Drilling/grinding fiberglass/epoxy

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Lou_tribal

Lou_tribal

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Joined
Jan 20, 2016
Messages
4,375
Location
Canada
Vessel Name
Bleuvet
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Custom Built
Hello fellows,
Was wondering if anybody would have any hint about drilling/grinding fiberglass/epoxy?
1. I have a crack in my fiberglass bow pulpit, I want to grind it and fill it with epoxy and fiberglass strands. What kind of disk to use to grind cleanly the crack?
2. I am redoing my anchor capstan fixation. My plan is to drill oversized fixation holes, fill them with thickened epoxy and drill proper holes through the epoxy. I already drilled through epoxy but was wondering about any tip for clean hole, like drill slow vs drill fast etc.

L
 
For minor grinding I use a Dremel with a grinding bit. For larger jobs I use a Roloc disc on a right angle drill. I use about 30 grit discs on the Roloc adapter. They cut very well and change quickly. The right angle drill allows much more control than a regular drill since it isn’t so far away from the work surface.
 
Comodave said:
For minor grinding I use a Dremel with a grinding bit. For larger jobs I use a Roloc disc on a right angle drill. I use about 30 grit discs on the Roloc adapter. They cut very well and change quickly. The right angle drill allows much more control than a regular drill since it isn’t so far away from the work surface.
Click to expand...
Thank you David, tonight I learned something! I did not know what is a roloc disk, now I know [emoji846]

L
 
I love the Rolocs for grinding fiberglass, they cut quickly and with the right angle drill are pretty easily controlled. I get them on Amazon.
 
Comodave said:
I love the Rolocs for grinding fiberglass, they cut quickly and with the right angle drill are pretty easily controlled. I get them on Amazon.
Click to expand...
Would you have a link to the one you get from amazon? there are a ton of them!

L
 
I looked and the ones I use are 50 grit and currently unavailable, like a lot of things.

3M Green Corps Roloc Discs, 3'' - 50 Grit DISC ROLOC 50GR 3 25/BX GREEN
Brand: 3M
 
Is the crack of cosmetic concern, or structural concern?

"V'ing (More like U'ing) out a crack" and filling is great for cosmetic repairs, especially shallow ones in gelcoat, e.g. crazing.

But, if it is structural, you need to feather a wide area around the crack and build up layers of glass to fill. Going 12x the depth of the crack around it is fairly typical. Then you put sheets of fiberglass back in, saturating them with epoxy, working from large pieces to small pieces to fill the hole to the correct shape, building a few sheets at a time to avoid excess heat while the epoxy cures.You may also want to drill holes at each end (and fill with the rest) of the crack before starting to interruot the propagation.


Happen to have a picture?
 
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Don’t forget the adapter.

Pro 3" Roloc Disc Pad Holder - 1/4" Shank
 
Instead of drilling a hole and sticking a bolt in it the local ACE should have a bronze bushing to fit the bolt .

The bushings will help the deck when the hold down bolts are tightened , and as a high load item the extra diameter of the bushing will also be a help in not moving..


Auto body discs come in a course enough grit to make fast work of a small grinding job.
 
gkesden said:
Is the crack of cosmetic concern, or structural concern?

"V'ing (More like U'ing) out a crack" and filling is great for cosmetic repairs, especially shallow ones in gelcoat, e.g. crazing.

But, if it is structural, you need to feather a wide area around the crack and build up layers of glass to fill. Going 12x the depth of the crack around it is fairly typical. Then you put sheets of fiberglass back in, saturating them with epoxy, working from large pieces to small pieces to fill the hole to the correct shape, building a few sheets at a time to avoid excess heat while the epoxy cures.You may also want to drill holes at each end (and fill with the rest) of the crack before starting to interruot the propagation.


Happen to have a picture?
Click to expand...
Not really structural as at the end of the pulpit, just a crack that I want to fill in to avoid water ingress that would permanently damage the internal plywood.

L
 
FF said:
Instead of drilling a hole and sticking a bolt in it the local ACE should have a bronze bushing to fit the bolt .

The bushings will help the deck when the hold down bolts are tightened , and as a high load item the extra diameter of the bushing will also be a help in not moving..


Auto body discs come in a course enough grit to make fast work of a small grinding job.
Click to expand...
I was also looking at using bushing of some sort, if I find some of correct length and material I will use this.

