At The Natural Plaster Company, every cornice, every moulding, every architectural flourish is a story waiting to be told. Today, we’re proud to unveil the next chapter in that story: In-situ Running Render — a high-performance, natural-cement mortar system specially formulated for the in-place repair, reproduction, and integration of period external cornices and mouldings.
Over two decades of heritage plastering in Cornwall have taught us many lessons: patience, craft, and the unrelenting importance of materials that are sympathetic, durable, and true to historic building chemistry. Our running renders are the fruit of those lessons — refined blends of natural cement, graded sands, and earth pigments — tailored into three complementary products:
Muffle Coat
A fast setting blend of Natural cement, coarse sands and fibres developed specifically for the running of base coats of external mouldings.
This is our Muffle coat mix where all the dubbing out and build-up is done in rapid succession with the muffle of the running mould in place. The fast set and coarse sand, together with fibre reinforcement, allows rapid build up with little to no shrinkage.
Top Coat
Developed to match the earthy brown tones of traditional Roman Cement this super fine top coat blends Natural Cement, fine silica sand and natural earth pigment to create a beautiful top coat finish. This stuff is a joy to run with.
Casting Blend
A very rapid setting, binder rich blend of Natural Cement, coarse sands and pigments. Heavily fibre reinforced for detailed reproduction of external cast elements. Best suited to silicone rubber moulds. Carefully de-moulded in approx 30mins.
Important note:
In-situ Running render is very fast setting. It is advised to always use in conjunction with Tempo retarder.
These blends are designed to be used together (and in concert with our Primer & Adhesive and Tempo retarder) to deliver seamless, richly textured, historically appropriate repairs. thenaturalplastercompany.co.uk
Why “In-situ Running” Matters
Cornices, mouldings and architectural profiles are among the most characterful—and vulnerable—elements on historic façades. They suffer from weathering, impact, repair patchwork, and mismatched materials. Traditional repair often requires removing entire sections or using heavy pre-cast elements that don’t quite fit.
Our in-situ running approach lets a skilled plasterer run the profile directly on the building. The benefits are many:
- Continuity & integration — no visible joints or seams
- Matched texture & tone — because the mortar itself is pigmented and graded to replicate historic surfaces
- Speed & precision — the fast-setting nature allows work to proceed more swiftly
- Reduced waste — less breaking out of existing fabric, less need for large castings
That said, the mortar is very fast setting, so use in conjunction with our Tempo retarder is strongly recommended.
Lath and Plaster 