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Finishing - Penetrol

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I recollect that someone on the list mentioned the use of Penetrol to improve the flow of varnish when dipping.  By "improve", I think it was reference to reducing or eliminating, spar varnish's tendency to draw back from sharp edges.  The product spec's recommend up to 25% Penetrol to 75% varnish.  This seems to be a lot.  Can someone who has experience with Penetrol comment on the product, mix proportions, and what benefits there are to using it.  Drawbacks, or cautions if any.  (Ted Knott)

Being in the paint trade for over 30 years I have had a lot of experience with Penetrol and its brother for latex Floetrol.  Both products are amazing and if thinned right they will give you great results.  As far as what proportions to mix I can't tell you because we always mixed by sight and in different temperatures and different humidities it works different.  A 75-25 mix though is a good place to start.  I also just thin my Man-O-War for my finish with mineral spirits and I brush my rods, here again I mix by sight but 80-20 is a good place to start here.  I guess the length of time and experience helps me in those respects.  Make some practice sticks and experiment with your finish and see what different mixtures get you.  Good luck and if I can help further don't hesitate to call me or contact me via email.  (Bret Reiter)

Mark Wendt (upon Bob Nunley's recommendation, I believe) told me he was using 10% Penetrol in his Minwax Helmsmen to help the varnish flow better and not shrug away from the corners. I went out and bought some from the local paint store since I have used Minwax for a while, and my tube of it was on the thick side.

I filled up the last 2" of my dip tube with it and then mixed thoroughly (so not anywhere near 10-15%). However, I have noticed that even with the small amount the varnish does indeed flow better, and the corners on the quads I have done since are "crisper" in appearance.  I have also used it with some PU that was rubbed into a bird house to finish it. It appeared to drive the varnish right into the wood.  My only caution is that if I did it again I would strain the Penetrol before adding it. On the first few coats it seemed to contaminate the varnish with grit of some sort. I have never experienced that before, but now it seems to be okay.

I would suspect that it would work very well with a spar as well.  (Bob Maulucci)

Sir Nunley advised me to start with a little, and work my way up with the addition of Penetrol.  So far, I've had really good luck with it.  My main problem with my finish was trying to do it in temperatures that were a little lower than advisable, and that's when the problems arose.  The addition of Penetrol virtually wiped out the problem of the finish pulling from the sides.  I would recommend it to anyone who's having those kind of issues, and others.  Penetrol is supposed to be effective in reducing fish eye, and orange peel too. As Bob mentioned below, it's a good idea to strain the Penetrol into your finish.  I too found some little gritties that would have made a mess of the finish.  (Mark Wendt)

It is a good idea to strain any additives, whether thinner etc to any finish you are using.  I even strain my finish when I first get it to get any crud out of it.  (Bret Reiter)

Thanks Bob.  I'll try your recommendations on my next rod.  It does make you wonder though, why the manufacturer doesn't add a flow agent.  (Ted Knott)

I know from painting with oil based paints that the  addition of Penetrol will make oil based paints flow on with a brush as easy as latex paints. Especially today when most oil base paints flow on like glue due to the restrictions on solvents. However, during the coarse of the day it will require several additions of Penetrol to keep this characteristic. I do not know if this is from evaporation of the open paint pail or a chemical reaction.  (Marty DeSapio)

I found the same thing when painting my boat, had to keep adding Penetrol. Pretty hot day, I suspect evaporation.  I could tell when I needed more by the brush starting to drag.  I also mixed by eye.   (Neil Savage)

I am wondering what is really meant by "better flow," however.  I understand that there seems to be better definition at the corners of the rod sections, but do you find that this additive makes the varnish less prone to run?  From at least one of the posts (and the name of the stuff) it seems as though Penetrol actually facilitates the penetration of the varnish into the bamboo.  Is this the case?  What else does or doesn't this product do?  Or do I, in fact, have things all mucked up?  (Carl DiNardo)

I think it thins and helps it penetrate into the bamboo. The thick coats cannot cling to the corners.   (Bob Maulucci)

Hey Bob, you confuse me.  I always thought that the varnish bled from the corners to the middle of the flat.  I had trouble one time trying to use tinted varnish.  The transparent stuff makes it hard to tell.  (Ralph Moon)

I haven't used the Penetrol yet, but I suspect that it reduces the viscosity so that there is less surface tension and the varnish will flow and "flatten" out.  You can see when sanding that spar varnish is higher at the corners than in the middle of the flat. IE: it flattens out but draws back from the corners.  Polyurethane varnish goes on a little differently.  It will be high in the center. IE: it doesn't flatten out.  (Ted Knott)

I believe that surface tension and viscosity are two different issues.  In photography, all the processing chemicals have the viscosity of water but Kodak makes what they call a "wetting agent" that reduces the surface tension (the tendency of water to bead rather than flow) so that one doesn't get "air bells" on his negatives or prints.

Another trick used in photo processing is referred to a laminar flow and is essentially a sort of "squeegeeing" on the finish.  Has anyone tried drawing a dipped rod out of the tank through a tightly fitting sheet of latex rubber?  (This, of course, would be for those who dip blanks not rods.)  (George Bourke)