Resins that have lost part of their flow during manufacture or storage must be corrected by the addition of a flow agent. The simplest means is often the addition of
water sprayed on the compound and mixed in well. If a resin is still capable of flowing, this procedure produces a resin with properties that are still acceptable. In cases where moist- ure content control is critical, it may be necessary to allow a little more time for ‘‘heating’’ to let the added moisture escape. However, if the flow is very low, and large quantities of water must be used to bring the flow back to normal, this method is not recommended. The large amount of water would cause longer ‘‘breathing’’ times to be necessary due to excessive volatile components, and excessive shrinkage may take place, causing too much stress on the glue lines. It must be kept in mind that excessive water addition causes UF resin precipitation. The best way to correct flow in these cases is to mix the resin with large amounts of an equal resin of the same quality that has a higher flow. Any proportion may be used to bring the flow back to normal. If increased flow is desired, 0.5 to 2.0% of spray- dried UF or melamine–formaldehyde resin can also be added to function as a flow agent. Methylol compounds, such as dimethylolurea, also increase flow, but they increase the water released during reaction more than do spray-dried resins. Lubricating agents such as calcium stearate are also able to give a fair degree of flow increase.