Why did I get epoxy repair voids

I filled in the hole and the major scratch on my Royalex canoe with G-flex epoxy today. After it dried I had a large number of small voids all along the lenght of the scratch and one where the hole was located. There were sections of the scratch that came out smooth and flat with no voids.

I used a plastic squeege tool to smooth the thickend epoxy into the crack. I then used packing tape over the top. I did not re-use the squeege on top of the tape.

Is there a trick to applying the epoxy so I get less voids. I am going to apply another layer to try and fill in the voids.


some epoxy gets pretty warm when curing. and any trapped air will expand. This could have caused voids in the epoxy. If this was the cause you might avoid it by brushing a thin coat of epoxy on the material to be repaired before placing any thickened paste.The voids probably won’t hurt anything if they are small. Good idea to use glass cloth over any significant damage.

don’t think you should put tape …

– Last Updated: Sep-29-08 10:49 PM EST –

...... over an epoxy when applying , will trap chemical reaction heat , probably caused some traped outgasing pushing your expoxy apart and leaving the gaps ..

Putting tape over top

– Last Updated: Sep-29-08 11:15 PM EST –

was specified in the instructions that came with the G-flex kit. They specified clear packing tape which is what I used.

That might be the problem. I would be disappointed if the instructions were the cause of the problem. Maybe I misread the instructions on when to use the tape. They have different instructions for different types of repairs.


tape is fine.
Using saran wrap or tape over an epoxy repair is standard practice. It eliminates the formation of amine blush on the surface of the cured epoxy, and makes a nice smooth finish for the subsequent steps.

My best guess would be that some air was trapped underneath, and it expanded as the epoxy cured.

We’ve had pretty decent results repairing ABS w/ straight Plexus 420A. Flex seems to match the hull. Epoxy tends to be harder than the rest of the hull, so the repair gets thrown like a scab.

Too late
Nobody mentioned Plexus in response to my “Royalex Repair” question. I picked the G-flex because it was represented to be the most flexible of the epoxy options. If the epoxy pops out I will try the Plexus. This repair is in a pretty flexible area of the hull (right where I step into the canoe) so my epoxy repair might be short lived.

Thanks for the info Charlie.


OnnoPaddle …

– Last Updated: Sep-29-08 11:54 PM EST –

Pat is the best source of tricks I have found if he reads this he will set you straight.

I've just done a few jobs but what I have found is that when you mix the resin and it starts to polymerize it is exothermic and you get trapped gasses in the mixture, that expand as the resin starts to set. I mix for about five minutes and then let the mixture sit for a few minutes and then apply, let stand a bit more, then cover. I do it when temperatures are falling in my garage or patio in the early evening. Keep it out of the sun or where it will get warmer.

One other lesson I learned is to mix small batches --- you get much less heat generated and more surface area to degass without bubbles... so mixing a few small batches is better than one big hot batch.

All the above, plus . . .
Be sure that you mix and apply the epoxy as temperatures are falling. This can’t be emphasized enough, as the heat of curing epoxy combined with the steady warm, or rising temperature of the room will cause tiny bubbles to form and expand, leaving bubbles in the cured epoxy. You may be able to take a small drill and drill them out, sand, then mix and apply some slower curing epoxy in the holes with a toothpick.

By slower curing, I don’t necessarily mean a different formulation. You can mix it in a wide container and keep the container on a cold pack, or ice, while you are doing your work. One trick is to turn the A/C down as you begin your work, or do your work as the evening temperatures go down. If you keep at it until you get it right, you’ll have a nice repair. Good luck.

Could be the temperature issue, but I wonder if the trapped air came about as a result of the speed of mixing, etc. With a more viscous substance, trapped air bubbles take longer (if ever) to rise to the surface to clear. (Picture frothed milk on a latte for the extreme.) The blending sticks that come with the G-Flex kit have the flat squeegee edge both for application and for mixing to 'knead’out the mixture on the mixing board provided. I’d be surprised if the repair pops-if the mating area was scuffed, the stuff is pretty flexible. I have a year plus on the footbrace channel mounting on my EFT and it’s in there.

In a lab setting, it’s pretty common to vacuum degas epoxies, molding compounds, etc. if voids aren’t acceptable. It’s impressive how much trapped gas comes out when you lower the pressure.

In this case, I’d suspect a combination of bubbles from mixing and heat from the exothermic reation.

Void where prohibited

Make sure
to leave the epoxy a little proud of the surface. After it sets, sand it down flush. That should help.

sometimes it does take multiple applications for a perfect repair. make sure to sand between applications if the epoxy has cured.

don’t worry
Mark - the G/Flex is very flexible - I used it to scarf cedar stringers which have seen huge stresses with no problems. People are confusing its properties with standard epoxy which is pretty inflexible.