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MG Midget and Sprite Technical - Painting preparation

I want to prep for a respray.
I intend to scuff the surface of the sound panels to provide a key for the new paints but want to avoid pushing any surface contaminants into the old paint layer. So the very first thing will be to wash the car thoroughly. What would be a suitable cleaner to use that will remove any grease and possible silicone without leaving a residue? Most car cleaners seem to have "shine" additives which is the last thing I want. I do have panel wipe, but that is for a later pre-paint stage.

When scuffing sound paint to provide a key would 600 W & D be best, or is that too coarse? Maybe I just need to use a coarse Scotchbright pad?

Guy
Guy Weller

I'd wash it with a bit of washing-up liquid; if you want to be purist you can hunt around for 'traffic film remover' but I reckon that's OTT. 600 will be fine for flatting off. I guess it all depends on what quality of finish you are after.
David Smith

Thanks David.

I do like simple solutions!

I think I will use an engine degreaser around the oily bits like the door hinges. Then hot water and washing up liquid.

Quality of paint finish - well, all the same colour and with a bit of a shine will do me fine!

Guy
Guy Weller

Guy...

Do NOT use washing up liquid... it has a high salt content!

Traffic film remover should be fine though.

Use Scotchbrite to prepare the surface and finish off with a panel wipe, this SHOULD remove silicones but you may be best to wipe over twice and in an ideal world, from two seperate tins, (the first will become contaminated if used directly from the tin.....

I hpe this is the Frogeye and not the Austin Sprite.... :-)

Mark.
M T Boldry

why bother scuffing the paint when you're intending to use rattle cans to paint the car ? :-)

If you polish it first, then the polish will shine through your new paint and give a really good deep shine.
Tarquin

Mark - I wish it was the Frog but I have er, just a little more bodywork to do on that first!
It is the Austin Sprite. Time for a freshen up - its nearly 18 years since I did it last. I know about salt in washing up liquid. I wouldn't normally use it for that reason but in this case I do need something that will take off the accumulated waxes and other residues before I start any rubbing down. At least the salt would dissolve and rinse off. But I guess proper traffic film remover is the right stuff to use.

Tarquin - what are you on about? - been sniffing the thinners again have we?

Guy
Guy Weller

Guy,
A paint sprayer that repaired one of my cars years ago advised using vinager to clean off old polish before painting.

Alan.
a cotterill

Guy. When using panel wipe use two cloths, one wet with the panel wipe on it and the other dry straight after the wet one. If you allow the panel wipe to evaporate on its own you can get strange patterns emerging in the paint finish, especially with metalic base coats. If you pour the panel wipe onto the cloth without the cloth touching the tin you shouldn't get contamination.

Bernie.
b higginson

Thanks Bernie,
I will remember that when I get to that stage. At the moment all I was wanting to do was to get rid of probable contamination from the old paint surfaces so that I didn't then grind the contamination into the old paint when I start rubbing it down.

Guy
Guy Weller

Guy-
Automotive paint stores that supply body shops can sell you a jug of the ultra-powerful detergent that painters use to strip away layers of old wax and such prior to going to work on the car. Pour it into an old window spray container and mist the car thoroughly, then rinse it all off with water. Just don't breath the mist or your lungs will feel as though they're on fire!
Stephen Strange

Please do not use washing up liquid to clean your car, it's basically salt mixed with acid!

I used to make the stuff.

Andy
Andy Borris

Nice one Andy. I'll be making sure the crockery gets well rinsed from now on. Reminds me that chip shop vinegar, also known as "non brewed condiment" is a by-product of petrol production! Have you noticed that if you put your own malt vinegar on your chips when you get home, they don't taste quite the same. Scary.

Bernie.
b higginson

Guy, as Steven says there is a specific product in the Automotive Refinishing trade that is designed for the removal of silicones and polishs....

Mark.
M T Boldry

OK, next stage, but I may as well continue with this thread.
I have got a 2K etch primer/filler to apply. Presumably this stuff goes off fairly quickly and cannot be left in the gun for too long once mixed.

