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Picture of How to Solvent Weld PVC Pipe and Fittings
Most PVC applications, i.e. the ones they are designed for, do not require very critical procedure for joining pieces together, because most of the time the fluid going through them is not under pressure. However, certain high-strain applications, such as Spud Gunning, require that the joints are strong and airtight. The way to achieve that is proper solvent welding.

The stuff that you get at the store to put together pieces of PVC is labeled "Cement." This is a misnomer. The "cement" class of adhesives, such as contact cement, rubber cement, etc, all are used to bond two, usually dissimilar, materials together. PVC cement is actually a solvent. Welding involves melding two pieces of the same material into one. (Hmm, I wonder if there is a connection).

When you solvent weld PVC, you are actually turning the two sides that you are joining into PVC mush, the molecules all blend together, and what you are left with is essentially one single piece of PVC.
 
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Step 1: Materials

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-Two pieces of PVC you want to join
-PVC Primer (it's usually purple, some places sell a really nice clear variety, if you want it to look nice you can get this stuff. Some spudders like the industrial look of the purple stains)
-PVC Cement
*Often you can get dual-packs of PVC cement and primer
-Gloves
-Paper towels

PVC primers and solvents contain mostly ketones. Using commutative logic here, ketones are strong solvents of PVC. Aside from bonding applications, PVC should NOT come in contact with ketones, as it stands a chance of weakening the pipe. Ketones, such as Acetone and Methyl Ethyl Ketone, should NEVER be used as fuel for combustion spudguns.

Step 2: Get ready to get messy

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Find a nice well-ventilated area. PVC solvent fumes are obnoxious smelling, carcinogenic in the State of California, and probably most other states as well.

Put down some sort of cover on whatever surface you're working on because a lot of times when you squish the parts together, cement will gooze everywhere. That's also what the paper towels are for.

Have some paper towels ripped off and at the ready, mostly so you can quickly clean off excess cement, because you don't have long before the cement starts eating away at PVC you don't want solvent welded. The can instructions say to wear gloves and goggles. You probably won't get cancer from it being on your hands for five seconds, but it will de-fat your skin. I did this all back when I was 16 and thought I was indestructible, as all teenagers do, and did a lot of solvent welding without gloves. Nowadays, I wear gloves.

Step 3: Deep Purple

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Warning: Science Content!
Primer for PVC serves almost the same purpose as priming in painting applications. Paint primer prepares the surface and gives the paint molecules a nice material to adhere to. PVC primer cleans debris, then "digests" the surface molecules of the PVC part, so that when the solvent/cement is applied, it can easily dissolve the outer layers.

This stuff contains 13-17% Methyl Ethyl Ketone, 70-80% Acetone (dimethyl ketone), 5-10% cyclohexanone, and negligible amounts of other nasty chemicals.

Open the can of (purple) primer. If it's the first time it's been opened, you might need a really big guy or a pipe wrench to break the seal. Most of the time, the swab is built right into the top.

Pull out the applicator, which is attached to the lid, and dab it against the side of the can to let the excess run out. This stuff runs like water and stains EVERYTHING. It will probably saturate the top of the can.

Cover each surface to be welded on both parts thoroughly. Just be careful about runs. If you are doing severalf fittings, you can go ahead and prime everything, it's perfectly fine to prime parts ahead of time, so long as they don't get dirty before cementing.

Priming is a chemical process. The solvent (acetone and MEK) molecules diffuse into and are absorbed by the surface of the PVC plastic. This roughs up the shiny surface from the molding process, and swells the plastic, loosening the long polymer chains. Both of these processes contribute to a strong weld. The primer is extremely fast at absorbing and evaporating, so the plastic won't be "wet to the touch" for very long. However, it is important for the plastic to be chemically "wet" with absorbed solvent, so I would not let the primed parts sit for more than 5 minutes before cementing. It can't hurt to re-prime.

Some people claim it's not necessary to prime. I'd personally rather not find out the hard way.

See external link:
http://newsite.oatey.com/Channel/FAQ.html#Q09

Step 4: Cement the fittings

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PVC solvent aka "Cement" is a clear, obnoxious smelling goop that looks like runny rubber cement. It also usually comes in applicator-cum-cap containers.

Open the can and dab off excess cement. Apply cement to the inside of the joints.

This is where a judgment call comes in.

If you put too much cement on, it will gooze everywhere, and possibly ruin threaded fittings. If you don't use enough, especially on large parts, the parts might seize before you can push them together all the way.

With small fittings, one application should be more than enough.

With large fittings, you might need to dunk the applicator and add more to make sure it's thoroughly wet.

Step 5: PUSH!

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The motion for solvent welding two parts together is pushing in while simultaneously twisting 90 degrees. This makes a more airtight joint. If you push straight in, there is a slight chance that you could have a channel run straight through the joint and allow air or water to escape.

With small parts, this is easy.

