I'm guessing you meant West System and not Smith System

While I've never tried using epoxy as a finish coat, I do know that they recommend at least two coats for a barrier coat - that is, any surface that needs to be protected from moisture. Here is their recommendation:

Apply a minimum of two coats of WEST SYSTEM epoxy for an effective moisture barrier. Apply three coats if sanding is to be done. Moisture protection will increase with additional coats, up to six coats or about a 20-mil thickness. Additives or pigments should not be added to the first coat. Mixing thinners with WEST SYSTEM epoxy is not recommended.

Cheers,
Brad

 

oop yes Brad, sorry yes I meant West Systems, can I get a free morning excuse on that? haha

Ah well that could prob be my downfall then, I didn't read any instructions as I just assumed one coat would be enough. That's all I ever used when I made some beer mugs awhile back.

Thanks Brad.

 

Maybe it just didn't cure all the way.. ?? I really don't know… lol

 

If it's moisture that's creating the white surface, I wonder if taking a heat gun to it might remove the white appearance and than go back over it with another coat or two? I might give that a try.

 

Did you let it dry or fully cure before getting it wet?

 

Was your mix accurate. Unlike polyester, epoxies must be mixed in accurate ratios. This is often difficult when mixing small quantities. The pump type containers are made to do the measuring for you but in cold weather they lack accuracy.
You also have to mix longer than you would normally expect. Most recommend five minutes.

 

Cured 48 hours.

Paul, I used small plastic mixing cups the kind that have measure lines on them but so mixture I'm unsure of.

 

Cured 48 hours.

Paul, I used small plastic mixing cups the kind that have measure lines on them but so mixture I'm unsure of.

I'm guessing all of these could be contributing factors?

 

Right. Is it hard or can you mark it with a fingernail? If the mix is off it may be a little "plastic".

 

It's a hard surface, can't scratch with fingernail. It's hard to tell but I could say it look a bit like plastic only you can't scratch it.

 

Then it is fully cured. Many epoxies have an "amine blush". This might be a part of the problem. I believe the treatment is to wash with borax. You could give that a try.

 

The "Amine blush" can be wiped off with a rag dampened with water… no need to go all Borax on it! IIRC, West System says to use water and a scotch brite pad… but it's still just water. I doubt that is the problem though, as it really only effects what you want to put over the epoxy, like another coat of epoxy or something like gelcoat. In those cases, and when the epoxy is fully cured, you need to sand/scuff the surface anyway, so the next coat has something to bite into (as it will only be a mechanical bond at that point).

Cheers,
Brad

 

Results on removal of amine blush vary. I was told the borax thing by Jim Peters. He was the chemist who founded Industrial Formulators of Canada and the developer of Cold Cure, which gets my vote for about the best boat building epoxy ever.
Borax is after all just a mild abrasive, like a Scotchbrite so I guess the methods are similar.

 

I'm going to take the shelf out to the workshop this week and see if I can work with it. I don't have any Borax but will try and see what I have on hand that will clean it up so that I can put a new coat on it.

Thanks everyone.

 

Randy,
I am wondering if using #207 Hardener might be a better choice since 206 states: "Not intended for clear coating applications."
https://www.jamestowndistributors.com/userportal/show_product.do?pid=2031

"...207 Special Clear Hardener was especially developed for use with West System 105 resin in coating applications where an exceptionally clear moisture-resistant natural wood finish is desired…"
https://www.jamestowndistributors.com/userportal/show_product.do?pid=2032
BTW, 207 has a 3:1 mixing ratio.

 

I wonder if it was mixed at 5:1 accurately. I have used West System on my hovercraft and it got plenty wet and never whitened. I used 105 and 207. It penetrated about 1 /32 into the wood.
What ever you do to remove the whitening, it may come back with more wetting. It sounds like it is getting under the finish somehow.

Cheers, Jim

 

Good luck Randy!

If all else fails read the instructions? Haven't a clue but I'm wondering about the wood? Does it have a high oil content that might interfere with the hardening process?

 

Mike, jim, Paul and Tom, I really can't explain what caused it, I took it to the shop and used an orbital sender with a number 150 on it, the white coloring appeared to be in the epoxy not under it and it was cured. I managed to get it sanded out and cleaned up. I went back over it with a different brand of epoxy, it was a 2 part 20 min epoxy sold from great planes. It's mainly used on balkheads on RC planes and other parts of the planes.

 

Was your mix accurate. Unlike polyester, epoxies must be mixed in accurate ratios. This is often difficult when mixing small quantities.

Just thought I'd mention this - For mixing small batches, a little gram scale works great (like this one for under $10 with a coupon, or this one for a bit more)... I use a lot of really small batches, mixed in those little 1oz Solo cups like you get at the take-out places. With West, you can measure by weight or volume, so the same ratio applies regardless of which way you do it. 2.5 grams of resin to .5 grams of hardener makes a really small batch

Cheers,
Brad

 

+10 on the small SOLO cups. I have continued to use the 2oz. for many years. Used to apply Obechi & carbon fiber veneer on foam core wings of RC sailplanes among other things… NOW, I have the 105/207 combo for future WW projects and such. Sure sorry I ever let my Gast vacuum pump go… 8-( when I quit the RC sailplane hobby… but life goes on.

BTW, even the 207 mix requires final coat of varnish for UV protection. No real answers, just wondering aloud.

 

Brad, I followed the I structions given for the west system 2 to 1 I believe? I can't say for positive it was Accurate I used small mixing cups that have measuring lines on them. Hobby stores sell them.

 

Brad, I followed the I structions given for the west system 2 to 1 I believe? I can t say for positive it was Accurate I used small mixing cups that have measuring lines on them. Hobby stores sell them.
- Blackie_

Oh My! If you did a 2:1 ratio with the West epoxy, then that is a problem! For the regular hardeners, it's a 5:1 ratio, and for the clear and extra-slow, it's 3.5:1. Other epoxies are different, so you need to check the instructions to see what a particular manufacturer calls for. Here are the instructions for West System.

And for the West stuff, I really recommend getting the pumps they sell. They are calibrated so you just do one pump each to get the right mix. And they make it much easier to dispense small quantities (like I described above).

Cheers,
Brad

 

Maybe I misspoke on the ratio, I used whatever was on their website instructions, only using those small cups I might of been a bit off on the accurate mix. I'll look into the pumps thanks.

 

Cups are the best in most cases. Pumps can give problems with cold material. If you have nice warm epoxy they are fine although I have a long standing mistrust of them …. just because I have to hope they are right. With cups I can see that it is right.
For really small mixes maybe a scale is a good idea. Most of my epoxy use has been in larger batches.

 

I've fixed the problem but still unsure what could have caused the whiting, once I sanded it out and cleaned it up I went back over it with a different brand of 20 min epoxy and the past three days in the shower it's holding clear.