Sandstone walls, concrete render cracks and damp

[zunetunes]

Our largish detached Victorian property is built in sandstone and has original concrete render. The concrete has been painted with modern emulsion.
The house has significant penetrating damp in numerous places which we’ve been trying to find the source of for the last 5 years! The concrete render is very strong. We recently had a chimney stack re-rendered as it was very damp. The concrete was very hard to get off and I can’t see that taking all the concrete off is viable.

Anyway, this is my question. There are some cracks in the concrete (no surprise) that have in the past been filled but have cracked again. Builders have said I should fill the cracks and that will solve the damp problem. However my feeling is that water isn’t getting in through the cracks but in fact gets in higher up the walls and comes out through the cracks. If this is the case it may be that rain is getting in at roof level or at the top of the wall and then is finding its way down behind the render until it finds a place to get out. The roof has no eaves or soffits to speak of and we’re in an exposed area with high rainfall.

If my theory about the cracks is right I don’t want to waste time and money getting cracks filled if doing so effectively is keeping the water in the wall! Any thoughts, folks?

 

[Keithj]

Having chased damp all around an old Welsh granite house, I can tell you it's not always easy to find where it's getting in. Sometimes it's very obvious - a damp patch on a wall where the earth is heaped up against the wall outside.

Ours, we found (eventually) was getting in through the roof. We'd not have found it then, if a knowledgeable neighbour hadn't pointed out the cause (without even knowing we had a damp problem).

There was a sort of parapet at each end of the house, and the slates butted up against it. Over the decades, water had frozen in the crack between slate and parapet, widening the gap which then allowed water through into the attic space. It ran down the timbers and appeared in several altogether different places. The fix was to remove the parapet and run the slates past the edge of the building.

The other problem with that Welsh house was that it was half way up a mountain. The wind there blows uphill and carries water under the slates. The knowledgeable neighbour explained that in a location like that, the slates need to project 18 inches from the wall to stop the rain getting behind them and into the structure.

He fixed both problems for us (for a very reasonable price) and the house was dry as a bone when we sold it.

Stand back and look at the house, starting at the top. If you were determined to get water into it, where would you do that? Are the chimneys sealed properly to the roof? Is the lead sound? Are there any "butt joints" where rain can sit? Any missing or cracked tiles/slates? Is there a TV aerial cable running downwards into the house? (They should loop down, and then enter the house in an upward direction).

If your walls are rendered with concrete, then cracks are pretty much inevitable. Filling them is a permanent and ongoing exercise. My inclination, if it's feasible, would be to cut a groove above the crack and insert a lead fillet to divert water from entering the crack.

 

[JoceAndChris]

Good post from Keith there - I'd just like to add from my observations that water gets in where it can, depending on wind direction and quantities of rain. Once trapped behind cement it causes problems. Our dining room was terribly damp when we came here as a consequence if this.

We still live with the same problem as yourself so I sympathise. Our plan is to remove the concrete eventually, but it is a daunting prospect I agree - 25 k. In the interim I've hacked off the concrete where the cracks were worst, and have a patchy house. Although that has fixed the damp, I don't really recommend my methods which were too brutal, but like yours, the concrete is very thick and stuck fast.

My understanding is that the concrete render can be patched with breathable lime render, so that might be an option for you for the bits that the rain and wind typically lash against, where the worst damage is. I don't know about your location, but here the weather typically blows from a south/westerly direction - that's where the house is most weathered.

 

[zunetunes]

Thanks for replies.
18 inch overhang? I've got about 1.8 inch! Those pesky Victorian builders! A bit more detective work today, scraping off the interior flaking paint has led me to the conclusion that one of the entry points may be in the top south-western corner of the house. Time to call that roofer again I think!