Epoxy and sand for fairing.

[GILow]

Hi all,

In my readings, I ran into a blog where the writer had used a mixture of epoxy and sand to smooth out the top of ballast inside an encapsulated keel.

6/22/14: Bilge Bulkhead, Tanks, Compression Posts | Thalassa Restoration


This caught my eye because I have a similar need for areas of my keel where the resin covering the encapsulated ballast ingots is very rough and water that gets in the area can form small pools. I would love to fair the area to improve run-off. Unlike the writer of the blog, I do not need to do this where I will be building my keel tank.

Has anybody else used this approach or heard of it before? Any pros/cons you think I should be aware of?

[boatpoker]

No problem as long as it's dry.

Cabosil is a very common resin thickener and is nothing more than fumed silica which is pretty much burnt sand.

[GILow]

Originally Posted by boatpoker

No problem as long as it's dry.

Cabosil is a very common resin thickener and is nothing more than fumed silica which is pretty much burnt sand.

That's good to hear. I've seen mention of Cabosil here on CF quite often and not realised what it actually was. I will go and search on its application to see what I can learn.

Thank you.

Edit: I note that Cabosil is described as being "extremely light". That's surprising for a something that started as sand. I am guessing their furnace is VERY hot.

[thinwater]

Originally Posted by GILow

That's good to hear. I've seen mention of Cabosil here on CF quite often and not realised what it actually was. I will go and search on its application to see what I can learn.

Thank you.

Edit: I note that Cabosil is described as being "extremely light". That's surprising for a something that started as sand. I am guessing their furnace is VERY hot.

Cabilsil is analogousd to carbon black in how it is made. it is NOT made from sand.

Carbon black is made by burning specific oils in a manner that generates mostly soot. In this way, the carbon particles are amorphos, are formed one atom at a time, resulting in an impossibly fine structure. Carbon black is not ground from carbon.

Fumed silica is made by burning silicone oil, the main combustion product being SiO2. Again, it is formed as atoms, is impossibly fine, and is NOT ground.



Ground silica is a dangerous material to be around. The fine crystals cause silicosys if inhaled. Fumed silica has not been implicated because there are no crystals.


Because carbon black and fumed silica are so fine they are quite light in the bag; most of the space is air. Because fumed silica is so fine and traps so much air, it adds a LOT of air bubbles to the epoxy, weakening it, but making it less vulnerable to shattering. It is hard to sand.

Yes, you can fill epoxy with clean, fine sand. This is commonly done in construction. The trick is getting sufficiently clean sand.

[Spot]

I thought fumed silica is a thickening/anti-slump agent and hollow glass microspheres as a lightening filler, and that one or both can be added to epoxy depending on the project.
https://www.expresscomposites.com/pr...-paste-fillers

[44'cruisingcat]

I've heard cabosil is also used to thicken thickshakes. Could be an urban myth though.

You could also use q cels, or phenolic resin (or a combination of both) to thicken your epoxy. Either will sand easier than sand or cabosil, if you'll need to sand the job.

[boatpoker]

Originally Posted by thinwater

Cabilsil is analogousd to carbon black in how it is made. it is NOT made from sand.

Carbon black is made by burning specific oils in a manner that generates mostly soot. In this way, the carbon particles are amorphos, are formed one atom at a time, resulting in an impossibly fine structure. Carbon black is not ground from carbon.

Fumed silica is made by burning silicone oil, the main combustion product being SiO2. Again, it is formed as atoms, is impossibly fine, and is NOT ground.



Ground silica is a dangerous material to be around. The fine crystals cause silicosys if inhaled. Fumed silica has not been implicated because there are no crystals.


Because carbon black and fumed silica are so fine they are quite light in the bag; most of the space is air. Because fumed silica is so fine and traps so much air, it adds a LOT of air bubbles to the epoxy, weakening it, but making it less vulnerable to shattering. It is hard to sand.

Yes, you can fill epoxy with clean, fine sand. This is commonly done in construction. The trick is getting sufficiently clean sand.

Fumed silica may be coated with carbon black. It is made from silica.
Suggest you look up both definitions.

PS. It's cabosil not cabisil.

