How to repair worn screw holes in fiberglass?

[ISABELLA5]

I did this just last Saturday, Used Elmers green lable (waterproof) and two toothpicks. forced some glue into hole then covered toothpicks well and inserted. Returned next day, cut off parts extending from fiberglass and reinstall grab bar. Worked wonderfully.

 

[fa102]

Looking for "how to" advice... The screws holding one of my bimini stainless mount brackets to my cabin top have pulled from the fiberglass. What is the best way to repair so I can reattach the bracket with screws? Should I just fill holes with gel coat then redrill pilot holes and attach again with screws and 4200/5200? Would filling the holes just with 4200/5200 and a couple wooden toothpicks to give the screws something more to bite into be a good idea? Would applying either 4200 or 5200 between the entire surface of base of stainkess bracket and fiberglass cabintop before reinstalling screws be recommended?

As posted by others; best to use ss. through-bolts with fender washers / backing plates. (surprising that the self tapping screws, considering the windage / loads imposed by the bimini, did not fail a long time ago).
If the screws / through-bolts are into a cored frp. structure; the core needs to be isolated
from the screw / throughbolt to prevent moisture intrusion into the core (typically of
balsa / plywood / foam) material.
If through bolting is not practicable suggest afix a ss. bolt (to act as a stud) into the frp.
structure secured in place by West System Epoxy / Marine-tex other such product.

 

[Jdaniel343]

Thru bolts would be the best with a backer plate.
Epoxy mixed with saw dust is another option. Mix enough sawdust till it is a thick paste and force into existing holes a little at a time so no voids are formed within the hole.
Let it fully cure and redrill.

 

[Stu Jackson]

All this mention of thru bolts for bimini frames misses one critical point: most of the places that the frames connect to the coamings have NO ACCESS below.

Which is why they used screws in the first place! :dance:

 

[scotmcpherson]

Back the fiberglass with plywood, and use a bolt.

 

[centerline]

Mounts for Biminis and dodgers can have a lot if stress on them (thunderstorm winds). Because of this I would recommend not using shirt cut repair using toothpicks, plastic mollys. They won't be full strength and they will like allow water ingress and bigger longtime issues.

One of the replies mentioned thickening epoxy mix with 'micro balloons'. While micro balloons are routinely used to thicken epoxy... this type of mix makes the epoxy much softer/ weaker/ and definitely not for strength applications. The micro balloon mix is usually used where you will need to do a lot of shape sanding/ fairing and no major stresses expected.

Straight epoxy is very strong but rather brittle by itself and can easily crack under stress. It's the strength medium like fiberglass that gives the epoxy mix it's great overall strength properties. In small repairs you can't fit the usual fiberglass cloth. So fill stripped screw holes with epoxy mix & cut up fiberglass threads from scrap fiberglass cloth. First root out any soft core under the surface decking described in another reply and fill with your mix. Then tape over with painters tape if it's on a angle to keep it from running out. I use fast epoxy which still takes 30-60 minutes to fire off. (Preheating the Part A and Part B and the repair area to slightly warm to the touch will significantly speed up the curing time).

I agree....

but the jb weld that has been mentioned in an earlier post, or any other good quality epoxy paste or putty such as the marine tex, por-51 ect, is NOT a brittle product and is ready to use as soon as its mixed...
stronger and better can be achieved with backing or fibers being added, but for the purposes of filling a screw hole, adding fibers is way overkill when using one of the quality epoxy paste/putties...
backing the hole with something is always a good idea anytime it needs filling, if only for the reason to smooth out the extruded filler at the backside of the hole. it will allow for more contact and better adhesion, which equates to a stronger repair.

 

[bwasileski]

Epoxy with microballons is only for non-structural applications. If there will be any stress or load on the screws then you should use something else. Bolts with rear plates and nuts would be best. If there will be any type of load then you can use a structural adhesive with chopped cotton flox. When cured it's tough as nails but can be drilled out and tapped for screws. No matter what you're still better off with bolts/nuts. The structural adhesive can be easily counter-sunk for a flush mount.

