Paint "Stars" in fenders

[Superhart]

Just wondering if anyone has any suggestions on how to minimize or prevent paint "stars" caused by stones being cast off tires onto the underside of the fenders. I thought about spray-on rubberized undercoating. I thought perhaps a 1/4 inch thick coating of that stuff might work (kidding). Someone suggested to me to use "Flex Seal", the stuff you see on TV that does everything short of stopping diarrhea. I wonder if they were kidding. Any ideas or suggestions welcome, especially if the method has been used and proven effective. Thanks.

[chrs1961815]

I would say that it is pretty much impossible to prevent it. You almost have to spray undercoating that is 1/4 inch thick. But then you will just have marks in that.

[jb-ob]

A function of speed, road bed, & sticky gumball tires........

[Reds34]

You could try "chip guard" paint. Maybe truck bed undercoating?

Red

[Lanny]

How about the magnetic flexible stuff that sticks to metal ?
Sign painters letter it for people to stick on their vehicles
for advertising. (like fridge magnets, only thicker), I think.





.

[old ugly]

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if you don't mind a textured finish on the inside of your fenders.
and you never want to scrape it off for any reason.

a good grade of pick up box liner will probably work. 2 part epoxy type. spray on.

ou

[Keith True]

Has this been a problem?I use single stage urethane on fenders,no sign of stone marks anywhere.I drive my A's on dirt roads a lot,even to the point I've had people following me turn around,they were afraid for their cars.I run 40 MPH on stone/gravel roads,I don't think I've ever seen damage from stones.

[Ruth]

Originally Posted by Reds34

Maybe truck bed undercoating?

Red

Hmmmm, I wonder how that would work... Lotsa gravel on the roads.

[jg61hawk]

https://www.amazon.com/VViViD-paint-...a-900448482442

Have not personally used this..read reviews....or this one

https://www.amazon.com/Scotchgard-Cl...04VG8DS0&psc=1

[Harpkatt]

From what I've seen flex seal is basically identical to the rubberized under coating. The only car I ever used this stuff on is the only car I've had with rusted floors. Seems to be more trouble than its good.

[GeneBob]

Here is an overkill idea. Some of the sound deadener materials are black. You could clean the underside of the fender really well and add a layer of sound deadener in the area where the stones are hitting. That stuff is REALLY sticky so it should stay on.

[Tacoma Bob]

MMM are the fenders steel or fiberglass?

[old ugly]

maybe something like this.

the rattle can epoxy primer is a cool idea as well

https://www.eastwood.com/por15-oem-b...=google&wv=3.1


ou

[Karl Wescott]

I have researched this issue of star cracking extensively as part of troubleshooting for our fiberglass fenders.


Executive summary: Star cracking of paint on fenders is primarily the result of failure of the primer layer, and/or the failure of the adhesion of the primer layer to the base material, due to the primer being too brittle or having less than desired adhesion.


A star crack happens something like this, road debris are thrown off the tire with enough energy to flex the base fender material without enough energy to dent a metal fender or actually crack the base material on a fiberglass fender. When the base material flexes if the primer is too brittle it will crack. If the adhesion is inadequate it will cause a blister which may over time result in the unsupported primer cracking. Once the primer layer is cracked it is very common for the paint layer to fail directly above the crack giving the visual "star crack". It is also common with a very flexible top coat to simply end up with blisters showing in the paint.


Air dry (lacquer) primers are ALWAYS suspect. They tend to be brittle and have poor adhesion. Modern "two part" epoxy and urethane primers tend to be more flexible with better adhesion and so are less of a problem. It is still critical to have the right primer designed to "stick" to the base. This may be different between steel, fiberglass, aluminum, stainless, etc. Ford's original painting system of pre-etching the fenders, then dipping in a fairly flexible alkyd enamel left a fender that was very resistant to "star cracking".


Issues can occur between any two layers including the base material, base primer, body fillers, surfacing primers, top primers, and top coat. Issues can occur due to materials being too thin, too thick, applied too cold, applied too hot, or in the wrong combinations. Manufacturers recommendations should always be followed (RTFM: Read The Manual).


Shielding under the fender is a great idea. Unfortunately there are no particularly good implementations. Rubberized undercoatings, which have great value for a low maintenance under surface, do little as in absorbing the energy from the road debris simply passing it on the the fender and remaining usual suspects. Bed liner can do some good but besides bulking up under the fender will still (as it is relativity flexible) pass most energy through. Anything on the concept of an inner fender with an air space to the fender could be effective but the practicalities of mounting, collecting dirt between it and the fender, and being structurally sound enough to not be an out right problem are just not overcomeable.

[WHN]

We under coated our 1929 in 1981.

If you don’t mind the look, it has worked fine. No stone chips anywhere. No rust problems either. You just have to prepare the surface before hand.

Enjoy.

[Superhart]

Thanks to everyone for their suggestions. I may try two or three coats of flexible undercoating after cleaning the underside of the fender carefully. If nothing else, the coating will make the inner fender well look better.