[s/v Jedi]

From Wikipedia:

Fumed silica is made from flame pyrolysis of silicon tetrachloride or from quartz sand vaporized in a 3000 °C electric arc

can be made from quartz sand or from silicon tetrachloride.

Used in soft ice cream, toothpaste, concrete, epoxy etc. for bulking and anti sagging properties

For boaters: combine it with other fillers. Example: laminating with micro fiber fillers, but for a vertical surface add ome Cabosil so it doesn't run down

[Singularity]

Originally Posted by GILow

....I have a similar need for areas of my keel where the resin covering the encapsulated ballast ingots is very rough and water that gets in the area can form small pools. I would love to fair the area to improve run-off....

I'm not exactly sure what you are trying to accomplish with respect to your keel tank, and I don't know if this suggestion will help, but you could just lay up a thin layer or two of ~6oz glass/epoxy on a piece of plastic sheet on a flat table...then cover the top of the layup with another thin piece of plastic sheet (like heavy drop cloth). When the layup is cured remove the plastic and you're left with a thin/smooth/flexible sheet that you can trim to fit into the bottom of your cavity, gluing it in about the edges, effectively covering over the rough under surface that you're considering filling with resin/sand.

If you strategically add peel-ply on the top/bottom of this insert (between the plastic and cloth before wetting out, removing after cure) where the sheet will be later glued, you'll have the tooth you need on the insert to glue it right in (assuming you'd tape it in).

Maybe lighter weight with less time working in the hole.

[Steve Bean]

Sawdust can thicken epoxy nicely.

[ausnp84]

Baby powder works a treat for thickening epoxy, PLUS it smells nice as well😁

I’ve used it for deck fairing, crack filling and also to thicken up epoxy when attaching the davit internal backing plates to the cat.

N

[valhalla360]

If I'm reading this correctly, it's purely a filler with no structural benefits needed. Also, as it's basically adding to the balast, weight savings is not an issue.

I wouldn't mess with epoxy or custom fillers. Do the bulk with cheap polyester resin and cheap play sand from a home improvement store. (wash if you are worried it might have salt in it). If you are worried about water infiltration, you can always paint on a layer of epoxy on top to seal it.

[GILow]

Originally Posted by valhalla360

If I'm reading this correctly, it's purely a filler with no structural benefits needed. Also, as it's basically adding to the balast, weight savings is not an issue.

Yes, you are reading correctly. And good point about weight not being a major issue. Not that I'm planning to go crazy with the stuff, I am looking at maybe 10 kg overall from what I can read about workable ratios. Also, good point about using something cheaper like polyester resin. Though oddly enough, I have lots of epoxy and vinyl ester at the moment, and no poly left at all. Might end up being a case of what is left over from all the other jobs, I hadn't really worried too much about the issue, it was only seeing what looked like such a simple solution that grabbed my attention.

Thanks to all for your comments, and the lesson in Cabosil chemistry.

[GILow]

Originally Posted by Singularity

I'm not exactly sure what you are trying to accomplish with respect to your keel tank, and I don't know if this suggestion will help...

Separate job with the keel tank, but good suggestions all the same, thank you.

This particular question related to fairing a bit of the keel area that will otherwise be left alone. I just liked the idea of improving drainage in that location. It SHOULD remain dry, but it would be nice to ensure that any water that does get there drains out cleanly and doesn't pool.

Sounds like this sand and epoxy approach is a good one.

[Tillsbury]

Originally Posted by Singularity

I'm not exactly sure what you are trying to accomplish with respect to your keel tank, and I don't know if this suggestion will help, but you could just lay up a thin layer or two of ~6oz glass/epoxy on a piece of plastic sheet on a flat table...then cover the top of the layup with another thin piece of plastic sheet (like heavy drop cloth). When the layup is cured remove the plastic and you're left with a thin/smooth/flexible sheet that you can trim to fit into the bottom of your cavity, gluing it in about the edges, effectively covering over the rough under surface that you're considering filling with resin/sand.

If you strategically add peel-ply on the top/bottom of this insert (between the plastic and cloth before wetting out, removing after cure) where the sheet will be later glued, you'll have the tooth you need on the insert to glue it right in (assuming you'd tape it in).

Maybe lighter weight with less time working in the hole.

I would definitely go with the filled epoxy plan. Making a void underneath will guarantee that it will fill with rancid water and junk.