Bolts would be the best solution, but if that isnt what you want to do get some epoxy putty or "marine tex", which is an epoxy paste and fill the hole. Its best to use something as a backer, no matter what the material is or how thick or thin it is, as it will allow for a better filling and backing of the hole and a much stronger repair.

As others have said, you can make your own epoxy paste or putty, but unless you need large quantities of it, its more convieniet to buy the stuff and keep in in the tool box. Its just handy stuff to have around.

 

[hotrodderjim]

one good way is to get some fiberglas" fibers, mix it with a glass resin & mush it all up & force it into the holes, stuff it real good in there, when it dries sand the top flat & redrill.but your best bet is to use a better screw. If theres places around you called "fastenal" go in there & talk to them. They'll have a solution. also if you use screws on fiberglas the threads actually chip away at the holes inside.Doesn't make nice clean threads in the glass.
PS theres a Fastenal in Portsmouth, NH
HRJ

 

[prettysailor]

I have used Stainless Steel machine screws in the past but make sure they are just slightly larger than the exisitng holes.

 

[Maciek]

one good way is to get some fiberglass" fibers, mix it with a glass resin & mush it all up & force it into the holes, stuff it real good in there, when it dries sand the top flat & redrill.but your best bet is to use a better screw. If there is places around you called "fastenal" go in there & talk to them. They'll have a solution. also if you use screws on fiberglas the threads actually chip away at the holes inside. Doesn't make nice clean threads in the glass.
PS theres a Fastenal in Portsmouth, NH
HRJ

This is the only correct and permanent method of repair. I'm using this technique on my carbon fiber catamaran all the time, just using carbon fiber fibers instead of glass. Works every time.

 

[bwasileski]

That's a bold statement. I can honestly say there is no "one" way to do anything.
The use of strutural adhesive and flox is most definitely a tried and true way of providing repairs for screws screw holes. While I didn't do it on a catarmaran, I did use this approach when building my plane. Technique taught and recommended by the manufacturer. I used this technique to hold on hinges connected to control surfaces and other things. It's 100% solid. In fact, cotton flox is actually better where is a possibility of torsional loads as glass is much weaker in shear and torsion. If you put glass in a container and "mush" it in the resin, the "mushing" actually causes breaks/discontinuities in the glass's ability to take on tension. cotton fibers, while not as strong, are much more flexible without loosing their strength. Overall, for tension and strain it may end up being about the same in tension but certainly not in shear or torsion. Again, there's no one way to skin a cat. I'm sure both methods will work for the application.

This is the only correct and permanent method of repair. I'm using this technique on my carbon fiber catamaran all the time, just using carbon fiber fibers instead of glass. Works every time.

 

[seascoutship27]

I would not use Gelcoat, I often use Marine tex or if the hole does not go all the way through I inject some very thin epoxy then after it dries fill any remainder with marine tex or epoxy with filler. redrill small holes, then put 5200 in hole, put 5200 on underside of plate fitting to deck or just put on deck, then re-attach to deck. These holes are the points of death to your deck and must be treated accordingly. never put screws or bolt into deck without 5200 or 4200 in hole first to seal from water, not for structural support or reinforcing. Just my two cents, this is how I teach my sea scouts to do it so we never have to touch it again.

 

[abarrow]

Threading the hole

A friend who worked as a rigger for several years showed me his method. He drills out the hole, hogging it a little with the bit as he drills by just wiggling the bit around inside (tilting the drill). The one he showed me didn't go all the way through the deck, so he made sure the bit didn't go all the way through. Then he fills the hole with thickened epoxy and lets it dry.

After it's dry, he drills out the hole, using a bit smaller than the machine screw he's going to use. He then taps the hole using a metal tap the same threads as the machine screw he's going to put in.

Finally, he coats the machine screw with unthickened epoxy, and screws it into the hole.

Of course, this is one that you really, really need to get right the first time, because taking the screw out later is a big job. It is possible, just a lot more difficult than if the screw were just screwed in with no epoxy.

There's a lot of situations where this might not be the best approach, but I thought I'd share it!

