Side-by-side comparison
Sherwin-Williams Extreme Block Interior/Exterior Stain Blocking Alkyd Primer Flat White vs Valspar Prep Step Drywall Primer Flat Tintable White
| Fact | Extreme Block Interior/Exterior Stain Blocking Alkyd Primer | Prep Step Drywall Primer |
|---|---|---|
| Use | Exterior primer, Interior primer | Interior primer |
| Sheen · base | Flat · White | Flat · Tintable White |
| VOC (untinted) | 338 g/L | <50 g/L |
| VOC added by tint | Not stated | Not stated |
| Emissions testing | Not documented | Not documented |
| Health certification | None found | None found |
| Safety Data Sheet warnings | 5 | 1 |
| Ingredient disclosure | Partial (environmental data sheet) | Safety Data Sheet only |
| Safety Data Sheet revised | 8/18/2026 | 8/18/2026 |
Highlighted rows are where the two products differ. Facts come from each maker's documents; "not disclosed" means the maker hasn't published it, not that the product failed a test.
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Scores summarize the evidence makers publish. They don't guarantee safety or predict individual health outcomes. How we score
Sources
Sherwin-Williams Extreme Block Interior/Exterior Stain Blocking Alkyd Primer
Valspar Prep Step Drywall Primer