How resin anchoring holds a bolt
In resin-anchored rock bolting, a steel bolt is bonded into a drilled hole by a filled polyester compound that cures around it. The compound is usually supplied in two parts kept apart until use — a mineral-filled resin mastic and a peroxide initiator paste — and mixed in the hole as the bolt is driven and spun. Once cured, it transfers load from the bolt to the surrounding rock.
The finished anchoring product is designed, tested and supplied by its manufacturer. Samrat Poly Resins’ SPR 301 RB sits one step earlier in that chain.
A base resin, not a capsule
The 2026 catalogue is explicit: SPR 301 RB is the liquid base resin for manufacturing rock-bolt anchoring compounds, not the finished mineral-filled mastic or capsule. It is an isophthalic unsaturated polyester, supplied non-accelerated, with a typical viscosity of 2,000–3,500 cPs, specific gravity of approximately 1.12 and styrene content of 35–39% by weight.
Its buyers are compound manufacturers. They add fillers and other ingredients, package the product, and take responsibility for the anchoring performance and approvals of what they sell.
A BPO-based reference cure
Most SPR 301 grades are catalogued with an MEKP and cobalt octoate reference cure. SPR 301 RB is different: its reference cure is BPO 7% with cobalt octoate approximately 0.4%, added separately during use. Benzoyl peroxide is the initiator type anchoring compounds commonly use, often packaged as a paste in the second compartment.
That difference is a practical warning as well. Cure data and dosages for the MEKP-cured grades do not describe SPR 301 RB.
Two gel-time bands
The catalogue gives two gel-time bands for the grade: ultra-fast grades at 15 seconds to 2 minutes, and delayed grades at 5 to 30+ minutes. Anchoring systems commonly combine speeds so that one part of the bond sets quickly while another stays workable for longer. The compound design decides which band is needed, and it should be stated when enquiring. The gel-time selection guide sets out how to frame that choice.