With large fittings, it's often more like, "EEERGGGAAARRRRDAMNIT#@$~!STUPIDPIECEOF$%&~!!!!."

If you're working with 4" fittings or larger, I'd suggest having a friend help.

Once you push and twist the parts together, hold them like that for about 10-30 seconds (longer for larger parts). You don't have to hulk-crush them the whole time, you are just making sure that the pieces don't back out. PVC slip connections are tapered, which means that sometimes, if you were to push it together and just let go, the inner piece would just slight right out, which is extremely frustrating.

After about 10-30 seconds the bond should be strong enough to keep the part from jumping out.

Wipe off any excess runny PVC cement. If it sits too long (more than about 3 minutes) on parts of the PVC you aren't welding, it can weaken the structural integrity.

Step 6: Wash your hands.

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If you wore gloves, like you should have, you shouldn't have to do this step. :P

I don't think it's terrible for you, compared to things out there like benzene, lead, uranium, arsenic, asbestos etc., but I wouldn't want to keep it on my skin for too long. So go scrub down.

If the cement has dried on your skin, it will give you a lovely plastic coating that will peel off like a massive blister and, along with the purple discoloration, will make people think you have a skin disease. Abrasive soaps work really well for getting it off, like Gojo, but any dish soap will work too.

Other than that, you're done. It will be about an hour before the PVC is really workable, but I personally wouldn't put pressure in it for 24 hours. The instructions say 1-4 hours (depending on diameter) at 60 degrees F, but if you're using it for a pneumatic, you're pretty much doing something that shouldn't be done in the first place with it, so it's good to be safe.

For more info on cure times, see this link:
http://newsite.oatey.com/Channel/FAQ.html#Q05

If you wanna see this parts in action, check out the Colossal Cannon

I see that is a DWV fitting. These explode more easily than pressure PVC pipe, but all PVC explodes easily with air and is like a shrapnel bomb.

I'm well aware. This is addressed in my PVC cannon instructable (link at the bottom of step 6. Basically, what I learned from the whole experience is that it doesn't matter much even if you use pressure rated pipe, with potato cannons, you're pushing the limits of structural strength (pipe is designed to handle predominantly static pressure loads, and cannons cause all sorts of weird shock loads), and ought to be operating in a manner in which you would be physically safe in the case of fragging, such as behind a barrier.

sola00052 years ago
BTW, here is what I will be making thanks to your advice on how to solvent weld PVC! I am making this for a neighborhood improvement project in St. Paul.
SolarzBenchDesign-BasicMsmts.jpg
DeusXMachina (author)  sola00052 years ago
That's really cool! So you will be welding the PVC "sideways", i.e. wall-to-wall? That's a little different than welding pipe-in-joint, but I think it can be figured out with a little experimenting.

Also, do you know about clear primer? There is clear primer available, though I don't remember where to get it at the moment.
sola00052 years ago
Oh...it's a bench.
SolarzBenchDesignJune2013.jpg
sola00052 years ago
Above, the author writes, "If you are doing tons of fittings, you can go ahead and prime everything, it's perfectly fine to prime parts ahead of time, so long as they don't get dirty before cementing."
Below, readers are in agreement to never let the primer dry before applying solvent.
Are these just 2 different opinions?

I am about to solvent weld 210 pieces of PVC pipe together. It would be super helpful to learn that I can prime ahead of time!
Thanks for any guidance.
DeusXMachina (author)  sola00052 years ago
The PVC cement contains the same solvents that are present in the primer, so if the issue is "wetness", then it doesn't matter much if the primer dries on the pipe. My understanding of what the primer is doing, is dissolving into the surface of the plastic, making it swell slightly and more porous. This allows the cement to form a stronger bond to the surfaces. If you let it get REALLY dry, like 30 minutes, then most of the solvent will have evaporated out and the plastic will shrink back to its original size, and it'll lose some effectiveness (but it'll still be "roughed up"). By "dry", I mean dry to the touch. It'll still have solvent dissolved into the plastic for a while.

Between evaporation and absorption into the plastic, it's virtually impossible to cement it while it's still runny-wet with primer. It's mostly dry to the touch within seconds.

Neither the primer nor the cement can instructions (on the cans I have) say anything about wetness or dryness of the primer before cementing. If it were critical, they would mention it.

This source says that it's okay to let it dry before cementing.

http://www.ehow.com/how_5664571_use-purple-primer-pvc-cement.html

However, Oatey, which is another brand I haven't used, says you should glue while it's wet.

http://newsite.oatey.com/Channel/FAQ.html#Q09

So, I wouldn't wait more than 5 minutes before applying the cement. For 210 pieces, you should do it in batches. I'll update the instructions to reflect this. (This is an OLD instructable...haven't done much to it in YEARS! :P )
shannonlove2 years ago
(This comment might be inappropriate and off topic comment but this chemophobia is really getting under my skin.)

