Plastic Adhesive and Plastic Repair


Summary:

The key to plastic repair is to identify the type of plastic being repaired and then by selecting the best repair method. For automotive, such as bumper repairs, the information below provides tips for plastic identification followed by the recommended approach to repair. Also explore a general repair method that can be used on a wide range of plastics (see below).

Plastic Bumper Repair Video

Plastics Type and Suggested Repair Methods

Symbol & Type How to identify Typical Usage Suggested Repair Method Repair Tips
PUR, RIM, RRIM Thermoset polyurethane Usually flexible, maybe yellow or gray, bubbles and smokes when attempting to melt. Flexible bumper covers (esp. on domestics), filler panels, rocker panel covers, snowmobile cowls. Method A w/ urethane rod or Method C with Uni-Weld Fiber Flex Don't try to melt the base material! Just melt the rod into the v-groove like a hot melt glue.
SMC, UP, FRP Fiberglass Rigid, polyester matrix reinforced with glass fibers, sands finely Rigid body panels, fenders, hoods, deck lids, header panels, spoilers Method E - two-part epoxy repair with fiberglass reinforcement. Use backing plate over holes, layer in fiberglass cloth for extra strength and to approximate thermal expansion
ABS (Acrylonitrile Butadiene Styrene) Rigid, often white but may be molded in any color, sands finely. Very pungent odor when heated. Instrument panels, grilles, trim moldings, consoles, armrest supports, street bike fairings. Method B w/ ABS rod (R03-01-03-WT), or Method D Insta-Weld adhesive repair, or Method E Two-Part epoxy repair Weld repairs may be backed with epoxy for extra strength.
EEBC (Ether Ester Block Copolymer) Flexible, off-white in color, similar in appearance to PUR (Lomod by GE) Rocker cover moldings, bumper extensions (91-96 DeVille) Method C with Uni-Weld FiberFlex (R10-04-03-BK)  
EMA (Ethylene Meth- acrylic Acid) Semirigid, molded in a variety of colors, unpainted (Bexloy W by DuPont) Bumper covers (Dodge Neon 1st generation base model) Method C with Uni-Weld FiberFlex (R10-04-03-BK) or Method B with slivers cut from scrap. Sand entire bumper for refinishing, restore texture with Flex Tex (3803).
PA Polyamide (Nylon) Semirigid or rigid, sands finely Radiator tanks, headlamp bezels, exterior trim finish parts Method B with nylon rod (R06-01-03-NT) Preheat plastic with heat gun before welding, mix rod completely with base material.
PC + ABS Pulse (Polycarbonate & ABS) Rigid, sands finely, usually dark in color Door skins (Saturn), instrument panels, street bike fairings Method B with Polycarbonate rod (R07-01-03-NT), or Methods D or E adhesive repairs Preheat plastic with heat gun before welding with Method B.
PC + PBT Xenoy (Polycarbonate blend) Rigid, sands finely, usually dark in color Bumper covers (primarily Ford products, 84-95 Taurus, Aerostar, some Mercedes and Hyundai's) Method B with polycarbonate rod (R07-01-03-NT), Method C, or Method E adhesive repairs. Preheat plastic with heat gun before welding with Method B.
PE Polyethylene Semiflexible, melts & smears when grinding, usually semi-translucent. Overflow tanks, inner fender panels, valences, interior trim panels, RV water storage tanks, gas tanks Method B with polyethylene rod (R04-01-03-NT) or Method C with FiberFlex (R10-04-03-BK) Applying filler or painting is nearly impossible.
PP Polypropylene Semiflexible, usually black in color, melts & smears when grinding Bumper covers (usually blended with EPDM), inner fenders, radiator shrouds, interior panels, gas tanks Method C with Uni-Weld FiberFlex (R10-04-03-BK) or Method B with polypropylene rod (R02-01-03-BK) Use 1060FP Filler Prep adhesion promoter when applying two-part epoxy filler
PPO + PA Noryl GTX (Nylon blend) Semi-rigid, sands finely, usually off-white in color. Fenders (Saturn & GM), exterior trim Method B w/ nylon rod (R06-01-03-NT), or Methods D or E adhesive repairs Preheat plastic with heat gun before welding with Method B.
TEEE (Thermoplastic Ether Ester Elastomer) Flexible or Semiflexible (Bexloy V by duPont) Bumper covers (especially on domestics, filler panels, rocker panel covers.) Method C with Uni-Weld Fiberflex (R10-04-03-BK) or Method B w/ slivers cut from scrap.  
TPE Thermoplastic Elastomer Semi-flexible, usually black or gray, melts & smears when grinding. Bumper covers, filler panels, underhood parts. Method C with Uni-Weld FiberFlex (R10-04-03-BK) Use 1060FP Filler Prep adhesion promoter before applying two-part epoxy filler.
TPO, EPM, TEO Thermoplastic Olefin Semiflexible, usually black or gray in color, melts & smears when grinding Bumper covers, air dams, grilles, interior parts, instrument panels, snowmobile cowls. Method C with Uni-Weld FiberFlex (R10-04-03-BK) or Method B with PP or TPO rod. Use 1060FP Filler Prep adhesion promoter when applying two-part epoxy filler
TPU, TPU - Thermoplastic Polyurethane Flexible, sands finely Bumper covers, soft filler panels, gravel deflectors, rocker panel covers Method B with urethane rod (R01-01-03-NT) or Method C with Uni-Weld FiberFlex (R10-04-03-BK)  

