UV resin yellowed when adding MEKP?

General Discussion
1

Lam coat on bottom kicked in sunlight…came out white.

Deck was done at night…added 2.5cc’s MEKP to 1.5 quarts of UV resin (that was the size of my containers…used two containers for deck)

It started gelling after about 30 mins…left it on racks and went to bed.

Next day it was cured, but the deck was a noticeable shade of light yellow.

I assume I over catalyzed…but the Surf Source rep thinks I under catalyzed…he thinks it will whiten if left out in the sun for a couple hours.

Should I use a different MEKP ratio to avoid this yellowing?

Thanks in advance,

Vince Hickman

NYC

2

Ive added both to resin and never had that effect

???

3

1.5 quarts = 3 pints

3 pints = 1419 cc

1 percent of 1419 cc = 14cc

Since I added 2.5 cc, the under catalyzed theory makes sense…14cc’s sounds like alot…I guess I must experiment. My goal is a 30 min gel time.

4
Quote:

Lam coat on bottom kicked in sunlight…came out white.

Deck was done at night…added 2.5cc’s MEKP to 1.5 quarts of UV resin (that was the size of my containers…used two containers for deck)

It started gelling after about 30 mins…left it on racks and went to bed.

Next day it was cured, but the deck was a noticeable shade of light yellow.

I assume I over catalyzed…but the Surf Source rep thinks I under catalyzed…he thinks it will whiten if left out in the sun for a couple hours.

Should I use a different MEKP ratio to avoid this yellowing?

Thanks in advance,

Vince Hickman

NYC

I think surfsource is right. Likely that it feels fully cured, but it really isn’t. Keep in mind, under catalyzed resin will soak into your foam. Better to shoot it off like a normal glass job, then finish curing it in daylight.

5

Yup, Mekp makes the resin a little brownish.UV catalyst only goes more of a bluish clear color.

On a normal lay up the sides are the same so no contrast.Look at your resin cup color.

They have resin samples at FH and the colors are night and day.

OOps, do a little rail art to get rid of the gray step color contrast.

6

Thanks for the comments…problem solved…not enough catalyst. Left board out in indirect sun for a few hours…turned as white as the bottom.

Glassed another board last night and my experience is that, like regular resin, you must stick between a .5% and 2% catalyst ratio to get desired results…that results in 5 to 20cc per quart…I had originally put the equivalent of 1.75cc per quart.

I was given low ratio amounts by the person who taught me how to shape…I believe he intended to give this “newbie” a LONG time to work out the kinks on my first solo glassing attempt. It may have worked if I was using regular resin, but not with UV (he has no experience using UV).

Thanks again.

7

G’day vhickman,

If the lap on the deck is nice and white I would say the foam has gone yellow from sun exposure.

I once laminated the bottom of a 6’2", put it in the sun, flipped when dry, then went in for lunch. Came back in half an hour and the deck had a nice tinge of yellow to it.

This was midday summer sun.

I have repeated the experiment with the same results.

Can I ask what foam you used?

regards

Daren

8

Same.

9

if I ever and only learned one thing while glassing (actually I learned a couple of things, and came here for a few more)… it is…

CAREFULLY MEASURE YOUR RESIN AND CATALYST. not doing so will lead to grief.

I made up a little chart with cups of resin in the first column, 0.5% catalyst amounts in the second column, 0.75% in the third column, and 1.0% in the fourth column. Very quickly I found that for my level of ability and quickness (pretty quick, but with VERY LITTLE waste), about 0.75% catalyst by volume would give me the needed working time in my area with say 70% relative humidity and temps in the low-mid 80s. YMMV.

But I religiously used that chart, and marked all my mixing jars in cups and got a little re-useable syringe for catalyst. Tips: the FH syringes are intended to be disposeable. The black rubber plunger doesn’t last. i got an all-plastic syringe. Next, MEKP will dissolve the cc labels from syringes immediately. Solution is to put clear tape over the cc markings.

10

Daren,

The blank in question was a 6’8"S Teccel blank. As mentioned earlier, it did go white after a day in the sun…too little catalyst caused it to gel, but did not fully cure…I did an additional test on a small piece of foam and the longer I left it in that “inbetween” state the yellower it got.

Regards,

Vince

11

GREAT tips…thanks Charlie.

I found a MEKP chart somewhere online…the syringe idea is excellent.

Boy you are not kidding about accuracy when it comes to glassing…I just glassed my third board and took extra care to consider the amounts and ratios…incredibly good result.

A new take on an old saying…“measure twice, glass ONCE.”

Thanks again,

Vince