Preparation: Removing mould from exterior timber

Mould commonly grows on the surface of exterior timber especially in wet and humid conditions. If you clean the mould away but don’t kill it effectively, it will keep coming back and can even keep growing under coatings causing the top coat to lose adhesion and peel.


Cleaning vs Killing Mould and preventing regrowth

Cleaning mould may remove the visible build up however, mould is made up of spores that are not visible. If mould is not killed properly and just cleaned from the surface using detergent or soap, the mould spores are able to continue growing causing the visible issue to come back.

Not all mould killers are safe for timber

Common mould killers contain harsh bleach solution which can be damaging to the surface of your timber and cause issues to the final finish of your coating. Intergrain® UltraPrep Mould Killer is a timber safe product that contains bio degradable ingredients that are gentle on timber fibres. As timber is a natural fibre, using a UltraPrep Mould Killer contains oxygen bleach which is safer for your health, the environment and your timber compared to hypochlorite bleach.

No matter what condition your timber is in, coated, bare, new or old. If it’s affected by mould or if your live in a humid climate, the first step to preparing your timber for coating is UltraPrep Mould Killer.



Fully dissolve UltraPrep Mould Killer in water. Dissolve 100g per 1L of water. Scrub the solution into the timber with a stiff bristle brush.


Leave for 15 minutes to let the solution activate and kill the mould spores, then thoroughly wash off the solution with a high-pressure washer.

NOTE: For severe cases a second treatment may be required. 


Before coating, prepare the timber with Intergrain UltraPrep products as determined by the condition of your timber.


NOTE: Always take caution when cleaning mould. We recommend wearing the following protective gear while completing your project.

  • Disposable shower cap
  • Rubber gloves
  • Eye protection
  • Appropriate clothing that can be laundered straight away or thrown out
  • P1 or P2 face mask