L
 
Comodave said:
Don’t forget the adapter.



Pro 3" Roloc Disc Pad Holder - 1/4" Shank
Click to expand...
Have we already met? How come can you know how much silly I am? Of course I could have forgotten the adapter lol :)
Thank you for the reminder!

L
 
I use a laminate router with a cone shaped bit to run down the cracks making a vee shaped groove then fill with epoxy and high density filler (404). Depending on location you may want to back it up with a strip of glass fabric under the crack.
 
Fish53 said:
I use a laminate router with a cone shaped bit to run down the cracks making a vee shaped groove then fill with epoxy and high density filler (404). Depending on location you may want to back it up with a strip of glass fabric under the crack.
Click to expand...
Good idea, did not think about using the router.

L
 
You may want to do something similar with drilled holes only just use a countersink. I do this with all my deck fittings, drill, countersink, apply nonthickened epoxy then make a ring of butyl around the bolt to squish into the tapered hole when tightened.
 
Bushing for bolts,,,"if I find some of correct length and material I will use this."

An auto body grinder can shorten a bronze bushing very rapidly.
 
For the Roloc, if you have an air compressor on board, you can drive it easily with an air powered die grinder. If not, you can use a battery powered die grinder like my favorite Milwaukee tool. Drills really aren't made to do that and generally turn too slow for grinding.

For cosmetic cracks, the smaller you have to grind out the better. A small diamond or carbide burr in a dremel to trough out a crack minimizes the area size while creating a surface for the epoxy to stick to.

I would not used fiberglass strands for cosmetic repairs, colloidal silica would be more appropriate (for a high traffic area) or even micro bubbles (for low traffic areas).

The question will be, how are you going to finish the repair? If you plan to use gel coat to match an existing color/sheen then epoxy based fillers is probably not the right choice. If you plan to paint then it's fine.
 
sbman said:
For the Roloc, if you have an air compressor on board, you can drive it easily with an air powered die grinder. If not, you can use a battery powered die grinder like my favorite Milwaukee tool. Drills really aren't made to do that and generally turn too slow for grinding.

For cosmetic cracks, the smaller you have to grind out the better. A small diamond or carbide burr in a dremel to trough out a crack minimizes the area size while creating a surface for the epoxy to stick to.

I would not used fiberglass strands for cosmetic repairs, colloidal silica would be more appropriate (for a high traffic area) or even micro bubbles (for low traffic areas).

The question will be, how are you going to finish the repair? If you plan to use gel coat to match an existing color/sheen then epoxy based fillers is probably not the right choice. If you plan to paint then it's fine.
Click to expand...
Paint it will be.

L
 
My right angle drill works great with the Rolocs for grinding. It is plenty fast IMO. Really wouldn’t want it to be any faster since it removes material quite fast.
 
I open the crack with a dremel for depth, then use a Wen Variable Speed Detailing File Sander with 1/2 x18-Inch Belt, #6307 to smooth it out and give a little width. I use epoxy with micro balloons for fairing. If a crack is really deep I'll layer with fiberglass. Rolocs are pretty aggressive and more suitable for large repairs but will work

You're good with drilling oversize holes. I still put butyl rubber under all screw heads just because.
 
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This guide is comprehensive and well written.
 

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Comodave said:
My right angle drill works great with the Rolocs for grinding. It is plenty fast IMO. Really wouldn’t want it to be any faster since it removes material quite fast.
Click to expand...

I suppose it depends on what you are doing. I find the die grinder to be very controllable, my cordless one has 4 speeds and a variable trigger. I use the rolocs with a variety of grits and even scotchbrite pads and like the higher speeds for some things, lower for others. I also use burrs with it when I want more cutting power than a dremel can manage.

Is your right angle drill an add-on to a standard drill or a purpose made right angle drill?
 
Mine is a Dewalt right angle drill, I don’t know the model offhand, but it isn’t an add on adapter. I had a cordless right angle die grinder but it wasn’t up to the job. Went through 2 of them before I went to the Dewalt right angle drill and have been using it for about 4 years and it is still going strong. Right now my neighbor is using it to grind out some glass on his boat.
 
Comodave said:
My right angle drill works great with the Rolocs for grinding. It is plenty fast IMO. Really wouldn’t want it to be any faster since it removes material quite fast.
Click to expand...

