Sand in my loft

[michael]

I’ve just been up in one of my lofts. This particular loft is under a single elevation sloped roof on a single storey building which abuts a 9” thick brick wall. On the other side of the wall is the street and pavement. The upper part of the slope on this single elevation roof is therefore fixed to the brick wall and has a continual length of lapped lead flashing sealing the join between the brick and the slates all of which are in relatively good condition.The wall elevates a further 3 ft above the lead flashing.

Unfortunately, I have discovered that a timber plate which sits in this wall within the loft space and supports the ceiling joists of the building is rotten in several places, more rotten than good in fact. To add to this I discovered that the plate and sections of the lath plaster ceiling close to the wall were buried in a pile of slightly damp orange coloured sand almost like a plastering sand. So far I have removed a sack full of the sand and I’m only two thirds along the length of the loft.

I am assuming that this sand has come away from the pointing on the brick wall within the loft but on inspection the wall looks fairly good, no spalled bricks, no missing pointing, however the pointing is not of the decorative kind and it is the same colour as the piles of sand I have found (orange).

On the street side of the wall, all looks fine, good condition bricks and a harder whiter looking lime mortar pointing.
The wall could be anything up to 190 years old. The capping bricks have an almost rounded top and all look fine. The only problem with the wall is that it has a serious banana shaped bow from one end to the other when viewed from the street and in plan however I understand it has been like this for many years. I recently had it inspected by a structural engineer. He only viewed it from the street and from high level using a ladder and he assured me that it is quite sound.
Considering that there appears to be no pointing missing from the brickwork joints in the loft, dose anyone know what this sand could be and dose anything sound amiss here apart from the rotten plate?

 

[Penners]

Perhaps the sand was left over from some pointing or similar work that was done in the loft, at some time. The builder might have thought that it was easier to spread it around a bit than to carry it all downstairs again.

That's purely idle guesswork - no expert knowledge was employed!

 

[BMcD]

To expand on Penners suggestion an repeat his diclaimer

purely idle guesswork - no expert knowledge was employed!

Are the flashings and slates original? Has the wall above the roof been rendered previously? Could it be possible that the slates or flashing was replaced at the same time render was removed, thus allowing debris to fall into the loft space? A bit of a worry it's slightly damp though, why would that be? Is the roof/flashing as sound as you think?

 

[Penners]

A bit of a worry it's slightly damp though, why would that be? Is the roof/flashing as sound as you think?

Michael's original post suggested to me that this isn't a pile of sandy debris, but pure builder's sand. If so, I have noticed that this material invariably feels a bit damp, regardless of where and how long it's been stored. Left undisturbed, it seems to form a dry crust, but remain damp underneath.

Could it be hygroscopic? Or is it perhaps just its coldness that makes it feel damp?

 

[michael]

I think the roof was re slated in the not too distant past (not by me) as the slates look to be of the Spanish variety. The rafters look original although it would seem that additional PT timber has been added, probably when the roof was re slated. This new timber is in the form of a 6x2 plank bolted into the face of the wall directly underneath the rafters which I think is also acting as a brace for the wall itself as well as adding additional support to the rafters. The upper part of the rafters sit on this new timber in addition to the original plate in the wall which seems to be fine.

In addition a new 2x4 PT timber has been laid across the original ceiling joists close to the wall and vertical columns of 6x2 PT timber have been inserted at intervals joining the 4x2 on the joists with the 6x2 fixed to the wall up above. A kind of belt and braces scenario.

The sand I’ve found just looks like plain sand but not quite so orange now that I’ve seen it in daylight. It’s not really very damp either i.e. it doesn’t leave your hand feeling wet. Its probably more cold than wet although its not very dry grainy sand. A little more clumpy than that.

I don’t think the sand has been spread around buy a builder, the continual position and shape of the mound against the wall suggests that it has fallen there naturally.

What I suspect is that this wall within the loft space, was repointed when the roof was reslated. What I fear is that they have used a very weak mix with too much sand but hopefully with lime, which is now deteriorating and falling from the wall.

As mentioned before there is no evidence of missing pointing however the pointing is perhaps a millimetre or ½ a millimetre recessed back from the face of the bricks.

It could be, I suppose, that the builder over did it with the pointing by building it proud of the brickwork face and what I’m seeing now is the erosion of what may have been protruding mortar.

I guess I’m just going to have to clean it up, do my repairs and keep an eye on it over the next year or so.

Very annoying about the rotten timber plate supporting the ceiling joists as this could so easily have been repaired when the roof was done.

As these are only ceiling joists, what I am considering doing now is supporting sections of the ceiling joists from below with acro props and then removing small sections of the defective plate and replacing with small sections of new PT timber. When all of the new timber sections are installed, join them together with metal face plates and screws so that they cant move independently of one another. Dose this sound feasible?

 

[Penners]

Dose this sound feasible?

If it's feasible, you could save yourself a lot work (and probably end up with a more satisfactory job) if you could replace the whole plate in one go.

Would it be possible to support all the ceiling joists together by placing a temporary support beam underneath them, with an acrow prop on each end of it? If that would be too great a span, perhaps another acrow in the middle might be needed.

Obviously the acrows would need to be well supported themselves, from beneath.

Then you could remove and replace the entire plate in one go.

 

[michael]

This is a fully decorated and carpeted room. I think that trying to install one full length of timber plate under the ceiling joists from the room would probably mean loosing some of my lath plastered ceiling and the plaster at the top of the wall if not the top of the wall itself. If I insert sections of timber from up in the loft, I might be able to leave the decorated room relatively undisturbed.

It’s a strange part of the building really which in total comprises of a bedroom, a bathroom and a small office. These rooms are effectively below ground whereas up in the loft you are at street level. This is because the property is built on a steep hill.

The walls at room level (below ground) are cavity walls. The retaining wall facing the earth must be at least 13” thick i.e. a 9” brick wall of stretchers and headers with a further 4” stretcher brick facing in front of it. In front of this is a cavity and then a further 4”stretcher brick wall which is the plastered wall of the bedroom/office etc.

Up in the loft (above ground) the decorated wall stops and the 13” retaining wall looses its additional 4” stretcher brick skin to become a standard 9” wall as it is now above ground.

In fact from up in the loft you can look down between the cavity of the decorated 4” wall and the 13” retaining wall and all looks very dry probably helped by hit and miss air vents at skirting board level in the rooms.

The rotten ceiling joist plate in the loft sits on the retaining wall where it sets back from 13” to 9”. The ceiling joists therefore effectively overshoot the decorated wall to sit on the plate.