Monocouche Rendering Rotherham: Scraped One-Coat Render

How the thickness is built

K Rend's application instructions for its scraped one-coat renders describe about 18mm built in two passes: a first pass of 6-8mm and a second of 12-14mm, sprayed or trowelled one after the other. After it sets, roughly 2mm is scraped off to leave a 16mm finish, and K Rend warns that going below 16mm risks ghosting, where the background shows through as a shadow. Its K Mono data sheet gives a minimum of 15mm after scraping for that product.

The same instructions give a scraping window of anything from 4 to 36 hours after application, and say that in moderate weather the wall is typically scraped the day after. It is ready when a thumb no longer leaves a print but a thumbnail still marks it, and the aggregate comes away without sticking to the scraper. Scraping is done lightly in a tight circular motion, then the wall is brushed down so any missed areas show up and can be scraped at once.

A small extension or a long façade

On a small domestic job, such as a single-storey extension, monocouche can be trowelled by hand; K Mono's sheet notes that coverage may be lower when hand-applied. The challenge is matching the main house, which is often painted render or brick, so a test panel beside the old wall is worth the wait.

On a larger contract it is usually sprayed by machine, which keeps the mix and thickness consistent across long elevations. Shade becomes the main risk: K Rend says early scraping gives darker shades and late scraping lighter ones, so a façade is set out in panels that a team can lay and scrape at the same stage, divided by beads, floor lines or movement joints.

Where it should not go

Monocouche needs clean, sound masonry or a suitable base coat. It is not designed to bond over painted render or old dash, and on uneven stripped brick a levelling base coat may be needed first. On soft old stone or brick that relies on drying out, a rigid cement render brings the problems SPAB describes, and lime is the usual alternative.

1. 1

   Check the blockwork or base coat is clean, sound and true.

2. 2

   Fix beads and mask frames, glazing and roof edges against overspray.

3. 3

   Lay the first pass, then the second, to full thickness; level at once.

4. 4

   Leave it to set until a thumb leaves no print.

5. 5

   Scrape each panel at the same stage, then brush down and correct misses.

6. 6

   Keep the new render out of rain and frost for the first 48 hours.

Details, weather and repairs

Reveals and quoins can be float-finished smooth for contrast. Ashlar grooves can be cut into the scraped face, and K Rend's guidance calls for extra thickness in those areas so enough coloured render remains behind each cut. The K Mono sheet rules out work below 5°C or above 30°C, with frost forecast within 24 hours, in wet conditions or in direct sun.

A patch in monocouche will rarely disappear, because it is a different batch scraped at a different time. If a whole elevation later needs a colour change, K Rend says its render can take masonry paint, so the wall can be resprayed rather than replaced.

A white haze on fresh render in cold, damp weather is usually lime bloom, salts carried to the surface by moisture. K Rend describes it as a temporary effect that does not reduce the strength of the render, and says the best prevention is keeping setting render protected from rain and from water thrown off sills, copings and scaffold boards. It is one more reason winter work on a big elevation needs sheeting.