Thinning resin

[smacrae]

Was talking to a pro boatbuilder mate of mine the other day about gluing with resin. He wipes both bonding surfaces with acetone before applying a priming coat, again to both surfaces, of resin he thins with about 5% metholated spirits. He maintains that the resin more readily soaks into the timber and as it cures the meths evaporates and does not affect the structural integrity of the resin. The thickened resin glue (with cab-o-sil) is then applied in the usual manner.

Does anyone else use this method?

[Charlie Jones]

nope.

The wiping with acetone, perhaps, except I use lacquer thinner most times.

NEVER have I thinned epoxy. It's discouraged by the Gougeons also.

I HAVE warmed the resin to around 120 or so and applied it hot. It thins quite nicely that way.

[Joe Nelson CS#35]

The new System 3 Silvertip epoxy is quite thin. I am thinking that it really wont be that much more expensive than their original formula...you can get a coat spread with less material because it is thinner. It also is no blush and can be recoated withing 72 hours without sanding. I like that!

Some epoxy products that are cheaper or thinner are not 100% solids (they have some kind of thinner added). Silvertip is 100%. I am using it now for the first time on my stripper canoe and am really enjoying it. Might be hard to go back to the original recepie?

[Hirilonde]

When I glue teak I clean both surfaces to be glued with acetone or alcohol. I do this to remove the natural oils teak has from these surfaces to improve the bond. I let the cleaner dry (only takes a couple minutes with tone or alcohol) so as not to contaminate the epoxy. I have never heard anything good about adding thinners to epoxy.

If I am gluing very porous materials with epoxy I sometimes wet out the 2 surfaces with epoxy with no cabosil or 406 for absorbtion. Then I add the filler and apply a second coat before bonding and clamping.

The heating idea Charlie mentions works well, but keep in mind it speeds up the cure as well, especially the stuff still in the pot.

[PAR]

Everyone has a method to their epoxy procedures, no two are the same.

Thinning epoxy with solvents, will weaken the molecular bonds, created when the hardener crosslinks with the resin. The result will be excess amine or glycol, depending on which was affected most by the solvent. Excess amine is a natural occurrence in some epoxy formulations, where all the hardener doesn't completely react, usually on the surface, because of ambient conditions. Some epoxies are less prone to residual amine.

If penetration is desired, there are only two ways to get it properly, use a penetrating formulation or heat. Heating the work and or the epoxy will thin it dramatically, causing good penetration, though is cracked up to be more then it needs to be.

Thinning epoxy requires a fair amount of chemical knowledge, how the molecules form and react or it's just a crap shoot. I was a chem. E major in collage, so I feel pretty confident about my experiments, but don't have much faith in the local "wife's tails" of other users, without qualification. I have found, that the best results are from those who understand their products of choice, follow the instructions and establish a routine that is strictly adhered to. These folks have learned how long the goo will work for them in differing conditions and are willing to toss a batch, rather then risk a bad bond or coating clean up.

Tests have proven, epoxy penetration has little to do with the moisture resistance of the substrate. An unthined coating is as effective as a heated or penetrating version in preventing moisture gain. This assumes the coatings are complete and intact.

Penetration can be of great importance in long term durability of a coating and why we look for good penetration. A deeper grip on the substrate can permit minor scratches to survive longer, then a thinner surface coating, that may get breached from the same depth scratch. In bonding, the penetration is less important, as the substrate usually is far weaker then the glue line and failure is in the substrate, not the adhesive.

Surface prep is key to any surface treatment, be this paint, varnish, adhesives or any coating. Some surfaces need to be washed down, like aluminum, oily woods, etc. or a poor bond will result.

Heating the work and applying slightly warmed epoxy is the best method. After the laminate is secured, moving it to a place where the temperature is lower then the warmed piece, will help prevent out gassing and other difficulties, when working with warmed epoxy. Of course, you'll probably want the slowest hardener you can find too. Ideal temperatures for part heating is 120 degrees, no hotter then 130. Epoxy should be in the mid 80's, but it better be slow stuff, or you'll not get it mixed and out of the pot before it kicks. West System 209 will have 45 minutes pot life at around 80 degrees, 20 to 30 minutes up to the mid 90's. Around 100 it will kick in just 10 minutes, but man it is thin stuff. I've used it to weep into cracks, from capillary action at this temperature, creeping into the smallest of places, which can be quite handy in some repairs.

Also try to control humidity if you can. This will help a lot in blush formation and on clear finishes.