Dry Dash Patch

[Mark 9002]

I've Just replaced my Garage roof. The hot water pipes for the HWC previously came up through the roof and passed through the gable end of the house. They were covered in by metal cowling that was fitted into a chase in the Gable end.. As you can see in the attached Pic I am left with the final job of patching this up. I think I have all the materials I need to do this but before I start I would like some advice if Possible
Should I just take the render / Dash off from around the penetration and try and fill in the Existing square chase with White cement sand mix and push Dashing chips in by hand in this section or remove the whole section out and start from there.
I was thinking 4-1 sand / Portland cement for the first coat and 5-1 Sand /White cement for the coat that will receive the Dash.
Should I PVA Block before first coat.
Is it worth using any additives to any of the coats, Its such a small area it hardly seems worth it and I would only be mixing a very small amount
Do I throw the Dash on as soon as the second coat is applied. How thick should the coats be
I really want to have a go at this myself so any advice would be appreciated

 

[Mr Chibs]

I had to do a section of dashing to my old property.
After knocking off the loose bits, I then primed with PVA, but think it's not recommended for external use.

I used similar for first scratch coat, and scored it with a nail. Mine was about 12mm thick
Second coat think I used 6-1 but think 5-1 better, around 8mm thick.

Wash the chippings in a trug until they are clean.
Put a sheet down, and if your second coat is wet you can throw the chippings in either by hand or small shovel... think I also used a bucket trowel.

When you've got it about right, I used a plastering trowel to gently press the chippings into the second coat.

This is only my take, so apologies if you get a better answer!

 

[Mark 9002]

Thanks. I didn't think about washing the chips. I've only got a 25kg bag so should be no problem. Did you throw the chips on wet?. Did you get advice not to pva on external render ?

 

[Mr Chibs]

I read afterwards about the PVA, but I used it, and nothing has fallen off.

Yes, after draining the chips, I lobbed them on. Mine were Canterbury Spa chips, small sharp multicoloured things.

I couldn't get anyone to do it, all the plasterers didn't want to know, hence doing it myself.