Posted on June 28, 2011
This is a follow-on from this post.
The uncured trial resin slab was surprisingly robust straight off the mould. At only approx. 5 mm or so thick, I expected it to be quite weak, but I was able to apply a reasonable amount of bending force to it and not break the resin. I concluded this to be a good trait because it means this particular resin has a degree of flexibility. Brittleness at this early uncured stage would have been a concern.
During the ensuing 24 hours, the slab gained noticeable stiffness without any further apparent shrinkage. So, it would appear that for a simple fairly thin section, the total room temperature shrinkage for this laminating resin might be about 2% or a bit less.
After 24 hours, I put the slab into my low temperature drying cabinet which I use for post drying and final dry for wood items. I runs at about 40 C on an on/off timer. I expected a lot of styrene migration once in the heated environment but it seems most of it vapoured off during the initial 24 hour air cure period. So, again, I'm pleasantly surprised.
I did some generic research into polyester post curing and turned up info suggesting 3 to 6 hours at 100 C ... after an initial 24 hour air cure period. I suspect this is a really good idea to produce maximum hardness and stiffness of the final resin.
Now that the resin slab is about 4 days old, it is quite stiff although can still be bent a little in it's length. The surface feels hard and 'plastic'. I am quite satisfied with the result to date. I will probably do a trial pour to the same standard using proper casting resin for a comparison.