Question 1

What's the ratio of the resin to hardener?

Accepted Answer

From West System's Instructions for Mixing it reads, "To measure 105 Resin and 205 or 206 Hardener by weight or volume, combine five parts resin with one part hardener. To measure 105 Resin and 207 or 209 Hardener by volume, combine three parts resin with one part hardener (by weight, 3.5 parts resin-1 part hardener)."

Question 2

can this be used for sealing a plywood hdroponics grow bed?

Accepted Answer

George, I don't see why not.  I'm not familiar with the process of building your project, so here's my takes.  
1.  If the plywood will be under ground and not exposed to the sun, you can get by with using the 205 hardener as UV exposure will not be an issue.  
2. If some or all of it will be exposed to sun, you have a couple of options.  First is to go ahead and use the 205 or 206 hardener(the 205 sets quicker than the 206 and they also have a 209 hardener for really warm climates,   All you would need to do is either tint the epoxy with some resin colorant(1-2% max. or paint  the exposed areas with a good exterior UV blocking paint.  I'd recommend at least scuffing the epoxy after it's cured with scotchbrite pads or steel wool for better bonding.  IF this grow bed will be indoors, then you likely won't have  UV issues to deal with.  An outdoor greenhouse?  Well, you likely know more about that than I......lol
3.  If you want exposed plywood in it's natural condition, West has a 207 hardener that has a UV block built into it  It's mixed at a 3-1 ratio 9instead of the 5-1, so you'll need a special pump for that can or hardener.  Prolly not a bad idea to buy a can of each if the budget allows.  The pump for the 105 resin does not need to be changed, and the 207 will cost a bit more due to you are buying more hardener in the can so theoretically the two cans will empty out at the same rate.  West is not cheap, but my motto has always been  "Buy the best and only cry once".

Sanding the plywood with maybe 100 grit on a belt sander will get the epoxy to bond better to the wood also.  West Systems epoxy was designed for bonding to wood and is used extensively for marine hulls and interiors, with our without fiberglass reinforcement, so you've made a good choice.  Shelf life on the resin is upwards of 20 years  and the hardeners are good for at least 5 or 6 years, so don't worry about buying too much, as you will be using this product for all kinds of projects around the house and shop.  I would spend the $11 and get the pumps, as they make accurate measuring a breeze.  Good luck with your project.

Question 3

1638 lft of fir porch flooring. how many gallons do i need and any prep work recommended and what stain can i apply? thanks.

Accepted Answer

West suggests 350-405 sf/gal of 105. You did not indicate width and whether it is 5/4” and tongue and groove. I believe 3 gal will be sufficient for 3 sides and ends, but ymmv. Good surface prep is key, followed by any decent exterior stain, and sufficient drying conditions and time. After curing, exposed surfaces will need uv protection that does not compromise traction in rain and snow.

Question 4

What pumps should I get for the 105 Epoxy resin and the 207 Hardner?

Accepted Answer

http://www.westsystem.com/ss/calibrated-pumps-make-accurate-measuring-easy/You have to get the whole set and can't buy them individually. Consequently, if you are using slow hardener and want to change to fast hardener, you have to buy a whole set, but they don't cost that much.

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West System105-B Epoxy Resin

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