Concerns when "potting" components in cement/mortar/concrete

Even dry-seeming concrete is a reasonably good electrical conductor - implements a resistor.

Joe

Most people use polyurethane or epoxy.

John Larkin Highland Tech Glen Canyon Design Center Lunatic Fringe Electronics

I figured a conformal coating would "isolate" the devices, electrically -- it worked well enough for salt pray.

But, I'm not sure how well that would address leads and the lime content.

Or, how warm things would get during curing (as that would affect the coating, too).

Hard to get firm numbers on that (*internal* temperatures):

"When curing, concrete can reach some impressive temperatures, thanks to the exothermic reaction during hydration. That’s right—concrete’s getting ts sweat on, potentially hitting anywhere from 70°F to over

Concrete shrinks during curing. You can buy thermally stable concrete (hydraulic cement) which is fairly stable. There are many factors that affect the amount of expansion or shrinkage. This might help:

Other things to worry about:

- Air bubbles from outgassing. That's why vibrators are used in concrete foundation construction.

- Shrinkage during curing which will cause cracks.

- High water content (about 50% water) in concrete will corrode components.

- High water content (about 50% water) can expand and crack concrete when frozen. The water can also turn to vapor when heated above 100C causing spalling.

- Chlorine (salt water) contamination will corrode copper.

- Lack of adhesion to components will produce a cavity for water to collect.

Instead of reinventing the wheel, perhaps you should consider using epoxy, urethane or silicone potting compounds.

I only care to the extent that shrinkage alters the mechanical characteristics of the "potted" devices. I don't imagine their presence will materially affect the behavior of the encapsulant, itself.

Conformal coating should maintain a barrier between the components and the encapsulant.

I imagine the mortar/cement/concrete will be installed with all of the above in mind. I can't protect against folks who don't know how to handle the material. I just want to drop something in while they are "doing their thing".

If the material isn't suited to the environment in which it is deployed, then that's not my problem, either.

Adds a step:

- pot in epoxy

- and THEN place potted item in mortar/cement/concrete And, makes the potted device arguably larger (than just a conformal coat would).

I'm trying to see if that first step can be eliminated and that second issue avoided.

Don't expose electronic components to cement or concrete. It is almost certain to cause problems. I think that encapsulating your circuit in silicone rubber will protect in two ways.

Yes it is. If the drop-in item is potted with a rigid material, and then embedded in a rigid cement, the stresses and strains in the cement will crack the item.

If the item must be drop-in, its "conformal" coat must be thick and softish, and is most easily molded or cast in a thin shell. As mentioned later [1], Polyurethane potting is likely to be suitable.

It would also be useful to include a thermocouple or thermistor in the item, so the actual temperature can be measured versus guessed.

Not clear. How big are these concrete things? If they are tiny, just make it all urethane potting.

Joe

That depends on the composition and thickness of your conformal coating. If the coating is brittle, it might crumble or crack. If it flexes, it might tear. If the coating has bubbles or gaps, you might end up with a biological reactor.

Full disclosure: I used to design marine radios. The art of protecting electronics from the environment is not simple or obvious. Most of the horror stories are true. I also worked as an "assistant embalmer" (which meant I mostly swept the floor) when I was in high skool. I didn't have any contact with the corpses but did get to watch the procedures. If you plan to bury something that is conformal coated in concrete, it might be wise to first consult the applicable state laws and regulations or at least consult a mortuary for burial advice.

Hint: Make sure that whatever it is you're burying is legally dead before proceeding. The un-dead have been known to inconveniently rise to the occasion at inconvenient times.

I'm not sure what you're encapsulating in concrete but this might help

That's called littering. I suggest you dispose of the incompatible material in an environmentally correct manner.

Burial pots and jars are available. Conformal coating of the contents are probably billed separately:

Conformal coating and potting can probably replaced by something more convenient. I suggest immolation, cremation or burial at sea as potential alternatives.

I imagine a conformal coating to act as an environmental and electrical barrier between the device and its encapsulant. When I was doing marine navigation kit, we coated everything (regardless of how deeply placed in its enclosure it might be) and never had problems with salt spray, fish guts, etc. interfering with the operation of the devices.

How would this be better/worse than a regular conformal coating? The durometer of the coating -- and its thickness -- would give a certain (predicatable) amount of protection to mechanical stress around the device. There are always limits to what a given approach can tolerate (I doubt anything embedded in the walls of the World Trade Center would have survived THAT sort of stress)

So, how did the conformal coatings we put on the radios, autopilots, plotters, etc. manage to survive in direct salt spray (e.g., the internal electronics in the plotter were "vented" by nature of the fact that the plotting mechanism required long openings to travel across the plotting surface)?

I worked on a device used to assay blood samples that had exposed circuit components that could be tainted with blood, reagents, etc. -- protected with a similar conformal coating.

Why "concrete and medical" implants? What were you trying to embed -- and, in what?

That depends on WHAT it is embedded in, right? And, what THAT is

Should I ensure that it could survive being embedded in the concrete launch pad under an exploding "starship"?

If I embed it in a decorative fountain cast from concrete, should it survive someone taking a jack-hammer to said fountain?