I think California is the only state in which "carcinogenic" is defined as literally a one in one million chance of giving you cancer with normal exposures. When they got to point they were labeling sand, sold for the express purpose of being used in sandboxes for children, as a "carcinogen" they'd pretty much jumped the shark and become worthless. Now people can't distinguish between phantom and real threats and they end up shying away from learn new skills like PVC solvent welding and instead take up benzene gargling instead.

The moral here is don't let politicized panic labels scare you off from making and learning new skills. Plumbers and builders work with this stuff for hours, every day, for decades and they don't have higher cancer rates than vegan liberal-arts professors. If they can survive years of exposure you can survive a few minutes.

The real immediate danger from working with PVC solvent or any other strong smelling volatile substance (including some food stuffs) is that almost all of them cause vasodilation in the brain which can lead to dizziness, fainting and disorientation. If you work in an enclosed, unventilated area, you're basically "huffing" and might hurt yourself while impaired. 

DeusXMachina (author)  shannonlove2 years ago
Well said. I'm a chemist myself, and I personally can't stand chemophobia and chemical paranoia. The warning is written a bit sarcastically (and I wrote it a long time ago), but I should revise it to accurately reflect the hazards.

The principle volatile components are MEK, THF, and cyclohexanone. Of those, only cyclohexanone poses really any concern, which is listed as non-carcinogenic, but mutagenic in mammalian somatic cells. I work with much, much nastier chemicals at work on a day to day basis.
nerfer1927 years ago
haha mythbusters say that
WARNING: SCIENCE CONTENT duh duh duh duh duh duh duuuuuuuuuuuhhhhhhhh
Derin DYLEGO6 years ago
duh
DYLEGO Derin6 years ago
duh
Derin DYLEGO6 years ago
duh
duh
duh
saturnv78906 years ago
Should I let the primer dry? Also, bang the can's top down onto somthing hard, it'll break the seal quite nicely.
NEVER LET THE PRIMER DRY!! sry but that would make your glue not adhere at all and it would go boom ><
nafango227 years ago
so what does "PVC Cleaner" do? when we built our potato ca-- i mean put together some pvc for legitamate reasons, we used cleaner, then primer, then cement.
DeusXMachina (author)  nafango227 years ago
I mean it won't hurt, but I don't think it's necessary. The primer itself is basically pure Methyl Ethyl Ketone and Ethyl Acetate, two really strong solvents, and what it does it soften the surface chemically so it can bond. In the process it takes off a lot of the gunk on the surface of pipe. I try to just clean the pipe up by conventional means, e.g. wiping dirt and dust off with a paper towel, and if necessary, I will take off any label stickiness with GooGone. I never use the cleaner product and never had any failures due to it.
You can also use Tangit for gluing PVC.We use it for all our PVC that is not heat welded.
  • Tangit is a Henkel product FYI.
DeusXMachina (author)  Derin6 years ago
As long as it's approved and pressure-rated for PVC pipe.
Kiteman7 years ago
Good idea! Now all the other cannon'ibles only need to include a line that says cement the parts together, see here to find out how.

I predict many future references to this project.
DeusXMachina (author)  Kiteman7 years ago
Yathink? :is flattered: I can't wait to put the video out, I already made one attempt and the camera's tiny mic made me sound like I had a lisp to rival Christopher Lowell. As for the glitch, I dunno, I think Instructables.com has been acting a little funny today.
what glitch?
Why not leave the speech off? Or add it as a narration?
TechDante7 years ago
i presume that this is not food safe and is there any food safe pvc solvents out there that i would be able to get out here in the uk. any help would be much appriciated. thanks
DeusXMachina (author) 7 years ago
Yeah I know....:guilty face: I mean if I wasn't a student and had unlimited cash yeah. But no, which is why there is home depot. But yeah for reference you should always get pressure rated parts.
MrCrowley7 years ago
I know its cheap but you shouldn't really be showing this picture with DWV parts if people are going to use this how-to when gluing their pneumatic gun together. Just say that its DWV and not to use it :P You should chuck this in the how-to section at SF while your at it.
drcrash7 years ago
Nice! BTW, what does the primer actually do? (I understand priming in conventional painting and gluing, but not for welding.)
DeusXMachina (author)  drcrash7 years ago
It's actually almost the same. Priming in painting prepares the surface for adhesion of the paint. PVC priming cleans the surface, then starts breaking down the molecular surface of the part. It digests it a bit so that it's easier for the PVC solvent/cement to dissolve it. IIRC primer is mostly acetone/methyl ethyl ketone
Kiteman7 years ago
Huh? I clicked + to show my approval, and the total rating came up as zero. Who's taken a dislike to it already? Why, for goodness' sake?
Alas, instructables does have bullies :/ It's unfortunate - I remember finding a few around contest times. But it really doesn't change anything as negatives won't change contest outcomes. It's especially disappointing when contestants do it to fellow contestants :/