Spider cracks in primer

HPCOBRA · #1 (**permalink**) 11-25-2010, 09:04 PM

I have an older (mid 90's) CR that has never been painted but is primerd. It has been bumped a little by the previous owner and has some spider cracks. What is the best way to fix these before repriming and painting?
Thanks

DanEC · #2 (**permalink**) 11-26-2010, 07:11 AM

[quote=HPCOBRA;1092026]I have an older (mid 90's) CR that has never been painted but is primerd. It has been bumped a little by the previous owner and has some spider cracks. What is the best way to fix these before repriming and painting?
Thanks[/QUOT

What do you mean by bumped a little? You need to find out if the cracks are just in the primer or in the gel coat. That means basically taking the primer off in the area. Then you can wipe the remaining gel coat down with Prep Sol or lacquer thinner and if there isn't any sign of the spider cracks you can re-prime. If you see the spider cracks in the gel coat you will have to sand down to the bare fiberglass and apply some spray on gel coat or epoxy primer to start back with. Hopefully the primer is just cheap or weathered and has shrunk up some and you can sand it off and re-prime.

HPCOBRA · #3 (**permalink**) 11-26-2010, 07:23 AM

Thanks for the response. I am sure that they are in the gel. My experience is fiberglass takes a lot of compression but minimal tension. These spider cracks are typical of the ones you would see on fiberglass in areas of twist (ie: around mirror attachments, etc). My car was bumped in the nose that broke are area around the air inlet area for the oil cooler. Some of the adjacient area has these spider cracks from the nose being flexed. Years ago I painted a Corvette that had spider stress cracks and there was an epoxy primer product that went on very thin. Capillary action drew it into the cracks and reknitted the cracks. They never came back. I looked for this product and it appears to be a thing of the past. I remember it had a lot of cautions on the label so it most likely was not good for the environment or humans!

mrmustang · #4 (**permalink**) 11-26-2010, 08:37 AM

As stated above, the primer is not cracked, the fiberglass underneath it is.

Bill S.

DanEC · #5 (**permalink**) 11-26-2010, 07:13 PM

Then you will need to use a Dremel or die grinder to V-grind out each crack deep enough to glass 3 or 4 strips of fiberglass back in. Cut the strips of fiberglass progressively wider to fill up the V-notch. Get a fiberglass roller and roll each layer in to remove excess resin and compact the mat. If any of the cracks go all the way through, then grind the backside and reinforce with more resin and mat. Grind flush and refinish with filler and primer. If an area is so severly cracked as to make grinding out the individual cracks prohibitive - then you will probably have to grind the entire area down sufficiently to build it back up with 3 layers of fiberglass mat (not cloth) and resin.

I have an old Corvette also and years ago some use to say that spray gelcoat could be applied over the top of stress cracks and it would heal them up and keep them from reflecting through. It doesn't work. I'm not familiar with the thin epoxy primer material you spoke of.

strictlypersonl · #6 (**permalink**) 11-27-2010, 08:46 AM

I think that the safer (and perhaps easier) thing to do is grind the entire area with cracks away, then cover with a couple layers of mat. Finally, after a full cure, shape the new glass down before using a final finish of epoxy filler.
That process will probably end up with something with a more stable base. I worry about "spot" fixing showing up in the paint eventually.

HPCOBRA · #7 (**permalink**) 11-27-2010, 09:09 PM

I was hoping that there was someway without placing cloth on the surface. Yiou have to look close to see the faint lines. The body is smooth and blocked. Is there ther anyother less evasive way to fix these? Thanks

Ant · #8 (**permalink**) 11-28-2010, 02:51 AM

Good advice already, first you need to remove any damaged material then bevel the edge of the hole/crack with a 12-to-1 chamfer, that is the area you scarf out will be approx 12 times the thickness of the glass, using a disc grinder or 36grit sanding wheel, then go through the process of laminating with the same material.

There is no easy way to do a less evasive job if the cracks are down to the actual reinforced glass or that is cracked through as well. The cracks will show back through the paint. Gelcoat has no real strength and is just there to cover the matt etc and for a painting base!
There are good fibreglass tips on Youtube or go to a reputable body or boat shop.