Sealant that sticks well to PVC cable insulation? - Page 1
Forum section: electronics / general

author: e100
author_rank: Frequent Contributor
timestamp: April 01, 2018, 06:29:58 am
content: I need to waterproof some outdoor sensor lead connections that have conventional PVC insulated copper wire.Can anyone recommend a sealant that bonds strongly to the PVC insulation so that water cannot creep between the insulation and the sealant to form a leakage path.PVC in the plumbing industry has a reputation for being non-stick unless you resort to solvent based adhesive/sealants that partly dissolve and bond with the PVC. Using something like a PVC gutter sealant somehow doesn't seem right. It also has a multi-day cure time and shrinks as the solvent evaporates.

author: mikeselectricstuff
author_rank: Super Contributor
timestamp: April 01, 2018, 08:20:51 am
content: Why not do it properly and use cable glands ?

author: e100
author_rank: Frequent Contributor
timestamp: April 01, 2018, 08:50:23 am
content: Quote from: mikeselectricstuff on April 01, 2018, 08:20:51 amI have 4 float switches that are mounted close together. Each has 2 wires, so 8 in total. The tails are short so I don't have much scope for spreading them out onto a panel with 8 cable glands.

author: tggzzz
author_rank: Super Contributor
timestamp: April 01, 2018, 08:59:00 am
content: PVC cables are flexible. Many sealants become less flexible over time. If the sealant is less flexible and the cables do flex, then there may be a crack for water ingress.Depending on how the water could arrive at the relevant points, it may be possible to discourage water travelling along the cable by putting a "u-bend" immediately before the relevant point.

author: mikeselectricstuff
author_rank: Super Contributor
timestamp: April 01, 2018, 08:59:07 am
content: You can get multiple-entry glands.e.g.http://www.directindustry.com/prod/protec/product-26739-552670.htmlhttp://www.sinoconnector.com/product_read.asp?id=178&sid=55

author: Electro Detective
author_rank: Super Contributor
timestamp: April 01, 2018, 09:00:34 am
content: Quote from: mikeselectricstuff on April 01, 2018, 08:20:51 amIt's a good way to go if the compressed rubber thingie inside the gland doesn't turn to goo or dry up and blow away in an outdoors scenarioOld school non acetic silicone anyone?

author: mikeselectricstuff
author_rank: Super Contributor
timestamp: April 01, 2018, 09:02:06 am
content: Quote from: Electro Detective on April 01, 2018, 09:00:34 amWell they are specifically designed for the purpose, so unlikely ( unless it's some cheap crap from Aliexpress..)

author: Electro Detective
author_rank: Super Contributor
timestamp: April 01, 2018, 09:10:30 am
content: Quote from: mikeselectricstuff on April 01, 2018, 09:02:06 amTwoHungLow Gland Corp. sell them on Ebay too

author: mikeselectricstuff
author_rank: Super Contributor
timestamp: April 01, 2018, 09:28:58 am
content: For small cables you can get glands down to about M6 in stainlesshttp://www.newark.com/lapp-kabel/52001860/cable-gland-mini-brass-m6-3mm/dp/98K9727and M8 in nylon, though these are quite hard to get hold ofhttp://www.avc-corp.com.tw/english/3_Catalogue%20Pages/210-1010.pdf

author: e100
author_rank: Frequent Contributor
timestamp: April 01, 2018, 10:10:00 am
content: The float switch wires are 1.4mm in diameter which makes it hard to find a suitable multi-hole cable gland.It's equally difficult to find suitable silicone rubber tubing that could be used as a sleeve to bring the diameter of each wire up to something that is more commonly available.

author: tautech
author_rank: Super Contributor
timestamp: April 01, 2018, 10:26:00 am
content: Quote from: e100 on April 01, 2018, 10:10:00 amWhat's wrong with heat shrink ?As for sealants...RTV and preclean with suitable solvents and lightly roughen with fine wet&dry paper.

author: BravoV
author_rank: Super Contributor
timestamp: April 01, 2018, 10:30:15 am
content: Heat shrink tube + hot glue cut into small pieces well placed evenly "inside" the tube, once heated, the heat shrink tube will squeeze out the melted glue, and shape and grip the inner PVC cable as whole.Just an idea.

