How to repair worn screw holes in fiberglass?

lillia28 · Feb 4, 2015

As Captain Queeg said, "There's a right way, a wrong, the Navy and My Way!" Take your pick. The right way depends on how you use your bimini, how thick the cabin top is ( whether it is cored or not) and how long you intend to keep the boat. You could get away with just putting in an oversized wood screw. The resons that pop into your mind as to why that is not a good idea wil point to the correct solution. The strongest solution will include a through bolt and a backing plate, but you may not need that much strength. One of the above answers discussed "casting" the screw in the epoxy. If you coat the screw or bolt with mold release, you can easily unscrew it. Epoxy is easy and fun to work with, once you get used to it. While not necessarily the least expensive, the West system is easy to use for beginners, easy to measure and they have some very informative pamphlets. I'd read through the pamphlets before starting. let us know how you make out.
Lou

wufibugs · Feb 4, 2015

I cannot help but think that a stainless rivnut is the answer. If one were concerned that the flange the rivnut tool makes is not enough, then it could be sunk in epoxy. This makes the installation almost equivalent to a backing plate where that is impossible because of lack of access while still allowing removal and reinstallation on a "nut and bolt" basis. I suppose the downside is if for some reason one needed to relocate the mounting hole he would have to remove the rivnut and repair the somewhat larger hole it left.

Ken13559 · Feb 4, 2015

Looking at the Mxbon105, it looks very much like Superglue ala cyanoacrylate. Anyone tried Superglue with baking soda for filling holes?

KZW · Feb 4, 2015

Ken13559 said:
Looking at the Mxbon105, it looks very much like Superglue ala cyanoacrylate. Anyone tried Superglue with baking soda for filling holes?

It can work depending upon the stress and vibration. Superglue tends to make strong, but brittle joints. When used with baking soda (much better than micro-balloons IMHO) the final mixture acts like concrete. It is a chore to sand, and very strong, but if you whack it hard, it can shatter.

My preference is epoxy with some baking soda, and cut up fiberglass fibers. Mix it up and pack it into the hole.Slow hardening is better to allow time to work it into the hole and get all the air bubbles out. It is easier to drill than superglue and baking soda, and will be more resilient to vibration.

Daveinet · Feb 4, 2015

Rivnut is along the right idea, but something much simpler would be a threadsert. This way the screw threads are not stressed and the holding force is held by a much larger screw. Since the thread is glued in place, it has less chance of walking around. Threadserts have a much deeper thread, so it will hold much better.
http://www.ezlok.com/InsertsMetal/stainlessSteel.html

When you have access to the back side, then you use a T-nut.

Trying to fill the hole in and repair the original threads is a waste of time. It already broke once because the fastening method was not adequate. Do it right once and forgetaboutit.

knot smart · Feb 9, 2015

My vote is to fill the holes with fiber glass resin.. mix some resin with some hardner and push it in..

Waybad · Feb 11, 2015

You can use thread inserts in Brass or Stainless steel. They come in assorted sizes. The fiberglass needs to be a 1/4 inch or more in thickness. You drill a hole for the size of the threaded insert, then thread it in with a screwdriver or a tool which works a little bit better.
I use a small hex head with lock nuts with threads to fit insert. I coat it with your favorite two part epoxy on the outside threads and it is then threaded in to the fiberglass like a sheet metal screw. the insert has a interior thread for a machine screw. Which you can remove at anytime if needed. good luck which ever way you go. Waybad

Bill Roosa · Feb 11, 2015

Don't try and glue it, fill the holes with FG resin putty (resin + plain old baking flower to make a peanut-butter consistency). Redrill the holes and install with life caulk to seal out water intrusion.