Classic cars forum & vehicle restoration.

[peppiB]

Hired a spray bay early March. Perfectly dry and heated.

Existing paint was flattened, 3 coats of bar coat applied, left to dry. 2 Coats of primer/filler, flattened, 3 coats of primer, flattened, followed by 5 coats of colour.

Disabled so it takes me a while to recover.

Today attempted to mop the paint. The bonnet paint cracked in raised areas and I could pull the whole lot off - back to bare metal. Thing is, there was loads of water underneath between the bare metal and the paint. Where on earth had that come from? Has me really puzzled

I have moved recently and that car now stands out, but I wasn't aware of any 'pin holes' to let the water in.

Anyone any ideas?

[Bitumen Boy]

Well, seeing as nobody else is having a go, I'll add my thoughts on this one, though I'm really not an expert.

I doubt that water has caused the paint damage - if it has then the paint was really lousy to start with, worse than any I've seen to date. I have seen cases where paint reactions have completely pulled originally sound paint away from the metal underneath - worst was when I sprayed the back of the garage door (steel up & over) with some leftover white cellulose to reflect the light. It was originally in a darkish grey paint which was sound, I tried a small area to test for reactions, which seemed OK, so went ahead and painted the lot. Looked good at first, but a week or two later it started to crack, shrink and flake off down to the steel underneath. Something similar must be what's going on here, with the water entering through cracks which have opened up under some sort of slow reaction. I say reaction: it may be more that the two paints behave differently with changing temperatures and expansion/contraction of the underlying metal, but the result is ultimately the same. Sad to say there's only one remedy, and you already know what that is - bare metal respray time

[peppiB]

Many thanks for that.

I have repaired the damage, taking the paint back to a solid edge and leveling with filler. thankfully the rest of the car, at the moment, is sound.

It had a bare metal respray 3 years ago. Because of the state of my lungs I used coach paint and was never happy with unusual gloss finish (looked like the car had been painted by the local bus company). i had it resprayed locally in 2 pack last summer. The bodyshop had the car for 2 months and made a real bog of it, hence I had to hire a spray shop and re do it myself.
The bodyshop is protected by 'gorillas' who are nowhere to be seen when you enquire or take the car in, but are very much there if there are any complaints!

At least if any more paint comes off it does so leaving shiny metal to work on

[Desert Fox]

[peppiB]

Thanks for that Desert Fox. The paint was 2pack with rocket hardener. Light coats applied to prevent runs and 40 minutes between coats

[ukdave2002]

[peppiB]

No. 3 years ago I did the bare metal respray and honestly no filler was required.

Car was washed, flattened, dried off, taken into bay and left to dry thouroughly (heated bay - half a day allowed) During this time it was masked up. It was then gone over with panel wipe and tack cloths before a single coat of bar was applied. Next day morning 2nd coat of barrier, 2 hours later 3rd coat. Left to dry

Day 3 - 2 coats of high build

Day 4 - high build flattened, 3 coats of normal primer applied (again after panel wipe and tack cloths.

Day 5 - morning primer flattened Afternoon and well into the evening yet more panel wipe and tack cloths and 5 thin coats of colour

masking removed and walked out of bay and closed the door. Left for the weekend.

2 pack used with 10% thinner and flow was OK. Water trap in the line at all times

As I said, it has me baffled but at least the repairs I have done seem to be holding. Nowadays I no longer take the car to shows, preferring just to drive the thing rather than sit beside it

Gear change cables have now started to leak oil in a big way so new casings needed very soon

[Desert Fox]

[peppiB]

Have sprayed 6 other cars with 2 pack over the years without a problem.
The only difference this time was a friend mixed the batches of paint for me. I positioned the bottles in order of use and left him to it BUT he is dyslexic and cannot read. I wonder if he has mixed them incorrectly. I noticed today that the edges of the paint on the roof have started to lift and peel as well.

Had plenty of time to look as I waited for the RAC to tow me home - blown head gasket

[Desert Fox]

Ok. During my many years in the paint industry, I have always told my customers to look at the most obvious and simple possibilities for failures first. I think you may have already answered just one possible reason.

Looking again at your application procedure I think there are two problems. As I stated earlier, there does seem to have been excessive paint applied which will cause shrivelling, crazing etc. However, the peeling of paint from the roof is obviously adhesion failure. You do not say if it is to the primer or the bar coat. This can be caused by either incompatible paint products, incorrect thinner (or cheap), incorrect preparation (unlikely due to your listed prep) or incorrect mixing of 2k and / or incorrect thinner.

Using the correct thinner allows the paint to "bite" into the primer for adhesion before curing. Incorrect mixing will not allow the 2k to "cross link" chemically, remember that 2k is a chemical cure not purely by solvent evaporation as 1k products. This means that if there is little or no hardener in the mix there is no chemical reaction and, therefore, only pigments, binders and solvent has been applied which will react with elements.

A simple test would be to take a rag and dip into a thinner (used for 2k), then rub an area of the paint on the vehicle lightly. You will remove some colour but, you should not be able to rub through to primer after 20 double rubs. This is a standard test in the automotive industry. If you rub through then there is no cure, if not, then there is a correct cure. Allow the area to recover for 20 mins before polishing.

Because the paint is peeling there is no other option than to strip the paint and start again. I would strip back to the original paint only. Or perhaps have it soda blasted back to bare metal.

[peppiB]

As the paint is peeling away it is not only lifting the recently applied paint, but also the bar coat, the previously applied (by 'professional' sprayer - although he wasn't very good. I learned later he used to be one of the best in the area until he took to using cocaine ) 2K and the coach paint I put on 3 years ago leaving very clean bare metal. I suppose the good thing is that as I will obviously have to strip and paint the thing again at least with the aid of a heat gun and scraper, removal will not be a problem! Or possibly just leave it for a week or 2 and the stuff will detach itself

[Mitchelld]

id say the amount of material, 5 coats is too many, 2 - 3 coats at most . you say thin coats but unless they were full wet coats the finish would have been terrible ?? yes it flashes off but will still stay wet under the surface.

i too use a water trap but its not always 100% this could also be the cause

[Desert Fox]

There can be many reasons why paint reacts, but generally it's the most simple causes that cause the greatest problems. Paint can be applied by inexperienced applicators with good results. However, the skill is in seeing the problem during application and putting it right before ruining all the work.

It is true that filler holds moisture, but there will not be enough to cause a puddle or wetness after curing. The presence of moisture in filler will show as blisters / pinholes or craters in the filled areas.

Any spray set up should incorporate a combination filter, that is to say a filter that will remove water and oil from the air ( a water trap alone will not always take out oil from the compressor). Water in the air will show during painting as bubbles in the paint when applied sitting on the paint surface and if you are lucky these can be flatted and polished out.

Compressors should be allowed to run for a few minutes and drained before use. Pull the trigger and let air pass through the lines for a couple of minutes, you will likely see some vapour as water can condense in the lines after the filters. The compressed air is hot and then cools as it travels through the lines producing moisture. I have a large compressor (175cfm) with a dryer for my soda and dry ice blast business that will dump 2 litres of water an hour depending on the dew point even on a hot day.

[peppiB]

The compressor was the one in general use in the garage (125 litre I think). I had a lead off from that. the adjacent bay was being used for tyre fitting.
I drained the water from the compressor each morning before using it

It will get another full respray in due course