Epoxy patch

[ffaubert]

Hi,

Just wondering what the consensus would be on the largest hole you would feel comfortable with patching with an epoxy, micro-balloon, silica mixture?

I removed a capped thru-hull from my transom and want to seal the opening. I am putting 5/8" epoxy-coated plywood on the inside of the transom and glassing it in place. I was then going to put a good vertical mixture of epoxy in the holes from the outside of the transom.

Can I do this with the thru-hull hole or should I build up glass from the inside? The plywood will be the physical support no matter what.

Also, what is the best way to remove silicone from the fibreglass? The PO embedded everything on the transom with it (including the insides of the holes in the fibreglass).

Thanks

 

[Ed Schenck]

Why can you not use more plywood for a plug in the hole? Then some f/g cloth and MarineTex to finish what I assume is visible on the back of the transom.

 

[ffaubert]

The MacGregor transom isn't very thick. The PO had placed numerous 1/8" aluminum plates to serve as backing and, what would seem to be, a lightning plate.

The 5/8" plywood is going to cover the entire transom on the inside to act as a stiffener and backing for things like the pintles, motor mount and back-stay attachment.

The transom itself is a little less than 1/4" thick and there are multiple holes (none as big as the thru-hull though). I was hoping to be able to do a "slap and dash" with epoxy since there were so many to fill.

 

[Ed Schenck]

So long as you have that 5/8" backing plywood well epoxied on the inside then I think your filler idea will be fine.

 

[RichH]

Proper way to do this is to sand down the existing hole to a 12:1 taper - taper on the 'inside', fill the hole with fiberglass ROVING, sand down the roving to be flush on the inside, fill the outside to be flush with epoxy filled with a high strength filler such as colloidal silica, etc. and then flat sand.

When you go to sell the boat a surveyor will definitely 'list' an improper patch ... and you will most probably have to do the job all over again, this time correctly. Wooden 'plugs' for such patches are usually rejected by surveyors.

 

[RON20406]

I agree with Ed Schenk in using a plywood plug of the original diameter of the core cut to a close tolerance of the hole and held in place with thickened epoxy.Then depending on the width of the hole- either glassing each side or filling the void with High Density West Systems epoxy. This is the correct way to do the repair. Good luck, Ron

 

[Ross]

If you don't bridge the hole with cloth you will always have a stress crack at the edge of the hole. just fair out an area about an inch bigger than the hole and fill the hole with your epoxy and lay the cloth over and squeegee smooth. Use very light cloth if you can find it.

 

[jepomer]

Repairing a hole from a thru-hull is very straight forward. I have repaired 2 thru-hull holes on my Cape Dory 25. It consists of grinding our a 12 to 1 taper (either inside or outside or both) then layering "patches" of fiberglass cloth cut in decreasing size. The largest layer is placed first. The smallest layer is placed last.

Follow the directions given here:
(http://www.westsystem.com/ss/assets/Uploads/Ew21practical.pdf) by Gougeon Brothers' West System for epoxy repair.

If you purchase the DVD, it does a great job in illustrating the process for a solid hull and a cored hull.

Other brands of epoxy work the same way.

 

[Ross]

This link is the best I have found for repairs. http://www.ericgreeneassociates.com/images/Repair_of_Composite_Boat_Damage.pdf

 

[JVB]

Very light fiberglass cloth at hobby shop

If you don't bridge the hole with cloth you will always have a stress crack at the edge of the hole. just fair out an area about an inch bigger than the hole and fill the hole with your epoxy and lay the cloth over and squeegee smooth. Use very light cloth if you can find it.

You can find very light fiberglass cloth at Tower Hobbies or other places that sell supplies to model airplane enthusiasts.
http://www3.towerhobbies.com/cgi-bin/WTI0095P?FVSEARCH=fiberglass+cloth&search=Go

 

[ffaubert]

Sorry to take so long to get back to everyone. I've been trying to find fibreglass stuff in a very un-boat sort of area. Polyester up to the ceiling but very little epoxy. Go figure.

Ok, read the links from Ross and Jepomer and still have a few questions: Ross, you said that if I just put epoxy in to the hole, it would develop a stress crack. you then said to "fair out an area about an inch bigger than the hole". This is on the outside, correct?

I'm following the advice of chamfering the hole on the inside to 12:1. For 1/4" thickness, that would be 3" around the hole. This would put a razor edge at the outside. If I put my cloth in (BTW, 6 oz. was the lightest I could find locally), that would mean cutting into it when I fair the outside. I think it would be better to keep the edge (and glass) slightly inboard so I can fair without hitting the glass. Does this make sense or does it matter?

RichH suggests roving as opposed to cloth. I've read the descriptions of each but haven't seen the products and can't visualize the difference. I would suppose that what I've seen is cloth. Why would roving be better? Would it finish as nice, or if it's going to to be away from the surface of the hole (as above), would it matter?

Sorry for all the questions but this is the first time I'll be glassing something where folks can see it even if it is low on the transom.

Thanks for all the help and suggestions. I'll post some pics of the "before and afters".

 

[Ross]

Ahhh, For a patch such as you are planning. bevel both sides. Initially you had planned to reinforce the inside with plywood and then fill the hole with epoxy. If you are now planning to replace the glass that was removed when they cut the hole then my previous advise is worthless. Bevel one side and provide some backing and glass the hole to about half depth from that side and then move to the other side and grind the bevel and glass that side. This will give you a good chance at uniform thickness across the transom. Then if you still want to add the plywood you can.

 

[ffaubert]

Ahhh, For a patch such as you are planning. bevel both sides. Initially you had planned to reinforce the inside with plywood and then fill the hole with epoxy. If you are now planning to replace the glass that was removed when they cut the hole then my previous advise is worthless. Bevel one side and provide some backing and glass the hole to about half depth from that side and then move to the other side and grind the bevel and glass that side. This will give you a good chance at uniform thickness across the transom. Then if you still want to add the plywood you can.

Thanks Ross and yes, the plywood backing is still going in. I've got a dozen or more holes in the transom that need to be filled but they're much smaller (1/4-1/2" dia.). The fairing idea is going to work well there.

Thanks again for the tip!