Here’s the process I use to apply an iron acetate stain. I use a water poly for floors as the finish.
- Mix up the iron acetate at least a week before applying. My formula is one steel wool pad to one pint / 473mL of distilled white vinegar. My most recent mixture used 5% acidity vinegar.
- Mix and store in a glass jar. I’ve found wide mouthed jars easiest to use - I can dip my brush directly into the jar and don’t need a separate working container. I use a two inch foam brush to apply the stain. The foam brush coats well and washes out easily.
- Sand all pieces with 120 grit paper, preferably before assembly. Inspect and make sure the all late wood cathedrals are thoroughly sanded (i.e. there’s no sheen on the cathedral face)
- Assemble. Remove all glue squeeze out and spot sand as needed.
- For filling voids or blemishes I’ve had good luck filling with pva glue then pressing fine sawdust into the glue followed by a sanding. Apply more glue and sawdust as needed. The sawdust surface is sufficient to react with the stain.
- Apply a liberal coat of stain and let dry. I usually wait overnight.
- Sand lightly with 220 grit paper. For splotches (usually from cathedrals) do a heavy sand. Consider using 120 grit paper. I highly recommend wearing a mask while sanding.
- I typically stain the whole piece then do a second coat only on the show faces. In this case, only sand the show faces.
- Apply a second coat of stain and let dry overnight.
- If there's a particularly bothersome area, sand that back to raw wood and re-apply stain just to that face.
- Wash all surfaces with water and a red scotch brite pad. Let dry overnight.
- Some sources recommend first washing with water and borax / baking soda to neutralize the vinegar acid and then rinse with water. I haven’t experienced issues by not using borax.
- Inspect and use a brown and/or black sharpie to hide any little blemishes.
- Apply a coat of 1 part water poly and 1 part water to all surfaces as a primer.
- Rub down with a red scotch brite and begin final coats. I tend to apply two coats of a 2 part poly 1 part water mix and I only coat the show faces.