Keel Ballast Repair

[Cats Paw]

As part of my project  I will have to replace/top off  the surface area of the keel concrete that was loose and had to be removed. Does anyone have any suggestions for the replacement product?   All purpose concrete / hydraulic cement etc.
I plan to let it cure for better than a month before coating it with glass and epoxy.

[cas206]

No idea.  But they make concrete canoes out of "Portland Type 1" (whatever that is).  But as a hull material you probably want a low density material.  I'm guessing keel should be high density.

http://www.popsci.com/diy/article/2013-09/concrete-canoe

I'd try sending an email to Hutchins to see if they can tell you what they used. 

If you still have a chuck of the old concrete, you can weight it and measure volume (either directly or using water displacement method) to estimate density.  That would be useful to know when shopping types of concrete.

[skip1930]

Ballast

"I also picked up 14 50-lb bags of Quikrete at the local building supply. A few weeks later, I picked up a cement mixer, got a few neighbors together and we started pouring the ballast."

-->Boat building in hindsight: "Overall, I was surprised by how well the ballast pour went. If I were to do it over again, I wouldn't use Quikrete-- I've since learned its not as good as what you can mix yourself." Just what I found.

I know from making cement lined water tanks for years that the lab says the dryer the mix is the tougher the cement will be.
We made a dry mix of two bags of cement and four bags of sand for twenty minutes in an cement mixer.
And our supplier, Portland Cement says that it takes 88 years for cement to turn to fully dry hard concrete. [First cement highway was laid down in Indiana]

Portland has cement of various kinds.
Portland also has non-shrink cement which really is not a non shrink cement but one cement that shrinks less then normal.
It's this non-shrink that is used for cement bridges and roadways.

My guess is this non-shrink would be fine to pour into a fiberglass keel.

Cypher the cubic foot of the keel and bare in mind that the back of the keel is hollow [well it is on a CP-19] and that is controlled by a wood dam at some location.
Know ponds per cured cubic foot.
Know pounds needed for a CP-16. [450 lb] 
Is scrap iron needed?
Knock the air out with a vibrator rented from ACE Hardware.
Try to do a continuous pour bucket by bucket.

skip.

[Cats Paw]

This is only going to be a repair not total replacement. About 25/30 lbs. of loose material shed away at the top. It appears to have been water damage/freezing at one time that caused the surface to spall. Otherwise the remaining ballast concrete is intact. Possibly have to use a bonding primer to get the new material to securely adhere to the existing. Yes water was in the lower part of the keel. I have opened it up along the sides by cutting windows in the fiberglass to allow for complete dry out before repairs.

[Pacman]

The keel of my C-16 was water/ice damaged when I got it.

The fiberglass skin was separated from the concrete in places.

Tapping the fiberglass skin of the keel with a plastic screwdriver handle made it easy to hear where the areas of separation were located. 

I drew circles around these areas in pencil so I would know where to inject epoxy resin to repair each one.

I drilled some small holes above the areas of skin separation and injected epoxy resin into the holes to fill the void and bond the skin to the concrete ballast.