With celly, I would have worked my way around the car with a sequence of sanding - spot-prime - sanding - high build primer filler - guide coat - sand - filler etc until it was ready for the top coats. I would keep one gun for the filler / primer which would stay in the gun for several days during this stage. Presumably I cannot do this with 2K though so I am going to need a more organised procedure.

But how long will the 2K be OK for in the gun?

Guy
Guy Weller

If you are gentle with the hardener, then 1 hour max I would say.
Might have to do larger parts of the car at once. The primer we used was high build, so you could skip a stage.
Tarquin

Yes, mine is a high-build 2K etch primer so it should do it all. Well, not quite - they haven't got round to adding the final colour coat pigment in as well - yet!

What ratio hardener to primer do you use?
Guy Weller

Guy.
According to the datasheet, the filler primer I'm using has a pot life of 2 hours. I would imagine most 2k products will be similar...

http://www.paints4u.com/pdffiles/Green%20Ti%20&%20Act.pdf


Graeme
graeme jackson

Sorry Graeme, I am getting a 404 error message on that link.

Anyone know a good website for 2K mixing and spraying technique. I am well used to Celly spraying, but never used 2K before so am being cautious. (I do have air-fed mask, paper suit gloves etc) Its more that I want information on the amount of hardener and thinners to use, gun pressure etc.

Guy
Guy Weller

Sorry Guy - didn't realise it would do that. try going into the paints4u website...
http://www.paints4u.com/productsbyCat.aspx?MainCategoryID=6&MainSelection=20&SubCategoryID=77&Subselection=2

then select primers - 2k primers then click on the view details button next to the 04109 green ti primer. then you can download the datasheet and health and safety PDFs. The datasheet gives full details for mixing, air pessure, drying times etc. All specific to this product but there'll not be much difference I'd have thought.
graeme jackson

Guy, the ratio varies, so you must ask the supplier of the paint. Or it might say on the tin. Ours was 3:1 with 10% thinners or as required. I was encouraged to put plenty on, as it evens out to a nice finish. If you go softly on the hardner it has more time to even out before drying. Worked for us anyway.

Mixing - I don't know if there are any special requirements. Maybe just google for it.
Tarquin

Thanks both! There is no manufacturer's name or data on the paint tin - it was mixed on site for me and put in their own (blank) tin. But I rang them to get the paint manufacturer and paint type - Octocryl and have now downloaded data and safety sheets from the internet.

Spent most of today prepping the car, except in the process I found some welding to do so that has taken a while. Car looks terrible now!
Guy Weller

I asked this on another thread, but got no replies....

Where a skim of filler is needed, is it better to apply this directly onto bare (keyed) metal or is it better to prime (acid etch) first. Seems that would mean that the filler is stuck to paint rather than the metal. I have done both ways in the past but am not sure which is the proper way.

Guy
Guy Weller

Guy, I believe skimming onto the bare metal is the 'correct' way.... I've always done it like that. Follow this with a coaut of primer and a 'guide coat' of a contrasting color then flat down. Take out any further blemishes with a stopper and repeat the process until its perfect.... :-)

Mark.
M T Boldry

Yes, that's logical. Thanks for confirming that Mark.

Guy
Guy Weller

Guy. Yes you can skim straight onto clean keyed metal. I usually use 80s grit D.A. discs, or you can do it by hand. The 2K primer I use is Mipa, a german company and I find it very good, as are all their other products like 2K solid colours, metallic base coats and clear laquer. I use primer 2 parts paint to 1 part hardener and 10% 2K thinner. It has a safe pot life of about 1 hour and I always clean my guns with celly thinners afterwards. I think you'd be better to do all the repairs first and then go round the car with primer after you've cleaned all the filler dust off.
I'm really looking forward to seeing the results. Should be good as you are taking so much trouble to ask all the right questions. I know if I have a problem there's always someone on the BBS to help and you have definitely helped me in the past. Good luck.

Bernie.
b higginson

Thanks Bernie.
Bit of background. This car was rebuilt by me from a true basket-case example that I was given back in 1989. It took almost 9 years to do but that was partly because I had another 1500 midget which I rebuilt and ran in the meantime. The Car had a lot of replaced body panels and I then grit blasted it to bare metal, etch primed immediately and painted it with celly. It has had a lot of use in all conditions and for the last 8 years has been my only car so it has taken a bit of wear and tare. I intended to respray it last year but it never happened!

