Problems painting the hardtop advice soughted

[feel_ixx]

I've been working a good while lately repainting my hardtop which was a bit weathered before. My painting process was to first sand down SOME of the old paint then priming it, adding a few layers of satin black paint, then adding a few layers of clearcoat, then a final small layer of gloss black as the clearcoat turned out a bit stripey. There was a 24 hour gap between each layer and was wet sanded and cleaned every time. The paint job went well (or so it seemed) and had a great smooth finish, but after about 5 days of drying I had it out in the 30 degree sun there cropped up a small patch of bubbles that I can only attribute to the heat.

My options are now:

Sanding down that patch and touching up the paint

OR

Sand it all off and go for an engine enamel paint

The first option is of course a lot easier and I could pull it off well but if its the paint I'm using that cannot take the heat, it is pretty much a waste of money. The second option though a bit harder I can do as well, I just don't know how engine enamel paint will hold up. It should definitely take the sun, but will it be able to withstand rain and all that stuff as well?

The paint I have been using is Sepitone Acrylic Automotive paint. Would the Urethane paint been able to take the heat better?

Thanks for any help, I hope we have some paint gurus in the forums.
Oh and please don't say take it to a professional. I've gone this far and have too much pride to back down now. Haha.

[Benny]

The heat shouldn't be a problem, as all paint likes some heat to cure properly, but could it be possible that you put acrylic paint over enamel paint?
That can cause the old paint to lift off due to a chemical reaction between the 2 different types of paint.

You mentioned you sanded some of the old paint.
Is this bubbling occuring at a spot where you didn't sand back the original paint?

You should be able to sand back the problem area and re-paint it, but if you see any more bubbling, you may have to sand back the entire roof to make sure it doesn't happen again.

[bigdog]

Rub the whole roof back with 600 grit paper (it will take a while) using a 3m colour sanding block from the auto paint suppliers (so you don't rub finger marks into the finish) you are looking for a consistent smooth surface (no need to remove all the paint). Degrease the the roof with wax & grease remover, then prime the roof with an acrylic primer surfacer (same brand as paint) rub that back with 800 grit till it is smooth, degrease again, let it dry and then paint it with 2-3 coats - a light sand between each coat using 800 or 1000 grit paper. Finished job will last for years if you do it right. If in doubt search the net for spray paint guides. Bubbling is caused by chemical reaction to under lying paint or by moisture - don't paint it on a humid day. I assume you were using pressure pack cans, not a compressor and spray gun (the compressor can introduce moisture unless properly trapped - don't ask me how i know that ).

[feel_ixx]

I'm not sure the type of paint that was used on the hardtop before hand. But whatever paint it was, it came off whenever I waxed / polished or went at it with a chamois. Benny, I gave the old paint an overall sanding, but not enough to see the bare white base of the hardtop. Even still I had used a layer of primer on the hardtop surface before using the acrylic paint, could they still be reacting?

Bigdog, what you wrote was exactly what I did for this paint job except instead of degreaser I had used alcohol. I was sure that the surface was dry before painting. So are you sure that acrylic products would be ok for such high heat / weathering?

I just noticed one hell of a lot more bubbling. Actually these ones are less obvious than previously but probably because it wasn't as hot, however, my hardtop now has an uneven ripple thing going on almost all over it that I'm sure will turn to bubbles if I had left it out any longer.

[bigdog]

Acrylic automotive paint was what all cars were painted with until the mid 80's when the newer '2-pak' paints came into the scene, so no problem with the paint handling heat or cold. What you are seeing is a chemical reaction with the old paint - if it was rubbing off before it had already become unstable - you may need to rub back to the fibreglass and start again - ie get rid of all the old paint altogether. Just to clarify - it is Automotive paint you are using, not household paint?

[Mr Morlock]

bigdog has obviously done this before. The bubbling might be paint boil and thinners may be making its way to the surface or as Benny said you may have mixed different paint types. . Enamels are not the way to go. My advice always is go and talk to the guy's who understand painting processes and that is not the salesperson at the general accessory place who probably does not know. Wax and grease remover- Prepsol ( very useful product in the garage) I can also recommend finding some books on painting- easy to find and you will pick up info very quickly. If you follow bigdogs advice you will not go wrong. Painting is 90% at least in the preparation. Quoting from Dulux the complete Refinisher "Blistering- the formation of dome shaped bubbles or blisters in paint films due to the lifting of the film from the underlying surface" "bubbling- a film defect temporary or permanent in which bubbles of air or solvent vapour are trapped in the paint film" Good luck.

