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I see people using brushes (hair or foam) to spread glue. This is not something I have seen in real life.
Without experimenting I have a feeling that spreading glue with a brush might be a good idea, but when the gluing setup is finished and one has time to clean the brush it is already set.
So every such gluing would cost a brush.
I can of course use a piece of wood or my fingers but the question is: Is the brush wasted if used for gluing? If not, how it is cleaned (water of course)?
Many of the brushes you see people use online to spread glue will actually be disposable. The type I'm thinking of are something like 50c each, and although they can be cleaned and reused they're cheap enough that probably the majority of users are comfortable using each brush once and discarding it.
but when the gluing setup is finished and one has time to clean the brush it is already set.
Most PVA-type glues have an 'open' time of between 20 minutes and about an hour, depending on local conditions. Even if you're doing a complex glue-up and you can't leave the work to get the brush to a sink for cleaning you could have a jar of water near the workbench to dunk brushes into to stop them from drying out until you've finished clamping up.
Once you get to rinsing out the brush it's advisable to use warm water, it really makes quite a bit of difference compared to using cold water; so where available use warm water. After thorough rinsing, washing the brush with soap and water can help remove the last traces of glue although this isn't absolutely needed.
While you can use brushes of nearly any kind to apply glue I would recommend you confine yourself to those with synthetic bristles. Synthetic brushes are generally stiffer and easier to control (nothing is worse than trying to spread glue accurately on a joint face using a very soft and bendy brush, I speak from experience!) and their bristles are more forgiving of trace amounts of glue being left in them from incomplete rinsing.
In addition to paintbrushes silicone rubber brushes (intended for basting meats or glazing pastry) are used by some woodworkers to apply glue. Although these are great in that hardened glue doesn't stick to them and it can just be peeled off the next day, I don't like them because they're too floppy. But silicone rubber spatulas on the other hand are well worth experimenting with as glue spreaders, they work brilliantly IMO.
I very often use cheap (can't get much cheaper than Harbor Freight) acid brushes to spread glue. If the glue happens to be a polyurethane glue, the brush is considered to be disposable - no great cost. If the glue is a PVA glue instead, I'm so cheap that I drop my brushes into a little copper pot (nothing special about copper, it's just what I happen to have) half-full of water. Every couple of days, I pull my glue brushes out & shake the water out of them, then rinse out my little copper pot. The brushes are immediately ready for the next job.
If your using pva glue when you soak your brush in acetone it dissolves the glue and make you brush fine again