Repair Method A

When a hot welder touches urethane, you will see discoloration and some smoke as shown above
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Urethane used for auto applications (also called PUR) is what is known as a thermoset material. It is made by combining two chemicals in liquid form in order to create a solid. It cannot be melted with a welder.

To determine if you are working with a urethane bumper, place a hot welder (make sure it is hot) on the back of the bumper. Urethane will turn to liquid and cause smoke and bubling. After the test area cools it should feel sticky when touched.

The method for repairing urethane is with an airless plastic welder using a process like brazing.

Area With V-Groove Damage

When preparing the repair area create a v-groove using a Teardrop Cutter Bit
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  1. Align the outer tear surface with clamps for aluminum body tape. An Insta-Weld thin adhesive can also be used to tack the tear.
  2. V-groove halfway along the back of the part with a 6121-T Teardrop Cutter Bit. Since the urethane does not melt, do not use a hot tool to melt the v-groove into the urethane.
  3. Use coarse sandpaper (80 grit or higher) to sand the v-groove. Remove any paint around the v-groove to strengthen the surface.
  1. Align the outer tear surface with clamps for aluminum body tape. An Insta-Weld thin adhesive can also be used to tack the tear.
  2. V-groove halfway along the back of the part with a 6121-T Teardrop Cutter Bit. Since the urethane does not melt, do not use a hot tool to melt the v-groove into the urethane.
  3. Use coarse sandpaper (80 grit or higher) to sand the v-groove. Remove any paint around the v-groove to strengthen the surface.

Melt Rod into V-Groove

  1. Using the temperature setting on the Airless Plastic Welder set it to "R1" or "clear." rod setting. Use the R01-01-03-NT Poluyrethane welding rod. Make sure that the rod comes out the bottom of the welders shoe melted and clear, not bubbling or discolored.
  2. Hold the welder's tip off the surface of the plastic. Melt the rod into the v-groove. Do not over heat the base material. Melt the rod on the surface. Note that the goal is not to melt the rod and the bumper together. YOU CANNOT MELT THE BUMPER MATERIAL.
  3. Use more than 2 inches of the welding rod in the v-groove at a time. Remove the rod from the welder tip. Before the melted rod has cooled, go back over it with the hot welder tip and smooth out the weld. Caution: Do not over heat the base material.

V-Groove and Weld Opposite Side

When the weld on the backside cools off, repeat the v-grooving and welding process on the opposite side.


Grind Weld to Smooth Contour

Now, use the coarse sandpaper to grind the weld to a smooth contour. The urethane welding rod does not feather well, so cover with 2000 Flex Filler 2 epoxy filler to refinish completely. Grind the weld slightly flush so that the filler completely covers the welded area. Follow instructions for Step 4 filler application.

Repairing Torn Bolt Holes on Urethanes

On both sides taper plastic around the hold down to a point usingRoloc Disc.

Use 6481 Aluminum Body Tape to create a bridge across the torn mounting hold. Melt R01-03-NT polyurethane welding rod into the area. Drill out hold when finished.

Repair Method B

If a bumper is not made out of urethane, the most likely alternative is what is called thermoplastic. This type of plastic can be melted with heat.

The most common type of material is called TPO (also now called TEO).

  • TPO: Thermo Plastic Olefin
  • TEO: Thermo Elastic Olefin

TPO and TEO plastics are repaired the same way.

Repairing V-Groove Damage

  1. Align the outer tear surface with clamps for Aluminum Body Tape. You can also use Insta-Weld adhesive.
  2. Run a v-groove halfway along the back of the part by either melting a v-groove in by turning the tip of the welder at an angle or with a Teardrop cutter bit.
  3. Remove any paint around the v-groove. Radius into the v-groove using a coarse sandpaper.

Melt the Base Material and Tie Rod Together

  1. Adjust the temp. setting on the Airless Plastic Welder to the setting that matches the selected welding rod. The rod should melt cleanly without discoloring (note that nylon melts to a light brown).
  2. Place the tip of the welder onto the plastic surface and going slow, melt the rod into the v-groove. Pull the welder toward you so that you will be able to see the v-groove being filled. Do not lay down more than 2 inches of welding rod into the groove at a time. Remove the rode from the welder tip and before the melted rod has time to cool down, go over it with the hot welder tip and thoroughly melt the base material and the rod.
  3. To mix the materials it can help to press the plastic with the edge of the welder tip, then proceed to go and smooth the area out. Keep the heat on until there is a good mix between the base and the rod.

