View Full Version : Penetrating epoxy observations

09-17-2007, 12:29 PM
I recently purchased a couple of gallons of FCI's penetrating epoxy, along with my regular epoxy order. I have always just thinned my epoxy to use as a saturating type. This time I decided to make a comparison of thinned 5-1 FCI epoxy, FCI penetrating 1-1 epoxy and CPES. I generally use naptha or mek as a thinning agent. I just happened to have a bunch of peices that need to be soaked (all mdo plywood). My experience with thinned 5-1 is that it is slow to set but seems to seal the wood fairly good. It will bubble after application and must be tipped with a brush to remove them. It leaves a hard slick surface and blushes a lot. The 1-1 FCI penetrating epoxy is very easy to mix but upon initial observation I decided that it was to thick for my immediate purpose, so I thinned it 25% with naptha. It went on smooth and did not bubble, penetration seamed to be good. It took over 24 hours to set (65 to 80 degree temps) and REALLY blushed. I tried it unthinned on a noncritical component and decided that the term "penetrating" is a stretch for this epoxy. Next was the CPES on the same type of material, MDO plywood. This was the first time I have used CPES, and there was no comparison in penetrating ability to the other epoxies, CPES was far and away the winner. The MDO absolutely sucked it up. It dissapeared into the end grain and the overlay. I was VERY impressed with this stuff, it works and it "penetrates" just like it should. I have always fell for the old "it's just thinned epoxy" bull and thinned my own. But, I was wrong, CPES is much better and I won't waste my time thinning epoxy again. YMMV.

Todd Bradshaw
09-17-2007, 02:13 PM
Just out of curiosity, who told you that naptha was a suitable thinner for epoxy resin?

09-17-2007, 03:10 PM
Possibly referring to this thread?


09-17-2007, 04:46 PM
I generally use mek for thinning epoxy but it gives me a skin rash if I get it on me and I don't particularly like it, except that it is a good thinner. I'll use naptha when I have to be in an enclosed area with the fumes, like saturating wood. I have used denatured alcohol, acetone, mineral spirits, laquer thinner, etc with decent results. However, I won't be thinning epoxy for wood saturation anymore.

09-17-2007, 06:23 PM
MEK is nasty stuff, all right, but it is what Steve Smith recommends using to prep surfaces before applying CPES or epoxy -- probably because of its volatility. I understand that caution should be used when applying solvents to wood before applying CPES or epoxy, as any leftover solvents or solids can cause problems with the glue and/or bond.

Wild Wassa
09-18-2007, 05:37 PM
The thing to watch when thinning epoxy, with whatever thinners are used, is that the thinner suitable for one epoxy isn't necessarily suitable for all epoxies. The thinner needs to be a reactive agent with the epoxy, otherwise it will weaken the structure of the epoxy.

The use of any of the denatured alcohols, like a denatured ethanol for example, used with BoatCraft Pacific's epoxy, will weaken the epoxy, ... sadly.

I thin BC P's epoxy with the timber preservative TPRDA. TPRDA is a reactive diluting agent. The TPRDA that I use will not ever see timber or even get close to it ... because I'm a big fan of CPES. TPRDA's use as a diluting agent far outweighs TPRDA's usefulness as a timber preservative.


PS, Today is International Talk Like a Pirate Day ... so cop this m'jollies. "Polly wants a cracker" and "Where's me Buccaneers? On ya' Buccanhead!" replied Captain Flint ... "OO iz'it" said Ben Gunn. "It's the ploomer arve coom t' mend tha' pipes."

09-20-2007, 04:20 PM
It seems my report on the FCI penetrating epoxy was premature. When I thinned it 25% with naptha it took a long time to set up, like 24 hours. After using it right out of the jug, with no thinning, it has not even begun to harden. 2 days of mid 90 high temps and mid 60 lows and this sh#t is still sticky. It is a 1-1 mix and I got it right. I read a similar report somewhere that stated the same problem. I will call the boys at FCI and find out what's going on.

Mike Keers
09-20-2007, 05:56 PM
Having used approximately forty gallons of FCI Penetrating Epoxy, I can tell you it's designed to work that way, or so they told me. Max re-coat time is six hours at 77 degrees, so it will be tacky when you re-coat. The purpose of the stuff is to be used as a primer for further epoxy encapsulation, or as a primer for paint, and the thinking is there is a chemical bond. It will cure eventually by itself, but much faster if overcoated with their regular epoxy (of which I've used about 100 gallons over the years).

I have painted acrylic latex directly over it while it was still wet out of curiousity, and both cured fine, and that was the toughest paint in a variety of tests I conducted on paints and epoxies--it survived a scratch-gouge test far better than LPU. I believe many acrylic latex paints (at least what I use) are amine-based, so there probably is some sort of chemical bonding as well as mechanical.

I have left about an inch of it in a mixing container to see what would happen, and it cured to a very interesting material, a nearly clear but rubbery and flexible sort of stuff. About four years later that test disk is still flexible.

09-20-2007, 08:26 PM
OK, I'll wait awhile longer, but why did it dry with the naptha and not without. This is on a window frame that can sit for months and not cauase me a problem. Should I just go ahead and paint it ? At the very least I would just scrape all the crap off anyway, and I will agree that pu paint would stick like stink to it right now.

09-20-2007, 08:33 PM
My Irish Whiskey is flowing pretty strong tonite,I'm sorry (you're not here). I find your comment about topcoating this stuff with acrylic to be very interesting. It is tacky enough that a decent coat of porch paint would stick like baby **** on a blanket. I'm going to give it a try (test). I'll get back. seeya