A penny for your thoughts - balsa core condition

C

C-Val

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C Dory Year
1988
C Dory Model
22 Angler
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Seaduced
brutus_balsa2.sized.jpg

brutus_balsa1.sized.jpg


Hi everyone

I removed the trailer tie down eyebolt from my transom today.

Around the bolt itself the balsa was powder but as I began to open it up with a nail it turned to chips. The cleanest chips in my hand were the last
to come out. By that time I had 2" circular hole.

The lower pic is what I vacuumed out of the hole including everything.

My thought is I am good now to make my epoxy plug.

What are your thoughts?
 
It does look like water got in that penetration and started rotting the core, but nothing near as bad as you see on 40 YO trawlers. So how to fix?

Given that the hole is now 2" diameter and it is used for a heavy load, I wouldn't just fill with thickened epoxy, let set and drill a new hole. I would fill with epoxy but then after it hardens I would taper back the glass layers another couple of inches around with an angle grinder and lay up a glass patch to reinforce the area. Grind and sand flush and paint with Interlux Brightside.

David
 
That is a great idea! I will certainly grind it back to a taper and fill.
That will secure the epoxy plug to the transom so the stress of the tie down will not just be on the plug!

You guys are collectively so helpful to me !
I am still such a student!

Thank you

C-Val
 
Just for another thought about your repair. I'm not sure I would grind away existing laminate if it was in good shape. This is just making more work. If the existing is in good shape then replacing it with a patch of the same thickness is not necessarily going to to be any stronger. If the hole is cleared back to good core and is first primed with neat epoxy and then completely filled with thickened epoxy it will have better compressive strength than it did with core. The trick is going to be filling the hole completely with the thickened. This is not the easiest thing to do. There is no need to replace the balsa in such a small void. If it was a 1' hole the weight difference might make it worthwhile to replace the core. However, grinding away the laminate to expose the 2" hole would make it much easier to completely fill the void. A 2" void can be successfully filled thru a 3/8"hole with a hypodermic. I use large horse hypodermics from hay and feed store. West Marine has "boat" hypodermics for a few more dollars.
Kushtanka has a thread about filling holes with a relief hole to bleed off trapped air. Here are photos from his pics but he also has a thread about the process.
http://www.c-brats.com/modules.php?set_ ... _album.php
There is no "one and only way" to do your repair. Glad you're willing to undertake it. It's closer to brain surgery but it ain't rocket science and if you're willing to try you probably have what it takes to be successful.
One last thought, be sure to reinstall the fitting with a good sized backing plate to spread out the load.
 
If you grind down the fiberglass (say 4" diameter), taper it, patch the area, and sand flush, I don't get what you gained - you just filled in what you ground out, how is that stronger than the original? What am I missing?

Jay
 
I think there is some confusion going on here about "hole is now 2" diameter." Is the "hole" just the diameter of the old fastener with the coring removed between the fiberglass panels back to a depth of 2"? (i.e, just the middle of the sandwich removed) Or is everything removed - fiberglass and coring - leaving a 2" hole through the transom?

I'm assuming it's the former.
 
Thanks for your thoughts

The core is removed between the panels approx 2” in diameter from the centre of the bolt hole
 
C-Green":3lmyyzti said:
If you grind down the fiberglass (say 4" diameter), taper it, patch the area, and sand flush, I don't get what you gained - you just filled in what you ground out, how is that stronger than the original? What am I missing?

Jay
Click to expand...

Tapering glass back and glassing over it is a standard fiberglass repair procedure. When you taper you don't grind it down to the balsa core you just form a taper on the outer glass layer that forms a bond with the new glass and gives you more strength than just an epoxy plug.

David
 
If you doubt the quality of the balsa, expand the hole until you see
whitish firm solid balsa. Now form your plug.

Want more beef? Add a backing plate, as above.

Aye.
 
"Sanding a taper" is just tapering through the gel coat to the first layer of glass? Then you build up more glass to strengthen? Then you don't "sand flush" because that would take most of the new glass out. Of course this leaves you with a non-flush surface to mount your engine or whatever to; how's that work? Do I have it right now?

I say don't mess with the glass and just use a beefy backing plate extending well beyond the epoxy plug.

Jay
 
Ok, here goes again:

The existing transom probably consists of three layers: 1/4" of glass inside and outside and 3/4" of balsa in the middle.

When you taper back the existing fiberglass layer outside of your 2" hole you are grinding it down to about zero at the hole and 1/4" thick at the 4" diameter point.

You then put layers of glass in concentric discs to fill the taper back to level. This probably means 3 glass cloth discs: one 4" diameter, another 3" diameter and a third at 2-1/2" in diameter. This builds up a layer of glass that bonds with the existing glass and is approximately level.

The inside may be much tougher to get to and it really doesn't need to be tapered as a 1/4" thick patch won't be visible.

The new glass layersbonds to and bridges from the old existing glass which provides much more strength than just an epoxy plug.

Here is a link to a detailed description with pictures of the process: https://www.instructables.com/id/Repairing-Fiberglass/

David
 
I think what I'm missing is that the hole in the glass is 2" diameter. I was assuming that the glass hole was the original bolt hole and the balsa core was chewed out to 2" diameter and filled with epoxy by surgical tricks.

Thanks, Jay
 
C-Green said:
.... I was assuming that the glass hole was the original bolt hole and the balsa core was chewed out to 2" diameter and filled with epoxy by surgical tricks.

Thanks, Jay

This is the correct assumption except I haven't yet filled it with epoxy yet
Thanks

C-Val
Click to expand...
 
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