Formulae for DIY EMF Shielding paint

I know you said DIY, but you do know you can just buy it, right?

Steel wool burns. Bad idea.

I've only used the spray on nickel type. Fry's carries it. I'm not sure I'd use any of these coatings on the outside of a product. I've only used the spray on the interior of a plastic case.

I want EMR shielding paint in quantity to _paint_ on, not spray. The altter is OK for small boxes, etc., but anything fFactory made would be quite expensive for large surfaces. That is why I specified DIY.

It's just latex paint with some suitable additives.

Martin King

Ok. Did someone build a cell site next door?

Wrong. Try to think of it as nickel powder held together with some kind of plastic binder, and NOT as paint with a nickel additive. There's much more nickel in the mix than plastic.

The problem is getting the proper flake sliver, nickel, or copper. Round particle powders do not work because there's no contact between the round particles. I know because I've tried it. It has to be flakes.

We bought some from Hunter many years ago. I had to buy 55 lbs which I think was enough to make about 6 gallons. The clear acrylic we used was basically casting resin. One gallon magically diluted itself into about 6 gallons when the nickel was added. I think nickel is about $8-10/lb. Sorry, but I don't recall the exact mix or cost. Please treat my recollections as potentially erronious. A good start might be the MSDS sheet for the MG Chemical mix shows 30-60% nickel by weight, plus a mess of volatiles: Be sure to measure a test batch for conductivity. You should get something at about 0.5 ohms per square.

Some sources for nickel flakes: Google for more.

Air bubbles produced during mixing can be a problem. We used a vacuum pump to draw out the air bubbles.

Good luck getting the mix right. We didn't know we had a problem until it went into a thermal cycle test. We didn't have enough adhesion to the base plastic causing the coating to just fall off. It was also quite brittle causing the same effect when the underlying plastic was flexed.

Good luck.

I was thinking he might be trying to make a shielded room on the cheap.

George H.

Steel wool burns. Bad idea.

I've only used the spray on nickel type. Fry's carries it. I'm not sure I'd use any of these coatings on the outside of a product. I've only used the spray on the interior of a plastic case.

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You have to watch out with this stuff. I used to have two can of RFI / EMI shield spray and a couple of years, I can't remember the brand, but after purchasing it, our security department in the Hospital that I worked at came down to my shop and strongly recommend that I give them the spray cans for safe disposal. Apparently they contained some cancer causing compounds in them.

I think that is where the finely shredded carbon fibre comes in. It links the carbon partilces. Given the wavelengths involved, the conductive surface can have some "holes" in it anyway.

I think nickle is a bit expensive now. Along with graphite, thanks to graphene. I might try aluminum powder, but I heard it is now restricted due to other uses.

Many thanks for the helpful info.

Martin King

The size of the "holes" can be quite large when round particles are completely surrounded by an insulating layer of acrylic or epoxy. A good example is the hardware store metal filled glues, where the metal is primarily to match the thermal expansion coefficient of the metal pieces that are being glued. An ohmsguesser will show that it's an insulator.

The problem is really the shape of the particles. There has to be some sort or projection or edge that makes contact to adjacent particles. A sphere will not work, but something like a spiked ball is closer. However, spikes make nice little fuses, so a surface to surface, or surface to edge connection is preferred. Very rough particles work tolerably well. However, flat flakes seem to be the best compromise between conductivity and mechanical strength.

Even if you get the particle shape correct, the binder (glue) can be a problem if it expands as it hardens. There may be perfectly good conductivity when the mix is wet, and very poor conductivity when dry because the expansion of the binder produces gaps between the particles. Try to mix something that has a large proportion of volatiles to control the shrinkage, but not too much or it will crack when it hardens.

If you're really going to paint your house with such paint, I think you'll find that a rather thick coat is required to produce decent conductivity. It will need to be at least the overlapped thickness of two nickel flakes in order to obtain a connection. Getting them to lie flat is not going to happen, so you have to assume that it will be at least the width of two flakes on edge thick. However, to get reliable end to end (3D) conductivity, a 3rd flake will be needed to fill the gaps. Painting multiple coats doesn't work because the surface is mostly plastic and therefore not very conductive. I think you can see where this is going. The paint coating is likely to be rather thick.

Ahem... Painting your house with thermite is not considered a good idea. While a domestic re-enactment of the Hindenburg disaster might make a great YouTube video, I suspect the local fire department and your insurance company might find it rather in bad taste. You may want to try a small scale burn test before applying to your walls.

Hint: You can buy foil backed wallpaper. Look for Victorian era reproduction wallpaper. Use aluminum duct tape for the seams. I built a cheap screen room where pagers and radios could be tuned and tested in the presence of strong on-channel transmissions. It was far from perfect and leaked in places, but was good enough to be usable for many years. It also worked well for several people that claimed to be RF sensitive and wanted their bedroom shielded from nearby cell sites. Judging from subequent email, wallpaper seems adequate. It has also been used by at least one business owner, who did not want his coffee shop to turn into a large telephone booth and used it to block cellular coverage without the expense of a cell phone jammer. There are also vendors of "frequency selective wallpaper" for blocking specific frequency ranges.