2. If the BFM paste gets too thick, or starts to harden in its cartridge, can it be reconstituted and used?
The best way to restore BFM-paste to its desired viscosity is to add in additional gel-binder to the paste. This gel-binder is often available from your BFM-paste supplier. But, if they refuse to send you additional gel-binder (perhaps because their company policy is to only supply a blended BFM-paste, with no sales allowed of only the gel-binder), then you may consider adding in some water (deionized water is best) to thin down the paste. But please understand that water is NOT gel-binder! Therefore, the new thinner BFM-paste will probably behave differently than the previously used BFM paste. Do NOT complain to your supplier, and do NOT expect identical extrudability with paste that you have thinned down with water. Having said that, I will again say to you that the use of water to thin down the paste may enable you to use BFM-paste that you would not otherwise be able to use and you would have had to discard. So, although it may not extrude in quite the same manner as the original paste, at least that re-constituted paste can be used!
a. What if BFM actually gets too hard in the cartridge or line? If the paste has actually started to harden, it may be possible to heat the paste sufficiently by placing a sealed container in a bath of hot water (almost boiling) for several hours, or over-night, to soften it, and then to reconstitute it according to the suggestions in the previous paragraph. But, if the BFM powder in the paste has actually hardened, I have actually seen people remove the paste from the cartridge, and on a very-clean surface, break the hardened BFM into smaller and smaller powder portions again, until it can be remixed with a gel-binder and re-used. Obviously, this may be impractical for some shops, but it does show that the BFM has not actually “gone bad”, but, with proper preparation, can actually continue to be used until fully consumed.
b. Can BFM settle out, or harden in the hoses if allowed to stay there too long? Yes, it is NOT wise to leave BFM paste in production hoses too long (overnight, or over a weekend) and then expect that it will perform as a creamy, free-flowing paste when the lines are restarted the next day, or the next week. It must always be remembered that the BFM-powder portion of any BFM-paste is merely a temporary suspension of heavy powder in a relatively thin gel-binder. It cannot ever be expected to remain “safely” in suspension for indefinite periods of time. The only place where it is safely stored for relatively long periods of time is in the original large paste containers, which are usually tight enough to prevent contact with air. Many of the plastic tubes used to transfer BFM paste from its pressurized containers are thin-walled tubes that can allow air to actually get into the paste through those thin walls. This may cause premature breakdown of the gel, or oxidation of the BFM in the paste, etc., which may then cause some of the BFM in the paste to separate out from the paste, and harden onto the ID walls of the tubing, further restricting BFM flow through the tubing in that location, etc. This becomes more and more of a problem if it takes a long time to consume the quantity of paste put into the container, or if you merely dump additional paste into the reservoir, right on top of almost-used previous lots of BFM-paste, without cleaning out the dispensing tubing/hoses on a regular basis. You must always have a schedule of regularly cleaning out hoses/tubing used for the transference of BFM-paste from its reservoir-container to the dispensing tip.