Frequently Asked Questions
The questions that come up while a specification is still being drafted.
Layer Selection
How many coats does a complete system actually need?
Usually one or two. On clean blasted carbon steel, the barrier goes directly on and that is the whole system. On every other substrate you add 7001 primer beneath it. A third layer — an aliphatic topcoat — is added only when appearance matters. Any spec calling for three or four polyurea coats is misunderstanding what single-pass build means.
When can I leave the primer out?
Only over freshly blasted carbon steel coated within the same shift. Everywhere else — galvanized, painted, concrete, wood, TPO, EPDM — specify 7001. It costs a fraction of the barrier layer and it is the layer that decides whether the system stays attached.
Is a topcoat required for corrosion performance?
No. A correctly specified barrier layer provides the corrosion protection by itself. Aromatic polyurea chalks in UV, which changes appearance and nothing else. Specify an aliphatic topcoat when colour and gloss retention matter — architectural steel, customer-facing structures, colour-matched fleets — and skip it otherwise.
Can I mix your primer with another manufacturer's barrier coat, or vice versa?
You can, and people do, but you inherit the compatibility risk. The most common failures we are called in on are cross-manufacturer interface problems where every product met its own data sheet. If you go that route, do adhesion testing on a representative mock-up first and get both manufacturers to comment in writing.
Writing the Specification
How do I derive a DFT rather than guessing one?
Start from exposure. Interior dry, 20 mil. Exterior atmospheric, 40–60. Wash-down or coastal, 60 with chlorides verified. Immersion and vessel interiors, 60–100. Aggregate abrasion, 80–120 in Flak Jacket Pro. Then adjust for remaining asset life — a structure with fifteen years to run justifies more than one scheduled for replacement in three.
What inspection hold points should the spec include?
Anchor profile verified by replica tape; chloride test result; substrate temperature above dew point at time of spray; wet film readings during application; final DFT survey; and holiday testing where containment or immersion is involved. Put them in the spec as hold points, not as suggestions.
How do I write the stripe-coat requirement?
Name the details explicitly: weld toes, cut and sheared edges, fastener heads and washers, back-to-back angle returns, and bolted connection perimeters. Require an additional pass at those locations before the full-field coat. Polyurea holds film at edges far better than thin-film systems, but stripe coating is cheap and those are the locations that fail first.
Should the spec allow SP3 prep, or insist on SP6?
Depends on whether you are protecting new steel or extending the life of an in-service asset. SP6 earns the full warranty and should be specified wherever the asset can be taken down and blasted. SP3 over sound, tight rust is a legitimate maintenance approach with a reduced-warranty note — write that note into the spec rather than leaving it to be discovered later.
Execution & Cost
What equipment does the spec need to require?
A plural-component proportioner with heated hose — Graco Reactor E-20 or E-30 class or equivalent — and an impingement-mix gun. State it explicitly. The barrier layers cannot be brushed, rolled, or applied with a single-component airless, and a bidder who does not have the equipment needs to know before they price the job.
How do the layers bond to each other?
Barrier over 7001 within the primer's recoat window bonds chemically. Barrier over barrier within about six hours bonds chemically with no re-prep. Past six hours, abrade and re-prime the surface before recoating. Write those windows into the spec so the crew is not guessing on day two of a large job.
How does a polyurea system compare in cost to a three-coat epoxy/urethane system?
Material per square foot is higher. Installed cost is frequently comparable once you count labour across three coats and the cure time occupying the asset or the shop floor. Over the service life the polyurea system generally wins, because there is no five-to-seven year maintenance recoat in the plan. Compare dollars per year of service.
How is the system repaired after damage?
Abrade the damaged area and a margin around it, apply 7001 primer, respray the barrier to the specified DFT. Minutes of work, and it restores the system rather than patching over it. Include the procedure in the spec so field crews are not improvising.
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