I agree with this, when I worked in a boat yard a corded dewalt right angle drill was the standard tool for using roloc disks. They gave great accessibility and control. I'm sure a cordless unit would be that much better but at the time, the battery powered units weren't as good for all day use and I needed to stretch a power cord out for a heat gun anyway.

After hurricane Isabelle came through the Chesapeake, we had a lot of boats in the yard (Smith's) with a lot of cosmetic damage. The strong storm surge was so high that boats on lifts came free or partially free. We had a lot of business repairing gelcoat on late model boats. Newer boats makes matching gelcoat much easier because it hasn't faded and the manufacturers can supply pre-tinted gelcoat. Understandably, the owners of nearly new boats wanted their boats to be flawless and this boatyard delivered, I learned a lot about finishing gelcoat that spring.
 
Are you going to gel coat after the repair? Do NOT gel coat over epoxy. If you plan to gelcoat after the repair, I would use vinylester rather than epoxy.

But if you are only reaming the holes larger then filling, I would start with either a die grinder and mill end bit (5/16” or larger) or Dremel Mototool with mill end bit or abrasive bit. In all probability the Dremel will work fine, depth might be the only concern.

To dress the surface properly, I would use a 3M Roloc flat disk. It’s about 2” diameter and fits a drill motor. Beastly expensive for what you get but 3M quality and a variety of grits. 80 grit should be good.

In all cases the old holes need to be ground away to clean, fresh fiberglass. Prep with QTips and paper towels prior to placing epoxy or vinylester in the holes. If your location is warm, I.e. above 70 degrees,m the the holes are large, use slow hardener for epoxy or low catalyst ratio with vinylester or polyester,(1%-about 4cc per pound of resin, no less than that).

Another hint, go back to Chemlab 101 in college, NEVER put the cleaning rag or towel against the mouth of the acetone container, POUR clean acetone into rag!!! Keep everything clean and avoid contamination of your surfaces!

If using epoxy, you can tape the underside of the holes to prevent the putty from being forced or running out. If using vinylester or polyester, the styrene will attack the adhesive so you might need to plug with a wood bung.

I’ve been a boat builder, composite manufacturer and done America’s Cup composites for 40+ years, that’s how I’d do it.
 
fixing cracks

boatworkstoday.com has a number of videos showing the step by step process to fixing small, medium and large cracks as well as restoring the structural integrity to the cracked area. not only are the videos very informative but he also tells you exactly what materials to use to achieve the best result. i have found his videos to be addictive though..lol
 
Transpacdan2442 said:
Are you going to gel coat after the repair? Do NOT gel coat over epoxy. If you plan to gelcoat after the repair, I would use vinylester rather than epoxy.



But if you are only reaming the holes larger then filling, I would start with either a die grinder and mill end bit (5/16” or larger) or Dremel Mototool with mill end bit or abrasive bit. In all probability the Dremel will work fine, depth might be the only concern.



To dress the surface properly, I would use a 3M Roloc flat disk. It’s about 2” diameter and fits a drill motor. Beastly expensive for what you get but 3M quality and a variety of grits. 80 grit should be good.



In all cases the old holes need to be ground away to clean, fresh fiberglass. Prep with QTips and paper towels prior to placing epoxy or vinylester in the holes. If your location is warm, I.e. above 70 degrees,m the the holes are large, use slow hardener for epoxy or low catalyst ratio with vinylester or polyester,(1%-about 4cc per pound of resin, no less than that).



Another hint, go back to Chemlab 101 in college, NEVER put the cleaning rag or towel against the mouth of the acetone container, POUR clean acetone into rag!!! Keep everything clean and avoid contamination of your surfaces!



If using epoxy, you can tape the underside of the holes to prevent the putty from being forced or running out. If using vinylester or polyester, the styrene will attack the adhesive so you might need to plug with a wood bung.



I’ve been a boat builder, composite manufacturer and done America’s Cup composites for 40+ years, that’s how I’d do it.
Click to expand...

Thank you for your input. No gelcoat just paint and work with epoxy.
In fact my main concern for drilling epoxy is the speed of drill knowing that if it getting too hot it will melt and can stuck the drill bit (don't ask how I know lol). That is why I guess slow speed drilling would be better but was looking for advices.

For gridding, I did a first try yesterday and the right angle grinder with a metal grinding disk is doing a fine job if you are careful.

L
 
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