# Help with West System Epoxy



## toffee (Feb 11, 2006)

I am thinking of using West System Epoxy for the first time on plywood. It seems like all West expoxy starts with 105 resin, but which hardener and fillers to use?

I am building a plywood wood light hood with a build in tray on top of it for aquaponic plants. The area that needs to be water proof will be 72"x13"x1" with a hole or bulkhead. Potted plants will be placed in this tray with water pumped from sump to plants via 1/4" tubes. For my propose, would epoxy be an overkill?

Thanks for helping.










http://www.westsystem.com/ss/product-selection-chart/


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## newfisher (Dec 20, 2008)

If you're looking for waterproof, epoxy is certainly a good way to go. From a structural point of view, it might be a bit overkill. However, the next best alternative might be to use a pre-fab plastic tray to fit inside your plywood structure, if you can find one.

Epoxy alone will waterproof, but it may crack (and leak) at the bottom joints. Might be an idea to use light woven fibreglass ... perhaps a couple of layers of ~6 oz cloth ... to avoid cracking.

The 206 is probably the best middle-of-the-road hardener for use at normal room temps. You might want to use 205 if working in a really cold space (below ~60F), or extra slow if you live in the tropics. 206 in a cold room will work, it will simply take longer to cure. Or build a small tent and move a space heater into it to push the cure (probably not needed in CA?). Rule of thumb, the longer epoxy takes to cure, the better, as longer molecular chains have more chance to form, giving a tougher, more flexible end product. A slower cure will also give you more time to work, important if you are new to epoxy/fibreglass?

If I understand your project, the filler you will need is what's called "micro-balloons" or "micro-spheres" ... 407 or 410 (can't remember which, you'll have to check wording on the container). Mix ~1/2 to 1 cup of dry filler with a bit of (thoroughly) premixed epoxy to make a paste the consistency of thick peanut butter. Use a tongue depressor to mix epoxy and filler, and to form a fillet at inner corners of your structure ... fibreglass does not like going around sharp corners, plus the fillet will distribute stresses, if any, around the curve as opposed concentrating stress at a sharp corner. Put the fillet down, then lay the fibreglass with it still wet, then wet the glass down immediately with a fresh epoxy mix without filler (can use the same pot, though). If doing two layers of glass, lay the second down on the wet one, then add only as much epoxy as is needed to wet the second layer (till the "white" disappears and all is clear). It will save time and epoxy and will give a stronger product. Allow the fibreglass to go ~1/2 to 1 inch past the edges of your plywood, then trim to the edge of the plywood with a sharp utility knife when the epoxy is still rubbery (but not tacky). Mix the epoxy in ~3 oz batches to give you time to work. It's better to mix more if you need it, than to have too much mixed, or to have it flash on you.

As a crude rule of thumb, use ~1 oz of epoxy per oz of fibreglass (eg. if using 2 sq yards of 6 oz cloth, you will need ~ 12 oz of epoxy), plus about 3-4 oz to wet down the plywood for a project the size you have. Having a bit too much on hand is always better than having too little.

One container of filler will give you tons left over ... for the next project?

Good luck, and please post pics of your project.


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## I3lazd (Dec 29, 2008)

try us composites it is cheaper than west systems and works just as good.


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## newfisher (Dec 20, 2008)

Either US Composites, or Raka ... both good general purpose laminating epoxies with comparable prices that are much less than West Systems or most any of the other epoxies. Both places carry fibreglass and Glass Bubbles (1 Qt, 4 oz should give you plenty).

A 2:1 epoxy mix is usually better ... better chemistry, easier to measure, and your mix is off by less if you do make a measurement error. Measure by volume, not by weight, and try to keep measurement errors below ~5%, although I've gone off a bit more with Raka without too serious an issue. FYI, too much hardener = a softer weaker finished epoxy; too little hardener = a slower cure but glass-hard and very brittle epoxy. Neither is good.

US Composite's slow hardener is REALLY slow. Raka's regular epoxies are all 2:1 mixes regardless of hardener type and the slow hardener will give you a cure in 8 to 12 hours at 65F to 70F, as opposed to 2 to 3 days at 70F for US Composite's slow hardener. ... I guess in the end it boils down to personal preference.


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## TNprogrammer (Jul 28, 2008)

I like the looks of the US Composites stuff. Heck, you can get a whole gallon of the resin plus hardener for only $60. That's a pretty good price.


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