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Technical Tips

Achieving leak-free solvent-welded joints is one of the most important things in a piping system installation. This is easily done in large diameter systems by using the right Weld-On® products and following the tips below:

  • When cutting large diameter pipe, use a pipe wrap or circumferential tape to produce an accurate line to follow when cutting. This will create a pipe-end that is “squarely” cut.
  • A swab or roller approximately one-half the size of the pipe diameter should be used for large diameter pipe. Paint or bristle type brushes are not recommended.
  • Use a mechanical pipe puller with a center-line attachment that assures proper pipe and fitting alignment during assembly. Do not  use heavy equipment like a backhoe as this could easily result in severe damage to the pipe and fittings.

Achieving leak-free solvent-welded joints is one of the most important things in a piping system installation. This is easily done in small diameter systems by using the right Weld-On products and following the tips below:

  • Pipe should be cut square and beveled to remove sharp edges and burrs. Use a dry rag to remove dirt from pipe and fitting. If oily, use cleaner to degrease.   
  • Apply primer to fitting, then pipe end, then fitting. While primer is still wet, apply solvent cement: pipe end, then fitting, then pipe end. For pipe sizes 1” and smaller, don’t over-apply primer and cement, particularly in the fitting socket (2nd application may not be needed).
  • After an even layer of cement is applied, immediately insert pipe into fitting  until it bottoms out and hold for approx. 30 seconds. Longer hold time is required in conditions colder than standard ambient temperature.

This month’s technical tips go over the best practices and proper usage of primer on plastic pipe and fittings prior to applying solvent cement.

  • If using purple-colored primer, be careful not to spill on surrounding objects, as resulting stains are permanent. Always tighten can lids before moving or storing.
  • For previously opened cans, test primer on spare pipe to determine its effectiveness.  If it’s too weak to scrape off pipe material effectively, dispose properly and use fresh product.
  • Apply primer using pressure on the applicator for 20-30 seconds (for 70-100° F) or 60-90 seconds (for 40-69°F) in order to achieve the desired softening. Apply twice to the fitting and once to the pipe ( >1”).
  • Ensure that both pipe and fitting socket are still wet with primer before applying cement.

Choosing the right solvent cement can involve a number of different factors. Make it simple for yourself by knowing what specifics to look for:

  • Proper selection of solvent cement depends on the pipe size, pipe material (PVC, CPVC, or ABS), ambient temperature, and piping system application.
  • In general, it is best to use a cement of a given viscosity for a specific pipe size range. For example: Heavy Bodied cements works best on 6”- 12” diameter pipe.

When solvent welding in cold environments, make sure to follow these essential guidelines in order to achieve the best results possible for your piping systems.

  • Cement that has become frozen or too thick to apply can be utilized by thawing at ambient temperature (68°F/20°C), then remixing the contents by vigorously shaking or thoroughly stirring.
  • Remove all moisture (such as water, ice, or snow) from the surfaces being joined.
  • Because solvents evaporate much more slowly in cold temperatures, allow for a longer cure time before pressure testing.

By following a few precautions such as the ones below, successful leak-proof joints can be made even in the most extreme hot weather conditions.

  • Store solvent cements and primers in a cool or shaded area prior to use. Make sure that both pipe and fittings have been sufficiently exposed to the same ambient temperature.  Always assemble pipe and fittings in shade, never in direct sunlight.
  • Use primer along with a higher viscosity (thicker) cement, which will allow for slightly longer working times.
  • Work quickly to assemble pipe and fitting immediately after solvent cement is applied and still wet.

Specific precautions should be taken when working with solvent cement in wet conditions. Follow these simple guidelines to ensure the best possible results for your piping system.

  • Internal flow in piping system should be completely stopped. Keep pipe as dry as possible and wipe clean before cement application.
  • However, Weld-On 725™ Wet ‘R Dry, 737™ Turf ‘N Ag, 738™ Hot ‘N Fast, and 750™ HotWeld are specially formulated for wet conditions, with fast acting solvents that evaporate quickly even in low temperatures.
  • When dealing with wet conditions, always hold a newly solvent welded pipe and fitting together for longer than the typical duration of 30 seconds

More than 90% of pipe joint failures evaluated by Weld-On are due to  improper preparation of pipe end. Follow these tips for the best results.

