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Old 05-03-2011, 11:21   #1
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Best Filler for Repairing Screw Holes in Fiberglass

I'm in the process of doing some cosmetic repairs to the coach. Repairing stress cracks, small delamination voids and such. The boat is equipped with ABI stainless ports which have a stainless ring plate on the outside. Since I noticed that a few of the cracks extended under those rings and I've been meaning to reseal the lil'buggers anyway I took them off.

Here is the problem. I noticed that some of the screws that attached the ring plate to the coach are the apparent cause of the cracks. You know, too small a pilot hole for the screw leading to radial cracks. Additionally, in some of the screw holes it looks like dry glass fibers that were never saturated with resin. I plan on grinding these screw holes out a bit, re-filling them and then drill new holes before resealing and re-attaching the ring plates.

Now my question. I'm a bit undecided as to what to use to refill the holes. My current choices are duraglass, an epoxy/micro-balloon putty, Marine-Tex, or just plain epoxy. I'm leaning towards the duraglass. Of course there is no way to get to the back of the hole, so I'm just going to have push in what I can from the outside and hope for the best. I have heard of a little trick of wadding up a small bit of masking tape and then pushing it into the hole prior to adding the filler.

Any suggestions ladies and gentlemen?

Rich
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Old 05-03-2011, 11:49   #2
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Re: Best filler for repairing screw holes in fiberglass

Resin alone isnt structural and neither is a microbaloon mix. The ballons just bulk out and keep it light, great for aero mouldings but you need something tougher for this.

Im not sure whats currently available as a stiffening mix but a fine glass powder would mix well. You could do worse than to collect up glass dust and mix it to a paste with epoxy
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Old 05-03-2011, 11:54   #3
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Re: Best filler for repairing screw holes in fiberglass

You can buy small bags of loose strands of fiberglass, they mix up well in resin and produce a pretty good goo for that kind of work.
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Old 05-03-2011, 11:59   #4
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Re: Best filler for repairing screw holes in fiberglass

The duraglass and the Marine-Tex harden like bricks. In fact, it's claimed that the Marine-Tex can be drilled and tapped. I don't think that this comes under the heading of a structural repair but rather a cosmetic repair. The rings around the port basically hide the original installation and provide another level of sealant. There is no force being applied to them.

Now, if necessary, I do have a supply of cabosil (sp) that I could mix in.

Thanks for the reply, I appreciate all input.

Rich
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Old 05-03-2011, 12:01   #5
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Re: Best filler for repairing screw holes in fiberglass

Quote:
Originally Posted by foamcore View Post
You can buy small bags of loose strands of fiberglass, they mix up well in resin and produce a pretty good goo for that kind of work.
I've got some of that but the fiberglass strands are way larger than the hole. The hole, even after grinding out, will be less than .25 in. The strands are about 2 in long.

Rich
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Old 05-03-2011, 12:35   #6
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Re: Best filler for repairing screw holes in fiberglass

Go to home Depot and get some of their plumbers epoxy. Take a countersink and open up the holes a bit, then fill with this stuff.

I bought some of this by mistake one day to use on reshaping a model airplane wing. Put the stuff on, let it harden and then spent about a week with a mill file getting it down to contour. The stuff is hard as steel, and it too can be drilled and tapped. Cheap too.



The stuff I'm talking about is the greyish blotches with the speckles. The other stuff (greenish) is called Milliput, also good for small patchs but its very expensive.


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Old 06-03-2011, 01:11   #7
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Re: Best filler for repairing screw holes in fiberglass

Milled fibers (not chopped) and silica are the "usual suspects", though cotton flock (West 403) and calcium metacilcate (West 404) also will bond well. As to the best, well milled fiber improves adhesive qualities on 'glass surfaces and is my typical choice for wood to 'glass and 'glass to 'glass bonds. Of course these wouldn't be cosmetic fillers, but structural.
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Old 06-03-2011, 03:25   #8
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Re: Best filler for repairing screw holes in fiberglass

For anyone that will be doing their own repairs, and doesn't already have a lifetime of experience at it, I suggest that you spend the bucks for the very expensive book: "Gougeon Brothers on Boat Construction". (WEST resin products) You have a number of different problems, caused by different building mistakes and/or age. They all require different remedies.

Gougeon Brothers = WEST resin, has a huge advantage, in that they have been around since the dawn of the W.E.S.T. technique. They also have led the way in testing, creating a variety of fillers for each job, and publishing their results.

