Can Gelcoat And Epoxy Bond?
Here is the first of 2 video’s where I look to see if there’s any truth to the belief that polyester based materials (such as gelcoat) won’t bond to epoxy. It’s been long believed that if you were using epoxy for your fiberglass repairs, you were more or less limited to having to use paint as your topcoat.
Over the years I’ve “broken the rules” on occasion and to date have not had any issues using gelcoat as my topcoat over epoxy. I’m not saying that it’s common practice, but in certain circumstances it’s something that I have done successfully.
When considering this idea, there are a few things to keep in mind (and these are VERY important)!
* Proper ratio’s of resin to hardener are VIP. Too much or too little can result un-uncured epoxy. A bond is only as good as the surface that you’re bonding to. If it’s not fully cured you’re going to run into problems.
* Presuming the mix ratio’s are correct, having everything properly mixed is another important step. Scrape the sides of the mix cup, scrape the bottom; repeat, repeat, repeat!. You want to make sure that all of the hardener is incorporated into the resin. I will typically stir for a minimum of 1 – 2 minutes. If you really want to cover your bases, transfer the mixed epoxy to a clean cup and stir a bit more. This will ensure that all the hardener is well incorporated.
* Cure time and temp. Depending on the temps you’re working in, epoxy can take a few days to fully cure. It is advised that you allow your epoxy to cure for at least 3-4 days before moving forward.
* A natural by-product of epoxies curing process is something called amine (or amine blush). This is a film that forms on the top layer of epoxy that will inhibit the cure of polyester material as well as create bonding issues. How do you take care of this? Simple.. Warm water and a scotch-bright pad 🙂 Amine is water soluble and is easily removed. Scrub the surface with clean water, wipe the surface dry with a clean papertowel and this detail is taken care of.
* Clean, Clean, Clean 🙂 Make sure that the surface you’re bonding to is very clean. A wipe-down with acetone and / or a wax remover both before AND after sanding will remove surface contaminates.
* Lastly, the bonding surface needs to be well scuffed with sandpaper to ensure a good mechanical bond. I will generally use 60 or 80 grit paper and sand the surface until it is uniformly dull in appearance.
Something that I want to emphasize is that the above steps are not only geared to epoxy. These are good general rules when working with composites; either polyester or epoxy. Regardless of the resin you decide to use, if the mating surfaces are not fully cured and clean it may come back to haunt you!
Next video will show the results of the tests!