Anyway, I have now made a start but the questions are partly because methods and products have changed in the last 15 years, and partly because qwhen I did it last time the BBS wasn't there to help so I just made it up as I went along!

The 2K etch primer filler and the hardener is by Mipa. The paint is Octocryl (Valspar)but the shop said to use the Mipa hardener with this. What they didn't supply was any data sheets. I thought I could get this off the internet but they are fairly generic and set upper and lower limits rather then optimum values. Any suggestions on a guide to gun pressure to use(suction, not gravity or shotgun)

I have had a good day- I finished the repairs to the rear tub - nothing much, some unwanted bumper bracket holes to weld up and a new section above the rear wing / sill joint line to let in. I have skimmed as much filler as is needed - which wasn't much - and shaped it up ready for some primer filler.

Guy
Guy Weller

Guy. I use suction guns all the time for no other reason than I've never tried a gravity feed one.
Mipa and most other paint manufacturers recommend between 3 and 4 bar for top coats and you could use the same for primer if you are going to go all over the car, but if you are just localising the repairs you can drop it a bit. The longer your airline the more pressure loss you'll get at the gun. Try it on a test panel first. (Correction to above primer ratios. Mipa primer is 4 parts paint to 1 part hardener with 10% to 15 % thinners.) Sorry mental abberation. For top coats and laquers use 2 parts paint to 1 part hardener and 10% to15% thinners. I normally do one dry coat all over, wait 10 minutes then two wet coats 10 minutes appart. If you want to have plenty to flat back before you polish it after it's cured, put on a further wet coat after 15 minutes.
I notice that you say you have an air fed mask which is the best option, but only if your compressor is not in the same room as you, or has its air intake ouside so that it doesn't suck in the 2K fumes and deliver them right to your lungs. You can now get regular respirators that are 2K compliant for about £25 with changeable cartridges and pre-filters which are very good and less cumbersome than air fed so long as you don't exceed the recommended volume of contaminant in the room which probably means an extractor fan and that brings its own problems with pumping unfiltered 2K fumes into the atmosphere for Joe Public to breathe in. Other people may have different advice which you may prefer. Hope this helps.

Bernie.
b higginson

Bernie,
Is this the sort of respirator that you mean...?

E-bay item # 350231371374
Guy Weller

Great advice Bernie, thanks from me too.
Andy & I have used the normal respirators for primering like you said, only drawback with these is that your face and eyes are still exposed to the fumes.

I have an airfed mask which I will be using for the top coat, compressor will be outside as usual.

As for filler on/below primer debate, as filler absorbs moisture (or does it any more?), I would have thought that rock hard 2 pack primer is better being next to bare metal than the primer. Thats what I've done anyway. Don't know if there is any real difference as to which way it goes on. We don't have a problem with putting more filler/stopper on after the first coat of primer to rectify any small imperfections, so I wonder if it really matters. I would like to hear either way from anyone in the trade if they're on here. (Is that you Bernie?)

Matt
Tarquin

Guy. Yes that's the exact one.


Matt. Yes I'm in the trade, although not a time served sprayer. I watched the experts in a body shop next to my unit and asked questions all the time, so I gradually picked it up as I went along. I'm a sort of jack of all, master of none some might say, but I get by. I do retail bodywork and paint, so I must be doing something right.
With regard to the primer debate, was that a typo where you said 2 pack primer is better next to bare metal than the primer. should that have been filler? I've also done it both ways. ie. filler on metal and filler on primer and it works either way. And yes, you're always going to get pin holes etc that require stopper, so I don't think you are doing anything wrong at all.

Bernie.
b higginson

In olden tyme, when primer was simple lacquer, the filler usually stuck better to clean metal than the primer did. But, rust travels easily under either, and fillers tend to hold or transfer water/salt. So, correct prep with zinc phosphate metal prep + primer, or acid etch primer, is best used under filler. It will prevent rust traveling, and the fillers will stick just fine on the primers.

