Interesting. Why has PU been discontinued? Environmental concerns or more basic reasons?
discontinued in my shop, not in general..
Parts being glued with polyurethane need to have a tight fit to be strongly joined. polyurethane is not a good gap filler at all which compromises strength.
As it sets it froths up and the froth hasn't any strength.
In very dry areas (low humidity like here) it requires moisture to set or it can set very slowly and not reach it's full potential.
Because it is sensitive to humidity in the air and the wood's MC, setting times are all over the map.
Because it tends to foam and squeeze out. If not tightly clamped everywhere the parts can be forced apart by the foam, weakening the joint.
The foam gives the illusion of gap filling, but there is no strength.
I believe that it hasn't the strength of PVA glues......
After its cured it is very chemically inert and safe but the intermediate phases are it is toxic and an irritant. cause allergic reactions. This begets polyurethanes have to be handled carefully, kept off your hands and not breathed in too much. do a search for the MSDS's of various brands to get more information. Read the warning label
: Contains isocyanate containing polymers. Contact causes eye irritation. Prolonged or repeated skin exposure may cause allergic reaction, irritation and sensitization. Contact may stain skin. Do not allow eye contact. Avoid prolonged or repeated contact with skin.
short shelf especially after opening and they are EXPENSIVE...
It is messy and sticky to use and always seems to get on everything.
Polyurethane is difficult to clean off hands, (gloves are highly recommended).
it takes Acetone or lacquer thinner to clean tools while still uncured.
it's not worth the extra work and hassles so I stopped using it all together...
this does does apply to construction adhesives such as PL Premium which I'm a die hard fan of......
and I'll stick w/ Weldbond...