Overview
Built for the job.
High-Build Primer Surfacer is an elastomeric acrylic coating for priming automotive metal, aluminum, urethane, and plastics.
SEM® 42003 High‑Build Primer Surfacer is a 20‑oz, black, two‑component primer formulated for rapid build‑up on a variety of substrates. It is designed for body shop applications where a durable, sandable base is required before topcoat application, delivering up to 11 sq ft of coverage at a 2 mil dry film thickness (DFT).
Key technical features include a 60‑minute work window and a sandable time of 15 minutes, allowing ample flash time for feather‑edge work. Full cure is achieved in 48 hours, providing a hard, impact‑resistant surface. The primer is compatible with aluminum, bare metal, e‑coat, fiberglass, OEM plastics, SMC, steel and existing primer layers, offering zero‑VOC composition for compliance with environmental regulations.
Handling requires strict safety measures: use eye protection, chemical‑resistant gloves, protective clothing, and a respirator in a well‑ventilated area. The product is classified with multiple GHS hazards (acute toxicity, flammability, oxidizer, etc.) and carries H‑statements H222, H280, H315, H319, H336, H350, H361, H371. Follow standard first‑aid procedures for inhalation, skin, and eye contact.
Why Pros Choose SEM SEM
- Provides superior adhesion
- Excellent filling properties
- Works on multiple substrates, including metal and plastic
- Easy to sand
- Topcoat with most refinish material
How to Use
For use on steel, aluminum, plastic, SMC and fiberglass
- Prepare the substrate: clean, remove contaminants, and ensure the surface is dry. Compatible substrates include aluminum, bare metal, e‑coat, fiberglass, OEM, plastic, primer, SMC, and steel.
- Apply SEM® 42003 High‑Build Primer Surfacer in a single coat to achieve the specified 2 mil dry film thickness (approximately 11 sq‑ft per 20 oz). Use a spray gun or HVLP applicator for uniform coverage.
- Allow the coating to become sandable after approximately 15 minutes.
- Maintain a work window of up to 60 minutes from the start of application for any touch‑up or re‑coat.
- After application, let the primer cure for 48 hours before applying subsequent finish coats.
Compatibility
Compatible substrates: Aluminum, Plastic.
Compatible paint systems: Urethane, Acrylic.
Specifications
| Part No. | 42003 |
|---|---|
| Product Line | SEM |
| MFR Model | 42003 |
| Standard/Approvals | California PROP65 Warning: Cancer and Reproductive Harm | GHS02 | GHS04 | GHS07,GHS08 | OSHA HCS Hazard |
| Application | For use on steel, aluminum, plastic, SMC and fiberglass |
| Manufacturer | SEM |
| UPC | 646786420030 |
| Brand | SEM® |
| Maximum Sale Quantity | 12 |
| Maximum Sale Day | 7 |
| Color | Black |
| Container Size (oz) | 20 |
| Curing Time | 1 hr Dry |
| Coverage (sq-ft) | 11 |
- Dry Time
- 1 hr
- Cure Time
- 48 hr
- Work Time
- 60 min
- Sandable Time
- 15 min
- VOC
- Zero
- Coverage
- 11 sq‑ft @ 2 mil DFT
- Compatible Substrates
- Aluminum, bare metal, e‑coat, fiberglass, OEM, plastic, primer, SMC, steel
About SEM
SEM Products specializes in paint adhesion systems, flexible coatings, and plastic repair — the go-to choice for interior and trim refinishing.
Frequently Asked Questions
What substrates are compatible with SEM® 42003 High‑Build Primer Surfacer?
It can be applied to aluminum, bare metal, e‑coat, fiberglass, OEM plastics, standard primers, SMC, and steel.
How long does the primer take to cure?
Full cure is achieved in 48 hours. Sandable surface is available after approximately 15 minutes.
What personal protective equipment is required when using this product?
Wear eye protection, chemical‑resistant gloves, protective clothing, and a respirator as specified in the SDS.
Can the primer be sanded and recoated?
Yes. The film becomes sandable after about 15 minutes and can be sanded before applying a topcoat.
What is the coverage rate?
One 20 oz can cover approximately 11 sq ft at a 2 mil dry film thickness.
Documents & Safety
- Safety Data Sheet (SDS)
- sem_42003_catalog.pdf
- dualmix_39337_service_manual.pdf
- 42003%20High%20Build%20Primer%20BlackUSA.pdf
Why Buy from autofxmart
- Authorized distributor — authentic, factory-fresh stock.
- Fast US shipping — most orders ship within 1 business day.
- 30-day returns — buy with confidence.
- Pro-shop pricing — bulk discounts available on request.
- Expert support — questions? Email us at support@autofxmart.com.
Specifications
Full data
Frequently asked
Good to know
SEM is compatible with Aluminum, Plastic. Always ensure the surface is properly cleaned, degreased, and sanded before application to achieve the strongest adhesion and a professional finish.
The curing time for SEM is 1 hr Dry. Drying and curing times may vary with temperature, humidity, and film thickness — always consult the Technical Data Sheet (TDS) for exact cycle conditions.
This listing ships SEM in a 20 (CN) container. Check the autofxmart catalog for other sizes and bulk pricing.
Most in-stock orders for SEM ship the same or next business day from our US warehouse. Expedited options are available at checkout. Freight-class items may require an additional 1–2 days for carrier pickup.
Yes. autofxmart is an authorized distributor of SEM products. Every unit is factory-fresh, sealed, and backed by the manufacturer's standard warranty. If you have a concern, contact support@autofxmart.com and we will make it right.
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