author: mikeselectricstuff
author_rank: Super Contributor
timestamp: April 01, 2018, 10:35:52 am
content: Quote from: BravoV on April 01, 2018, 10:30:15 amYou can buy this - it's called "adhesive lined heatshrink"But all that gets you is a bigger diameter cable you still need to seal to the panel

author: BravoV
author_rank: Super Contributor
timestamp: April 01, 2018, 10:40:10 am
content: Quote from: mikeselectricstuff on April 01, 2018, 10:35:52 amThats the idea, and then wrapped at the panel side with hot glue and make sort of seamless join to the cable part.Another interesting long term (years) characteristic of this hot snot glue exposed for "years" in salt water and sun, from another forum fellow (Rufus), read carefully this particular ->POSTand subsequently the ->Proofs, quite interesting and convincing imo.

author: SMdude
author_rank: Frequent Contributor
timestamp: April 01, 2018, 11:17:06 am
content: Probably the best way to go is the glue lined heatshrink.Another personal favorite is sikaflex 227 over the soldered joint and a bit to each side, then heatshrink over the lot. It's nicest when the sikaflex spooges out from either end of the heatshrink. Wear gloves, it's messy!Tip for sikaflex: When not in use, store it in the freezer. It will then last for years in storage.

author: e100
author_rank: Frequent Contributor
timestamp: April 01, 2018, 11:29:16 am
content: Quote from: BravoV on April 01, 2018, 10:40:10 amInteresting posts.It would also appear that hot melt adhesive heat shrink is used for insulating mains voltage cable splices.Is it 'regular' hot melt glue, or special in some way, I have no idea?

author: e100
author_rank: Frequent Contributor
timestamp: April 01, 2018, 11:42:06 am
content: Quote from: SMdude on April 01, 2018, 11:17:06 amHere's the datasheet.http://aus.sika.com/dms/getredirect.get/au01.webdms.sika.com/107Like many manufacturers they manage to avoid saying what it actually sticks to other than saying 'plastics' which is meaningless given the huge diversity of plastic types.

author: SeanB
author_rank: Super Contributor
timestamp: April 01, 2018, 11:49:38 am
content: Liquid electrical tape as a seal also works, and sticks to PVC well as it is solvent based and chemically bonds to the PVC itself. The glue lined shrinks do work well, and you can use them as a cover for the join, followed by wrapping with regular 3M insulation tape and then overcoat with self amalgamating tape, then cover with more 3M insulation tape and a final coat of liquid tape to make a join that will still be there when the rest of the cable has disappeared from UV exposure, and the copper inside has corroded away.

author: DerekG
author_rank: Frequent Contributor
timestamp: April 01, 2018, 12:21:29 pm
content: Quote from: e100 on April 01, 2018, 06:29:58 amOK, I can help you here.We use this product to seal PVC pipes that pass through concrete & fibreglass pool walls. Never had a failure in 8 years of use & the pipes are either under suction or pressure. These pipes are permanently under water & subject to chlorinated water. Only comes in white. It is a hybrid polymer.https://www.bunnings.com.au/selleys-480g-3-in-1-silicone-sealant_p1230061And we use this product to seal glass into PVC window frames. It is a co-polymer & would appear to have a higher volatile solvent content in it than the one mentioned above. The solvent smell is quite strong until it sets:https://www.bunnings.com.au/selleys-260g-all-clear-multipurpose-sealant_p1210350Even after category 3 cyclones, the sealant is still holding on strong to both the glass & the PVC frames. Note these are smallish windows. Once you get into larger windows, the frames must be either aluminium, steel or wood laminates to comply with category 5 cyclone requirements.If you are still worried, you could de-grease/clean the PVC cable first with some ?isopropyl alcohol before applying the sealant.

