Morris Minor Owners Club

Johnathan Allthough not about a moggie(but may apply to anyone with fibre glass wings fitted) I have a scimitar gtc and it has developed micro blisters under the paint. Seems to be between the gel coat and the primer. When you prick these a small amount of water?fluid,is expelled. There have been several threads on the scimitar site re this problem. I'm asking how is the best way of curing the problem I don't want to respray the wing and bonnet for it to happen again,is there a barrier primer that can be used. One of the theories is that it is caused by osmosis alowing water to penetrate from the underside and that at certain times of the year it is worse than others. What about heating the area with a gentle heat would this drive out the moisture from the blisters. Also another theory is that it is caused by respraying with 2 pack paint, (which it has been at some time since it a clear over base finish) something about expansion,should fibreglass be only sprayed with celly.Don't know if you have come across this problem before,just looking for advise before I decide the best way of dealing with it,Cheers

Osmosis sounds right on the money - always a problem with FG boat hulls particularly sandwich construction ones (or yoghurt pots as they are sometimes known)
glad you brought this up as thinking about 2 new FG wings - a definite will be to paint the insides as well, underseal type something.

It could be one of two thinks really. The most obvious is moisture, which is trying to escape through the paint, this could have been an issue caused during the repray where the car has been sprayed in a damp environment, or in a propane heated garage/room, or that the primer has not been left to dry thoroughly after wet flatting it. (normally 24 hours unless you have a heated booth.
The second possible cause is solvent pop, when too short a time is left between coats of paint, should be 15 mins minimum, or if too much or incompatible thinners/activator has been used. Remember every time you add another coat of paint it re activates the one below. If one hammers on the paint to thickly then the top surface will dry leaving a 'puddle' of paint mix trapped between coats, this will try and work its way out through the paint layers and will present itself as small blisters, maybe weeks or months after the car has been painted.
A third possible problem could be that the car was baked after spraying, or the spray booth was to hot during spraying, this will cause the symptoms mentioned too.
The remedy unfortunately requires all paint to be removed preferably back to the gelcoat, and the car re sprayed correctly.
Kevin is correct in saying one ought to paint the underside of the wings too, not only as a seal but to provide a surface on which to apply a decent underseal, as protection against stone chipping.
Hope this helps

Hello Kenatt,

I may be wrong and don't have my manuals to hand, but glassfibre I think benefits from being heated prior to painting. I'm sure,if that is the case the temperature has to be such that it allows the paint to be sprayed without affecting the paint; a rather special technique?

Alec

Alec 20C is the normal spray temp and all parts benefit from being pre- heated. The trouble with glass fibre is that it often contains lots of air bubbles/pockets, and when this is heated the air has to expand somewhere,normally through the gel coat.We reduce the booth temp when painting glassfibre to around 16C,

thanks all .I take on board everything said but it's still a puzzle Its about 6 years since the car was resprayed,and only just started to blister in the last 2 months also some of it is on the bonnet which dosnt have water spray from the underside. At first it started on the front offiside and I assumed it was vapour from the overflow bottle which was directly below this spot.But now it's starting on the offide of the bonnet as well,and on the top of the front wings.Fortunately I can spray paint to a reasonable standard so it's not going to cost me a fortune to sort out in the spring when things warm up.THink I will paint the underside of the bonnet and wings as suggested Cheers.

Can also be caused by UV breakdown of the paint. Mainly caused by direct sunlight when the car is wet and water beads are sitting on the paint due to wax finish. Each droplet acts like a tiny magnifying glass and causes temperature differentials across the paint. The fact that the micro blisters contain water, does suggest the water is coming up through the FG and gell coat though. To repair, you will need to get the car bone dry top and bottom of the panels. Treat the underside, then respray top surface after perp work.

Just Note to say- I had a similar problem when my car was sprayed, the wings are fiber glass, they reacted after being baked, as Jonathon said because of air pockets within the fibre. the problem was solved by not baking and leaving over night to cure( sounds like meat) and taada no reaction, the oven was already warmish from days work, but just cooled with the car

James

is it a 5 0r 6?
the se5's were prone to this as they often were not allowed to cure properly before paint & final finishing.
the moisture trapped in the gel coat will try to get out any way it can-it can take years to develop & usually rears its head when the paint is applied too thick.

i once painted a 5 for a friend after doing my v8 engined 6, the 6 was a breeze, the 5 was a nightmare!

hi devilpaint its a se8 gtc and the blistering is isolated to only(Up to now)the very front of the front wings and the front of the bonnet.On closer examination it has been repainted,and its only blemished the new paint and primer the original colour underneath is ok so has to be something to do with the respray. May be moisture in the primer who knows Its not that bad yet so might just leave it, At least it can't rust like my splitscreen .