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Old 15-02-2006, 15:05   #1

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How do you fix stripped screw beds?

Hi Everyone,

Does anyone know how to fill in screw holes in fiberglass that have been stripped? I thought epoxy was the trick, but it didn't work. The epoxy couldn't hold a screw (even several days later).

This is for a couple of leaky ports I am in the process of re-bedding.

As always... thanks for the input.

I'll be sure to post up some more pictures of the boat, since so many people on here have been so kind as to help me out with my never-ending questions.

Here are a couple new pictures of 3 areas that are 100% complete (except the cabin sole).

You have all helped a lot with advice on boat work. I appreciate it!

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Old 15-02-2006, 15:20   #2
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The usual method is to upsize the fastener so you get a bite on existing glass. I have also filled with 5200 and had good success.


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Old 15-02-2006, 15:28   #3

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Thanks, Larry. Upsizing the fasteners was my backup plan, except I had hoped to avoid drilling larger holes in the port frames. The current fasteners are as large as the port frames can take.

I suppose I'll go for it though. Thanks for the advice.
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Old 15-02-2006, 15:34   #4
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First, if thru bolting is not an option, I am assuming you are filling the holes, not just adding epoxy and rethreading. If not, the holes should be completely filled and redrilled. Oversize fasteners are a good idea if that is an option. When you epoxy the hole, add some fiberglass fibers to the epoxy. this will give it more strength. These should be in addition to, not in place of the adhesive filler. You can by the fibers, or just cut up some cloth. Do not use mat, as the binding agent in mat does not react well with epoxy.If you are going into a wood core, make sure you drill deep enough to add a wood plug as well. One last thing, make sure you over drille the holes before filling to get a fresh surface.
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Old 15-02-2006, 17:20   #5
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I mix fiberglass resin with milled fiberglass, till quite thick, add the hardener then put this in a plastic syringe & fill the hole with the mixture. Has worked well for me ... hope it helps you.
Bob & Lynn
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Old 15-02-2006, 20:41   #6
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Thumbs up Ditto on the last two

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Old 15-02-2006, 23:01   #7

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This is the technique I'll use! Thanks.

I had used this technique (minus the fibers) without success. I'll add the fibers this time.
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Old 15-02-2006, 23:13   #8
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Don't forget to enlarge the holes. This is very important to get a clean surface for the epoxy to adhere. FWIW, I prefer epoxy, but as Wahoo Sails mentioned, polyester resin will work fine. Your call on that one.
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Old 15-02-2006, 23:58   #9
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Hope that you'll get that situation fixed? Stripped out holes suck. I've dealt with them before. But not on a boat like what you're doin' Sean!!

"Those who desire to give up Freedom in order to gain security, will not have, nor do they deserve, either one." - Benjamin Franklin
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Old 16-02-2006, 08:07   #10
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Srew it

I did not answer to this thread, I listened. I need to replace all the screws that have come lose around the two main windows. I now have a plan.
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Old 23-10-2007, 14:56   #11
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I used to try to fix stripped threads in plastic--now I enlarge the hole and fit a threaded insert--which allows the original bolt to be used but gives a much stronger anchor in the hull. I am not exactly sure what the alloy was but I think it was monel or some version of stainless steel. Brass ones are available cheaply but I am not sure the alloy is any good in the marine environment. You drill out the hull and tap it to fit the new oversize insert. Once bedded I used waterpump grease in the female bolt threads to make sure they did not corrode later--I may want to get them out one day. Do not let any grease get into the coarse-threaded enlarged anchor hole in the hull material. The threaded inserts are themselves coarsely male threaded and can be pan headed, blind headed or countersunk. I prefer pan headed fitted with gaskets if required. They are first coated with Loctite or some epoxy locking compound--which keeps the inserts firmly in place once fitted. If you can not buy the marine quality insert--do not use the shirt-metal grey ones or some of the cheap brass ones--you may be able to make your own from threaded bronze rod by drilling and tapping cut lengths to suit. Drill and tap to the diameter and thread of the original bolt. I do not think Tufnel would be suitable as a permanent repair but a cut down tufnel bolt might be OK as a temporary fixture. They can be bought at most hardware stores as the screw-down fittings for plastic toilet seats--

Why they do not fit marine quality inserts to begin with beats me. Loaded small bolts often strip from hull fibregless unless it is fitted with inserts. Bolting right through is an even better option--where one can.
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Old 23-10-2007, 15:42   #12
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Threaded inserts may work, but check out a German company called Ejot, (formerly Eberhard Jaeger i think) who are thread forming fastener specialists with large anchor strength. They have an "Applitech" lab in Bad Laasphe in Germany, though probably use it only for high volume applications. A thread forming screw of the right dimension would allow superior "stripping torque" while fastening to the original bodywork. I know they are great in metal or plastic, fibreglass you would have to verify, but worth a try . . . .
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Old 23-10-2007, 20:28   #13
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screw holes

My boat is foam / glass & I find the best way to deal with this is to use a small plug made from round PVC. I use a drill with a drill stop to preventing going thu the bottom skin. The PVC is good with epoxy glue & then either tap the plug or use course self tapping screws. Plastic Engingeering firms is a good place to get the PVC. I've done hatches /windows, mounted pumps & other components & no failures. This method allows bits to be removed & put back on without any trouble. (I rough up the outside of the rod before glueing) Total waterproofing is also assured.

Regards Bill Goodward
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Old 23-10-2007, 22:11   #14
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Is through-bolting a possibility? Is there enough thickness in the material to countersink a flathead machine screw and then fill it in with something that does not look bad?

If the screw pulled out then it may be a good idea to go ahead and through bolt it anyway...even if it is not as pretty as original. You will never get the original strength of the glass fiber that is now torn.
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Old 18-11-2007, 20:41   #15
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replacing stripped threads

Lots of good ideas on this.
A different one that I have some success with is essentially casting in the threads in the hole. After I have removed (typically with a drill bit) any broken material from the hole, I will fill it partially with some expoxy resin that has been thickened with chopped glass fibers and sawdust. I then screw the screw into the hole (before any hardware is mounted and let the epoxy set up. However, I put a releasing surface on the screw before I put it in. This can be done several ways, and it pays to experiment before you try this on the boat. Really cheap spray paint works pretty good. Spray a coat on the screw threads the day before, so it drys. If you have decent heads on your screws, you can back the screws out of the epoxy after it sets because the cheap paint will fracture. You have to make sure that the hole depth created by the screw is a bit deeper than you need, and so you end up with custom threads. This technique works a lot easier on horizontal services. Its one you need to experiment with, again not on the boat, but once you get the processes worked out its kind of handy.

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