Need help - fibreglass is dry, but not hard

[Tenkos]

Hello, I've been making props for a few years now, so I think I gained some experience, however I encountered a strange problem. I live in the UK so I've been using the David's fastglass and had no problems with it until now.
I had a few months long break, and when I came back I looked for a cheaper alternative and decided to buy Lloyd's resin, only to find out that when it dried, there was absolutely no difference in hardness, but it also wasn't sticky so I'm certain I got the mixing proportions right. I repeated the process a few times on the same model with different proportions, and after about 4 layers the model is still soft.
I decided to come back to the David's fastglass again, and guess what? The same thing happened. I noticed that the instructions on the back of the can changed a little bit, and instead of saying to add 2-3cm of hardener, it says to add a pea-size of it to 20ml of resin. Is it possible that they changed the content and it does not harden as well?

So, is there any way to make already applied resin harden, or should I just keep trying different brands until I find the one that actually works?

 

[weaselflinger]

If it's polyester resin, you can try brushing some catalyst on the surface or possibly using a heatgun to carefully encourage the curing process.

 

[frizzen]

without knowing what type resin that is, I'd try warming a test piece of it to around 150-200F to see if it cures, with heatgun or oven. I'd be very careful not to go too hot or it could overcure and trash the piece. Could have just been a bad batch from the factory too.

 

[Tenkos]

According to a website I bought it from David's fastglass is "a fast curing opaque laminating polyester resin".

 

[stigmorgan]

According to a website I bought it from David's fastglass is "a fast curing opaque laminating polyester resin".

I use the same stuff from halfords and have not had any issues so far other than it stays a little sticky for ages, you could try mixing p38 easy sand filler in with it at equal quantities then pour it inside the piece and roll it around to coat the surface, withing 10-15 minutes its nice and solid

 

[GaryArm]

I am not an expert with resin, but there is a number of reasons for resin to react strangely.
It could be the room temp is too low or too high affecting the core temp of the curing resin.
The weather i.e. too much moisture in the air reacting badly with setting resin.
The age of the resin, as it does have a shelf life
Or some type of contamination on the surface of your mold, to name a few possible causes.
I once layered up a polyester fiberglass box, it cured and was not sticky to touch but when I tried to pop it out ,it war flexible like a rubber item.
It never went hard, even letting it bake in the hot summer sun
To find your problem you may have to try to eliminate each one of the possible causes, one at a time
good luck
Gary