This would never be recommended for any construction purposes. So how does the primer work? The active ingredient in PVC primer is a chemical called tetrahydrofuran. PVC is soluble in tetrahydrofuran. When you add the solvent, tetrahydrofuran, to PVC it dissolves the outer layer of the pipe. Do it to two pieces, stick the together until it hardens and the two pieces are now fused together on a molecular level.
Since getting the tetrahydrofuran to penetrate deep beneath the surface is not feasible, you will be stuck with a surface bond, necessitating the use of an adhesive to make sure the fitting and pipe are not pulled apart from pipe pressure or outside forces. If you add primer to a piece of pipe, you may notice that the smooth surface becomes somewhat softer than typical.
This roughness is ideal to help the adhesive bond the fitting and pipe. When the primer and PVC dries, it re-hardens. This is why it is so important to add your adhesive to the joints before the primer fully dries. Because the application was a manual process, a few seconds of exposure to air that the primer had could have dried it such that it formed a barrier to the cement to prevent the two materials from fusing together with the help of the cement.
Yet another reason the primed joints were weaker than the unprimed joints may be that the primer presoftens the plastic more than the cement alone, so when the plastic hardens again, the molecular structure may have changed.
The hardened plastic may not have the same strength as the original plastic material. The final reason why the primed joints could be weaker than the unprimed joints could be that because the cement contains most of the same ingredients as the primer does, the primer may not have added any real benefit to the joint strength.
The primer may have actually made the joint weaker. The concentration of these ingredients in the cement alone may be more conducive to making a stronger joint than the concentration of the ingredients in both the primer and the cement combined.
Therefore, cement alone may create a stronger joint than a two-step process of primer followed by cement. While curing, the joints were not close to full strength. According to the manufacturer, the cure times for CPVC pipes are 1 hour at most. Based on the tests conducted at 2, 4, 6, and 24 hours, the strength increases greatly as time progresses, which is an indication that the cure time for the joints takes longer than the cure time suggested by the manufacturer.
Most plumbers in the field would pressurize and test the system minutes after solvent welding. This means the premature testing in the field could potentially lead to unnecessary joint failures.
There are many practical applications of this experiment. This investigation is of value to the plumbing and engineering community as it provides an answer to a highly debated subject. Many people have argued about whether primer serves a positive purpose in solvent welding on professional plumbing forums.
There are differing opinions based on previous experiences of plumbers. Yet, many plumbers follow this method because of the requirement, not because of the belief that it creates a better joint. If primer does not make a stronger joint, then the step of applying primer can be skipped resulting in tremendous amounts of time and cost savings. This report attempts to prove one way or the other whether primer is an essential component of creating a strong PVC joint.
Plumbing Terms. View Cart. Toggle navigation Help View Cart Contact. However, just like any industrial product, PVC primers can be tricky and ultimately unforgiving.
Applying PVC primer properly requires timing, technique and a bit of know-how. This guide will tell you exactly why PVC primers are necessary to create airtight joins and, more importantly, how to use it effectively. The softer the pipe is thanks to the primer the better the joints will be cemented.
PVC cleaner is used to remove oil, grease, and other dirty substances from the outer layer of PVC pipes. However, it cannot do what a primer can do, which is softening the pipe and preparing it for a secure connection. They are also two different materials, but for best results, they should be used together.
To put it in simple terms, the priming fluid sets up the PVC cement to do its job properly. The primer acts as a cleaner, removing grime as a PVC cleaner does, and it also softens the surface that it is applied on. PVC pipes are joined together through a change in their chemical composition. It is the solvent cement that does this, effectively making the two parts inseparable. The softening of the PVC surface as a result of the primer application makes this bond much stronger. PVC primer is a substance made mostly from two main chemical components: acetone and cyclohexanone.
The chemicals tetrahydrofuran and methyl ethyl ketone, among others, are also added to some products, depending on the brand. PVC primer is naturally clear in colour, but the most common variants are coloured — typically in purple or red.
Or is it simply an unnecessary product purchase that benefits only the manufacturers? What is the best glue for PVC? There are various grades of cyanoacrylates available. Flexible grades such as and are ideal for bonds in which the flexibility needs to be maintained.
What is PVC cement used for? PVC Cement. PVC pipe is designed for drains, vents and waste flow. When it is applied, the pipe will visibly soften and then solidify as the cement sets to form a joint that is stronger than the surrounding pipe and fittings.
How long should PVC glue dry before turning on water? After joining the pipes you must hold them together for 30 seconds until the plastic hardens or they can slip apart. It takes another 15 minutes for the joint to harden to a point at which it can withstand water pressure and two hours to fully cure.
Is PVC cement safe for drinking water? How much PVC glue do I need?
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