help on repairing a small dent please..

peterp · Feb 7, 2005

Hi all
Can anyone please offer advice on repairing a small dent please?
I'd like to have a go myself and would like any hints & tips,products to use and where to best get a colour match paint.

Thanks a lot
Peter

Luke · Feb 7, 2005

peterp said:
Hi all
Can anyone please offer advice on repairing a small dent please?
I'd like to have a go myself and would like any hints & tips,products to use and where to best get a colour match paint.

Thanks a lot
Peter

It may pull out, is the paint actually broken?? Also is the metal creased, or just pushed in?

peterp · Feb 7, 2005

Hi Luke
Upon closer inspection there actually is a 1/2" tear through the bodywork.The whole area to for repair is only about 3" square though.
I'm not really looking for any miracles here but merely trying to avoid extortionate garage bills if its possible to do a reasonable job myself.

Cheers
Peter

dave · Feb 7, 2005

haynes manual tells you roughly how to do it (any one its not car spercific), but rember the better the preperation the better the job, use filler in thin layers dont try and fill big holes all at once

Luke · Feb 7, 2005

dave said:
haynes manual tells you roughly how to do it (any one its not car spercific), but rember the better the preperation the better the job, use filler in thin layers dont try and fill big holes all at once

If there is a big gap to fill then try using some p38(? could be p40

) - Fibreglass bridging compound, then use filler in layers to bring it level. Make sure you sand it all down using different grades of paper, the finer the better when you're getting to the level you want. Then a couple of coats of primer, rub it down again with your finest paper (removes any small grit scratches). Final layer of primer then its ready to paint with whatever colour you need.

Halfords do a project pack of sandpaper which should get the job done

AND MAKE SURE YOU USE A SANDING BLOCK!!!! Dont use your hand otherwise it wont be smooth and when you come to paint it, when its dry it will stand out a mile.

chaos · Mar 2, 2005

I would use aluminium tape first (after treating the bare metal with kurust or something) before adding any sort of fibreglass/filler. If you can access the dent from behind, hammer it out so its only slightly lower than the surrounding bodywork. You may also be able to close the gap on the tear.

The Negotiator · Mar 2, 2005

Hmmm, doesn't aluminium increase the rate of rusting with steel?

chaos · Mar 2, 2005

The Negotiator said:
Hmmm, doesn't aluminium increase the rate of rusting with steel?

No, I don't think so, as Al will oxidise first thereby protecting the steel. It's like Zinc blocks on ships hulls - the zinc reacts first, protecting the steel. Galvanising is the same. Anyway, Haynes say to use Al tape, so it must be alright.

chaos · Mar 2, 2005

Besides I said to treat any bare steel with rust killer!

The Negotiator · Mar 3, 2005

Zinc is different, it does work like that but aluminium doesn't.

It's to do with the magnitude of the negativity of the equation. I honeslty can't remember enough about it to explain properly but trust me, aluminium AFAIK speeds up rusting - it makes electrons more available which are necessary for the oxidisation reactions.

I am going to try and teach myself again about it again when I get chance to explain why.
I was sure I had it on my website but looking where I would expect it to be (http://www.paulharrison.netfirms.com/Chemistry/ocean_revision_notes.htm) I don't have it.

Hmmm...

The Negotiator · Mar 3, 2005

I remember now, it's to do with electropotentials of REDOX reactions. This why zinc works and aluminium doesn't. I will remind myself of the exactly principles when I have time but I am very surprised Haynes would say do that.

The Negotiator · Mar 3, 2005

For the record I now am persuading myself i am wrong lol

arseofbox · Mar 3, 2005

The Negotiator said:
Hmmm, doesn't aluminium increase the rate of rusting with steel?

Would make sense, thats why they say yu shouldnt clean aluminium heads with wire wool (Well apart frm the fact that it'll gouge into the Al, it'll leave bits in it!)

chaos · Mar 3, 2005

Al and Zn have similar electronegativities, and similar oxidiation states.
They would therefore be close to each other in a reactivity series, and would therefore oxidise at similar rates.

The Negotiator · Mar 3, 2005

OK, I took the easy way out, I know with what I can remember it WILL stop rusting but I just remember something in the back of my head saying "no, aluminium speeds up rusting" - hence my original post. I therefore have emailed my head of sixth form and chemistry teacher, an Oxford graduate....he's a good bloke so will know pretty soon

The Negotiator · Mar 3, 2005

I am wrong, I have persuaded myself I think, I will wait for the reasoning from my old teacher. I also think that alu is better than zinc.

Sorry for being so wrong

I was thinking of copper I believe.

chaos · Mar 3, 2005

The Negotiator said:
I was thinking of copper I believe.

Don't worry about it - what course are you doing?
Oh by the way don't you think this has become :Offtopic:? Oh well.

The Negotiator · Mar 3, 2005

No, i think it's important....It also proves to me that my memory retention isn't as good as I hoped!

I am doing a MEng (masters) in Chemical Engineering at Manchester.

The Negotiator · Mar 3, 2005

Ok, my very kind teacher has emailed me back as expected.

I hope he doesn't mind me quoting him:

happy to help if I can

From my recollections both Al and Zn can be used to coat steel in processes called aluminising? and galvanising. Both metals are more reactive than iron and so react better in air.. Both form oxide coats which stick, I think the M2O3 structure and MO have similar molecular sizes to the arrays in their metals underneath. They thus stick hard to the metal and thus water/air must penetrate a layer of oxide and another metal before getting to iron.
I suspect technical or
financial reasons might mean Zn preferred. After all Zn is from a blast furnace and whilst not v strong itself makes agood coat as above. Al needs electrolysis and again I recall the extraction costs are v high, I think the obtaining of Al2O3 pure from bauxite ore is as costly as the complete extraction of iron and thus presumably Zinc. Also Al has more worth as it is as a metal esp once oxidised or anodised to thicken the oxide coat. Al however is not v strong so overhead cables at 150000 volts (is it?) are actually Al because CU too dear and yet the Al has a core of steel cable to give strength, so few Al structures around of a big scale...no bridges but plenty of masts etc light and limited strength? Probably some replaced by decent plastics now.
Anyway as I am waffling now hope that's enough to chew on. Look up some key words on a web engine for a decent chemi dept or the Institute of materials
Good wishes as ever
****

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