Stain Blocker is General Finishes's revolutionary water-based white primer for interior projects. Stain Blocker can be used to protect pigmented finishes from stain, dye and wood tannin bleed-through. Use over an existing finish, raw wood or MDF as a base coat for light colored General Finishes Milk Paint, Chalk Style Paint and Pigmented Polys.
General Finishes Stain Blocker is designed for effectiveness, not price point. A successful primer requires a sophisticated resin system and an atypical formulation. Use on pieces where you are concerned about bleed-through.
Product colors: White
Base type: Water
Interior or Exterior: Interior only
Type: Stain blocking primer
Coats: 2 coats
Application method: Brush, roll, spray
Usable over existing finishes: Yes
Spray tip sizes: HVLP 1.8mm-2.0mm
Dry time - touch: 1+ hr
Dry time - recoat: 2+ hr
Can sizes: Quart
Coverage: 125-150 sq.ft./quart
Viscosity (cPs): 1500-2000
Weight solids: 35%
VOC: 32.907 g/L
How Do I Prevent Water Based Topcoat or Light Colored Paint from Yellowing?
All bright white paint will yellow slightly with time, with or without topcoat. Water-based topcoats are reactive and more likely to draw out substances in the wood such as tannins or unknown substances in existing finishes causing the topcoat to yellow. This is an industry-wide issue and we have added warning labels regarding the yellowing of topcoats to our bright white paints, Snow White Milk Paint and Chalk White Chalk Style Paint.
General Finishes background was originally on the professional side, and the incidences of yellowing topcoat over white paint were almost nil, and when our sprayable professional finish, Enduro White Poly, is used, there have been no incidences. But as the use of our paints has increased in the up-cycling and furniture refresh markets, we have heard more reports of our topcoat yellowing. Our original response was to teach about prepping, testing your finish schedule and finally creating Stain Blocker, our stain and tannin blocking primer, but this is not enough. Just as we advocate prepping all finishes, we are now advocating NOT using a clear water base topcoat over BRIGHT WHITE paint.
We are listening and General Finishes is in the process of developing a brushable version of our professional Enduro White Poly (available only in gallons), but that will take some time and rigorous testing before we can release the product. Here is what you should know to protect yourself and also some immediate suggestions to decrease chances of yellowing.
There is no way to reliably predict yellowing ahead of time. Sometimes yellowing occurs, sometimes it does not. Every existing finish is different and we rarely know the finishing provenance on an existing piece. Every tree is different and every piece of wood is unique. Wood can bleed tannins immediately after the topcoat dries or months later with a change in temperature that comes with a change in seasons. Oak, pine, mahogany, and Douglass Fur are particularly prone to bleed-through.
As is true of most "water-white" topcoats, our High Performance Water-Based topcoat is a clear drying finish over a non-reactive substrate such as plastic. When white paint sealed with a water-white topcoat is applied to something as unpredictable as wood, all bets are off and the reason is often unknown. Yellowing can be caused by the top coat activating the tannins in raw wood or aniline dyes, stains or contaminants in a pre-existing finish. This is most evident when using BRIGHT WHITE paint and most prevalent in the sculpted details of furniture, where the topcoat can collect, intensifying the color change to an unacceptable level.
To add to this issue, all bright white paint will yellow slightly with time, with or without topcoat. You have probably tried to touch up white woodwork in your home after several years and noticed that the new paint is brighter.
- Whites have a lower "hide" quality and are more transparent than most other colors. Most bright whites require additional coats to achieve the desired color and minimize color variation. This can increase the cost of paint finishing. Always include a clause in your contracts addressing the need for additional coats to achieve coverage. Bright white paints can yellow over time with or without topcoat.
- The underlying finish or wood species can affect the final color of light paint.
- Details and inside corners are difficult to cover with any paint color, but this property tends to be more noticeable with whites. This is a naturally occurring phenomenon in paint application and does not necessarily constitute a defect in the paint finish or your technique.
- The more porous the paint (chalk paint vs an acrylic paint), the more likely that yellowing will occur. The topcoat is actually seeping through the spaces caused by the larger particles of filler that give chalk style paints their texture.
How Can I Improve Coverage When Using White Paint on Furniture?
A primer is your best defense under light-colored paint.
Another technique to avoid the slight color change that sometimes occurs when applying topcoat is to add 10-15% of the paint you are using to your topcoat. This technique layers additional coats of color over your piece as well as providing the protection of a topcoat. If you don't like measuring, just add enough paint until you can see a bit of the hue in the topcoat. This method works with a brush or a spray gun.
To maintain the full-strength protection of the topcoat, DO NOT TINT YOUR FINAL COAT of topcoat.
Remember, NEVER EVER paint an existing piece of furniture with a light paint without proper preparation AND a stain blocking primer. Topcoats can activate tannins in the wood, or dyes in the previous finish, causing yellow or pink bleed-through. We recommend General Finishes Stain Blocker, which has been developed specifically for upcycling furniture and has proven to be 100% effective when two coats are applied.
Here is a sample finishing schedule:
- Prep clean and sand
- Three coats of paint (or four if needed)
- Two coats of topcoat mixed with 10-15% paint
- One coat of topcoat
My Stain Blocker is Thick, Clumpy and Hard to Stir. Is This Normal?
Time and temperature play a roll in Stain Blocker's thickness and settling in the bottom of the can. What you are seeing is some of the fillers coagulating.
This is normal as long as it is soft on the bottom; it does not diminish its quality or effectiveness. You should be able to reincorporate the contents of the can - use a paint mixer if necessary because it is a thick, heavy product. However, you should not see any hard settle at the bottom of the can.