[bensale]

Good thread. When I painted my windscreen frame I had the same problem, although from the sound of it to a much smaller extent as my bubbles are on a small amount of serface area and are not noticable unless you know they are there.

I was quite careful in prep but must have missed a little bit of the original paint and it reacted, thanks for clarifying why I've been having the problem guys.

On an aside it amazing the finish you can get out of a spray can if you prep right and take your time, you can hardly tell the difference between the can and factory finishes.

[feel_ixx]

Awesome guys, thanks for that. Yes its automotive paint, the brand was Sepitone and K&H bought from supercheap and autobahn. Both were acrylic paints. I talked to a lady at MXmania today, she suggested to buy paint from Autobahn, ones that they mix for you and said that that was the type of paint that they use. Does anyone know the difference between their mixed paint and the ones they sell by other brands? Is there some kind of protective thing in there?

[Hammer]

I'm not sure the type of paint that was used on the hardtop before hand. But whatever paint it was, it came off whenever I waxed / polished or went at it with a chamois....

While we're at this topic, what's the go with this?

It's been 20yrs since I've owned a solid coloured car (ie. non-metalic paint), but I just washed, polished, and waxed my new 2nd hand red NA and the buffing microfibre cloths that I used had red stains from buffing. Both application of polish followed by wax and the buffing was done by hand, and I'm using Meguiars Products - non are cutting compound, and are clear coat compatible.

So why is the paint coming off? Is this normal or is this a symptom for something more severe? I also just acquired a red hard top (from a different seller) and this too is leaving red stains on my buffing cloths. I'm really baffled by this.

Any advise?

[grump]

If using 2pak polyurethane paint, don't sand the primer with anything finer than 320# sandpaper. some paints need a mechanical bond as well as a chemical bond. you run the risk of delamination of the top coat, especially if you use normal (white)masking tape on it. Acrylic is a very forgiving paint and needs to be wet and dryed and buffed to get a good finish. you won't get a final finish of the gun. 99% of 2pak paints are wet and dryed and buffed to remove orange peel etc, but a good operator should be able to get a good off the gun finish.
If you use a good primer that is both compatible with acrylic and polyester derived paints then you should have a good base to lay your top coat on to and should minimise the risk of any problems. Its surprising how good of finish you can get with a spray can on small items, but on larger items they really are not suitable as you have very little control over the amount of paint being applied, fan width etc.

[Mr Morlock]

felix if you want advice on paint ( apart from the forum) then ask a paint specialist.The suppliers you mention are not paint specialists. In my area I have a small family style auto paint supplier who know the products and processes inside out ( ex pro painters panel beaters) and they can of course mix paint including by eye. You might need to ask around for auto paint guys in your bailiwick.
Hammer- red is known as very prone to fading and deterioration and guess this must be related to pigments. In the "old" days it was quite normal for polishing cloths to show some paint transfer and I would not be concerned at what you are seeing. I also would not over do the polishing and avoid heavy cutting which you are doing.
grump - agree with your comments. Personally I would be very careful with 2 paks from a health viewpoint.

[Hammer]

.... I also would not over do the polishing and avoid heavy cutting which you are doing.

I didn't think the Meguiars products where cutting compound. After this major clean. I'll usually just wash and wax it (I usually do polish only once a year). I use either Maguiars Quik Detailer or their Cannubra wax. They claim to be clear coat safe, so I'm assuming they don't have any cutting compound, is that right?

[trader]

I think we may have the same problem feel-ixx. Mine gradually started to bubble when I used it a few years ago in the heat (it had been standing for at least a season after I had painted it with no problems) the bubbles gradually got worse. I am sure my problem is the fact that it was initially a black grained top which I filled with primer/filler before sanding. I think the black was some sort of rubberised finish - you may have had that finish originally. I have used the same process painting other parts of my car with acrylis and never had a problem so that's what I think mine is. Rarely use the hardtop now so not losing sleep over it. Would like to know your outcome though!

[grump]

Mr Morlock I totally agree,With all 2pak paints a proper respirator and gloves should be used. Remember to use the right filters in the respirator, for fumes not dust. Best to leave 2paks to the professionals.

[Mr Morlock]

Hammer I do not know those specific products but it will probably tell you on the containers what is the application. Kitten products had numbers and a description of application. I would be surprised if what you are using is not suitable. Grump or bigdog might know the products.