Microscopic Paintwork Pimpling

[LEO]

Hi,

 

I am considering the practicalities of re-commissioning a car (an MGB) I have had in dry storage since 1980 and have been removing protective sheeting from the car.

 

All the paintwork seems to be in good condition except for the bonnet which has microscopic pimpling - the firm I may be working with on this project said this problem was not uncommon.

 

History - the car was new in 1971 and has a low mileage (around 30,000) it was a BLMC 'one coat finish' and in 1975 I removed all body fittings and had it re-sprayed at a coachworks.

 

As said, the bonnet is the only area affected and I think this may be formed in aluminium. All flat surfaces have been covered in cotton and felt overlaid with polythene, the boot and wings are OK the sides have been protected by hardboard panels.

 

I thought that 'pimpling' problems on boats painted recently may have been due to paint changes the EU required, but it seems that cellulose paint made in the 1970 or earlier is affected.

 

L.

Edited February 10, 2017 by LEO

[AndrewIC]

I have some sort of pimpling problem on a boat spray painted with 2-pack paints 12 months ago (although the problem appeared a few months after painting). Mainly along the outer edges of the roof. The painter doesn't seem to know why.

[WotEver]

I have some sort of pimpling problem on a boat spray painted with 2-pack paints 12 months ago (although the problem appeared a few months after painting). Mainly along the outer edges of the roof. The painter doesn't seem to know why.

If I recall correctly there was a spate of this on many narrowboats a few years back and no-one was really sure why at that time either. Lots of theories, all unproven as I recall.

[Chewbacka]

You may find this interesting, but it is written from the paint makers view - https://www.hmgpaint.com/PDF/knowledge-base/KNB0030.pdf

Edited February 11, 2017 by Chewbacka

[Tony Brooks]

A while after the discussion on here I emailed Phil S asking if he had got any conclusions and he said it was caused by frozen snow trapping water against the paint film that is apparently slightly porous. Italics my conclusion from the replay and what I have observed under wet rags left on paintwork.

[dave moore]

This is why coils of rope left on a cabin top are a bad idea. I've seen many instances of blistering when they are removed after some time. They may look pretty, but....

 

Dave

This is why coils of rope left on a cabin top are a bad idea. I've seen many instances of blistering when they are removed after some time. They may look pretty, but....

 

Dave

[jddevel]

Just a thought but if the bonnet is aluminium ( My 72` B`s bonnet is steel as I believe the originals

were)- check with a magnet- then if the bonnet wasn`t etched before spraying, blistering will more than

likely occur.

[bizzard]

These pimples could be a touch of Acne, perhaps mixing the paint with a drop of boiled cabbage water might prevent them. Wax polishing paintwork, especially red can cause outbreaks of pale burn spots, caused by the sun being magnified through globules of rain, like a lens, which tend to remain on the surface in globules for quite some time before finally drying up. I never polish anything outside.

Edited February 11, 2017 by bizzard

[Cheshire cat]

There were a few years when MGBs were fitted with Aluminium bonnets from the factory. All MGCs were fitted with Aluminium bonnets.

[ditchcrawler]

If I recall correctly there was a spate of this on many narrowboats a few years back and no-one was really sure why at that time either. Lots of theories, all unproven as I recall.

I was told it was because I left it out in the snow

[WotEver]

I was told it was because I left it out in the snow

Yes, Tony B was told much the same by Phil Speight.

[MtB]

These pimples could be a touch of Acne, perhaps mixing the paint with a drop of boiled cabbage water might prevent them. Wax polishing paintwork, especially red can cause outbreaks of pale burn spots, caused by the sun being magnified through globules of rain, like a lens, which tend to remain on the surface in globules for quite some time before finally drying up. I never polish anything outside.

 

 

I'll go with this. The OP's MGB was a teenager after all...