sponge like epoxy

[ecgossett]

With my boat upside down working on finally repairing, checking accident stuff I found some epoxy fairing work I did around inside of centerboard trunk and hull is sponge like and peels out. I used West Systems 406 & 407 mixed with epoxy to fill it in. Any ideas?

The strictly 406 filler (white structural stuff) underneith is just fine, the areas where I added more of a fairing 407 mixed with 406 later on top so I could sand is the sponge, and peels right off the underneith layer. It used to be hard and was find when I built.

[wkisting]

Not sure... I've never had epoxy harden and then turn sponge like afterward. Either it cures or it doesn't. Possibly you had a very thick mixture and the sponginess is the 407 fairing stuff with too little epoxy. Theoretically, if you put in a lot of filler and didn't mix it thoroughly enough, it might be possible to get a ball of spongy 407 fairing filler that only felt hard temporarily because it was skinned over with epoxy but not thoroughly saturated. Once the epoxy "skin" wore away, then it might result in the spongy fairing filler.

Maybe?

[PAR]

407 is phenolic balloons, which I don't use under the LWL, precisely for this reason. What happens is the balloons are broken during the fairing process and can absorb moisture, if immersed. 406 is silica and a thixotropic agent, used to control viscosity. Most every mixture will have a little silica added. Above the LWL, I have no issue with 407, below it needs to be sealed or another light weight filler used. Sealing it means at least another coat of straight epoxy over it after fairing.

What I think has happened may be three fold in your case. First I think surface prep wasn't as good as it could have been, when you put on the fairing compound. You may have been shooting for a sand free coating, but the chemical activity window had closed enough where it might have required "toothing" (sanding). Or the sanded surface may have been contaminated with blush, dirt or whatever when the 407 went on.

Secondly, the ruptured balloons absorbed moisture at the surface and found pin holes or other "avenues" to the interface between the silica and 407 layers.

It's also possible you used too much balloons in the mixture, which can make it too dry to bond well with an underlying substrate. This is a common mistake, you keep putting in balloons (a bulking agent) trying to get a thicker mixture, when you really needed to add a thixotropic (silica) to get the viscosity you need.

I'm sure you know the fix for this, but it could have been much worse. Good catch Edward and I'm sure a fix is on the way.

[ecgossett]

your right on ballons, the filler on side doesn't say anything about that, I just selected it because it looked good on usage chart for what I needed. However, on West Marine site it does call it microballon filler, no where on actual container.

[hokeyhydro]

Strange. I am not fond of 407 because it seems soft from the get go, but it sure sands nice. As PAR noted, 407 is phenolic balloons, and I have no clue how phenolic reacts with water. I use 3M Micro Bubbles I get from Aircraft Spruce. 3M Bubbles are glass, and I seriously doubt that water has any effect on glass. A broken from abrasion micro bubble may collect a micro dot of water but I imagine the water just sits, and therefore I will not worry about above or below waterline use.

Other additives I use are cotton flock, which could suck up water if the fiber hasn't sucked up resin, and milled glass fiber which creates a rather strong piece. Oh yeah and fumed silica - all of the aforementioned from Aircraft Spruce = less $$$.

[ecgossett]

I'm a little worried about the couple above water surface on the deck that I used 407 for fairing.... Luckily it has a coat of epoxy over and then primer.

The stuff on bottom pulled out decently easy with a chisel pushing, the structural 406 by itsself underneith was just fine. Thankgod I did it the right way with 406 then 407/406 mix for fairing areas on bottom. Problem was it was done upside down, and never painted over in those areas, I didn't think to put a layer of epoxy. In one or two areas after removing it found a layer of mud on back side.

I also put on kevlar for my keel today, 10 ounce I think.. Hope I wetted it down enough, hard to tell. Only 3/4" wide strips, and one layer should be enough supposedly. My other choice was to use a 1/2" brass pipe and beat flat then drill some holes like fishermen used to do. I did read about heating and flattening a PVC pipe, wasn't sure if it could become brittle and provide less protection at some point.

[wkisting]

Edward, do you have a metal protective strip? I installed a long piece of 3/4" wide x 1/8" thick stainless flat bar running the full submerged length of my keel and it has held up wonderfully well. All I had to do was drill and countersink it every 6 - 8 inches, then screw it in place. I've always been glad I installed it.

If you're using kevlar felt, I found that kevlar felt can be shaped fairly effectively after the epoxy cures by using a block plane, in case you need to clean up the shape a bit. That's how I did the leading edge of my centerboard.

[PAR]

I always try to use a sacrificial piece on these abrasion areas, such as the keel. HDPE, half ovals, etc. work well and no bonding, just screws of fairly tight centers (6") and bedding (3M -101). They get beat up and can be pulled and replaced as required. Bonded abrasion strips (Kevlar, etc.) need to be faired (fairing Kevlar truly sucks) and they become part of the boat, meaning you patching not replacing, which I find self defeating. On really light boats, like a canoe, I can understand this approach, but not a boat you can't pick up a carry home.

[ecgossett]

My keel is isolated by a thick layer of thickened epoxy from skin of boat. I'm headed to WA state and know about rocks, so I thought that epoxy with kevlar or anything was a better alternative then possibly replacing my keel in near future. I would have used SS, but didn't have money or time to order it right now. Future money is being set aside for next boat build (more to follow as soon as plans are officially ordered from B&. Fourth kid is on the way and the CS17 will not be big enough long term for 2 adults and 4 kids.