  • Use a file or a beveling tool specifically designed for plastic pipe and chamfer the exterior pipe edge to remove burrs and sharp edges.
  • Raised burrs and sharp edges on pipe end can scrape the inside of pipe f itting, potentially interfering with the solvent welding process of the joint or causing joint leakage/failure. 
  • Beveled pipe end should be angled 10° – 22.5° with a width range of 3/32” – 5/16” (2.5 to 7.9 mm) depending upon the pipe diameter.

Apply primer long enough to soften the pipe and fitting surfaces, which can be confirmed with a “Scrape Test”:

  •  On a scrap piece of pipe, drag a knife blade across the wet surface.
  • A small amount of material builds up on the blade when the primer has been applied long enough.
  • For proper solvent welding of pipe and fittings, the applicator should be approximately half the pipe diameter
  • Swabs are the best applicator to use for solvent welding any pipe diameters greater than 3”
  • For anything less than 3” in pipe diameter, a dauber  such as the SuperDauber™ is optimal, due to more precise dauber control resulting in a smoother application of cement or primer.

Accurate estimations are essential to cutting costs by preventing over or under buying. Save yourself the time and hassle when doing cost and usage estimates by using the following tips:

  • The two factors that determine the amount of cement you need are pipe diameter and the number of joints in the project.
  • As a general rule of thumb, the amount of primer you need is approximately half the amount of solvent cement.
  • Estimate the easy way using our Cement Quantity Calculator on the Weld-On Toolbox mobile app or try the desktop version, both available for download at   http://www.weldon.com/technical-support 

Here are some tips to avoid leaks and wasted water:

  • Use only the highest quality cement and primer to ensure a leak-free joint: Weld-On offers high quality, reliable cements and primers for every application
  • Make sure your crew is properly trained in solvent welding techniques: Weld-On offers FREE ASTM D2855 / ASME B31.3 training. Contact your Weld-On rep to sign up today!
  • If you do have leaks: Contact Weld-On for after support service using the LIVE tech hotline at 1-877-477-8327. Consider using an easy repair product like Weld-On 810™, 811™ or 845™

A simple step-by-step process on how to repair leaking joints using Weld-On’s reactive adhesives, such as Weld-On 810™, 811™, and 845™:

  1. Remove all dried cement, debris, and moisture in leaking area, then roughen up pipe surface with coarse sand paper.
  2. Apply Weld-On 810, 811, or 845 reactive adhesive to leak area. 
  3. Cut thin fiberglass mesh to provide ample coverage over the entire leak area, then wrap it around the pipe.
  4. Immediately apply more adhesive over the entire mesh wrap, which must be completely  saturated to be effective. Work out all bubbles under the mesh.
  5. Let repaired area cure before pressurizing. Although not a  guaranteed fix, this process has proven successful in most  applications as a temporary repair.

The key to preventing evaporation and extending shelf life of previously opened cans is properly sealing the can lid in between uses.

  • Never use channel lock pliers, which damage the cap, leading to evaporation and premature gelling of the product.
  • Use an Easy-Twist™ Can Opener to properly open and reseal new and used cans, and is designed to grip the lid without damaging its threads.
  • Once properly resealed, try to store the can in a cool location but never outside of the storage temperatures printed on the can.

A safe work environment is vital for any successful piping system installation. Follow these essential safety guidelines when using Weld-On solvent cements and primers.

  • In case of any emergencies, read and become familiar with the Safety Data Sheets (SDS) for the Weld-On products you use.
  • Always wear proper protective equipment, such as NIOSH approved respirators, when solvent welding in enclosed areas or any area with inadequate ventilation.
  • Solvents in primer & cement evaporate very slowly, especially in poorly ventilated environments. Solvent vapors can linger in a closed piping system until flushed out. If exposed to ignition sources such as flame or sparks, these vapors can dangerously explode.

Weld-On’s free training program teaches the proper solvent welding techniques necessary for a long-lasting piping system. Weld-On has trained more than 100,000 contractors over the past 50 years!

  • Get your crew trained and qualified to gain a competitive edge with Weld-On. An increasing number of contracts specify that bonders be qualified to the ASME B31.3 standard.
  • Qualification leads to a decrease in costly failures and may reduce liability insurance premiums.
  • Weld-On’s ASME B31.3 bonder qualification training regimen consists of a classroom seminar, hands-on practice and actual pipe sample testing. And it’s FREE!

Understanding the difference between Set and Cure time is essential to knowing when a freshly solvent cemented pipe is safe to handle and also when its ready to be pressurized.

  • SET TIME: Time that must be observed after assembly of each joint before carefully handling
  • CURE TIME: Time that must be observed after assembly of each joint before introducing pressure