More than anything, you will be using their silica filler, (thickened like mayonnaise), and injecting it with a syringe. Just remember to sand prep and solvent wash any surface that you want resin to stick to... This includes inside of holes.

It is a very extensive process, that is too lengthy to discuss here. Start with the book, and their thin "how to" manuals. Best of luck,

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Old 06-03-2011, 03:39   #9
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Re: Best filler for repairing screw holes in fiberglass

Calling the West System tech support line is also a good idea. They are amazingly helpful in my experience. Only open Monday to Friday though.
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Old 06-03-2011, 03:53   #10
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Re: Best filler for repairing screw holes in fiberglass

Quote:
Here is the problem. I noticed that some of the screws that attached the ring plate to the coach are the apparent cause of the cracks. You know, too small a pilot hole for the screw leading to radial cracks. Additionally, in some of the screw holes it looks like dry glass fibers that were never saturated with resin. I plan on grinding these screw holes out a bit, re-filling them and then drill new holes before resealing and re-attaching the ring plates.
In the end the screws provide no structural qualities for securing the ports. The bedding compound is what secures the port. It has the ability to bridge between the dissimilar materials and flex with heat, cold and stress just enough to hold and not leak. The screws are just there to hold the port in place while the caulk sets. The variation between the two coefficients of expansion between fiberglass and metal are such that the screws mean nothing after the job is properly completed.

If you remove the screw and attempt to remove the port you find it's as stuck to the boat without the screws as it is with them. The rings don;t come off easily either. When replacing the screws you don't want them as tight as possible, but tight enough so the caulk gushes a little around the edge and keeps the alignment so the port looks straight. Placing painters tape before the caulk is applied can help. I find the good Sikaflex easily comes off if you don't fuss with it until well after it has cured. Make sure both surfaces are as clean as possible.

Unless the holes are too loose to hold the screw long enough to set the caulk it won't matter if you fill them. My ports use shoulder bolts to secure the ring through to the other side but it's just to float the port inside the over sized hole in the cabin. if the screws are too tight it will crack all over again.
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Old 08-03-2011, 21:14   #11
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Re: Best filler for repairing screw holes in fiberglass

Paul gave some good advice.

We are in the process of prepping to paint our deck (we are 1 weekend away, after a year of occasional weekends). We used MarineTex, and this is why:

While it can be the nastiest stuff on the planet (it ends up EVERYWHERE - I tell my wife it's like the bathtub ring in the Cat in the Hat), it works well, has a decent pot life, and sands well. IT IS ALSO UV RESISTANT, and most epoxies are not. This means I can leave them exposed, without worrying about it. It is way easier to mix than West with microballoons. AND it smooths and cleans up with water.
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Old 08-03-2011, 21:45   #12
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Re: Best filler for repairing screw holes in fiberglass

The duraglass won't hold. It's only good as a filler. It's a damned strong filler but in my experience (20 years in auto body) it's too thick to really bond well enough and the screws will just pull it out. I would use epoxy and make my own chopped glass if I couldn't find any for sale. I just cut fiberglass cloth diagonally into about 1/8" long strands, mix up the epoxy according to the directions and mix in my chopped glass. I would also chamfer the holes as recommended above. Additionally, get it perfectly clean with acetone or lacquer thinner before you mix up your stuff, whatever it is.
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Old 09-03-2011, 00:23   #13
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Re: Best filler for repairing screw holes in fiberglass

One more vote for MarTex. The white stuff is white but the black stuff is the tough stuff.
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Old 14-04-2011, 18:47   #14
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Re: Best filler for repairing screw holes in fiberglass

I totally agree with this answer. Go with the West system epoxy and filler. We use the micro light filler for cosmetic stuff, because its easily sanded.
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Old 14-04-2011, 19:17   #15
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Re: Best Filler for Repairing Screw Holes in Fiberglass

The OP has stated he intends to put the scews back in at these spots... meaning you can't just do a cosmetic repair.

Here's what I would do: drill the hole one size bigger and then countersink it. You want fresh material everywhere. Vacuum it to get the dust out; don't touch it with anything else incl. solvents... they just contaminate.

Mix some epoxy with hardener. I would use West System but any will do. Now, add some micro-fibers filler until it becomes ketchup consistency. Next, add some colloidal silica filler until it becomes peanut butter consistency. Fill the holes, let cure, re-mount hardware, done.

ciao!
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