Paraffinic / Linseed oil

[RPetry 564]

More fun. A stain manufacturer and I have been having discussions on the susceptibility of boiled linseed and paraffinic oils to mildew, mold, and general discoloring due to moisture and environmental exposure.

I have agreed to a test. It has been approved by the other party. Any suggestions would be welcomed.

Western Red Cedar 2 x 6 board, new wood purchased last year and never stained or exposed to the weather. It has been cleaned with Restore sodium percarbonate wood cleaner, lightly pressure washed, and brightened with citric acid a week ago. The citric was gently washed off with water after about an hour of brightening.

The cedar is very dry, Delmhorst reads at 8%. It is in my office at the moment.

The plan is this. The cedar board will be divided into 4 sections. One section will be treated with boiled linseed oil, the most common oil in exterior wood stains. It has been confirmed by the manufacturer that it does not contain any fungicides/mildewcides.

One section will be treated by paraffin oil. No Ken, not baby oil, one refining step down. Again as with the linseed, no additives.

One section will be untreated and left alone. The last section will be wrapped in plastic.

Both the linseed and paraffin oil will be allowed to dry inside for at minimum a week. Reason for this is it is Spring, and I do not want any pollen to accumulate on a "tacky" surface.

The board will then be set outside my home in a shaded area, about 1.5" from the ground to encourage moisture exposure.

Any suggestions on protocol are welcomed.

[RPetry 564]

Beth,

That board was stripped and brightened last October. The WRC was cut into pieces and used for the wood classes at the ***** convention.

[JamieP 14]

It has now been ~ 4 months since this little experiment started. Pics as follows:

Pic #1 - Four sections of the test cedar board. From left to right, untreated cedar, paraffin oil, boiled linseed oil, untreated cedar wrapped in plastic.

Pic #2 - Closer shot of the untreated, paraffin, and linseed oil sections. Discoloration was evident on all three, with the linseed oil test section darker and most noticeable.

To determine whether this darkening was dirt and/or mold/mildew, a 3% sodium hypochloride drop was applied to the three sections. Immediately below the "drops", a water/Dawn soap solution was applied and scrubbed with a toothbrush.

Cleaning with the soap/water solution shows no visible difference. There is no doubt that this is mold/mildew.

Pic #3 - A close up of the paraffin oil (left), and the linseed oil (right) sections.

Initial conclusion: The untreated and paraffin oil cedar sections are virtually identical in appearance and mold/mildew growth. From a layman's perspective, it could be deduced that pure paraffin oil does not promote growth.

The boiled linseed oil section is harder to interpret. The earlywood is clearly much darker in appearance than the latewood, which is to be expected as it is more "porous" and absorbs more oil.

Visually, it could be concluded that there is more mold/mildew growth due to boiled linseed oil than either paraffin oil or untreated cedar. But other factors, for example discoloration due to UV or wood/oil chemistry changes due to environmental exposure could be the cause. It would take sophisticated laboratory analysis to find an answer.

I'll put the test board back outside, and take another look next spring.

Rick,

Just throwing this out there; but would the boiled linseed mildew growth not be attributed to moisture vapor and relative humidity?

[RPetry 564]

Jamie,

No doubt moisture and an organic food source is required for mildew growth. I'm not sure what you are stating ie: linseed oil and moisture barrier.

[godfather927 14]

I'll put the test board back outside, and take another look next spring.

I've noticed that this thread has been buried for a couple months. Some great and very interesting info in here, and was wondering if any updates or photos were available now that we are well into spring.

[RPetry 564]

I've noticed that this thread has been buried for a couple months. Some great and very interesting info in here, and was wondering if any updates or photos were available now that we are well into spring.

As stated 3 posts back, the test board was cannibalized for wood samples for a class I was teaching last October.