Using Christy's red hot blue glue and purple primer

Before using, I have surfed around and came across some users saying not to use purple primer because it will weakened bond in the future.

What should I do?

Texavants

 

There are about a gazillion solvent welded joints out there done with primer without issue.

Around here, if you don't use primer (on PVC) you *will* fail inspection. May be different in TX.

 

Even if you use primer it must be the purple primer so it is visible to the inspectors... or you will fail the inspection. So, if it is plumbing inside the home I'd go with purple primer. If you are gluing up an irrigation system do whatever you want.

 

Purple primer it is.
Thanks

 

Just to confirm, our inspector wants to see the purple primer on the pipe and on your hands !! Not really, but he is a stickler for using it, so let it be pronounced on the pipe below the joint.

 

Primer no longer required in Michigan.

This may be why:
(click)
Primer weakens PVC joints

 

When PVC piping was first introduced there was no such thing as a primer. The instructions were to lightly sand the end of the pipe and the socket of the fitting to remove the hard glaze and wipe with a clean cloth. Then slather the solvent cement on the end of the pipe, into the socket and again on the end of the pipe, finally inserting the pipe, giving it a quarter twist and holding for several seconds for the initial "set" to keep the fitting from moving off the pipe.

Well, the people doing the assembly got lazy and didn't clean the glaze off the pipe or fitting and THAT lead to joint failures simply because the solvent cement didn't properly melt the plastic. Primers were then introduced that were far more aggressive to the glaze and the rest is history.

Because I followed the original instructions I have NEVER had a non-primered joint fail.

 

The link is to a test where the author found that primered joints are MORE likely to fail than non-primered. One of his several explanations is that the solvent in primer (acetone) might harden the PVC and make it harder for PVC cement to melt into the joint.

In any case after the assembled joints have sat for 24hrs or more there was no difference in the primer/non-primer strength.

 

It's an interesting study, but also a good indication of engineering in practice. The pressures he was testing with, especially considering the joints were intentionally not seated fully (to focus on the question at-hand), would never be hit in any standard installation.

At 100psi (residential pressures), or even higher possibly commercial pressures, none of these "poorly made" joints would have even come close to failing.

Good news for us, we really don't need to worry about properly made joints failing!


I happen to agree with Furd's explanation, which is outside the scope of this study. In 10,000 joints made, far fewer primed joints will fail - even if it is attributable to incorrect workmanship.

 

I don't understand your conclusion. If the use of primer makes a weaker joint in ultimate-strength testing, why would you believe it makes stronger joints in normal use?

The author's conclusion was primer offered--at best--no value in ordinary use.

(I work in a testing lab so I find this stuff fascinating)

 

I don't know about the softening effect purple primer has. I do know it will present a clean joint. Pipes are drug around on the ground, allowed to become pitted and dirty, oily and greasy. All of these situations can cause the joint to fail. Cleaning the joint is of utmost importance. If it is clean the glue will work. Dirty it could fail. Soften?? Not sure.

 

The purple PVC primer most definitely softens the hard outer surface of the pipe and fittings. It is extremely volatile so it has a tendency to evaporate before softening too much.

According to instructions you are supposed to swab on the primer and before it all evaporates swab on the much more viscous cement and then make up the joint. Work fast and only do one joint at a time.

 

I also found it interesting to learn that even though PVC cement uses the same solvent as primer it's thicker because they add PVC to it.

A little like adding sawdust to wood glue to fill gaps.