Fungi Conclusions
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Joined: 09 Mar 2014
Posts: 15
Location: texas

PostPosted: Sun Feb 07, 2016 1:49 pm    Post subject: Fungi Conclusions Reply with quote

In my attempts to understand the mildew problem better i've come to some conclusions and would appreciate any further insights or discussion.

Mildew seems to be a potential in really any climate...
The commonly stated ingredients for mildew to develop are the following:

1. organic material
2. temp 77-88 F
3. 70-93 RH
4. oxygen

Another addition to this list might be expanding #1. If a surface is irregular or sticky or has holes, organic material and spores are more likely to accumulate.

When dealing with fungi and old wood, these are the steps i've summarized:

- Is there fungi on the surface of the wood, embedded in the wood, in the joints?
- If the fungi is embedded, mildewcides can do very little and are ultimately more toxic than it's worth. infrared can theoretically deal with imbedded fungi.
- If fungi is only on the surface (how would you really know?), you could just clean it off with bleach i suppose.
- In the process of removing fungi from existing wood, along with paint removal, sanding, opening joints, etc. obviously a lot of dirt is expelled, organic material is created for fungi to thrive on again.
- The wood needs to be thoroughly clean, which is more difficult with closed joints and severely weathered wood. In this case, HEPA vacs probably aren't enough but there will have to be some detergent and water used.
- Once any existing fungi and loose organic material have been removed, there are now steps which follow that present some new problems for fungi to thrive again.
- Linseed oil is blamed for encouraging fungi growth while at the same time others use it with no issue. Cheap "boiled" unrefined linseed oil is considered to be worse than pure protein-free linseed oil because the fungi are attracted to the proteins. You could get one step closer to fungi mitigation by going for the protein-free linseed oil but this still wouldn't explain those who use the boiled kind with no issue.
- If the wood substrate is indeed free of fungi and indeed free of loose organic material you would not have to worry about fungi coming back or organic material/spores getting adhered with the oil. However, if pre-treatments/glazing/allback paint are used in an environment with circulating pollens/organic material/circulating spores (like in an exterior environment) these things could get into the oil mix.
- Because linseed oil dries so slowly, it only increases the odds that spores can get "stuck" in the coatings/glazing/etc. Not to mention that apparently fungi is attracted to linseed oil (and i guess any oil)
- In the 'National Painters Magazine' Vol 48, there are some informal studies done using zinc white/oxide additive. In this article it is interesting that the main problem with fungi is not the oil but the fact that the exterior linseed oil paint remains tacky for so long. Zinc white/oxide is used *primarily* in these studies to speed up drying time AND create a hard surface that organic material can "slide" off of. It is also referenced as a mildewcide.

So in conclusion, the likelihood of the surface to MECHANICALLY attract fungi almost seems the largest issue, but certainly not the only issue. The TECHNIQUE of working with linseed and old wood seems to be a prominent factor in whether fungi will be more or less likely to form. In the studies mentioned in the article, ALL zinc white additive linseed paints remained clean and true color at 25%. Allback paints suggest, i believe 10-20%. Interestingly enough, Allback does not make any claims about zinc white being a mildewcide, but does make claims about its affect on drying time and hardness.
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Joined: 14 Nov 2019
Posts: 8
Location: Belgium

PostPosted: Sat Jan 04, 2020 1:18 pm    Post subject: Reply with quote

You forgot to mention pH. Below 2 and above 8 most mildews (which are most of the times actually yeasts) will not grow.

Regarding temperature, raising the temperature above 60°C/140°F will kill most mildews/yeasts.

The problem with vegetable (linseed) oil (triglycerides) is that the yeasts can digest it because they contain an enzyme called Lipase. This digesting will not happen or stop when the oil is polymerized.

The sooner your oil is polymerized, the lesser the chances for the fungi/yeasts to grow.

If the conditions are right, you can get fungi/mildew within two or three weeks on wood, oiled or not.
I did an experiment on a piece of wood treating it with different types of oil: none, coconut oil, olive oil, linseed oil, sunflower oil and grape seed oil.
After 4 weeks (I started on nov. 4th 2019 - autumn season) the area's with coconut oil and linseed oil had minor black spots, all other zones had severe black spots.

Regarding Allbäck and Zinc White
This is what they state in their Concise Handbook About Linseed Oil Paint on page 9:

No pesticides
When you get dirt and mould on painted surfaces, wash them with Linseed Soap.
When painting surfaces that are exposed to various kinds of mould, pure zinc paint can
be added to all our paints, to a maximum of 20%.
This zinc paint is marked with the “Dangerous for the environment” symbol
depicting a dead tree and a dead fish.
Take care with it.

I read that as Zinc white being a mildewcide...

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