Rendering question

[dab49]

Had my bungalow rendered about 6 months past, the extension was built from breeze/thermal block. The remainder of the existing building was brick.

Unfortunatly the render on the new part (block) has cracked in several places, any recommendations in the best way/product to repair these cracks so the repair is not too noticeable when painted?

many thanks gents.....

[Brucieboy]

I was always taught 6:1 base and 5:1 top coat. More flexible base for movement, harder top coat for weather resistance.

Other way round. The top coat should always be a bit weaker than the base coat. Too strong a top coat will shrink more than the base coat with the likelihood of cracking / delamination. Preferably better to add some hydrated lime to the mixes to enhance adhesion and flexibility.

[seanandruby]

Always best to give breeze blocks a good soaking prior to rendering. Chase out along the cracks making them wider break along the edges so they're not straight lines, then prime with sbr, scratch coat and finish slightly proud along edges, then sand down with a mouse, or similar tool.

[dab49]

Sean, thanks for that. I soaked the blocks but unfortunately the scratch coat had'nt taken care of the cracks (renderer also used lime in the mix). How much should I widen the cracks please....

Dave

[seanandruby]

I'd go 20 ml or so each side of the crack.