Adding epoxy to

[Lori Kleinberg]

already cured epoxy. I am thinking that this shouldn't be a problem, but thought I would double check to be sure.
I filled a saw blade wide cut with a mixture of epoxy (system three) and dye. This was my 1st time doing something like this. Came out pretty good except for a couple of small air bubbles and I did not fill it high enough. So I thought I would let it harden completely
(:eek:almost there before I realized I hadn't topped it off) then add some more on top__ Okay??

[Wade Lippman]

Properly speaking, you have to rough it up first. The surface of cured epoxy is contaminated and fresh epoxy doesn't stick well to it.
However, if you won't have any stresses on it, it probably won't matter.

[Mike Langford]

Lori, what happened when you thought you had filled it up with enough epoxy at first is that when it cured it settled and shrank.

Like Wade has suggested, you need to roughen the surface a bit to break the shiny surface and give the next application something to take hold of.....

.....I've taken a xacto knife and lightly cut a crosshatch pattern in large area cured epoxy before I put the fresh epoxy over it, but since your area is only the width of a saw cut.....then all you have to do is rough up the shiny surface with some sandpaper and reapply!

Build up the second layer as high above the cut as possible 'cause it's also going to settle and shrink when it cures.....then after it fully cured you can sand or scrape the raised epoxy flush to the surface....


HTH

[Chris Bruno]

Some epoxy systems work a little differently and though a little roughing up with a fine sandpaper or emory board should work fine, you typically don't need to do much more than wiping it well with acetone. The acetone will remove any amine blush from the top of the epoxy, allowing the next coating to bond well.

This is what West Systems and Wolverine coatings both specify with their epoxies.

-Chris

[Alan Schwabacher]

System 3 epoxy doesn't blush, so cleaning off the surface is not so critical. If the join had to be as strong as possible, sanding the surface would be important. But for filling a crevice, just adding more epoxy will work fine. And if you do it within about 24 hrs of the first, there is no need for sanding even if you do need great strength.

[Lori Kleinberg]

Thanks for the responses. It has been more then 24 hrs since the original "pour". I really thought I had over filled so I guess it does shrink. Sanding that small strip will be easy and then I will add the epoxy and see what happens. Thanks again.

[Chris Padilla]

In short, epoxy bonds to epoxy. See Bob Smalser's excellent thread:

Are your glue joints repairable? (http://www.sawmillcreek.org/showthread.php?t=21822)

[Cliff Rohrabacher]

Amines would be the reason you'd need to abrade the surface. Amines form on the surface of many epoxies in the form of a waxy coating.
Some epoxies are amine free. Some one posted that Sys' 3 is amine free. Then you are in luck

As an aside for best adhesion: apply second layer while first is still tacky. That way you'll get molecular intimacy of the long chain molecules as they form up

[Lorne Steed]

Hi Lori: If you wish to do the same in the future ( I am assuming that you have already done your overfill) you may just have to wipe or brush a small amount of MEK ( Methyl Ethyl Ketone) over the first fill to soften it and then after about five mins go ahead with your second fill. MEK is the proper solvent for epoxies and will soften cured epoxy, but not strip it.