Search This Blog

Monday, 29 September 2014

Lime render and doors

Replacement doors tend to be held in place by screws, not inbuilt frames
The door on my house has seen a lot of changes. Since I have owned it we have had 2 doors. The removal of the render showed that the original door and frame must have been at least 10cm wider (there is a pillar of bricks on the far side in this photo).

When we changed the door we fitted a new frame as well. However, this frame is held in place using screws set into rawl plugs in the wall. This gives a firm enough finish, but it does move when slammed, so what to do with the new lime render, will this get affected by repeated use?

Well the thought is that yes the door will effect the render. As the door vibrates the render can be weakened and a really hard slam could shift and crack the new finish. So the plan is to counter this by using a cement and mesh to really tie the frame into the wall. With a firm and secure frame in place the covering render will be protected from any movement.

Purists might be up in arms about this as it is not lime (well cement is a lime, just a particularly hard and strong type), however this is about being sustainable and I feel that having something that will last longer in a potentially susceptible zone is better than having a purer version fail. The other important element to remember here is that the cement will be covered with the lime putty render, so this will be effectively buried into the wall and the lime will keep it dry.

Friday, 26 September 2014

Brick detailing ruined by cement

Lovely brick arch revealed on front of house
If it weren't for the addition of cement render over the years I think that this detail would have been recoverable, however the cement has pulled off the surface of the bricks and also caused them to break over time.

This detail would have been nice to re-instate on an otherwise bland looking terrace house, but without replacing all of the bricks it is just not possible.

The use of inappropriate materials therefore has an aesthetic effect on older properties as well as the fundamental damage that they cause by changing the way in which they work.

The damage is caused by the cement being too hard and strong. Basically the mortar and / or render should be weaker than the underpinning structure. Having a harder material means that it is the structure that is damaged when the outer coating is removed. Mortars should just be there to keep the main structural blocks apart and the render is there as their protective external wearing layer. Instead cement changes this to a system where the render is the dominant player and the main structure becomes it servant. Surely we can see that this is fundamentally wrong.

Anyway, my wall will just be a plain render finish (as planned), but seeing that lovely level of detail that was in the original house just illustrates to me what has been lost through the use of modern building materials on an old property. Shame.

Monday, 22 September 2014

Steel reinforced lime

Stainless steel EML screwed into place over areas with different materials / old cracks
I have been busy on the house preparing it for its new coat of lime putty render. One of these jobs has been to mesh over any major cracks in the sub-structure and where there are different materials exposed. This is because the movement in the house may crack the new render. Whilst this is not catastrophic for the render, it is always better to have an uncracked surface aesthetically.

So I have been using stainless steel EML (Expanded Metal Lath) AND stainless steel screws and washers. So I have been drilling into bricks, mortar and an occasional stone to ensure that the mesh is tight to the wall.

The high spots of the dubbing out had to be rubbed back (using a nasty looking studded float) so that the EML would sit quite flush to the wall.

The only major issue was that I was doing this on my own and the EML is really sharp, even on the main surface, so I have managed to cut my fingers quite a lot!

So the EML now covers the main wooden lintel at the front of the house, a thin brick pillar that was constructed to make the door opening narrower, the zone between an old extension where the bricks were not tied in very well, a wooden strip that runs horizontally along the first floor and the junction between a brick element of the house and an infilled concrete block area (an old door way).

So the wall is getting there for being ready for the render. Welsh Lime Works starting today!!

Friday, 19 September 2014

Cement render = Rotten wood

Removing render exposes timber issues under cracks
One of the other issues that the removal of the cement render exposed was the condition of the wood in the structure.

Admittedly the house has a strange array of wood that has appeared in the most unusual places - joists that go all the way through the house from external surface to external surface. The trouble is that this change in underlying surface meant that the cement render was more likely to crack here. Of course, being cement, it did and this in turn allowed water to get behind the render. This concentration in damp behind the cement of course then fed into the wood.

This is one of the big concerns with cement rendering old houses as it it not obvious until it eventually gives way. One of the many problems that we are storing up for the future generations, by not understanding older properties well enough.

So, if you do have a solid walled house make sure that you maintain any render really well - remove cracks when they form etc. If you do get around to needing to re-render, then do so using a lime based render but also expect to un-earth a range of problems.

I feel that this is a similar situation to the climate change arguments. It is out of sight and so out of mind. It is also largely controlled by large companies with vested interests and so they will not lead the way for change as their industry is profitable as it stands, so why rock the boat, even if you know what you are supplying is ruining the environment (the built one that is rather than the natural one).

Dubbing Out

Haired lime putty render thrown into deep holes in wall
One of the jobs associated with re-rendering the house has been to make good the walls before the main render coat is applied. This involves getting hold of some lime putty render (same as the top coat) and throwing it into the main holes that were left by the removal of the old cement render.

The walls were quite a mess after the initial removal. The cement render is far too hard for the walls and so it takes off lots of the underlying mortar and also breaks bricks etc when it is removed. The removal process also involved fairly heavy equipment in the form of breakers and if they are not used carefully then they too can remove parts of the wall. If using breakers then it is advisable to use lower powered ones rather than being all macho about it. So medium breaker, with a wide chisel end, used in as parallel an angle as possible is the way forward.

Anyway the upshot of the job is that rather than expecting some areas of render to be 10cm deep and others 2cm it is best to 'dub out' the holes to make the surface more even.