    V-Groove and Weld Opposite Side

    Once the backside weld cools down, repeat the welding and v-groove process on the reverse side.

    Weld Opposite Side and V-Groove

    If the plastic needs to be finished, grind the weld to a smooth contour using coarse sandpaper. Grind the welded area slightly flush so that filler can cover the area welded. Follow the manufacturers instructions.

    Repair Method C

    Method C involves the use of a material called Fiberflex. It can stick to any plastic substrate (called a hot-melt or thermoplastic adhesive.).

    The air welder is used to apply the adhesive. It is used to repair TPO (most common plastic used in plastic auto bumpers).

    Fiberflex can be used on many types of TPO and other plastics. If you don't know what type of plastic you are repairing, it is worth experimenting with Fiberflex.

    Method C involves the use of a material called Fiber Flex Flat Sticks . It can stick to any plastic substrate (called a hot-melt or thermoplastic adhesive.). The air welder is used to apply the adhesive. It is used to repair TPO (most common plastic used in plastic auto bumpers). Fiberflex can be used on many types of TPO and other plastics. If you don't know what type of plastic you are repairing, it is worth experimenting with Fiberflex.

    V-Groove Damaged Area

    Align the outer tear surface with clamps or aluminum tape. Remove the plastic in a broad V-groove halfway along the back of the part with a die grinder and heavy duty round cutter bit or round burr. The v-groove should be 1-1/2 inches wide. Put some "grit" in the plastic by using a low speed grinder to grind the groove with coarse sand paper. Remove paint around the area with a DA sander using 80 grit sand paper.

    Apply FiberFlex

    Using an Airless Plastic Welder, set it to the highest setting. Then use a 6028RT Round Tip to melt the Fiber Flex welding rod on the surface. The ideal adhesion is created by pre-melting one side of the end of the rod, then flip the rod so that the melted portion sticks to the plastic. Cut the melted part of teh ribbon off using the edge of the welder tip. Spread the Fiber Flex into the v-groove.

    Don't melt the FiberFlex and the base material together. This process is best compared to brazing. When the FiberFlex cools on teh back, repeat the welding adn v-grooving process on the opposite side. Build up the FiberFlex higher than the surface (it can also be sanded).

    Let the FiberFlex cool and then sand with 80 grit paper using a DA sander at low speed. Use finer sand paper to for finer finish. Add more FiberFlex or Flex Filler for low spots.

    Plastic Repair Method D

    For this approach, Insta-Weld adhesives can bond on auto plastics, particularly SMC, polycarbonate and ABS. Aluminum Tape can be used to back up any holes.

    Fixing Plastic Cracks

    Spray areas to be repaired using Insta-weld Activator Sprayer.

    Align and Assemble Parts

    Use aluminum tape or clamps to hold parts. Apply a small quantity of Insta-Weld to crack or joint. The adhesive can be wicked into the crack. Use the thicker Insta-weld 2 if parts do not perfectly fit. Spray the Activator to cure the area.

    V-groove and rough sand, then blow away any dust, all around the hole. After applying the Insta-weld activator, fill the hold with weld compound and a few drops of Insta-weld. After 5 to 10 seconds apply another coat of Activator. When ready, sand area or if needed for repair, the area can be drilled.

    Repair Method E - Repairing Plastics  with Two Part Epoxies

    1. The backside of repair area should be sanded with 50 grit or higher sandpaper. Groove the plastic to improve bond strength. Next, stand lightly with 80 grit sandpaper to improve adhesion.
    2. Identify the plastic that is to be repaired (see table above for properties of different plastics). If PP, TPO or TEO plastic, apply Filler Prep Adhesion Promoter using a brush on sanded areas.
    3. Use fiberglass reinforcing tape over the area that was damaged. If the damaged part is SMC, cut a piece of scrap SMC as a backing panel. The panel should extend 2" beyond the damaged area.
    4. Select a two-part expoxy adhesive that best matches substrate hardness. Good choices are:
    5. In equal parts, mix the expoxy adhesive and apply over fiberglass reinforcing tape on back of repair. Before handling, allow to cure 15 minutes. If working with SMC, apply a bead of SMC Hardset Filler to the backing panel. Before handling, allow to cure.
    6. Sand the front of the area using 50 grit sandpaper or higher number coarse sandpaper. V-groove away from the tear. For a stronger repear, use a wider and deeper v-groove. Be sure to remove any paint in surrounding areas and radius into the v-groove with 80 grit in a DA. If working with PP or TPO, apply Filler Prep
    7. Prepare by mixing and then apply the adhesive epoxy. Build just above the surface to allow for sanding. Wait 20 minutes for curing before sanding. If working with SMC, layer pieces of uni-cloth fiber glass coth in the v-groove. Be sure to use expoxy to wet the cloth.
    8. Smooth and contour the suface use 80 to 180 grit sandpaper.

    References Plastic Repair

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