Minimizing bond failure when fiberglassing over original polyester

[ondarvr]

Thanks for providing the shear and tensile results of the Instron testing…valuable info. What conditions/situations do you see an exception to the failure mode being transferred to the weaker laminate, or in other words avoid using epoxy filler only? Example that comes to mind is treating large hull blisters: epoxy filling (only) the 12:1 bevel vs. laying up glass.

In almost any situation where you are applying epoxy over an old polyester laminate the failure point will be in the polyester laminate.

The more filler you add to the epoxy the weaker the bond will be, but it will still be stronger than the laminate unless you add a lot. No need for a 12:1 taper on filling blisters, typicaly there is nothing structural about a bister repair. If there is you would be adding a layer or more of glass to the entire hull, which eliminates the need for a taper.

 

[fallguy]

Generally speaking, was taught to maintain glass on glass where possible on structural works.
A 6Oz. plain weave or something else? Without space for a standard bevel, how would you stack the layers?

If you decide glass is required, csm is far better choice than woven. And I’ve used it with epoxy. The way to do it is take a piece of clear poly and temp tape over the area. Use a sharpie and trace the hole edges. Move the plastic and make a bit smaller drawing of same. I like to use an arrow up reference. Anyhow, repeat until enougj thickness.

Then cutout the poly templates and draw onto the csm, but do not cut it, just tear the patches. Keep the arrow on the glass; it helps if you have 10 areas. Then repair small pieces first. I like to put patches in bog, Add the larger over, making sure a bit of bog is available to avoid air in the repair. When done; the csm fibers are easier to sand fair than cut edges. Try to use a fin roller; it helps reduce air and helps the csm bond better to the other layers no matter the resin system.