How to Repair “Spiderweb Cracks” on Polyurethane Bumpers

How to Repair “Spiderweb Cracks” on Polyurethane Bumpers

Although Urethane bumpers are quite rare on
late-model vehicles, the need may arise for one to be repaired from time to time. This bumper belonged to a 1992 Chevrolet Camaro,
and, as you can see, it has developed what we call “spiderweb cracks”. These cracks are the result of dirt and grime settling inside cracked paint and eating away at the plastic over time. Let’s take a look at how to repair these cracks
using products in Polyvance’s plastic repair line. STEP ONE: Using 80 grit sandpaper and a six-inch
sander, sand away the paint from the area you’re going to repair. Once the area has been sanded, push up on the underside of the bumper in order to see the depth of the cracks. If the cracks are only surface-level scratches,
you WILL NOT have to do any grinding into the plastic, and you can now skip ahead to
STEP SIX. These cracks, however, will need to be sanded
due to their varying depths. STEP TWO: Using 36 grit sandpaper, grind away at the plastic until the shallow cracks have been removed. As you can see, all that remain are the more
severe cracks, which will need to be welded. STEP THREE: Using a 6122 round cutting burr,
v-groove into the deep cuts until the cracks are gone. STEP FOUR: Now, using one of Polyvance’s airless
plastic welders, melt R01-01 Polyurethane welding rod into the v-groove until it is
filled out to the surface. Since these cracks are not all the way through
the plastic, we will only need to do a front-side repair. If both sides had been cracked, we would have
repeated the process on the other side as well, filling both sides with the melted welding
rod. STEP FIVE: Allow the melted plastic to cool
completely, then use 36 grit sandpaper to shave the weld even with the existing plastic,
then sand again with 80 grit sandpaper. STEP SIX: Mix together 2000-T Flex Filler,
making a uniform grey color. Smear the Flex Filler over the welded area, making sure to fill any pinholes that may cause air bubbles. STEP SEVEN: Allow the Flex Filler to cure, then,
using 80 grit sandpaper on a DA sander, grind the filler until it is even with the existing plastic. STEP EIGHT: To further insure that the filler is even, sand again using 80 grit paper and a sanding block. STEP NINE: Once you have block sanded, smooth
the repair area again, using 180 grit sandpaper to remove any sand scratches made by the block
sander. STEP TEN: Next, prime the repair using one
of Polyvance’s waterborne primers. Allow to dry, then block sand again using 320 grit
sandpaper to blend. Repeat this process until you are pleased
with the texture and appearance of your repair. As you can see, even tricky polyurethane repairs
like this one can be simplified using Polyvance’s comprehensive line of plastic repair products. Look to Polyvance for all of your plastic
repair product and training needs. We offer I-CAR Industry Training Alliance
courses as well as other hands-on classes in addition to the video resources you can
find on our website and on our YouTube channel.

15 thoughts on “How to Repair “Spiderweb Cracks” on Polyurethane Bumpers

  1. Hello .
    I'm in the Ukraine and did not have the opportunity to buy your rods, but you have a lot of experience in the repair of bumpers .
    I want to ask you for advice.
    Rods I buy in Poland they are high quality .
    When welding rod between the bumper and the bumper appears white coating and seam does not hold . This happens very often with PP- EPDM.
    I welding with air at a temperature of 570 – 700 F
    You are faced with such a problem ? What can be done ?
    I would be very grateful to you for the answer .

  2. This is a really detailed video and short and to the point. Using 80 grit isn't too course to remove the paint if I'm doing the entire thing by hand?

  3. How do you know exactly if you can skip to step 6? How do you differentiate between surface cracks vs deep cracks that need sanded with 36 and dug out?

  4. Was wondering if it costs more to have a shop do this and repaint the bumper or just buy a brand new bumper or aftermarket bumper?

  5. Seems like allot of labor and material cost when you can get a bumper cover in most cases under 500$ in mint condition with no possible material failures. Urethane plastic is tricky.

  6. Visit this video page on our website to see the full list of products used and other helpful tips:

  7. God that looks so hard so what about repairing fiberglass spider web cracks? It should be easier right just use fiberglass to repair it instead of plastic welding material

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