encapsulated cement keel repair

from my previous post you may remember the encapsulated lead/cement keel on my Y39 has separated from the fiberglass shell and i want to fill this void before moving on to other projects on this boat. i like the idea of "attaching" the cement to the inside of the shell by simply filling the void with epoxy/fibers, but in the process of cleaning the gap by flushing acetone through it, ive determined the total volume of fill to be about 18 gallons. suddenly an epoxy fill/repair is getting a little expensive, but not prohibitively so.
before i commit im wondering if a thin (self leveling ) grout or concrete mix would do just as well as the epoxy at a fraction of the cost. seeing as how the original concrete wasnt "bonded" to the inside of the shell, is there any significant advantage to epoxy in this situation or is it just very expensive ballast ?

thanks as always...

and now that i think about it, any water based filler like concrete or grout will have a very hard time evaporating all that water in the cure as the exposed surface is only about 8 sq ins. so maybe poly/fibers ? although the post cure bond of poly is poor (relatively) to epoxy...maybe that doesnt matter ? or is there a fill material im not thinking of ?

 

cement type grouts does not dry, it cures. H2O is chemically absorbed into the cement/sand matrix and forms the bond. Concrete can cure underwater, no need for exposure to air to evaporate moisture (in fact in hot try climates you have to keep the surf moist or the evaporation will weaken the mix).

If you have no strength requirement the grout should work fine. You just want to make sure you do not trap moisture inside the bond or within the structure because it will promote rot or corrosion. You might consider lining the inside of the cavity with epoxy, and than fill with grout. Than I would coat all of the outside surface and seams with a good sealant. I would also use a high strength water proof mixture as well. Several brands of waterproof patching mix available, shop wisely.

 

you add sand to 'bonds to wet surfaces' epoxies which will make a heavy 'epoxy cement'. The sand will almost double the volume of the epoxy - so instead of 18 gallons of epoxy you probably will need about 10 gallons of underwater epoxy.

paul - progressive epoxy polymers inc.

 

Call a cement company. The can use a pumpjack to fill the cavity.

 

thanks petros. yeah, i guess i wasnt thinking...of course the water stays in. so then a water thin grout (vinyl ? ) pored down the thin crack should work. ive only got 1/4" max between the concrete ballast and the inside of the keel shell so other than flushing with acetone i dont have a way to clean or coat it. im hoping the acetone will remove any water at the same time.

but back to epoxy / poly... is there an advantage to bonding, essentially re- encapsulating, the cement to the inside of the keel shell? it seems like a longer term fix as water wont be able to get between them in the future. ill epoxy/biax the bilge so water wont be able to get in from the top, im thinking of accidental groundings at some point letting water in...wouldnt that argue in favor of an adhesive filler ? im also thinking thin epoxy is going to flow and penetrate deeper into fine cracks than grout will, but i dont know that for sure...

ideas ?

 

Patch the inside of the cavity well with epoxy, and paint again with a couple of more coats. Once you have something that looks like cone shape, wax it. Make yourself some steel to put in cement like an old anchor or an old chain. Then pour the Concrete (5000psi o better is best) dry into hole, filling half. Then the water, mix a little, add more water if necessary. Then repeat. The idea is to make a plug insitu that could be removed in the future without having to bring a chipping hammer.

 

cement doesn't stick well to cement. Cement repairs (airport runways, step edges at commercial sites, etc) generally repaired with sand filled epoxy.

 

If you can not clean out the cavity, than you will not get much bond no matter what you use. Use the concrete grout and than coat the outside gap and bilge both with epoxy and biax fabric. Concrete grout will also add more ballast to your boat, and cost much less than epoxy.

If you do a hard grounding, no matter how you fix it, you will need to do a detailed inspection for damage anyway. Epoxy will not prevent a separation in those conditions (especially if you could not clean out the cavity anyway), you have to rely on the structural strength of the primary keel attachment method, not patch epoxy.

Good luck.

 

update...

i should make clear that im trying to fill a very narrow gap between the concrete ballast and the keel shell on both sides, im not removing the ballast itself as its fine. at this point ive flooded the gap with 16 gallons of acetone, this was just enough to bring the level over the top of the concrete. id let it sit and the air bubbles to stop, then drill a small hole near the bottom of the keel and drain it out. ive done this 3 times now over the last week. the acetone drains out pretty close to clear and i recover about 13 gallons. i assume the loss is due to evaporation, spillage and some unable to drain and evaporating in time. with no other way to clean out the gap i figure this is the best i can do.

so decision time now about what to fill the crack with...epoxy / fibers is still my preference although expensive. from the comments so far, precision grout or plastic cement could work, i just dont know if they are thin enough to make it to the bottom of the gap before viscosity stops their flow. any ideas ?

and still curious if there is any structural advantage to epoxy bonding the shell to the concrete. im assuming the grout / cement approach wont achieve a bond but will only fill the gap.

thanks as always

 

I'm having trouble visualising the setup, but in my mind I see a rounded fibreglass shell around a concrete plug, with about 1/4" gap in places.

The suggested idea of pouring epoxy in to fill the gap would work OK, but as you say expensive.

Adding sand or other additives is also a good idea, but i would be worried that it would form voids, and not flow evenly where it encountered irregular surfaces as a thickened 'goo'.

I would like to suggest you look into these "self levelling" products, that they use on factory floors to make a hard , level surface. They are very runny when mixed, and would flow into all the nooks and crannies, and though expensive, nowhere near as much as epoxy. I understand they have good water resistance as well, though if you have an outside shell, that's probably not a big issue.

 

rwatson..yes to all that...my thoughts exactly. i believe what you are referring to IS called precision grout. even when mixed to whats called "flowable" consistency, will cure out to 8,00psi in 7 days and will not shrink...so the bag says. i happened to find a bag of "plastic cement" mix that was open and it is baby powder fine and no aggregate. im thinking it will also be close to water thin when mixed and could work but there was no info on the packaging. my understanding is it is self leveling and impervious to water once cured. even thought of a light vibration on the outside of the hull to help shake it down, whatever i use.

im sure im not the first one to do this...

 

Probably worth a small test first - mock up some gaps and see what it does. Vibration sounds like a good idea to me.

The manufacturer of that bag may have a website with some more instructions.

Good luck.

 

Filling the gap

I emailed the Cheoy Lee factory because I have the same problem, but even worse as I can shove a stick six inches from the bottom of the keel and hit damp, soft deteriorated cement. Unfortunately, I did not realize the extent of the gap and patched the top of the deteriorated bilge already. They told me to drill a series of holes about three inches apart starting from the bottom and then fill in with epoxy starting at the bottom hole until I reach each successive hole and eventually reach the top of the void. The self leveling cement sounds like the perfect answer for me as the void is large. Thanks, for the ideas! John