Screeding upto UPVC door cills

[Mileso1]

Hello
I'm in the process of screeding my conservatory floor
It already has a rough and bumpy concrete slab the builder half finished before going bankrupt (long story don't ask)
its roughly 3.33 x 2.80 meters square and I want it 40 mm thick at a 4:1 mix, by a calculator its suggesting 21 bags of sharp and 7 cement which seems a lot but for the area but hell ill go with it.
anyway
1/ will i have to paint the slab with a acrylic primer agent like setcrete first ,some people have said yes other have said not to bother

2/ will i need to add a Plasticiser as the sand will be very wet already. Getting in 25 kg bags from wicks

3/ There are two door cills which I need to chop out as my 40 mill will be above these one is wood the other UPVC, these were two external doors on different walls now enclosed inside the conservatory my question is .. can i screed right up to the bottom of the door frames or do i leave a few mm gap, i'm worried about these expanding at different rates to the screed and tiles when the weather is better.

Thank you for any help or suggestion all warmly received

 

[^woody^]

As the screed is thin, then a primer or a cement slurry should be used to bond the screed and slab. Consider adding fibres too, as it might dry too quickly being that thin.

No plasticiser in screed. And it needs to be almost dry when it comes out the mixer or you will never get it flat and smooth.

Screed right up to the frames.

 

[Mileso1]

thanks woody your a diamond geezer