My friend Sal Marino , like myself has been around the block a time or 40 , here is a article he wrote some time back on compatability , its as true todayas it was then, but now we have issues as we look to use like substances… compatability in this case means not only that they work together but also one does not disturb the other.. here is Sal’s
I read today’s thread on the forum on “When the finishing dvd will come out” and your reply as to having to go back due to changes in product formulations as a result of VOC regs. Many years ago I wrote an article on topcoat finish/dye satin compatibility. You most likely know more on this subject than I do, especially since I have not been keeping up to date as much as you on the changes in product formulation.
The basis of my article was that solvent type, stain type and the type of solvent used in the finish all determine compatibility. Some of this info may no longer be accurate due to changes in product formulas, but it’s a good sound base of info regarding the problem in general.. I don’t know if this may be helpful to any of the readers but I have put together a summary in the event you may want to use it anywhere you wish.
1. Dyes – True dye powders completely dissolve in their appropriate solvent. Unlike pigmented stains, true dyes do not have any any binders or resins to lock in the color. If you apply a finish that contains the same solvent the dye was dissolved in, you will get some bleed back (even when spraying) of course not nearly as much as wiping or brushing the finish over the dye. Allowing the dye to dry for longer periods of time will not greatly reduce the amount of bleedback because as soon as the solvent in the finish comes in contact with the dye, it will start to re-activate, thus causing the bleedback and loss of color retention. The mechanical action of wiping or brushing worsens the bleedback.
Examples of soluble dyes:
Alcohol dyes =de-natured alcohol
Oil dyes = petroleum based solvents like turpentine, mineral spirits and naphtha
And of course water dyes =water.
Examples of incompatibility:
Water based finish over true water soluble dye
Oil based poly or varnish over true oil soluble dye
Shellac over true alcohol soluble dye
Examples of compatibility:
Shellac over water true soluble dye
Water based finish over true oil soluble dye
Water based finish over true alcohol soluble dye
Oil based finish over true water soluble dye
The bottom line is “if the finish contains the same solvent that the dye was dissolved in, you will have to deal with some bleedback and color retention problem, unless you first lock the color in with some type of sealer or wash coat finish that will be compatible with the dye prior to applying the finish that contains the same solvent as the dye.
2. Pigmented Stains – Unlike true dyes, pigmented stains contain binders, such as oils in oil based stains and small amounts of polymer resins in water based stains. Once applied and dry, these binders help to keep the pigment lodged in the pores of the wood and held on the surface. While solvent compatibility and color retention can still be somewhat of a problem when wiping or brushing finishes over these stains, the amount of bleedback should be much less than a dye, especially if the stain has dried properly.
Naturally, there are advantages in using both dyes and pigmented stains (which is an entirely different subject) however it’s important to have a good sound knowledge of just how dyes and pigments react to finishes.
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