Window frame render mix

Hi there,

So my job for boxing day was to remove the kitchen window and fit french doors. Pleased with the results.

Now I need to fill the ~1cm gap in the render on the top half around the jamb/lintel and fill/repair/add render to the bottom half. It's a check reveal so the frame butts up to the back of the exterior brickwork.

What cement/sand mix to use and do I use any additive? I have come across waterproof PVA, SBR, plasticiser and waterproofer which on the labels all seem to do a similar thing. Is it a case of mix it up and spread it on, or is there any prep work to do to make it stick?

Not too fussed about it matching as I can paint it when done. Also not bothered about the roughcast patch where the cill was as I'll deal with that much later.

Thanks

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Fill any larger gaps with expanding foam.

Damp down the bare brickwork 4-1-1 sand, cement, plasticiser block out and scratch...let dry overnight

Then 5-1-1 to finish. let it take up then finish with a sponge/float.

Brown low modulus silicone to complete.

Thanks very much for the reply.

Couple of questions - firstly on the ratio 5-1-1, That's 5 sand, 1 cement - but surely not 1 plasticiser? Unless there is some other plasticiser than the liquid stuff I have seen.

Also on the type of sand - do I use the same same for both the first and final coat - plastering sand?

Thanks again.

5 1 1 is 5 parts plastering sand 1 part cement 1 part lime with a dash of waterproofer in the mix only a dash dont go mad or even a small patch like that will hand for ever

Thanks very much. I'll post up the results once I'm done!