We're restoring some old furniture - sofas with a lot of carving, whole wood book shelves, et al. We've stripped the old varnish and are redoing the job with poly. We did 2 coats of PU sealer and 2 coats of PU Matt, all with a spray gun. Most of the wood's teak stained with walnut, some of it is rose wood, so we're getting a nice dark brown.
For some reason, when spraying the top coat say onto one side of say the sofa's arms / legs or a shelf's side, the other finished sides pick up rough grey patches. The contractor reckons it's air from the spray gun that's causing that and says it's inevitable when using matt PU. We'll be trying again by covering the finished sides with paper and painter's tape, but we can't do this with the sofa's arms / legs as easily.
We also tried wet sanding with 1500 sandpaper - which removed the roughness, but left the grey patches - followed with 3m finesse it paste wax; it's too shiny for our liking and it raises the wood's grain, the grey patches / new scratches are now visible.
This is the brand of PU we're using: https://www.bergerpaints.com/products/wood-finishes/56/imperia-luxury-polyurethane
Is this normal? If so how do we avoid these rough grey patches in the first place?