What could be causing this? I’ve tried different gelcoat and resin combos, different mold release, letting the gelcoat cure overnight and I’ve tried laying up while it gelcoat is still tacky. Sometimes the gelcoat will blister and sometimes it won’t. I can’t seem to pin point the cause…
The is probably air trapped between the reinforcement matrix layer and the gelcoat layer. Even though you might’ve laid the reinforcement fiberglass layer after the gelcoat had dried, it will still bubble like that if there is air trapped, in a way that you’d only imagine it being capable of doing if it was still in a more liquid state
Looks like gel coat is too thin. Do you use a mil gauge? I try to have my gel at 20-25 mil.
I try and get my gel cost at thin as possible… I almost get fish eyes in it… I have never had that problem…
The image is wet lay polyester and vac bagged…
I would have thought it be more like bridging and a high temp when curing so he gel softens then as it cools the remaining air cools and sucks the soft gel off the surface under the bridging… I could be wrong… I usually am…
too thin or undercured. Search for elephant skin on this forum, lots of info
Indeed, elephant skin. Cause by too little cure in the first layer of gelcoat. Do one or more of the following things (you will probably know yourself which one are the most likely causes:
-use more catalyst
-higher temperature
-thicker layer
-mix better
-less streaks / more even layer
-wait longer
I will see if I can compile a “gelcoat problems” list.
Guess I have been lucky then… I put the surface layer down at the tack stage and put the gel on as thin as possible. Although I do always mix 2.5% catalyst in the gel coat.
Alligator/ elephant skin. Most of the causes have been mentioned. I find that one of the biggest factors is even spraying of gel coat and full cure. If you layup and infuse or laminate to quickly before a full cure, the styrene has bad reaction with the uncured thin areas.
Second are you spraying gel coat or brushing it on. If your brushing it on what is your application technique? If you can explain more maybe we can pinpoint the issue.
Thanks for all the info. I’m going to try more catalyst (2.5%) and spraying it on a little thicker this time (25 mils). We’ll see how that works…
What gelcoat system are you using? 2.5% seems high compared to other systems.
using gelcoat from tap plastics. I’m sure its not the greatest.
I’m unfamiliar with that system, is it polyester or vinylester based ?
it’s polyester based
2.5% is not uncommon. What is the temperature?
Herman is right 2.5% is not uncommon, and all of the possible causes that he has listed all will contribute to alligatoring. The only down side though, to using more catalyst is that you increase the level of hydrogen peroxide in the gelcoat which causes a greater degree of gassing to occur in the gelcoat and as a consequence of this is porosity. You may not see the porosity at first however, when time comes to sand if it is required, you will definitely see it then.The other thing is not all gelcoats perform the same. You may have a gelcoat with a relatively quick gel phase but a poor film cure phase. This means compromising film thickness will cause this to occur more often than not. Release systems will generally not cause this, other than if you have an excess of the release on the surface of the mould which will cause fish eyeing to occur, this will compromise film thickness. The other thing is, was the gelcoat old? or was the catalyst old, and not necessarily sitting in your shop. The supplier may have had it sitting on their shelf for ages. Old gelcoat may not necessarily go lumpy, but the promotors deteriorate over time, which means you will not get the cure you need. As one of the posters said, need more info, as it isn’t just one thing that can cause this to occur. Hermans info is a very good start though, you need to systematically eliminate each variable to fix your problem. There also various grades of gelcoat as well, as one poster above said that he sprays his gelcoat very thinly and does not have a problem, he may not have the same grade of gel coat as you!
Orthopthalic
Isophthalic
Blends of the above together as well to gain the benefits of each are often produced by gelcoat suppliers. Manufacturers of gelcoats also blend additives like Neo Pentyl Glycol into each of the above grades which improve weathering and offer greater water and chemical resistance.
Isopthalic based gelcoats do not tend to be as forgiving on film thickness or low level additions of catalyst as Orthopthalic based gelcoats are. So check with supplier what type of base gelcoat they have supplied you with. Walking in to a shop that uses an Isophthalic NPG gelcoat as an example, and asking them to buy some of there gelcoat to spray thinly over a carbon component is not a good idea. Also did you buy a spraying grade and then try to apply it, by brushing it? You won’t get the spraying grade to apply as evenly and as thick as a brushing grade will. You can more often than not, two coat the gelcoat. Or as some will say “backup the gelcoat”.
Check with your supplier first, how old was the gelcoat you were supplied and how old was the catalyst. Do you have the right grade, and the correct application grade.
If they were ok then do some non critical low cost layups taking Hermans recommendations into consdideration.
Catalyst levels
Film thickness
Ambient temps
Also, allowing enough time for the gelcoat to cure. You want to run your clean fingers along the gel coat and hear a squeaking sound, then your ok to go.
Oh, one last thing very long geltime resins on compromised gelcoats will also see this happen. So when you hear someone say, they used that gelcoat with out a problem. May also be that the gel time of their resin maybe shorter than yours. This means that the resin stays liquid for a shorter period of time on the gelcoat, thus minimising the styrene attack, that causes alligatoring.