How far do you dremel these cracks out

Before you put in some kitty hair? Do you grind away just the gelcoat or go half way deep into the fiberglass? I started with a weak dremel from harbor freight and it has no power so going to buy a real one. Thanks for your help guys.

http://www.flickr.com/photos/59077920%40N06/5816574589/
http://www.flickr.com/photos/59077920%40N06/5816574079/
http://www.flickr.com/photos/59077920%40N06/5817142756/

Hopefully Schubbie (Dale) will reply as he has a great deal of experience (with more to go on his recent Speedie redo). I burned up a Dremel (motor spins but gear is gone - so use a reddish Harbor freight knock off (bigger than the old Dremel). The little $6.99 one is probably the one you have. Dale seems to go down to the fiberglass base - like you did (maybe a tad deeper). Try using a narrower bit to just get the crack out and not adjoining gel coat. He uses the West Marine 105 System of epoxy resin/hardener/filler. It dries very hard and doesn't shrink or pop off (like cheap Bondo and spot putty do). Tad expensive - $50 or so for kit. I used it to fill dash gauge holes and defroster cutouts. The powdered filler is added to make it like smooth peanut butter.

http://www.westsystem.com/ss/the-105-system/

Matt,
I spent huge time w/ my last car doing this exercise and there are a few tricks. Understand - using the system Wolfgang mentioned you are getting the car ready for paint. I don't know if you could use the dremel and the fill w/ gelcoat - never tried that.
I use a carbon grinding bit ( you can buy them at Lowes or H/D and look like a small steel grinder w/ ridges ) that is about 1/8" or a bit wider and start in the crack somewhere and work your out each direction till you get about 1/2" past the end of the crack you can see. You do this so in case it goes past what you see the crack does not come back. You kind of want a v-shaped groove ( so pick your bit to make this shape ). Take the groove down till you get through the surface and into the base ( through the gelcoat ).Use the West system and buy the mixing pumps for the bottles so you get the right mix - mix on a paper plate or bowel and then add the filler( they have different types - make sure you add strength )and add filler til it gets like peanut butter and spread in the crack. Let it dry till the next day - this way you can grind till your tired and then stop and mix and fill all the cracks at one time.
Start w/ heavy sand paper on your power sander and work your way down till it matches the material on either side. If you missed a few spots add more mix till you get it right.
It is lots of work, but worth it in the end.
Spotting putty can be used at the end for pin holes and the like - you can double check for them after you do a light prime coat.
If you are going to do your own primer before you have someone paint - make sure you use the correct primer that will work w/ your future paint - check w/ your painter or auto paint store.
Dale

Dale,

So is the bit your using for a dremel or for a regular power drill? How wide do you drill out the cracks? After reading info on another forum it seems like spraying primer at home requires a lot of equipment I may have to get it to the point right before primer and let someone else do the rest.

I hear you are supposed to epoxy primer, high build primer, base coat, and finally clear coat. Is that the steps you took Dale? What grit did you sand the gelcoat before you primered it?

Matt,
Ya-it's a dremel bit you can get from the hardware store.
Use it on the dremel - high speed - knock it right out.
It looks like a little grinding bit and comes in different
widths - Use one about 1/8" to 1/4" wide - smaller for the
hairline cracks and a bit larger for the wider ones. No
special deal here - the first one you do will be a bit nerve
wracking ( scared to hurt something ),but after a couple it
is no big deal. You can always fill it in.
V- shaped groove is better I think, but it should work w/
most any groove if you go past the end of each crack and
down through the gel coat.
If you are worried about the primer just use the cheap-off
the shelf-primer to check your sanding on the repair till you
get it right and then sand off the primer - no big deal.
My painter asked me to use like 420 grit on the gel coat before
paint - he did not want it too smooth so his primer would stick
and then sanded between coats.

Wolfgang wrote: "I burned up a Dremel (motor spins but gear is gone"

Actually, there are no gears in a Dremel. What you destroyed is pretty common, and it's a splined coupler inside that's made of Nylon. Go to the Dremel site and get into the parts lists, find your model (there are several) and find the coupler part. When you find it and go to buy it, get a half dozen because the shipping is about the same for all as it is for one. The part itself costs a couple of bucks or so.

Replacing it is easy - the hardest part is getting the case halves apart and back together - the rest is very straightforward.

Sorry for the Hi-Jack, Matt: Grind out the cracks to a width of about 1/8" and a depth of about the same. You have to get through the Gel coat and into the substrate in order for the patch to bind properly. Dremel sells a router-style bit that works great for this (it has a conical point), and I usually run the Dremel speed at about 7-8 out of ten. If you use a Dremel, it's helpful to use their router accessory as it will hold the cutting bit at the same depth for you. I think that fixture also works for their grout cutter bit.

I have done a few kits in my day and offer the following advice:

1. To fill in the dremeled out spider cracks I wouldn't use kitty hair. Top of the line stuff is 3M HSRF. If you can't use that I would make the cracks a little wider and cut up some fiberglass matt and resin, mix it in an aluminum foil baking dish (I use little ones) and press it into the repair. Sand smooth with 80 grit on a DA and finish with a quality filler like Rage Gold. Don't go into the glass if they are only in the gelcoat. use a shop vac to suck up the dust so you can see what you are doing as you go along.
2. There is really no need for an epoxy primer. I use epoxy for sealing metal cars, but for fiberglass cars I use Evercoat G2. You can buy a cheap gun (with at least a 1.8mm tip) from Harbor Freight and shoot it outside. I like to prep the surface with 80 grit although you can certainly use 120/150. 3 coats of G2 will easily cover 80 grit scratches. Spray some guide coat and block with 150, 320, then 400 (for solids...600 for metallics) and shoot your base and clear. You can thin the G2 by 10% with acetone to help it flow a little better. You can also thin down some epoxy and use it as a sealer after the G2 and sanding if you like. I never have.

isn't kitty hair just slang for HSRF?

Gordon - Thanks for tip on repair for Dremel. So many tools these day are throw away - refreshing when you can actually repair one!

No..the 3M HSRF is different stuff all together. Its about $32 a quart while kitty hair is about 1/2 of that.

Plus it is designed for fiberglass boat repair and is so much more compatible with the fiberglass bodies.

Guess I've just never seen it capitalized like an actual product name. Anyway, looked up the differences, Kitty Hair is long strand fiberglass with a polyester resin, 3M's HSRF is short strand fiberglass with a vinylester resin. Vinylester's the better resin because it absorbs less water and has less shrinkage.

Does anyone make an epoxy filler with embedded fiberglass? I've only seen epoxy putty and straight resin. Epoxy would be the strongest if you could get it.