Sikaflex will not set!

[antaris]

Try spraying or painting a small section you've applied already, or on some of your batch on a solid surface, with an ammonia solution. The cure (X-linking) mechanism is normally free isocyanate + water ==> polyurea ( the "polyurethane" part of the final product is already pre polymerised in the material in the tube). The Isocyanate + water reaction in itself is pretty slow and needs catalyst to be present to have any decent rate.. The isocyanate + primary amine reaction is very fast indeed and does not need catalyst, ammonia is even more reactive with isocyanates than primary amines.

If ammonia does not result in any cure, there are no free isocyanates in there to react with water and the material will never "set"

If ammonia does result in cure, there are free isocyanates available and it will cure on reaction with absorbed water, albeit very slowly for this lot it seems. Probably due to low catalyst level, but increased acidity also retards the cure. One of the oldest used catalysts is "Dabco" ( TEDA, triethylene diamine) which used in a solution in ethylene glycol, propylene glycol or 1.4. butane diol. A GRP resin supplier might be able to supply it. Applying such a material to the surface will allow diffusion of the catalyst into the sealant and bring on cure if there is any isocyanate to react up.( catalyst levels do not need to be high and TEDA is very mobile in the polymer)

Sika probably erred on the side of caution with the catalyst level; the same catalysts catalyse the isocyanate+ isocyanate reaction, so reduce shelf life. Maybe to products for the Greek market have reduced catalyst levels, to minimise to the isocyanate+isocyanate reaction rate, as it's also temperature dependent.

Impressed. Will try, too! Many thanks!

Might even piss all over my mate's boat

 

[nigelmercier]

Sikaflex 291i... which does not seem to want to set...it is still sticky, 3 weeks later ...

What a pity it doesn't last that long in the tube

 

[duncan99210]

290i DC is the black caulk for decking and the like. Just used it to redo the caulking on the deck here in Crete. Took about 24 hours before it was completely set, which is longer than I remember from last winter. Perhaps the air's too dry?