How to Prep Hood from Engine Fire

[MoparBoy72]

I have been reading this forum alot and would like to thank all that post as I have gotten lots of good direction by just reading.

My current (non-P car) project had a light engine fire from a con. rod exiting the engine block near the turbo...therefore fire.

I am at the step of repainting the fire damaged hood as it is not warped (under hood sound pad worked well) and would like advise on the proper way to prep this part to ensure proper adhesion and finish longevity.

Body shops I have talked to are hesitant to refinish due to fear of paint failure on this fire damaged hood.

Please let me know your experiences;


Thanks again,

Andrew

[962porsche]

being a long time VW and Porsche air cooled fan engine fires tend to also happen from in line fuel filters being placed near the distributor they will leak and then go up in flames .

you should not just sand the engine lids . the best is to media blast them using plastic media .
this should not in any way warp the panels !

from there you would use a epoxy primer mixed as a adhesion promoter or low mil build .
this will replace the galvanized coating that was burned off in the fire and aid in the primer and top coats to adhere .

so no there is no reason to replace the panel if you just go thru the proper sets on the repair .

[MoparBoy72]

Thank you for the clear direction here; I have just talked to a local blaster and he does plastic media but did report that it does not work that well on single layers of paint. Is more aggressive media not suggested due to warping/ further heat?

Thanks again!

[962porsche]

we have our own blasting booths at my shop we use it all the time with the proper blasting equipment and pressures it remove the finish and does not warp the panels .

if he can't do it then have him do something he can use that will take out the fire stains finish and not warp the panel .

you could use 000 or 001 sand but personally I wouldn't .
soda is just out for steel panels !
clean strip blasting water with glass maybe but I wouldn't use it for that it would not remove the fire damaged area .

[MoparBoy72]

Thanks again; I just got the hood to the media blaster and will report back.

[hellblau82]

Hi mate how did you go with this?

[MoparBoy72]

I am still waiting for the hood to be returned from the media blaster; I will keep you posted. Hopefully it is returned in the next week.

[hellblau82]

Excellent look foward to the result. I been searching around and found this comment from someone ..
Iv been in the body buisness for 27 years now, and I will tell you that if the burned metal is sand blasted then immediatly sanded and coated with an epoxy etch prime, you will not have any peel problems. The peel problems occur when the metal is not properly preped and the pores of the metal were not cleaned out with a blasting abrasive, weather it be sand, aluminum oxide or glass. Plastic Media will not do the trick because it doesnt clean the metal, just takes paint off..
Thoughts anyone??

[962porsche]

that is a bunch of BS ! my thoughts are after 27 years the body man did not learn all that much !
not surprising why when we look to hire a new person it takes interviewing 100 to find one .

[962porsche]

this is a list of common blasting medias used .
I do not agree with all of the list and medias they pick for some substrates .
like soda for metals as you could have a problem with products sticking to it .
but it's from the CO we buy our medias from .

some people refer to media as plastic . this is not true !
all abrasives are media plastic is just one of many !

1st about plastic media it's offered in different grits .
just as sand , glass along with many other medias are offered in different grits .

is it for cleaning yes it is .
that is just what you want to do clean the metal so it's smooth with out pitting the hell out of it and warping the panel .
this is why we use it for fire damaged panels .




this is getting blasted as I'm writing this .
it's a spec Miata rear QTR .


the OP I believe stated the shop that was going to blast the engine lid said it's to course of a media .
now it's being said it's to fine of a media .

the reason why we ended up buying all the equipment to do all our own blasting .
we have 3 blasting tents all for different types of medias is 1st many blasting shops will only want to use one media two at most .
so what we found was a blasting shop will tell you . that one media is not good for this or that when the reason they are telling you this is because it's simply not a media they are set up to use . it's called sales and business !

so how can plastic media remove rust but not a burn mark ?
when rust penetrates into metal more then a stain from a burn .
this you can see if you have ever heat shrunk a area with the torch .
you can sand the heat mark out .
that being only on bare metal but the problem is the paint on the substrate burn it's self onto the panel . it's the burnt paint stain your looking to remove .
you could remove it by grinding but that is a PITA as you then have grinding marks to deal with . this brings us to blasting it off the panel .
there are other medias to pick from . glass or a ultra fine sand are just some others .
the down side to many other medias as they will pit the substrate more and then you will have more prep work to sand the pits out .


now look at air pressures for blasting .
just like the air supply for your air tools sanders and spray guns you have to adjust the air pressure .just as you do for the medias your using and to the substrate your blasting .
I found most all blasting shops will and do not do this they just blast away .

in the blasting booth right now we are blasting two different substrates . one is a aluminum motorcycle frame that was polished and clear coated with the clear pealing off . the other is the rockers and QTRS of the spec Miata .
for the frame we turned the pressure down some not to eat up the aluminum and we bumped up the pressure for the Miata.

as for coating after blasting .
it's always a good idea to use a etch or epoxy primer over a bare metal .
blasting will remove the thin coat of galvanized coating auto makers put on the cars .
cars after the 1980's you will find a galvanized coating on .
all the E primers are doing is replacing it .
you could also use a DTM filler primer personally I do not like DTM filler primers .

does a epoxy or etch do any thing for the burnt metal ?
NO !
this should be taken care of from the blasting and not some going over it .

back in the day we used to do many porsches that went up in flames . the reason they would catch fire was people would install in line fuel filters with there carbureted engines and they would leak onto the distributor or plug wires and up in flames they go .
this is the same with the old air cooled VW's .
engine fires on them are rare now .

[MoparBoy72]

Well the hood has been returned. The burned areas have cleaned up well; the unburned sections did not blast well and I am left to sand the rest off; currently it has a speckle finish...

962 speaks the truth. Blasters only want to use the one media for all and pressure/technique is one setting for everyone...

[hellblau82]

Fantastic looks like they have done a great job

[MoparBoy72]

There was quite a bit to sand but I did finish it and drop the hood back to the painter.

[MoparBoy72]

Sorry I forgot to update this thread with the final painted hood; Turned out quite well. Thanks to all for the advice. It has been two months and no reason for concern.

[962porsche]

that's great it worked out !
you should have no problems ever with it .