FRM
Fletcher R Millmore

Bernie,
Can I contact you direct - off list - for a bit more advice please?

Guy

First nameAT last name -lakes DOT co DOT uk
Guy Weller

Guy you've hurt my feelings!

Yes Bernie, I meant 2 pack primer is better next to metal than filler. I'd like to see moisture get under the primer we've used.
Tarquin

Guy. You have email.



Matt. Sorry, forgot to mention. Yes filler still does absorb moisture. They've not invented one that doesn't yet. Could always use lead loading though. Not easy, but very satisfying when you get it right.

Bernie.
b higginson

I always used to flat down filler with wet & dry - so how do you do this without water penetrating the filler?!
Guy Weller

Guy. I've been watching American Hotrod on Quest for the past few months and they seem to dry sand the filler then spray a few coats of filler primer, dry sand that, more primer, a wet sand, spray the colour really thickly (i.e. >7 coats) then wet sand the colour. More work than the average enthusiast is willing to go through but well worth it for the end result I suppose.

Graeme
graeme jackson


Question: How do you sand a highly convex surface (or concave for that matter) and be assured that you're taking the primer down evenly across that surface? What's the secret/trick? I know there are simi-flexible sanding pads but I don't think I've seen any that would flex enough to meet the shape of the top of the rear fender, for instance.
JM Morris

We dry block sanded the filler with a bit of MDF and 120 grit paper. rips it down to size lovely. When it looks and feels right, primer it, then dry sand that to double check. When the whole car was done we put another coat of primer on and wet sanded that.
Exactly like Graeme says they do it on the telly. Surely no need to wet sand filler? That would take ages!
Tarquin

Best way to check contours is to use a very light guide coat dusted over the primer. Then wet sand and any irregularities will show up as the guide coat is removed - or not!

But I do find that dry sanding with hand blocks clogs up the paper very quickly.
Guy Weller

I am not sure what I need to do to properly key the existing sound cellulose paint finish before applying the first coat of 2K primer/filler.

I wet - sanded it all with 400 grade W & D, but that exposed some areas of bare metal which needed careful drying to avoid any surface rusting. And I now I also have some areas with a skim of filler that I don't want to get wet again.

I think it needs dry sanding once more to key the surface, but what grit should I use? (hand sanding)

Guy


Guy Weller

I have never had filler swelling when ever I used (Isopon/Holts) Metallic filler

Ordinary whit-ish filler is resin loaded with talc as a filler, talc is always capable of absorbing water, given that rubbing its particles will erode resin off the surface of it.

Water can migrate through it fairly easily

Metallic filler is mainly aluminium particles loaded into the resin, so even if resin is rubbed away the aluminium wont "take in" any water

Hence my opening statement

Of course it costs more

but it saves more too

I am just rebuilding the rear panel on my car which I built fifteen years ago

rotten as a pear- inside where water that got into the boot sat rusting the steel away in its lowest crease section

The filler I used on the outside panel is as good as new, OK it WAS as good as new.

It has just been all ground away so I can weld my new piece in.

We'll see if the MOT man likes it soon enough
bill sdgpm

Thanks Bill, but too late for me for that advice! I have already used the standard pale green stuff. Which is the same as I used some 18 years ago and it lasted pretty well. But I still don't want to wet it more than absolutely necessary - hence the next sanding will be done dry.

I just need to know what grit to use. I want it to key to the old paint properly but don't want deep scratch marks to show through the 2K primer!

That joint across the back of the floor is a real rust trap. It is bound to get damp in there - if only from condensation inside the boot panels. I filled the whole seam on the inside with semi-setting mastic seam sealer, building it up in layers until it was flush with the floor. That has worked very well and there is no rusting at all along that joint on mine this time.
Guy Weller

I'm building in drainage holes and using copious amounts of Hammerite, (the old fashioned metally looking version rather than the posh Smoothrite type)

We'll see in ten or more years if that did the trick wont we

remember to remind me to check will you...

I use a roughish paper that has been once used if I want a fine finish (400 ish) that wont show the scratching, but I'm only ever guessing about that
bill sdgpm

This thread was discussed between 28/05/2010 and 27/06/2010

MG Midget and Sprite Technical index

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