HSE approval 11113-GBPST 4336 / 11119Professional use onlyOver 18sSale to Great Britain only

How to Use AK Exterior Biocide DDAC 50%

Dilution rates, coverage, application method and the mistakes that waste product. Everything here is an industry guideline for trained users: the product label and safety data sheet always come first.

Work out how much you needSafety data sheet
HSE approved, approval 11113-GB
Made by working exterior cleaners
Collect in Kettering or GB delivery
Professional use only

Before You Start

This is a professional-use biocide. Before you open a drum, make sure you have read the label and the safety data sheet, and that you have the training and competence the HSE expects of anyone applying a professional-use biocide.

  • Wear the protective equipment the safety data sheet specifies
  • Check the forecast: the treatment needs to dry on before heavy rain
  • Protect plants, ponds, drains and watercourses from spray and run-off
  • Keep people and pets away from the treated area until it has dried
  • Use a dedicated, clearly labelled sprayer for biocide

Step by Step

  1. 01

    Assess the surface

    Identify what is growing: green algae, black spot lichen, white lichen, moss or mould. Heavy moss, especially on roofs, needs scraping off first. Spraying over thick moss wastes product and stops it reaching the tile.

    Clean or scrape roofs before treating for the best penetration.
  2. 02

    Dilute correctly

    Mix the biocide into clean water at the right ratio for the surface. Always add biocide to water, never water to biocide.

    Roofs and render 1:25. Ground level 1:50.
  3. 03

    Apply evenly

    Apply to a dry surface with a low-pressure sprayer or a soft brush so the biocide can soak into porous material. Work from the bottom up to avoid streaking, and make sure every part of the surface gets contact.

    Coverage: about 4 m² per litre of mixed solution.
  4. 04

    Let it weather clean

    Do not rinse it off. The growth dies back and rain and natural weathering gradually wash the dead matter away, leaving the surface clean without any mechanical damage.

    Results are typically visible within 4 to 8 weeks.

Dilution Rates by Surface

SurfaceDilutionMixed solution from 5 LArea from 5 LNotes
Roof tiles and slate1:25130 Labout 520 m²Scrape heavy moss first. Apply in dry conditions and let rain do the rest.
Render (K-Rend, monocouche, painted)1:25130 Labout 520 m²Brush away loose material. Soft brush or low-pressure sprayer only.
Brick and natural stone walls1:25130 Labout 520 m²Porous masonry soaks up more, so expect less coverage.
Driveways, patios and paths1:50255 Labout 1020 m²Best applied after a clean to hold back algae and moss.
1:25 means 1 part biocide to 25 parts water. Figures use the industry guideline of 4 m² per litre of mixed solution. Stronger mixes for stubborn black spot lichen must stay within the product label.

Coverage Calculator

Enter the area you are treating and the surface type. It works out the mixed solution, the concentrate and the cheapest combination of drums to buy.

25litres of mixed solution
1.0litres of DDAC 50%
£10product cost at 5 litre price

Based on 4 m² per litre of mixed solution. A guide, not a promise: very porous or heavily contaminated surfaces take more.

What Affects the Results

Surface porosity

Porous surfaces like render, sandstone and old tiles hold the residual for longer but take more solution. Non-porous surfaces still get an immediate kill but hold less residual.

Temperature and weather

Growth and treatment both behave differently through the year. It needs time to dry on, so avoid spraying straight before heavy rain.

Shade and shelter

North-facing, shaded and sheltered areas under trees stay damp and see regrowth sooner, so they may need a stronger mix within the label or a repeat treatment.

Application method

An even, soaking application at low pressure works far better than a quick mist. Missed patches are where the growth comes back first.

Common Mistakes to Avoid

Most disappointing results come down to one of these:

  • Spraying over thick moss instead of scraping it first
  • Rinsing the surface after treatment, which washes the biocide off before it has worked
  • Expecting an instant result. The surface cleans up over weeks, not hours
  • Mixing by eye. Measure the concentrate so every batch is the same strength
  • Spraying in wind, where drift reaches plants, cars and neighbours
  • Pressure washing render or roof tiles, which can strip coatings and force water under tiles

Storage and Disposal

Store the concentrate in its original, closed container, out of the reach of children and away from food and animal feed. Keep it off drains, ponds and watercourses when mixing and applying. Sections 7 and 13 of the safety data sheet give the storage conditions and how to dispose of the product and empty containers.

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