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-   -   How to patch a 3/16 inch holes with glass mat (http://www.sailnet.com/forums/gear-maintenance/42075-how-patch-3-16-inch-holes-glass-mat.html)

saurav16 04-08-2008 03:38 PM

How to patch a 3/16 inch holes with glass mat
 
I am drying out my rudder: I have drilled 3/16" holes in it about six inches apart.

I plan on filling the holes 3/16" in diameter with thickened epoxy. I have to then patch the drain holes further with glass mat according to the don casey book

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I have a few holes 3/16" about six inches apart some 3 inches apart. How do I patch the holes that are so tiny with glass mat; i have done bigger holes but nothing this small. Anyone done this before?

Valiente 04-08-2008 05:37 PM

Make the patches 1 inch square and wet them out. Let them cure and then sand them down to fair. Casey aside, for 3/16", I would probably just use chop or strand cut down with nail scissors and put THAT into thickened epoxy, and then fair that, and then coat the entire rudder in two-part barrier coat, and then paint.

But that's me. Probably Casey's method is belts and suspenders.

sander06 04-09-2008 06:17 AM

+1. Going beyond thickened epoxy seems like overkill to me when patching some little piss-ant 3/16th size holes.

TrueBlue 04-09-2008 07:13 AM

sander06 is spot-on with his suggestion of using epoxy - this is a job for West System and NO glass mat. In fact, the pros routinely use nylon dowels for plugging larger drill holes - first dipped in epoxy, pounded in with a nylon mallet, sanded and then sealed with a barrier coat.

This was the process the yard-workers used for draining sections of my last boat's keel, after my surveyor discovered a couple of voids.

saurav16 04-09-2008 08:48 AM

Thanks for the replies. Which applications require the use of glass mat? Should I use the glass mat in the areas where the original cracks in the rudder are? Is the epoxy without the glass mat water tight?

sailingdog 04-09-2008 09:05 AM

The epoxy is water-tight without the glass matt, but I would use some layers of fiberglass cloth over the areas that had the original cracks to reinforce and strengthen the area. I generally don't recommend using fiberglass matt with epoxy since, IIRC, much of the fiberglass matt is sized with a compound designed to help it work with polyester resins, that is harmful to it bonding well to epoxy resins.

Resin, by itself, is very brittle and not very strong. The best fiberglass layup has very little resin in it... and is mostly fiberglass with just enough resin to wet it out and bind it properly.

luckytexan 04-09-2008 10:29 AM

Hello Friend:
I had a split and cracked rudder some years back, being new to epoxy work I may have gone a little overboard however I am pleased with the results.

First like you I had drilled some drain holes and was going to let it dry out, however the more I looked at it and thought about it I decided "If I try to rebuild this thing and fail I will have a great excuse to buy that kick-up rudder I have been wanting." So I am going to ruin it or do it up right!
So where the crack/split was I ground out a very large Vee groove. I actually split the rudder as much as I could. I lay the thing in my garage for a week in the hottest part of the summer with a heat lamp shining on it until I was sure the thing was dry. It lost a lot of weight during this time, there is a lot of water in the things. It may be closed cell foam but it still holds a lot of water.
So with all the bad areas ground away all cracks, splits, swells, removed, also in the seam area where the long crack was, I removed a little of the foam filler as well, not much but enough to get some epoxy and glass globbed in there. Make sure to grind your bad spots out and then feather out to an area that is sound
Do some shopping online for epoxy products, the west system is way expensive and for where I live too hot (it cooks off fast) I also had some 6 oz biaxial cloth laying around from a boat I built, so I took some of that and chopped it up to fine small pieces, also take this time to measure out little FG cloth patches to fit in the groove, make several for each area ever larger until you have one that is going to fit all the way across and onto the good area that you feathered to.
Mix the chopped strands with your non-blush epoxy of choice and glob, stuff and cram it in the holes, cracks, splits. Let it harden till you can work it, Within 24 hours (as soon as it is hard enough to work with) grind it down flush (for the Holes) or a little low "Grooves splits big holes", clean everything real good and lay your previously cut and sized biaxial cloth patches in the groove, wet to get it to stick and continue building up with ever larger patches until you have the groove built up flush. At this point I then took a long piece of cloth and wrapped around the trailing edge to make sure it would never split again. Finally I vacuum bagged my rudder but you don't have to go to this extreme. It just saves so much sanding!
Once everything was cured I used an epoxy fairing compound (Micro-balloons and epoxy)to fair the holes and the edges of the glass cloth. Then I water proofed with a coat of clear epoxy and then a coat of white.
Just make sure to plan ahead so you do all your work at once. Don't let it cure too long in-between the epoxy glass work or else you won't get that super chemical bond, you will just have a glue bond.
Hope that helps and good luck!

Luckytexan

luckytexan 04-09-2008 11:33 AM

Answer to Pm
 
Sorry I can't answer PM's until I have at least 10 posts and I have just joined here.

The little holes were filled with chopped fiberglass strand and epoxy only, then I faired with the microballoons and in a couple of places just epoxy. The chopped glass and epoxy is near bullet proof when dry, however I have read that the glass will wick moisture in so I made sure to always sand a little below flush and get a coat of epoxy over the top to seal it.
I made a composite wooden rudder once, I filled a couple of holes in it using epoxy mixed with sawdust (woodflour) this made an excellent filler as well! The theory is that Epoxy resin is going to be brittle without a filler or some tough fiber to give it a mechanical structure, however with a hole so small you couldn't ever convince me that it would ever be a hazard or problem. I tried filling small holes with pure epoxy but it was too thin and was going to fill my dagger board with epoxy before the hole was filled. Other wise it should be no problem.
One caution tho! I am not sure how much glass work you have done, but approach your finished work with caution, as the glass "Hairs / fibers" are now like hypodermic needles and are razor sharp, many times I have walked up to my work and felt it for dryness, or to see how smooth it is and walked away feeling like I just dug thru the sharps bin at the hospital!

sailingdog 04-09-2008 11:50 AM

BTW, microballoons aren't the best fairing additive for underwater use, since they can absorb water. Chopped glass is better IMHO.

saurav16 04-09-2008 02:09 PM

Do you recommend barrier coat paint for this or just clear epoxy to barrier coat the rudder?


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