Epoxy - Liquid vs paste vs putty?

In following up on the replies to my “Royalex Repair” thread I have come up with some more questions.

In seems that epoxies (even with the same name like PC-11) come in either liquid, pasted or putty formulations. I am guessing that the difference is the amount of filler in the formulation. Is that correct or is there something else?

For each of the types (liquid, paste, and putty) is there a specific application where they are most appropriate?

Flexibility was mentioned as a possible problem with my Royalex repair. Is there something to look for in labeling or formulation that would indicate a particular product would be more flexible when cured?

Some expoxies are specifically labeled for marine use and mention use in water applications and some even mention underwater cureing. If not specifically labled for use in water (JB weld is that way) is there something to look for in the labeling that would tell me it would be good for hull repairs?

Is there anything else to look for in labeling in case I can not find specific recommended brand of epoxy that would make the substitute brand suitable or not suitable for application to hull repair?

Sorry to be so dense, but it is kind of overwhelming looking at all the different expoxies and plastic welders and not knowing if there is a particular one that is wrong or one that is really better for a particular application.



– Last Updated: Sep-28-08 12:28 PM EST –

Liquids are good for wetting cloth when doing layups, or saturation coats on bare wood. Thicker formulas are good for filling gaps or when you need something that won't sag.

Flexibility varies widely among epoxies. If they're designed to be flexible when cured they should say so.

Here's one:

you can get fillers from West Systems to make paste to whatever consistency you want. West System epoxy without filler is rather thin when first mixed. The silica filler is good for compressive strength, the glass microballoons for light weight and workability. I think I have seen fiber fillers, which should be good for tensile strength and bending. Look for them at West Marine, etc.

West System G/Flex is a fairly new product. It comes somewhat thickened, like honey. It has high flexibility and is suitable for plastic hull repair, and will even work on damp wood. I’ve used it some this past summer and it is good stuff - I think it would work well for Royalex. The instructions that come with it have detailed instructions for plastic boat repair.

You might want to check out the archives at cboats.net. Those guys have great experience beating royalex hulls to death and bringing them back to life.

I still say JB weld, which can be found in any hardware store, will work just fine on the small ding you describe. However, if you feel the need to go top of the line, look to West Systems epoxy or Raka if want the same quality that’s a little more affordable. If nothing else, the Raka Epoxy web site has plenty of great information.


Here’s a second vote for G-Flex. I’ve used it quite a few times (securing footbrace channel on EFT, bungee attachment points for surf ski, tacking down cable guides and fabricating guide tubes for rudder on wooden tandem,and even crafting 1’ of rudder destroyed on a rock). In their Epoxy magazine, they show a repair on a canoe, maybe Royalex. You could probably call them and request the article, or find it at West Marine, where I got it from. Amazing stuff.