Rain blowing through?

[Keithj]

I'm wondering how water-permeable lime render should be...

When we have strong winds and heavy rain, such as twice in the last week, the water leaks in on the south (windward) wall. It seems to be coming in round the horizontal oak plate immediately above the downstairs window and dripping from there onto the floor. We mopped up about a litre each time.

It's been an ongoing problem (it did the same last winter). Last summer I got stuck in with the lime putty and filled the gaps where the green oak from the repairs had shrunk, and once that had carbonated I gave it several coats of limewash. It looks good when it's dry. However, the rain comes in just as before.

There is a large area of lime render (on laths) above the window in question: is it likely that the wind is causing the rain to permeate through the lime, and then run down the inside till it reaches the oak plate? Or should I be looking for something leaky that I've missed?

 

[Lime]

Most probably the rain is entering the wall in a position you have not noticed.
Rain usually runs along timber to its lowest point so you need to examine the outside wall in detail above and to the side of the point where you can see the leak showing.
The rain penetration could be a considerable distance away from where you see it.

 

[Penners]

Lime is right - water ingress can be very difficult to pin down to a specific location.

However, if it appears to be coming in along the top of a window, I would suspect that it may be seeping through at the point where the plaster meets the top drip-bar of the window - if it has a top drip-bar. If it hasn't, then wherever the plaster meets the wooden frame is likely to be a potential point of capillary seepage.

The ideal solution is to install a vertical lead flash which starts underneath the plaster a few inches above the top of the window frame, then kicks forward right on top of the window frame to create a new stopping point for the plaster. The lead should then be extended a little forward of the line of plaster (always angling downwards) and dressed vertically downwards.

If you are unable or unwilling to do this, then I'm afraid you may have to cast aside your period property conservation credentials and try to solve the problem by running some exterior frame sealant silicone along the line where the plaster meets the window frame.

 

[Keithj]

Thanks for those thoughts. I've recently seen a water ingress problem that was at least 50 years old resolved by a wise old builder - he stood out in the pouring rain and watched where the water went. I've tried (and failed) to use the same method here. It may yet come down to silicone sealant, but I'd rather not.

The problem only occurs with heavy rain and a strong southerly wind to blow it in. Hence I wonder if it's permeating through the lime and down the inside. I'll play "hunt the gaps" in the spring, and pack them with lime filler. Then maybe do some tests with the hosepipe