Replies

1. 
   Westchester | Feb 12, 2014 07:40am | #1

   Mold

   I've never seen this happen - I'd be interested to see what others say here.  Was this chair used outdoors ? Did you only use one coat of varnish ?

   SA

2. 
   SteveSchoene | Feb 14, 2014 07:03pm | #2

   Mold under the varnish means the varnish is failing.  Whether this is normal depends on which brand of varnish it is   Big box varnishes are generally weak and likely to fail.   True marine spar shouldn't fail in a year in the sun, but if in lots of sun even the best should need a refresher coat about every year.

   From this point unfortunately you will need to strip off the varnish, clean off the mold, and then reapply a top quality spar varnish.  That should mean about 6 coats, with light 320 grit sanding between coats.

   To really keep a clear finish on a piece that lives in lots of sun, the best plan is to cover it with a cover main from a material such as Sunbrella.

   .  

3. 
   Bob_Besley | Mar 05, 2014 07:25pm | #3

   I wouldn't blame or throw out your varnish too quickly. It may be just that there was a dampness problem??

   Mold spores are everywhere but they only germinate/grow when the conditions are right/damp.

   Spar varnish is probably BLO with different additives that indoor varnish for UV and to remain a bit more pliable.. Varnishes develop micro porosity in short time in sunlight and repeat changes in humidity. Spar poly would be similar.

   The mold probably grew because the chair was allowed to remain too damp cumulatively for several days. Mold will even grow in/ on BLO if the area is dampish for very long.( E.g.- The black stain around the ground in clear finished outside walls and decks.) .Wood over about 20% moisture content will mold as in damp basements.

   If needed, removing the finish and possibly cleaning with oxalic acid, drying the wood, and refinishing should restore the chair.

   ensuring the chair gets dried and stays dry for other than brief periods might prevent further mold but in some locations it is difficult.

   It may be all irrelevant  but mold doesn't grow on dry wood although the spores remain and wait.

1. 
   SteveSchoene | Mar 07, 2014 11:47am | #5

   Spar varnish is NOT BLO with some additives.  It is varnish.  Some brands may have been made with BLO (and/or tung oil) as ingredients, but the oil has been chemically reacted with resins (alkyd and/or phenolic) to create varnish.  Spar varnish is a "long oil" varnish.  THAT does not mean oil has been mixed into the varnish, it means that the proportion of oil to resin, was relatively large.  After the chemical reaction that creates the varnish the result will be relatively flexible.  Additives to protect the varnish and the underlying wood are then added to the varnish.  

   BLO is the last thing one would apply to wood that may experience mold growing conditions, since BLO is very susceptible to mold growth.  Mildrew seem to thrive on it.   

4. 
   Bob_Besley | Mar 05, 2014 07:25pm | #4

   I wouldn't blame or throw out your varnish too quickly. It may be just that there was a dampness problem??

   Mold spores are everywhere but they only germinate/grow when the conditions are right/damp.

   Spar varnish is probably BLO with different additives that indoor varnish for UV and to remain a bit more pliable.. Varnishes develop micro porosity in short time in sunlight and repeat changes in humidity. Spar poly would be similar.

   The mold probably grew because the chair was allowed to remain too damp cumulatively for several days. Mold will even grow in/ on BLO if the area is dampish for very long.( E.g.- The black stain around the ground in clear finished outside walls and decks.) .Wood over about 20% moisture content will mold as in damp basements.

   If needed, removing the finish and possibly cleaning with oxalic acid, drying the wood, and refinishing should restore the chair.

   ensuring the chair gets dried and stays dry for other than brief periods might prevent further mold but in some locations it is difficult.

   It may be all irrelevant  but mold doesn't grow on dry wood although the spores remain and wait.