MK3 Roadster coupe rear deck panel

Technical Area Body, Interior & Styling
2

Morning folks, 

I noticed this morning I have some slight bubbling on the rear panel that opens and closes on my MK3 roadster coupe. 

It looks like rust type bubbling and has even broken the surface in a couple of places. 

I thought this panel was plastic so I’m a bit confused. 

Has aanyone else experienced this or offer any ideas as to what is going on?

Regards

Derek

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Are they tiny bubbles? I have some on the leading edge of the cover that I noticed recently. It can’t be rust, googling suggests moisture in paint when sprayed but this is the original paintwork, could it take 8 years to appear? The rest of the car is spotless.

4

I’m coming at this problem from a completely different angle, so could be way off beam, but please bear with me, it is to do with the hygroscopic properties of some plastics.

Some years ago I had to design something that used a circuit board that could be folded up, and it was great until a rework change was needed, and after it had been soldered it was totally unserviceable, a bin job.  It turned out that the flexible plastic inner layer is hygroscopic, (ie it traps moisture from the air) and when it had been soldered the moisture turned to steam and de-laminated the board breaking the through-hole via connections.  The only way to solder the board was to autoclave it first for several hours at about 80C to entirely dessicate it. The production run was sold with a big red sticky label inside each cover warning the customers not to even think about soldering the ÂŁ350 PCB.

Now we come to the point, frost will have a similar effect on trapped moisture! Most car body plastics have a gel-coat layer, and depending on type this can also trap tiny amounts of moisture.  The problem is that it becomes a gradually worsening process, at first the layer just swells a tiny bit on the freeze, not much but it grows a slightly bigger void, enough to wick in some more moisture when wet again. After many, many freeze-wet-freeze cycles the bubble will become visible.

How to cure it?  Make sure the surface is really and truly fully dry (stoveing is good), rub down and fill the affected area, cook dry it again, and repaint with a good thick properly waterproof solvent paint, NOT a water-based paint.

How to prevent it? Make sure there are no scratches or bruises in the paint, and if necessary only touchup-seal it when the sun has been cooking it roasting hot for several hours.

Yesterday I retouched two bare white plastic points on the outermost edges of the deck cover panel on my Niseko’s PRHT where the paint has been shaved off at some time in the past, after having been pondering this for a few weeks.  The fan heater had playing been on them (gently) overnight in the garage, just in case.

Good luck

Richard

5

 

yes that exactly what I’ve got. Car is a 2007 galaxy grey roadster coupe. If I start rubbing down and spraying etc it’s going to turn into a nightmare of mismatched metallic paint etc.

I’ll try the drying/baking and touch up with Mazda’s own touch up kit.

 

Derek

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The issues of mismatch on the rear deck can usually be sorted by suitable blending…if done properly you should not notice at all. 

 

 

7

 

It’s used daily for commuting and been getting very coated in salt spray, do you reckon then that hosing it down frequently with very cold water to get the salt off over the past few weeks could have caused it?

 

 

 

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More likely the cold weather.

Water-based paints… another stupid thing we can thank the interfering EU for mandating.

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“It’s used daily for commuting and been getting very coated in salt spray, do you reckon then that hosing it down frequently with very cold water to get the salt off over the past few weeks could have caused it?”

I don’t think so. Simply getting wet is not a problem, not even the salt.

It is the damage that the freezing causes when the microscopic amounts of water inside the base or just under a pinhole in the paint turns to ice and expands. Think of that drum-tight bottle of frozen milk in the freezer!

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What do you mean by “suitable Blending” and what do I need. Is it a specialist paint shop job or something I can try at home with a bit of patience and elbow grease.

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mine also has this bubbling, quite a few in a line around 10-15mm from the edge nearest to the rear window. I noticed the first one or two about 6 month ago and more have appeared in that time. No break in the paintwork or any of them and they are only about 3mm dia at the moment.

I am of the understanding that the rear deck is manufactured from aluminium the outer skin which is supported by a steel “skeleton” for want of a better word, underneath. So perhaps it’s galvanic corrosion taking place from the underside of the paint?

Mine is on a 2006 56 reg car with 74k on the clock used daily and left outside in all weathers. It is, I might add, kept clean and polished regularly.

hmmm just noticed - it’s the same colour as yours!!! 

 

Edit 16-08-16 - I have since found out from the manufacturer of the PRHT’s -Webasto-Edscha Cabrio GmbH - that the material is UP with glass fibre reinforcement. 

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Hello Folks,

Have recently noticed blistering on the edge of our coupe’s roof.

Had a local body shop have a look. He said that it was the kind of thing he would normally associate with moisture. Puzzled that it has taken so long to show. However reading earlier posts this is explained by others.

Suggested that I take it up with the main dealer.

Has anyone raised the issue with their main dealer ?

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Hi all, first time poster on the site… My wife has a 2010 sport tech rc which has exhibited these issues, the panel was inspected by my local Mazda dealers body shop who have confirmed its the beginning of corrosion. the car has always been serviced by Mazda so the body shop believe it will be covered by the 12year anti corrosion warranty as the car has had its yearly body inspections etc. The chap who inspected the car believed it could be as a result of water sitting in the seal where the deck meets the rear window. Waiting to hear from Mazda. 

This is on a black car so don’t think it’s specific to any particular colour

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Just an update from me. After a bit of chasing up my dealer has been informed by Mazda UK to arrange for the panel to be replaced as a goodwill gesture… Waiting to hear that the panel has arrived in the country but it should be imminent.

1 Like
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Interesting. I’ve just had a local bodyshop respray mine. I’m not the original owner so I doubt Mazda would have done anything from a goodwill point of view for me.

The panel is plastic. When I took it in, the paint shop thought that they would just be able to do the one little patch. When they started to rub it down he said the whole panel was a mess and so he repainted the whole panel.

He’s done a good job though. I’m really pleased with the finished result. I’ll just have to keep on top of the polishing to keep the moisture out

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The deck panel and roof are all composite plastics not carbon fibre but fibreglass basically.

Always feel dumb when i put my ptg that measures on ferrous or nonferrous paint depth and politely tells you i do not have a clue. The only metal parts are the boot doors wings bonnet and rear 3/4 panels.

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This bubbling occurred on mine.

It suddenly appeared after coming back from the paint shop where they had resprayed a scratch on the wing.

They say it was baked in the oven at 80 degrees.

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Hmm, 80C should not have caused that, because it does not produce a pocket of steam, just a slow drying out.  I could easily be wrong, but I think they were impatient, not prepared to wait a couple of hours, and cooked it too hot.