I've been looking at and thinking about a few related topics...

...and I decided to throw out this question. I've seen professional circuit boards with chips and all that are 100% waterproofed via clear-coat finishes across the whole board. Is it a reasonable, good method to just dip a whole, final, soldered circuit board, such as a completed Arduino Nano project with all wires soldered, into polyurethane or lacquer to give it a protective finish against water, corrosion, humidity, chemicals, etc?

I'm thinking of using these products specifically:

If this is a reasonable thing to do, which is better: satin, semi-gloss, or gloss?

Dipping into an (oil-based) Minwax Gloss Polyurethane 1 qt can sounds the most reasonable to me at the moment.

The one exception to this technique is to simply ensure you don't cover up any sensors that destroys their ability to function (ex: barometric pressure sensors, humidity sensors, etc). Also, I'm sure the board won't cool as well...

Looks like the keyword I needed was "conformal coating." Here's one source mentioning polyurethane as a good choice: http://www.conformalcoating.co.uk/Conformal_Coating_Material_Types.php

  • \$\begingroup\$ Ack! No on the Minwax! You don't know what solvents they use. \$\endgroup\$ Sep 25, 2015 at 3:50
  • \$\begingroup\$ What do you recommend instead? I have no experience with conformal coatings. And...I think the solvents may be listed on the can in fine print. \$\endgroup\$ Sep 25, 2015 at 3:56
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    \$\begingroup\$ Solvents may be listed. Do you know the effects and compatibility of the solvents? As for recommendation, buy a formulation specifically labeled "Conformal Coat". Google. Try Amazon or Zoro, or any one of hundreds of others. \$\endgroup\$ Sep 25, 2015 at 4:07
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    \$\begingroup\$ Looks like someone here is subscriber of GreatScott. \$\endgroup\$
    – Ridham
    Dec 30, 2017 at 9:04
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    \$\begingroup\$ Also, I think we (myself included) sometimes get way too wrapped up in academic BS when the best test is to just go try things. The best answer to my question cannot be given until someone tries polyurethane from a hardware store and then reports back. My circuit boards are cheap. One of these days I'm going to try it. At the end of the day, what we need to answer this question is a good chemist to explain the theory, and some DIY enthusiasts (perhaps myself) on penny budgets to just try it, providing the experimental data we need. \$\endgroup\$ Dec 30, 2017 at 17:46

1 Answer 1


To expand on a brief comment: do not dip a board into any woodworking polyurethane as a conformal coat, unless you really like gambling.

First, you have no idea whether or not the solvents in the varnish are compatible with your parts.

Second, dipping into standard polyurethane will produce a thick coat, and drying stresses may damage your board. If you must do this, try a spray formulation which will give the thinnest coat possible.

Third, no matter what conformal coat you decide to try, the board must be scrupulously clean. That means cleaning with alcohol, and handling with cotton or latex gloves afterward. Adhesion to PCBs can be tricky.

  • \$\begingroup\$ And not to forget the now massively reduced heat dissipation abilities.. \$\endgroup\$
    – PlasmaHH
    Sep 25, 2015 at 7:34
  • \$\begingroup\$ @PlasmaHH OTOH, if the device is going to be submerged in water (which may or may not be the case), this significantly helps with cooling. The question is whether it will be enough. \$\endgroup\$
    – yo'
    Dec 30, 2017 at 13:57

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