How To: Bumper repair with G/flex epoxy
It’s always painful when you damage your car in any way and damaging your bumper is not an uncommon occurrence; whether it’s by accidentally reversing into something hidden from view, or by other drivers scuffing it whilst parking. Whatever the reason, here we are going to help you fix it yourself in 11 easy steps:
1) First begin by washing the back of the bumper and thoroughly drying it.
2) Then, using a hot air gun, you can begin taking the twisting out – the hot air gun will soften the bumper enough for you to be able to rework the area and shape with the back on a spoon moved in a circular motion. It’s important to take care when doing this to make sure you don’t rework the dents and twists too far back out on the outer face, as final fairing would take place with a shallow skim of filler before painting. Do not over heat the surface and we would always recommend testing this process first.
3) Once you are happy that the main damage has been closed over sufficiently, you can start prepping the surface around the damage. Clean the surface with an alcohol pad to remove any contamination. You can now abrade the surface with 60 grit sand paper removing all glossiness of the plastic into the tear. Brush the dust away and wipe down the surface once more with a fresh alcohol wipe.
4) Once the area is ready, create a repair patch by cutting to shape and size biaxial glass cloth along with some peel ply fabric just slightly over size of the biaxial cloth. This will be wet out with WEST SYSTEM G/flex 650 epoxy later.
5) The next stage will involve flame treating the surface – however, before this you should mix your epoxy ready to apply to the surface as soon as possible after flame treating. Open your pack of G/flex 650 epoxy and dispense two even amounts of resin and hardener, mixing them together.
6) The final stage of surface preparation involves flame treating the plastic surface with a propane torch. The purpose of this is not to re-work the shape but to improve the wetting out of the surface of the plastic with the G/flex epoxy. The propane torch alters the chemistry of the plastic to create a hydrophilic surface. This is demonstrated by a dropping a small amount of water onto un-treated plastic. When the water touches the surface it beads up into little droplets. However, after flame treating the water does not bead but flows out over the surface. Please note extreme care must be taken when using a flame torch. It must be a very quick passing of the flame over the surface. Do not hold the torch directly over the surface. If required, please contact us for further information on this procedure.
7) Once the flame treatment has been conducted, you can then proceed to apply the mixed epoxy to the surface. The G/flex epoxy should be applied with a WEST SYSTEM 804 reusable mixing stick as it’s easier to force it into the small splits. G/flex 650 is a liquid epoxy but has a higher viscosity than the WEST SYSTEM epoxy and it spreads out well with a spatula or mixing stick.
8) With the area wet out apply the 450g/m² biaxial glass patch and the G/Flex epoxy underneath will quickly begin to wick through and wet out the cloth. Apply more G/flex epoxy to the outer surface of the cloth and work it in for a couple of minutes until it is evenly wet out to a semi-transparent finish.
9) Then apply a layer of peel ply over the patch, ensuring that it is evenly wet out.
10) Leave the peel ply in place overnight while the patch cures and then remove it. This will give a nice even factory type finish on the inside of the bumper, covering over any damage done by the hot air gun when working the tear out. Doing this part of the repair on the inside will leave an even outer surface for final fairing and painting on the outside.
11) You can now fill and fair the outer surface to complete this repair. Typically 9 fills of the outer surface will be required and as the surface nears completion the grade of sand paper should be increased from 40 grit up through 80, 100, 240 and then 400 grit before priming. You may find after the first layer of paint you start noticing the last few imperfections. In this case you may need to do a final fill, fair and re-priming before a final paint finish is applied.
So there you have it, our easy guide to fixing a bumper!
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