Was searching a parallel subject and stumbled across this: [www.westsystem.com]. I’m making the assumption that most epoxies are created somewhat equal; and I only included below what I felt were rod building–related blurbs that jumped out at me (emphasis added via capitalization)

Thinning West System Epoxy
A question frequently posed to our technical staff is "can I thin West System epoxy so it will flow or penetrate better?" The answer is "yes, but not without consequences." Many of the advantages to thinning epoxy are offset by disadvantages in other areas of epoxy performance.

Thinning epoxy with solvent
Adding solvent is a quick, simple method of thinning epoxy, but unlike using heat to thin it, the strength and moisture resistance of the cured epoxy are drastically affected. Below are some of the effects adding solvent has on West System epoxy. While there are a large number of chemicals available to thin epoxy, we selected acetone, lacquer thinner, and denatured alcohol for discussion because they’re commonly available and do a good job of reducing viscosity. Additionally, these solvents evaporate quickly and are less likely to be trapped in the cured epoxy – an important characteristic. For a variety of reasons, fast evaporating lacquer thinner appears to be more appropriate for thinning purposes than acetone or alcohol.

• Adding a small amount of one of these solvents has a significant effect on the viscosity of the epoxy; eg, adding 5% lacquer thinner makes ~60% reduction in viscosity (Figure 3)

• ADDING 5% LACQUER THINNER TO EPOXY REDUCES THE EPOXY'S COMPRESSIVE STRENGTH BY 35%, A BIG HIT IN MECHANICAL PROPERTIES. THE ADDITION OF MORE THAN 5% SOLVENT RESULTS IN AN EXCESSIVELY FLEXIBLE CURED MATERIAL. Thinning epoxy with solvent causes enough loss of strength that we (and most other reputable epoxy formulators) can’t recommend using it as a structural adhesive.

• Adding a volatile solvent extends the pot life and cure time of epoxy AND JEOPARDIZES THE RELIABILITY AND PREDICTABILITY OF CURE. Additionally, with slow rate of cure, it takes longer before work can be sanded.

• ADDING VOLATILE SOLVENT MAY CAUSE SHRINKAGE OF THE CURED EPOXY. Applying thinned epoxy in large confined areas (like consolidating a large pocket of rotted wood) is likely to trap some of the solvent. IN THICK APPLICATIONS, THE EPOXY CURES VERY QUICKLY AND NOT ALL THE SOLVENT HAS TIME TO EVAPORATE BEFORE THE EPOXY HARDENS. OVER TIME, THE SOLVENT WORKS ITS WAY OUT, AND AS THIS HAPPENS, THE CURED EPOXY SHRINKS AND, IN MANY INSTANCES, CRACKS.

SHRINKAGE ALSO CAUSES PRINT–THROUGH. You may have a surface sanded smooth, only to have the resin shrink. This SHRINKAGE OFTEN REVEALS THE TEXTURE OF THE SUBSTRATE. Shrinkage can continue to be a problem until all the trapped solvent works its way out of the cured epoxy.

• ADDING SOLVENTS, ESPECIALLY ACETONE, ALTERS THE COLOR OF CURED EPOXY. WHILE THE EFFECTS ARE NOT IMMEDIATE, ADDING ACETONE TO EPOXY CAUSES THE COLOR TO CHANGE FROM SLIGHTLY AMBER TO VERY DARK AMBER.

Does thinning epoxy make sense? In some situations, thinning is appropriate. In others, it’s not. We feel that IN MOST CIRCUMSTANCES, USING HEAT TO THIN EPOXY IS PREFERRED TO USING SOLVENTS. AS LONG AS THE EPOXY DOESN’T OVERHEAT DURING CURE, THE FULL PHYSICAL CHARACTERISTICS OF THE CURED EPOXY REMAIN. ADDING SOLVENT IS A QUICK, SIMPLE METHOD OF THINNING EPOXY, BUT THE STRENGTH AND MOISTURE RESISTANCE OF THE CURED EPOXY ARE SIGNIFICANTLY REDUCED.



Not looking to start something, just thought it might provide food for thought for those who still choose to thin epoxy for one reason or another . . .

Ralph O'Quinn has made these same points here on this forum many, many times. Thanks for bringing it back. It may help inform some of the newer folks here.

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There are a lot of folks that think finish needs to be thinned for better penetration. This is a great reference to show folks the disadvantages of thinning.

There is a wide range of product viscosity out there, from urethanes to lite and high build finishes. I'm of a mind to think that the manufacturers have tested a product to work well in a specific application and when we start taking the product outside the manufacturers recommendations, then problems happen.

Good stuff Steve.

Terry

I have experimented with thinning and it's a waste of time and you get mixed results. I have found for the best results 50/50 Afcote and threadmaster first coat and 20/80 afcote/threadmaster give me the best results. I like Afcote for it's bubble release abilty and threadmaster for it's harder finish. Both have the longest "stay clear" results having tested them against others. They all yellow but these two seem to take longer!!

Never found the need to thin finish epoxy, if you want it thinner use a lite version. I always apply heat with a small torch mainly to lower the viscosity so the small bubbles will escape but it also helps the levelling and maybe penetration. Thanks Steve and Ralph O'Quinn as your posts provides plenty of reasons for not thinning the stuff.

ESFNEM Col
Port Kembla, NSW
Australia

My first coat I usually use FC lite for penetration. After that has set up for a day, the next coat is FC high build and if another coat is needed, I will use FC high again. On my feather inlays,,,,I'll use 3 or 4 coats of FC high to get the depth I want.

Jerry Cook

I have been using West System (no relation to West Marine - although one can buy it there) for over 35 yrs. for various high stress applications - on my boats to bond hardware, to making compression sleeves in side foam cored decks - to hurricane shutter installation in FL.
The stuff is wonderful. I use it now in fly rod grips and attaching arbors and seats.

Let's not forget though that West System is a true (marine grade) epoxy where our thread finishes are not epoxies - albeit two part also.
The West System epoxies do not need to be thinned because they are very thin out of the container. They can, however, be thickened using their various fillers.

FYI - for those who use West System, it is little known that they now have a new totally clear hardener that will not discolor with UV exposure. I use it for cork work. It is "207 special clear hardner" - very expensive though. Not that the other West stuff is inexpensive.
Herb

Herb,

I use a good deal of the West Systems 207 hardener each year and unless they've very recently changed something, it is among the worst when it comes to turning yellow. In fact, I don't know of any rod building thread coating epoxies that turn anywhere near this yellow. I know it's labeled as "special clear hardener" but none of the two gallons I used last year stayed clear for more than a couple weeks.

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In that case I will still thin mine I have never had any problems ???
They are also talking from the link that is going onto wood Don't know if that makes any difference or not

Bill - willierods.com

Just going by memory here......and I should check before answering....but, IIRC the 207 is intended to be very clear....to let wood grain show through....but must be top coated with a UV "filtering varnish".

What I have always wondered....is if you put the west on something and don't get around to top coating....and a year later it is a dark amber....has it been structually compromised? Or is it just a looks thing?

Russ in Hollywood, FL.

Just looks. And it turns more white than amber. The epoxy you buy in the hardware store is a polyester ana that turns amber.

Tom,
We HAVE to be talking about two different finishes. You would never use West System of any sort to coat threads. Unless you did so as an experiment. Two gallons!!!! My first car didn't cost as much as two gallons of the 207 special.
Herb

I don't use it to coat threads - I use for boat building projects and to wet out carbon fiber grip skins. It yellows badly. Very badly.

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