Sanding Stihl Plastics - How Far To Go?

[SteveSr]

Hello,

I am attempting to restore some somewhat faded Stihl plastic. This air filter cover was actually in pretty good shape except for places where stickers adorned the top of the housing. I have started sanding and have noticed a couple of issues.

First in the locations of the stickers the plastic is actually several thousandths thicker or most likely the un-stickerd plastic got thinner from sun/environmental exposure. The second issue is the plastic strengthening ribs appear to be indented and are not being hit by the sandpaper.

I know that Brad @blsnelling has done some plastic restoration so might be better able to comment. My main question is how far should I go down into the plastic before I start going to finer and finer paper? Does it need to be flawless at this stage or will later stages cause all of this to blend together? The photo below was taken down with 320 grit wet/dry paper.

Thanks,

Steve

 

[Chainsaw Jim]

It'll only be worth doing if the plastic is still hydrated all the way through. If you scratch at it and it crumbles then it will never keep a finish.

 

[SteveSr]

It'll only be worth doing if the plastic is still hydrated all the way through. If you scratch at it and it crumbles then it will never keep a finish.

This plastic isn't that bad and passes your scratch test with flying colors so it should be salvageable. It just looks bad now because it has already been sanded.

 

[Chainsaw Jim]

This plastic isn't that bad and passes your scratch test with flying colors so it should be salvageable. It just looks bad now because it has already been sanded.

I should have added that yours pictured looks like a prime candidate for buffing out.

 

[Stihlofadeal64]

You will probably have to either keep sanding or change grit. You will need to get a reasonably even surface before you apply any clear coat. Like painting the finish is going to look like the surface. I used like a 220 (I believe??) and then went finer from there. Get it evened up and then go with a finer grade sand paper. I have even wet sanded them before. Make sure before you try to put any clear that you remove all the residue from sanding. Choose wisely on the type of clear as well. Some rattle can clear turns yellow in the Sun.

 

[Wood Doctor]

In addition, I've also had some pretty good luck with a 40:60 mixture of boiled linseed oil and xylene, rubbed down with fine steel wool. The xylene will not evaporate as rapidly as mineral spirits and seems to work better for me. Mineral oil is another alternative.

 

[1Alpha1]

When it comes to plastics, I have the best results wet sanding with fine grit sandpaper.

 

[SteveSr]

You will probably have to either keep sanding or change grit. You will need to get a reasonably even surface before you apply any clear coat. Like painting the finish is going to look like the surface. I used like a 220 (I believe??) and then went finer from there. Get it evened up and then go with a finer grade sand paper. I have even wet sanded them before. Make sure before you try to put any clear that you remove all the residue from sanding. Choose wisely on the type of clear as well. Some rattle can clear turns yellow in the Sun.

Looks like I may have to go back to 220 grit in the finishing sander to get the surface uniform. I am sort of surprised by the material differences under the labels. The material that wasn't covered by labels appears to have significantly out-gassed and shrunk.

I may indeed end up putting clear coat on top but would like to try sanding and buffing first. At least this would be as durable as the original material whereas I have questions about the durability of any (even good) rattle can clear coats.

 

[merc_man]

what about trying a headlight restoration kit. 3m makes one with a drill attatchment. It cleanwd my headligjt like new and would do the same on saw plastic i would think. You would just have to clear coat it mabe when done.

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[SteveSr]

what about trying a headlight restoration kit. 3m makes one with a drill attatchment. It cleanwd my headligjt like new and would do the same on saw plastic i would think. You would just have to clear coat it mabe when done. Sent from my SGH-I747M using Tapatalk

Saw plastic and headlights are different animals. Headlights are polycarbonate which is a hard plastic with no fillers. Saw plastic is 6/6 nylon filled with fiberglass for added strength. The nylon is much softer than polycarbonate and it degrades leaving the glass fibers exposed which gives the rough washed out appearance.

I did get and will be evaluating a sample kit from Micro-mesh but before I start with this I would like to make sure that the underlying surface prep is correct.

 

[Jeff Lary]

I may indeed end up putting clear coat on top but would like to try sanding and buffing first. At least this would be as durable as the original material whereas I have questions about the durability of any (even good) rattle can clear coats

I will follow you with interest to see how you make out with the clear coat good luck. Maybe if I say what happened to me someone will know why and save you some grief.
I wet sanded a Partner cover I had then primed and painted it waited a day then one more coat of paint it looked really nice. About 2 days later I put on a coat of Clear from a rattle can then the under coat of yellow started to pucker and wrinkle and ruined the under coat of yellow.
So in effect I had to start all over again. I repeated the sanding priming and painting once more, but this time I did not re-apply the clear. I bet there is a simple reason why this happened but I never found out what it was. Maybe some good soul will tell you how to avoid my problem. I can tell you this," you don't want to have to re-do all of your work twice like I did" , good luck and ask around about the correct way to use clear I did not. Jeff

 

[merc_man]

I may indeed end up putting clear coat on top but would like to try sanding and buffing first. At least this would be as durable as the original material whereas I have questions about the durability of any (even good) rattle can clear coats

I will follow you with interest to see how you make out with the clear coat good luck. Maybe if I say what happened to me someone will know why and save you some grief.
I wet sanded a Partner cover I had then primed and painted it waited a day then one more coat of paint it looked really nice. About 2 days later I put on a coat of Clear from a rattle can then the under coat of yellow started to pucker and wrinkle and ruined the under coat of yellow.
So in effect I had to start all over again. I repeated the sanding priming and painting once more, but this time I did not re-apply the clear. I bet there is a simple reason why this happened but I never found out what it was. Maybe some good soul will tell you how to avoid my problem. I can tell you this," you don't want to have to re-do all of your work twice like I did" , good luck and ask around about the correct way to use clear I did not. Jeff

If you use water base paint then oil based clear that would happen.

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[Jeff Lary]

well this is gonna sound dumb but I did not know spray can spray paint could be water base? Does it say so on the can someplace?

 

[merc_man]

well this is gonna sound dumb but I did not know spray can spray paint could be water base? Does it say so on the can someplace?

Check the cleanup section on can. If ot says clean with mineral spirits then oil based. Of clean woth water waterbase.

And i really dont know if spray paint is all oil based or not.




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[Jeff Lary]

Well that's what I am thinking but may be crazy too so...