I.e., in the former case, one would anticipate that it is possible (even if not "highly likely") that an explosion could occur in the environment and some assessment of the cost of losing that bit of kit weighed into the cost of embedding it.

In the latter case, one would anticipate that the most likely stresses encountered would be if the fountain (was) toppled (through mechanical intervention or high winds, etc.)

It only has to be soft enough to absorb *enough* of the flex that might exist over the dimensions of the embedded object, beyond what the embedded object can tolerate on its own.

You only need that when the device is potted. If the temperature gets too high, what recourse do you have -- the device is already

Measuring (without necessitating the presence of the embedded device) is necessary just to ensure the chosen process (for the particular application) won't subject the embedded device to extremes that could damage/destroy it as that would, presumably, necessitate discarding the embedding structure (considerably more costly -- labor -- than a device)

I want a technology that will let me make the "pottable devices" as small as possible. E.g., if I want to slip one into a mortar line between bricks/blocks, I don't want to impact the process that is normally used to lay brick/block.

Yes, I designed LORAN receivers, plotters and autopilots. I am well aware of what salt spray can do to kit -- in very short order.

My B-in-L was an embalmer. Kinda creepy but someone has to do it.

If the device is embedded in another device and the other device fails, then it's not "litter" but "debris".

I worked for Intech Inc, Santa Clara at SJC airport. In 9.5 years, I helped design a 27MHz pager (yech), AN/SRD-21 VHF homer, AN/SRD-22 VHF Doppler DF, VHF "sign post" vehicle locator, various 1.6 to 30MHz SSB transceivers, various HF power amps, some minor test equipment, some UHF SCADA transceivers for SoCal Edison, and probably some other stuff that I can't excavate from my failing memory. (Note that I did not design the entire transceiver). For the military direction finders, passing the MIL-STD-810 salt fog test was difficult.

Much later, I somehow ended up doing damage control on various consumer electronics designs. There were some devices environmental problems. Typically, the culprit was a high impedance design, where a small amount of water would literally short PCB traces or components. Sometimes, the high impedances were necessary, but recalculating the components to lower impedances usually solved the problems. The lower impedance also helped the device survive in a high humidity and/or moisture condensing environment.

At various times, I've resided in the "fog belt" near the ocean. I don't recall seeing any wrought iron hand railing. As I vaguely recall, the hand rails were redwood with layers of sealer, stain or paint.

As long as he doesn't try to raise the dead, he'll be ok. I found the relatives of the deceased to be far more creepy than the staff. The TV show "The Addams Family" was probably their template.

When viewed from a distance, there is little difference between litter and debris.

Working and living minutes from the ocean (atlantic), we could usually find someone willing to take us out to "field test" our kit -- usually small (35 ft) "working boats", no enclosed bridge, etc.

And, we had our own shake-n-bake facilities in the shop. So, before we *got* to sea trials, we were reasonably sure we had a viable product. Whether it was a radar, loran/omega receiver, position plotter, autopilot, etc.

I've not encountered any other shop with the range of technologies that were available, there. (metal shop, paint shop, wave, microwave testing chamber, etc.)

The plotters were the most vulnerable devices as they had mechanisms that couldn't be enclosed/protected from the saltspray. And, the skippers would usually dick with them while at sea instead of letting them just "do their thing".

Early on, we discovered they were frequently opening the protective cover in order to mark the chart to indicate where they'd dropped a lobster pot or found a school of fish. This prompted a last minute hack to allow them to "press a button" to have the plotter draw an 'X' in the hope that they would leave things covered.

This, of course, was a win for the crew as they could extend the pushbutton control (like the handheld "devices" used on quiz shows) so they could stay aft and keep working instead of having to run up to the plotter to manually make those marks.

We used to vacation in florida, a few blocks from the sea, each year. I distinctly recall seeing wrought iron railings (to keep folks from falling off their porches, etc.) that were *etched* from the salty air. "Gee, out wrought iron railings at home don't look like that!"

He seemed to think nothing of it. He would often disappear for a few hours to "plug some guy". I didn't want to know any of the details...

Litter is intentional. Debris is usually the result of an accident.

You have suddenly reminded me of a problem I had with a particular IR remote control.

The side of the PCB that touched the rubber membrane with the buttons got wet after few months of usage, and the buttons would not act. I would disassemble the thing, wash and dry it, and close again, but eventually they thing got wet inside.

I'm not sure if the liquid was slightly oily, though. Long ago.

My family had a house at a place in Spain called La Manga. It is a long strip of land between the Mediterranean and a very salty inner sea. In that place, aluminum corroded. Stainless steel got (big) spots. Salty humidity almost like living in a boat.

El 01/06/2026 a las 13:10, Carlos E.R. escribió:

The liquid is silicone grease due to a bad curing of the silicone membrane, it is like the membrane is sweating. Most used keys are more prone to fail, as pressing the keys makes the liquid go out, similar to pressing a sponge.

Ethanol will clean this, although it will return in a while (about three months for bad remotes, years for not-so-bad ones).

That figures.

Can't imagine why you would want to, but I'd seal the package in conventional, flexible materials first, to protect from environment and absorb stress.

Small packages can be inserted into preformed concrete through drilling and filling processes.

RL

I think those are likely high-impedance inputs, easily "misled".