Today I checked on my coach to see how she had fared over the winter. The weather cold, but dry. I found that some areas varinished last summer had discolored to a whitish tone and that some of the lustre had gone. This was not that consistent from area to area so I couldn't say "I did that there, but not there."
I used an interior true varnish, not polyurethane and thinned it as directed by the manufacturer although I didn't always use their brand of thinner contrary to advice on the can. The varnish didn't like the change in temperature and/or humidity. Oddly, areas varnished the year before, thus on their second winter, seemed unaffected. Not a big job to resand and recoat, but how? Would a spar or exterior varnish be a better choice or should I have stuck rigorously to the manufacturer's thinner? Or can you think of something else?


davidwoodbury@adelphia.net

> Today I checked on my coach to see how she
> had fared over the winter. The weather cold,
> but dry. I found that some areas varinished
> last summer had discolored to a whitish tone
> and that some of the lustre had gone. This
> was not that consistent from area to area so
> I couldn't say "I did that there, but
> not there."
> I used an interior true varnish, not
> polyurethane and thinned it as directed by
> the manufacturer although I didn't always
> use their brand of thinner contrary to
> advice on the can. The varnish didn't like
> the change in temperature and/or humidity.
> Oddly, areas varnished the year before, thus
> on their second winter, seemed unaffected.
> Not a big job to resand and recoat, but how?
> Would a spar or exterior varnish be a better
> choice or should I have stuck rigorously to
> the manufacturer's thinner? Or can you think
> of something else?

If I recall, we're talking about a wooden coach which is stored outside. Are you varnishing only inside surfaces, or outside as well?

I'm not sure what you mean by "interior true varnish". What brand and type? The word interior should be a serious warning flag - the conditions even inside the car will be much more like the exterior than interior of a house. I've had good results with spar varnish, McCloskey Man O' War to be specific. My cars have always been stored in a barn, but there's still huge temperature and humidity swings, and condensation on all surfaces is not uncommon. Surfaces I last varnished 25 years ago (yikes!) are still good, I think. The label on the can says it's good against salt water and hot Diesel fuel, but I haven't tried either of those on the inside of the car....

I don't believe there can be any significant difference between different brands of mineral spirits. So that's not the answer.

Gee, I love this subject!

> Today I checked on my coach to see how she
> had fared over the winter. The weather cold,
> but dry. I found that some areas varinished
> last summer had discolored to a whitish tone
> and that some of the lustre had gone.

My best guess would be moisture or humidity. Going back many years to the use of an old hobby product, Walthers Decal Dulling Varnish, it was a 'true' varnish. It was very sensitive to humdity as to rate of actually totally drying, and would often develop a whitish 'blush' if applied or dried at high humidity.

I believe there are usually two steps involved in paint or varnish 'drying', at least the very durable coatings we strive for. One is the physical evaporation of any solvent or VOC carrier. That happens pretty quickly. The second step involves a 'curing' step where the resins or other body components of the coating polymerize or undergo a chemical transition to a more or less permanent form. This film may be very dense and impervious to moisture or maybe somewhat porous, at least on a molecular scale. Even a coating like linseed oil undergoes this curing step before becoming more or less permanent and durable.

Since you are noticing spotty areas which are unsatisfactory, maybe the application was slightly thicker there and conditions may have changed, (cooler, moister) before it totally cured out. Below 50 F the curing can be significantly slowed or almost retarded to the point where it might take days to reach final conditions.

Many varnishes and shellacs remain sensitive to the environment and we have noticed some cars in our collection where interior wood surfaces become "sticky" during hot, humid summer days.

Depending on what was underneath and how the surface was prepared, could it have reacted with remnants of an original finish or coating, or if on totally bare wood, is there any chance of moisture migrating from the backside via a concealed leak or other buildup of moisture?

So there might be a reason to consider using polyurethane clear finishes. Many of the so called 'varnishes' sold today in fact are polyurethane based. I personnally prefer the traditional oil based finishes, anyone have any experience with the water based acrylic 'polyurethanes'?

Bob Kutella


68trolley@comcast.net

> So there might be a reason to consider using
> polyurethane clear finishes. Many of the so
> called 'varnishes' sold today in fact are
> polyurethane based. I personnally prefer the
> traditional oil based finishes, anyone have
> any experience with the water based acrylic
> 'polyurethanes'?

> Bob Kutella

Bob - used some on interiors of cars kept under roof with decent results, but not on wearing surfaces like floors.

Would a Japan Dryer aded to the spar (or whatever) varnish eliminate the slow drying / glazing problem in cooler temperatures?

dave

irondave@bellsouth.net

> Would a Japan Dryer aded to the spar (or
> whatever) varnish eliminate the slow drying
> / glazing problem in cooler temperatures?

> dave

Japan Dryer is one of the essential tools we use, but have not had to use it on any clear finishes. While it would help varnish "dry", cool temps would still probably retard the cure of the coating.

Many of the colors used on rail cars are deep, intense, highly saturated colors and when you get a custom mix, it often has so much pigment in it that the drying time is VERY slow. I guess that makes sense since the pigment colors and vehicles stay for days or weeks in the paint store in the dispensers without drying out. We have added a capful or two of the Japan Dryer (per gallon of paint) to polyurethane enamels with good results.

Bob Kutella

68trolley@comcast.net