author: e100
author_rank: Frequent Contributor
timestamp: April 01, 2018, 01:56:11 pm
content: Quote from: DerekG on April 01, 2018, 12:21:29 pmInteresting, the "Selleys 3 in 1" says for "most plastics (not for polyethylene, polypropylene or teflon)", which is a lot more specific than most other manufacturers are prepared to say about their products.The related (perhaps the same) "Selleys roof and gutter" also specifically list PVC roofing.Based on the sketchy information on the Selleys web site these appear to be 'modified silicone' adhesives rather than polyurethane based.The safety data sheet says that there are no hazardous ingredients which is highly unusual for any adhesive. Any volatile solvents or would be automatically listed as hazardous.The Selleys All Clear is a different beast altogether. It is solvent based and takes a long time to fully cure and shrinks as the solvent evaporates. The SDS says that it contains up to 30% cyclohexane and heptane, so you would expect the long term shrinkage to be similar.

author: e100
author_rank: Frequent Contributor
timestamp: April 01, 2018, 02:03:46 pm
content: Quote from: SeanB on April 01, 2018, 11:49:38 amI tried liquid electrical tape and was not impressed. It really didn't have much sticking power. The cured film could simply be rolled off using my fingers. Perhaps it only works reliably if it has mechanical protection?

author: reboots
author_rank: Regular Contributor
timestamp: April 02, 2018, 07:10:44 pm
content: Quote from: e100 on April 01, 2018, 10:10:00 amThe compression sealing element in those glands is just a neoprene plug with molded-in holes. So replace the plug with a blank piece of neoprene or similar rubber stock of the same length and diameter, from McMaster-Carr (US) or your friendly local materials supplier, and drill or pierce your own holes specific to your needs.

author: mikeselectricstuff
author_rank: Super Contributor
timestamp: April 02, 2018, 10:32:20 pm
content: Quote from: reboots on April 02, 2018, 07:10:44 pmI'm told they are easier to drill if you put them in the freezer for a while first.

author: DerekG
author_rank: Frequent Contributor
timestamp: April 02, 2018, 10:45:46 pm
content: Quote from: e100 on April 01, 2018, 10:10:00 amDon't forget there are plenty of panel grommets & cord anchors available. These give a professional look. In the past, we have simply dribbled some contact adhesive (made by UHU or Selleys) around the cable/grommet/box panel on the inside of the box. This anchors the cable & does make the cable entry waterproof & it isvery quickto do which is important when production volumes go up. The solvent in the contact adhesive slightly "melts" the surface of the PVC box enclosure, so you know the grip is strong.https://www.digikey.com.au/products/en/cables-wires-management/bushings-grommets/491?k=cable%20grommets

author: e100
author_rank: Frequent Contributor
timestamp: April 03, 2018, 02:39:52 am
content: Quote from: DerekG on April 01, 2018, 12:21:29 pmI did some tests and it didn't stick strongly to soft PVC cable jacketing. The harder PVC used for electrical boxes or PVC pipes didn't work much better.It's strange stuff to apply as it has the consistency of lumpy toothpaste. Once cured it's like a semi-hard silicone rubber.

author: e100
author_rank: Frequent Contributor
timestamp: April 03, 2018, 07:07:03 am
content: Has anyone tried casting their own compression gland using silicone or polyurethane?I already have some 2-part silicone so I could block one end of a compression fitting, pour in the silicone then drop some dummy bits of wire in to make the channels. Getting them evenly spaced so they don't make contact with each other would be the tricky bit. Once set I would remove the dummy wires and push the sensor wires though.

author: tautech
author_rank: Super Contributor
timestamp: April 03, 2018, 07:25:16 am
content: Quote from: e100 on April 03, 2018, 07:07:03 amNever bothered as it's much easier to add heatshrink to a cable to increase it's diameter to fit......whatever.Even when wires are 'within' the range that a gland can compress to, it's a good idea to add heatshrink to spread the bending moment over a longer radius/area to increase service life of both the insulation and the conductor.

author: KL27x
author_rank: Super Contributor
timestamp: April 03, 2018, 10:34:08 pm
content: Hundreds of years ago humans figure out how to combine sinew and glue and horn and wood in just such a way that you could shoot arrows over 500 yards through the air with a bow that weighs only 5 lbs.If you want the silicone to stick to the pcv insulated wire, you can give it something to stick to. Smear a little silicone over the wire, then wrap some string tightly over the wire. Then cover with more silicone.