Need to re-plaster around window from outside

Laci

Hi All, I'm new here on Boards.ie. Also new to plastering :-)
Could someone give me instructions on how to go at it?
I have a 100+ years old stone cottage. About 10 years ago the previous owner put in some PVC windows. And probably some time before they already re-plastered around the windows with cement based plaster.
The problem is that the water can seep in somewhere around the windows. The plaster is jut right up to the edge of the window frame and filled in with tubs of sealant...
It was a bad job done the first place, but I want to correct it.
I already started to wack off the plaster from around 2 windows. Should I use lime based plaster or cement plaster? If cement would do, can I just put another layer of plaster on top of the old one or I need to wack off the old?
Also how far should I plaster on to the window frame? About half inch will do?
There is no DPC in around the windows. Is it a problem or can I get away without it? As it is a stone wall, not even sure if it is possible to put in one.
Apologies for the novice questions, but just learning and don't want to cock it up.
Thanks a lot.

DublinDilbert

I've seen lots of dodgy window installs but never seen one leak cause the window is usually so far back into the opening very little water can get in. Are the windows near the front of the opening?

Laci

They are set back about 4 inches. The rain hits them from the side though. Also some rain can gather on the old cut stone window sills too. could that result in a rising damp problem? Thanks

Right2Write

What sort of finish is on the exterior walls - I'm guessing it's rendered, maybe pebble dashed? Yes, hack off the old plaster a bit to get to a good surface. Sand/ cement / lime mix will do you fine. If the surface is very dry, you can spray it a bit, so that it doesn't suck all the water too quickly. You'll probably find it best to put on two thin coats, rather than one thick - scratch the first coat a bit when it's gone off to give a key for the second. Plastering the underside of the reveal at the top of the window will be a touch harder than the sides, but if you don't overdo it, it should hold up fine. About 1/2" overlap on the frames should be fine. DPC is a bit redundant if they are solid walls with no cavity and PVC which won't rot anyway. That's my 2c anyway

Right2Write

Laci wrote: »

Also some rain can gather on the old cut stone window sills too. could that result in a rising damp problem? Thanks

It shouldn't - generally sills, even old granite ones have a little 'upstand' on them at the inside edge. The window frame has a corresponding 'L' shape, so that when it sits on the sill, it overlaps a little. You could always squirt in a little bead of mastic, if you think water is getting sucked under the frame.

Laci

Thank you for your very informative 2c.
Good guess, it is pebble dashed render. As is now, the old plaster i'm waking off is barely touching the edge of the frame. At places, not at all. Only a bit of silicon is covering the 1-2 millimeter gaps... So I think I'll do maybe 3 layers (some places need to be over 2 inches thick) as I'm taking it back to the bare stone/brick and the end finish will be ticker by about a half inch.
Also could you please advice the correct sand/cement/lime ratio? Should I add some waterproofing agent?
What kind of lime would you use? I'g guessing its not the one from the farm supply store.
Sorry for the amateur questions.
Thanks a lot

Right2Write

I've used a 1:1:5 or 1:1:6 - cement:lime:sand mix. Lime is your standard builders lime - a fine white powder, you get it most places you can buy cement. You can also add a waterproofing liquid to the water as you wish.

Laci

This is great, thanks a lot. Hope it will work just fine. Will give it a go tomorrow.

Laci

" Plastering the underside of the reveal at the top of the window will be a touch harder than the sides"
So through. But got there eventually. 3 windows are done now. Just another 3 to go. Thanks again for all the help.

Right2Write

Yeah, anything to do with openings in a building is trickier - windows, doors etc. Ideally you'd just built a nice cube or whatever with no openings - simplicity almost. You'd spend more time on the details around the opes than the rest of the gaff.