Hello wooden boat folks,

I have started a wooden drift boat build and ran into (created) a problem I would like some advise on. I am using West System 105/205 epoxy and using the 300 mini pump set. I checked the calibration by volume, I could not find a scale, it seemed very, very close. Although, I now see that something is terribly off. I have used about 1/2 gallon of resin and a full quart of hardener! Way off the correct ratio. I have used this improper ratio on all of my scarph joints and to glass one side of a side panel. This mix worked well on three test scarph joints, the plywood broke not the joint. The epoxy seemed to behave fine, it did not cure to quickly or slowly and its application properties were very workable.  The problem will stop here, I will find a set of scales or measure each batch by volume.

My question are these:

1) Will this ratio have sufficient strength? Or will the remaining fiberglass work provide enough strength to compensate for the improper ratio?

2) If I must break these parts apart and start over, how would I go about that?

Any other insight would be appreciated! Thanks in advance for any help.


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Iv e been using the same set up for my entire build, I really like the pumps. I might guess you have the wrong pump on the wrong size can? 205 and 207 will say hardener and be different in size of the cap, but the cap size is the same on the 205 and the 105 gal. Smaller size cans might have different size holes too.....the resin pump will say resin too, and there is a code on each can, like 205B. I havent noticed any issues with my pumps.

Might want to call West and talk to a chemist for the effects, other than the resin setting up super fast with more hardener. I havent been able to keep a close on mine as Ive used way more 207 clear than the 205. I used the 205 for bonding and I did use it for the glass on the bottom so it would set faster. Its alot darker in color than the 207 clear so I used that for my side glass and coating almost the entire boat thats geting varnished.

A couple times I needed just a tiny bit for something and just guessed at half pumps, and it worked out just fine. I dont know that the metric volumes are one to one cans.

Post up some pics of your build!!

There is a margin of error where things will cure just fine.   I use epoxy which is 2:1 and cures fine even up to 10 percent off.  I used pumps for years.  I no longer bother.   I use 2 cups or small cans.  One for resin, one for hardener each with it's own stick for scraping it clean.  Mix in a third cup.   For small amounts I use squeeze bottles.  I squeeze out 2 quarter size drops of resin the 1 of hardener.  I some times squeeze out parallel lines.  Never had a problem.  If your epoxy has cured with a mix  error and it's not tacky, or it's close to as hard as properly mixed test quantity don't worry about it.  

Working with epoxy is a learning experience and you need to test things.  Mix some up with the error you think you have.  Do a test glue up then smash it.  It's the only way to learn.

Thanks for the reply's,

I had hoped that using west pumps with west epoxy would have made it a little easier to get the needed accuracy. I did re-read the directions and check my installation, with the group "B" (1 gallon resin and 1 quart 205 hardener) the set up is as simple as it gets, no mods at all just screw em on. The second hardener pump included in the kit has a different cap size. The pumps seem to dispense at about a 2:1 ratio. No more pumps for me, I think I will weigh all batches from now on.

Sorry. enough complaining! I should have tested more thoroughly.

I ended up removing the fiberglass mat, it came up pretty easily. Half of it with no heat, just grabbed the corner and stared working it off. The scarf joints seem better in that they seem harder.

My new plan of attack is the leave the scarf joints, with some added resin (properly mixed this time) and fiberglass tape. Once the rest of the existing fiberglass is removed, I will replace it, again with the proper ratio.

I will put up some pictures as soon I start moving forward again!

So what was the reason you figured you had to remove the glass? It should have been set up good using more hardener. Ya that 2nd bigger cap for hardener is for the 207 special clear. The pump puts out very little 205 hardener compared to the resin. (more hardener with the 207)

You removed the fiberglass mat?Just a typo?You mean glass yes?

typically too much hardener makes it brittle,not enough makes it soft.

Put your resin in squeeze bottles,use the same style cup/container.2 cups resin one cup hardener.

and as you already know..... scales are the way to go.I dont know why west and other epoxy suppliers don't push them more.

Mike and Tungsten, I performed a quick test and tried to peel off the fiberglass mat I applied about a week ago with the improper mix ratio just make sure it had set up properly. When I grabbed the corner of the mat I was able to pull up half without any trouble at all, just peeled right up. I had to use a heat gun to get the other half up. It clearly did not set up well at all!

I did start using a scale today, still used the pumps so I did not have to pour. Gonna try the squeeze bottles once I can find some.

Did not like going backwards this weekend, but feel much better with where I'm at now.

Eric,welcome to the "Oops, I measured this batch wrong" group! I think is it one of the rituals we must all pass through. There are a few more coming up, your experience may vary!

Rick Newman


A word of caution!

If you use a digital scale , DO NOT weigh the resin and hardener to the same mix ratio as by volume.   One liquid Oz of hardener does not weight the same as one Liquid OZ of Hardener.  You need to read the manufacture's specifications to determine the correct ratio by weight.

Harbor Freight has a couple of low cost scales, 500 and 1000 Gram digital scales for around $10-$15. They work just fine.  They are all I use, even as low as 10 Gram batches.



If your test fracture broke the plywood and not the glue, I'd say carry on, you're fine. But those pumps are notorious for inaccuracy. What is much easier than weighing is buying cheap plastic calibrated mixing cups. Just hold them at eye level and pour. Quick and easy, and you don't have to worry about getting epoxy all over your expensive scales.

Yes to what Brad said. Inexpensive calibrated mix cups are easy to use and found at the local hardware store. When finished, swish a little acetone around in them and wipe out with a rag. They will be reusable for quite awhile.

Mixing cups, mixing sticks and such can be cleaned up with White Vinegar too. It's a lot cheaper and easier on your skin. Works pretty good too.
Yes to Philip. Vinegar for clean up. (from the dollar $tore) I either throw stuff away or clean up with vinegar. I use epoxy all the time and could not tell you for sure if there is still a can of acetone in my shop. Horrifically toxic stuff. Right up there with toluene, lacquer thinner, and WEST fast hardener.


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