How to repair render cracks?

[AndyDavis]

The outside of my house was sand/cement rendered some years ago, and painted over with two coats of Dulux Weathershield. I’m going to repaint and want to fill-in some cracks in the render. The cracks are mostly hairline, although a few a very slightly bigger.

Should I fill the cracks with a sand/cement mixture or get some filler like Polyfilla? Which will last longer?

 

[JasDou]

If you can manage to fill the cracks with the same sand/cement mixture then do that.However polyfilla is as good as it is designed for this kind of use.
As for which one of them will last the longer is difficult to say.
What was the cause of th cracks?

 

[AndyDavis]

Not sure what caused the cracks, but the polyfilla box says I've got to use an oil based primer before painting. I was just going to paint after the filler dries. Is that OK?

 

[JasDou]

Hi,
Polyfilla is actually quite porous like plaster and will absorb too much water from the paint. So I would recommend the oil based primer.
Let me know how it is going?
Good Luck

 

[kevintaylore]

You could use an acrylic filler for the small cracks. Sand/cement would be good for the larger cracks but might be worth adding some SBR to give some flexibility.

 

[AndyDavis]

Thanks for that. OK so I apply the polyfilla, then the primer and then two coats of paint. Will that work because the walls were previously painted and I thought you normally apply a primer when its fresh plaster.