 

[Charlie Jones s/v Tehani]

No real difficulty in removing a screw, bolt etc set in epoxy. Heat the head with a soldering gun, the epoxy will go soft, unscrew the fastener. No biggie.

 

[KZW]

Mounts for Biminis and dodgers can have a lot if stress on them (thunderstorm winds). Because of this I would recommend not using shirt cut repair using toothpicks, plastic mollys. They won't be full strength and they will like allow water ingress and bigger longtime issues.

One of the replies mentioned thickening epoxy mix with 'micro balloons'. While micro balloons are routinely used to thicken epoxy... this type of mix makes the epoxy much softer/ weaker/ and definitely not for strength applications. The micro balloon mix is usually used where you will need to do a lot of shape sanding/ fairing and no major stresses expected.

Straight epoxy is very strong but rather brittle by itself and can easily crack under stress. It's the strength medium like fiberglass that gives the epoxy mix it's great overall strength properties. In small repairs you can't fit the usual fiberglass cloth. So fill stripped screw holes with epoxy mix & cut up fiberglass threads from scrap fiberglass cloth. First root out any soft core under the surface decking described in another reply and fill with your mix. Then tape over with painters tape if it's on a angle to keep it from running out. I use fast epoxy which still takes 30-60 minutes to fire off. (Preheating the Part A and Part B and the repair area to slightly warm to the touch will significantly speed up the curing time).

Exactly so. Cut up fiberglass will thicken the epoxy. Use slow cure for working time. Force the epoxy into the hole and use a toothpick or small diameter metal rod to poke the mixture in the hole and work out any air bubbles. Let it cure overnight. Drill a pilot hole and screw in the screw.

 

[Steener19]

I was introduced to a delightful product a couple of years ago: MXBon105 that works on most materials. The active ingredient is cyanoacrylate, the same as in crazy glue, but more fluid. Fill the holes with ordinary baking soda (it's basically inert) and pour the MXBon into it. The cyanoacrylate bonds to the baking soda and soaks into the strands of fiberglass as well, locking everything together. It's instant, solid, tough, waterproof, drillable and permanent. You can redrill and use the better self-tapping screws as suggested.

You can check their website (www.mxbon105.com). I'm sure there will be a number of wiser people sneering at this but try it on something before you shrug it off - I was amazed by it and I have no stake in it.

 

[Genesis V]

Widen hole some what and fill hole with west-epoxy that has some filler mixed in 404 for extra strength. Insert the bolt wiping off excess epoxy that oozes out and let cure. (Bolt should be clean and sprayed with WD40 or some kind of lubricant and wiped off clean before inserting). After full cure use a screwdriver to break the initial grip of the epoxy and to back out the bolt.
What you're left with is super strong elongated embedded epoxy nut. They're installing keel bolts with west epoxy.
See. http://www.westsystem.com/ss/bonding-hardware/

 

[bob328]

fill with 6-10 epoxy (thickened epoxy) and redrill. You can add a layer of fiberglass cloth with the 6-10 if you want a heavier support inside the hole. This stuff works great and doesn't run. You don't have to use the mixing nozzle. Just put the tube in you caulk gun and run a ribbon, mix the two parts with your popsicle sticks and apply to the area. Six-10 epoxy is made by west system and is sold at west marine.

 

[captjim1]

Looking for "how to" advice... The screws holding one of my bimini stainless mount brackets to my cabin top have pulled from the fiberglass. What is the best way to repair so I can reattach the bracket with screws? Should I just fill holes with gel coat then redrill pilot holes and attach again with screws and 4200/5200? Would filling the holes just with 4200/5200 and a couple wooden toothpicks to give the screws something more to bite into be a good idea? Would applying either 4200 or 5200 between the entire surface of base of stainkess bracket and fiberglass cabintop before reinstalling screws be recommended?

Well I have change most of all my fittings with stainless bolts and hex nuts with locking material, (Plastic). Anything I screw in to Fiberglass must not be under too much strain.

 

[Batman]

A lot of the screws in the cabin sole were loose so I used plastic anchors. I use the tapered ones with a very small shoulder. The plastic expands into the fiberglass without tearing it like the course screw threads do. Worked for me.