Glassing over a removed thru hull. What glass should I use?

[lost soul]

I have removed a 2 inch diameter thru hull fitting in my fiberglass sailboat. The hole is underwater and the hull is ½ inch thick at that point.

My main question is regarding the type of glass I should use in making this patch. I will be using West System epoxy.

I have seen much info about doing such a repair, but what fabric exactly I should use remains a question. I would like to make the repair as strong as possible.

Some say use 1708. Some say 1708 with mat, some say 1708 without the mat. Some say 12 oz cloth would work.

My guess is that most any fabric would work, but I have to choose one. I do have confusion over chopped strand mat. I know there is the stitched type that would be compatible with epoxy. But is the CSM necessary?


If I had to do it right now, I would use 1708 with no mat….

I feel confident in my ability to lay up the glass from both the inside and the outside. The inside does not have as much room for tapering the patch, but I can still do some lay up.

So what fabric should I use?? Please, thank you!!

 

[LeeandRick]

If there has been no failure around the old thru hull and no new thru hull is near then you are really just trying to plug a hole and keep water out. To properly bring the area back to full strength would require tapering more than 6" radius around the hole at 1/2" hull thickness. You would probably weaken the hull if all the lamination's were not perfect. In my boat building days mat was basically used to keep cloth from printing through and for filler. I've always liked using a lighter weight glass so I can keep my resin to glass ratio more consistent. Just takes more layers.

 

[lost soul]

Thanks LeeandRick,
I have the hull tapered and ready for some glass, lol.
i just have to decide what glass to use.
so what glass should I use?

 

[Crazy Dave Condon]

Some will tell you one thing and another. There are some keys here for a successful repair. Although many would not do what you have done but to prep the hull, I would go on the outside and taper the hole from the outside to the inside. Some forget about water pressure. Secondly, I would use vinylester resin vs. polyester resin below the water line. First I would glass from the backside or inside two layers of glass. The next layer should be the size of the hole from the outside. Let sit overnight and this will give you a base to start with. Not only you have a base but with each successive layer of glass to fit the area you are laying glass in, you in a sense are locking the glass in. With each layer of course successfully layered or cut to the size being laid in so excess will not flop out on the hull, I suggest a resin roller and bet the small one to smooth out the glass and get the air bubbles out. After building out to the hull, I use to spray paint either black or gray and then start sanding the glassed in area. After sanding smooth, this would give you an idea of any valleys that would either need extra glass and/or two part epoxy. I used two part Watertite although more expensive and a slow cure, it was the best I used. Sand and reapply watertite and then wet sand smooth. I learned from the old timers and major yards over the years.

In those areas not accessible from the back, I removed the jagged areas and sanded the edges from the inside or outward a minimum of 45 degrees. Then had sanded on the inside around the edges, took two layers of glass on cardboard with string running thru, applied hardner but kicked quicker, added resin to the inside and inserted into the hole aligning it the cardboard and held the string with glass in place until it started to hold and then pulled the string out and let dry. Good way to fix catamaran hulls damaged.

I used woven roven as we use to call it but the key here is to get the air bubbles out, lay it down flat with a resin roller, use vinlyester hardner below the water line, lay several layers at a time and let dry and so on. Do not even think you can lay glass all at one time if the hull is thick. Hope this helps.

 

[Gene Neill]

Lost Soul, I'm right behind you, getting ready to eliminate a couple through hulls also. You've probably already found found these two articles, but just in case:

http://www.westsystem.com/ss/repairing-machined-holes-in-fiberglass/
http://www.sailmagazine.com/diy/holes-be-gone/
http://www.sailmagazine.com/diy/holes-be-gone/
Neither of them seem to attach much importance to the type of cloth used.

 

[lost soul]

Thanks everyone.
I ordered some 10 oz cloth and some 1708 stitched and some 6 inch tape.
I just made a pattern and now have to cut some circles. Just need to guess how many layers will do it. Probably use just the 10 oz..

 

[jibes138]

The higher the glass content versus resin the higher the strength. So do what Crazy Dave recommended and roll out any air bubbles and excess resin. The glass has to be fully wetted out but any excess resin weakens it. I would use epoxy for higher strength and better bonding.