is the actual drying or curring of the paint film. To speed the cure along metal dryers in small amounts were added. They included lead, manganse, and colbalt. Lead at less than 0.01% solids would  cause a quick surface  cure , and the other two were deep film cureing agents. Once the piant film curred it had very good durabilty and weathering properties as well as mold and rot resistance. For extemely damp location a fungicide, like mercury, might be added but otherwise the cured film would not support mold growth.

   Liquid linseed oil, be it raw or boiled will spoil and gow some really nasty looking and smelling stuf, but a cured (oxidized) film of either  will not.

1. 
   Piffin | Jul 10, 2009 01:45pm | #5

   Oxidation is the process of combining with available oxygen to change properties. How fast and by what means that happens changes the outcome.For instance take a pile of sawdust and wood shavings. you can oxidize it by fire and end up with the ash on the ground and the Carbon dioxide in the airOr you can let bacteria and other micro-organisms take care of oxidizing it over a longer period of time and end up with the same result more or less, except that the ash is gradually combined with the parasitic organisms as it is separated out. Another difference tho is that more of the carbon is combined with those 'waste' growths instead of being released to the atmosphere.Linseed oil does contain food for mildew organisms to feed on, so it is likely to turn black from that unless it is catalyzed so as to cure fast and hard or has mildew inhibitors added. 

    

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1. 
   DaveRicheson | Jul 10, 2009 06:59pm | #7

   Oxidation is a chemical reaction that combines O2 with the oil. The reaction can take place slowly  as with the formation of rust or rapidily in the form of a fire. It can also take place at rates in between those, and that is what happens with lindseed oil.

   Lindseed oil is a medium to short molecular lenght  oil that has sevral sites that allow atmospheric O2 to bond to it. In short and medium lenght oils the diatomic molecules of oxygen will combine with two molecules of oil and because there are sevral bonding sites in each oil string they become bonded to one another. As the free carrier solvents evaporate  and the process continues a film of oxidized oil is formed. The use of "catalyst" in most short and medium lenght oil formulations that are ment to air dry use to use lead, manganse and cobalt metals that merely accelerated the oxidation. The reaction however will occur without any catalyst being present once the oil is exposed to air.

   In it's wet state lindseed oil will indeed provide the organic food needed for mold to grow. In it's fully oxidized state it does not. It becomes a solid film of cross linked oil molecules that has very good portective qualities. It does darken with age and that is a result UV degradation, not continued oxidation.

   When mold and mildew growth does occur when linseed oil or linseed base paint is used it is likely cause by the same thing that causes it when other coating are used. There is moisture and and organic food source in the form of wood for it to grow on.

   We tested linseed and soya short and medium lenght oil formulations on metal panels over the course of sveral years and never saw a mold or mildew bloom on that substrate. Use the same formulation on wood and yes we did get blooms, so we surmized that the substrate was the source, not the coating.

   I'm not saying that linseed oil is the best product to use for a protective coating. There are many more and better products available on the market today that have higher UV  amoung thier other coating characteristics.

   My point was to debunk the notion that linseed oil will cause mold and mildew to form. It was used in coating for many many years, along with soy based oils and that was never an issue. Coating life and performance where. That is why it is not used much any more. There are simply better product available.

    

1. 
   mike_maines | Jul 10, 2009 10:16pm | #9

   Actually you're both wrong.  Oxidation is what happens when a substance loses or gains one or more electrons.  Often it takes place in the presence of oxygen, but it doesn't have to.

   I think we can all agree that there are better penetrating finishes for exterior use though ;-)

2. 
   CCI | Jul 10, 2009 10:39pm | #10

   Actually oxidation is when you lose an electron.

   When you gain an electron it is technically called reduction.

   No, I am not a chemist but my daughter is a chemical engineer.

   I guess some of her knowledge spilled over.

   Edited 7/10/2009 3:40 pm ET by CCI

3. 
   mike_maines | Jul 10, 2009 10:48pm | #11

   D'oh, you're right.  It's been a while since chemistry class.  I was thinking oxidation number, which describes how many electrons are lost or gained.

   I'll get down off my pedestal now....

4. 
   Piffin | Jul 10, 2009 11:49pm | #13

   Hey, leave me alone with my practical chemistry. my customers don't have good enough eyes to see electrons!;) 

    

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5. 
   Piffin | Jul 10, 2009 11:45pm | #12

   Maybe you are right that in lab test conditions linseed oil will not CAUSE mildew, but in reality, it is far more likely to see mildew grow than with other film surfaces. Maybe there is a lot of incompletely cured linseed oil out there. 

    

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6. 
   fingersandtoes | Jul 11, 2009 02:14am | #14

   Bypassing the oxidation question (which is beyond me): Ponytl had a thread on using BLO on the steel railings he was making. He described heating the metal or BLO when applying it. If the linseed oil is already boiled, what does heating it when applying do?

7. 
   Sphere | Jul 11, 2009 02:31am | #16

   Ever eat refried rice? Or refried beans?

   There ya go.

   BTW , Zorro was right, it PolymerizesSpheramid Enterprises Architectural Woodworks

   Repairs, Remodeling, Restorations

   "If Brains was lard, you couldn't grease much of a pan"Jed Clampitt

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8. 
   DaveRicheson | Jul 13, 2009 01:18pm | #18

   BTW , Zorro was right, it Polymerizes

   Just another fancy word for cross linking.

9. 
   Sphere | Jul 13, 2009 01:28pm | #19

   'zactly, I too worked in coatings. Hydrocoat products. Crosslinking and coalescing polymers.  When waterbased finishes and stains were new, there was a lot to be learned and shared.  Whole different animal from evaporative cured finishes and catalytic conversions.Spheramid Enterprises Architectural Woodworks

   Repairs, Remodeling, Restorations

   "If Brains was lard, you couldn't grease much of a pan"Jed Clampitt

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10. 
    brucet9 | Jul 11, 2009 04:59am | #17

    Heating linseed oil or any alkyd resin in the presence of oxygen will accelerate the cross-linking reaction. The resultant finish becomes rapidly harder and tougher than when air dried.BruceT

3. 
   Piffin | Jul 10, 2009 01:04am | #3

   My recall ( could be wrong) is that raw cures by a slow oxidation process, while 'boiled' has been precatylized so it cures faster.

   By cutting it deeply with spirits, you may have not noticed the slower cure rate.

    

    

   Welcome to the
   Taunton University of Knowledge FHB Campus at Breaktime.
    where ...
   Excellence is its own reward!

4. 
   Danno | Jul 10, 2009 09:53pm | #8

   One thing you may know or not, is that oil soaked rags should be opened and allowed to dry, or sealed in metal container, as they can spontaneously combust.

    

5. 
   McDesign | Jul 11, 2009 02:31am | #15

   <Is there a reason for using one over the other. >

   The taste