Len, I’d be interested to hear where you got the idea of using bicarb from? The usual methods of bulking out cyano to fill gaps are microballoons and talcum powder as they are both inert substances. Bicarb is very reactive which makes it useful for all sorts of things but I’d have thought that adding it to cyano might give unpredictable results. Yes, it may have gone instantly hard, but has it affected the bond to the materials it is bridging?
I don’t much like cyano myself as eventually it seems to go brittle over a few years and fittings stuck on with it fall off. I am also allergic to it, as a single whiff of the standard stuff causes severe hay fever symptoms which last for three days. I can manage the odourless variety (which really needs a kicker) and I do use this in situations where it is the best option.
I particularly like Deluxe materials Superphatic which wicks deeply into a joint and gives a really strong bond. It is also useful for bonding absorbent materials to non absorbent ones so it works pretty well with wood to plastic joints.
For wood to wood I either use Deluxe Aliphatic or alternatively Epoxy. The 5 minute variety is handy but the 15 or 30 minute types give a stronger bond.
Aliphatic and Superphatic have the great advantage of water clean up which is very useful in many situations and are easily sandable. You can plank a hull quickly using cyano, but the joint lines are harder than the material which can cause problems when sanding as Richard mentions.
There are also some interesting acrylic based single part tube adhesives such as Bostik Power Repair and UHU All Purpose Power which are handy for awkward situations with dissimilar materials.
As Richard says, liquid poly in it’s different types (they are not all the same) enables plastic joints to be literally welded together and a joint doesn’t come stronger than that but it does have a downside as I found when making the wheels for my paddle steamer. It is of course a solvent and evaporates as the joint cures. I made the mistake of using too much and the evaporation resulted in shrinkage which pulled my carefully aligned floats out of line overnight. Lesson learned.
There is nothing new about dissolving sprue and scrap plastic in liquid poly, it was used a lot back in the 70s when the specialist fillers we have today were not available.
Colin