The process I have used is to throw the mix into the holes as this gets more air into the mix and hence it cures quicker. I have also had to replace some half bricks. Any exposed wood has been treated using Osmo 4005 and the windows have been insulated into any void reveals. Next will be to sort the various joints in the wall so that any variety in movement of the walls does not crack the new render.

Friday, 12 September 2014

A trip around the block in Canton Cardiff

Part of my walk around the block
We are based in a residential part of Cardiff. Lots of solid walled properties and also some newer infill houses with cavities. Despite the ravages of time that have been served out by well meaning but not necessary best informed builders and DIYers, it still has great character - lots of different colours, features etc all based on a common theme.

All looks rosy then and in fact it is an area in demand as far as estate agents are concerned. Can you feel a but.... coming on??

Letting my casual eye wander across the urban landscape I did spot lots of very common issues affecting the houses, so here goes:

No end of cement render (should be lime based and ideally the mix I advocate)
Cracked render everywhere (letting rain into the structure)
Re-pointing with cement (rather than lime)
Damp proof course injected into bricks (should be into the mortar - if used at all)
Damp proof course holes not filled (thus letting water into the structure above the DPC)
Ground levels clearly above the internal floor level (there should be a 15cm difference between inside and out)
Blocked vents for the floor (suspended floors require good draughts under them)
Paint peeling off of dress stonework (should be left bare, or painted with a breathable paint eg. silicate)
Guttering broken, warped, joints snapped, loose downpipes, .....
Window seals broken (they need to be checked and repaired regularly)
Phone and internet lines roughly drilled through walls leaving holes around them (should be sealed up properly)
PV panels covered in pigeon poo (aerials need to be moved to remove the temptation!)
Letter boxes broken (should be repaired to ensure better airtightness)

And that was a quick 15 minute stroll along three streets!!

Correct maintenance is really important with buildings otherwise we shall see these houses slowly degrade. In the heart of the city we need a well informed population, but who apart from us is trying in Cardiff??

Invisible touching up

I was a little perplexed about which picture to choose for this post and I eventually realised that the only one really is the one pictured.

Basically I had to paint over a mark on my bedroom wall. Now with many paints this touch up would have been visible, but thanks to the anti-static nature of the claypaint it is virtually invisible. Why anti-static you ask, well...

Most conventional paints have oils in them and this has a slight charge associated with it. This static charge attracts dust to it, so over time the walls become dirty. However you would not notice this until you get around to having to touch it up. You are then left with the choice of having a visible repair, washing down the whole wall or not bothering in the first place.

Claypaint, doesn't have any oils in it and so does not actively attract dust to it, so when you have to do a bit of a repair, you can just get the left over paint out (or in my case a small tester pot) and paint it over. Job done.

Although I do have to admit that it took me two testers to find the right colour!! So another tip is to ensure that when you have finished painting your room, decant the remainder of the paint into an airtight jar / container and then remember to label it both with the colour and the room that you used it in!!

Monday, 8 September 2014

Earthborn Moisture Vapour Transmission Test

A piece of testing equipment!
I had a question last week about which paint to use on a lime plastered wall that would be subject to heavy traffic. Now I had always used the official data for this answer, which was that the sd value for the Earthborn EcoPro and the Claypaint were the same at 0.2. However, being an inquisitive sort I thought that I had better check with the powers that be at Earthborn.

I was answered very promptly (as they are very good there) with the following chart. 

Moisture Vapour Transmission (g/m²)

So the solution was to use the claypaint with a couple of coats of wall glaze over the top. This is especially important on the internal surface of external walls as they need to be the most breathable. Internal wall surfaces on internal walls could take the EcoPro, but I would not really recommend that Midsheen here as it is not porous enough. 

All paints will of course be fine on gypsum plastered walls, but for lime we would recommend using the clay paint at all times (unless you wish to use an alternative silicate or lime paint - Auro do an excellent white lime paint for instance) and if you need the extra protection of the glaze to make it more wipeable, then the earthborn wall glaze is a great partner to the claypaint.

Thursday, 4 September 2014

Lime and Steel

The difference can make or break (literally) your project
These products do the same job. 
They also look very similar
One will work, the other will not

Fixings are used a lot in the construction industry. My render job on the house is no different. I shall have the following types of metal in my wall:

Expanded Metal Lath (EML)
Stop Beads

The EML will be used to tie together those parts of the wall where there are junctions (points where the risk of movement and cracking is most acute).
The Stop Beads will be used around the base of the wall
The Screws and Washers will be used to hold the Beads and EML in place

The important thing is that they are ALL stainless steel. Lime (and cement) attack steel and galvanisation is only a thin coat of zinc over the top of mild steel, so any slight removal of this protective covering will allow the moisture in the render to rust the steel. The galvanised steel will also slowly react with lime and this will cause the structure to fail as the rust expands and cracks the render.

Using galvanised and stainless steel together also creates a electrolytic reaction between the two and this will also lead to the render failing.

So when you are using a lime product it is vitally important that you use ONLY stainless steel (and / or plastic) in your fixings. Don't think that you can get away with using good quality beads and EML and then fixing them with some ordinary screws / nails. It will not work.

Stainless is a bit more expensive than galvanised, but in the long term it is very much cheaper! No point having work done only to need it redoing in a couple of months / years.

It is also worth noting that on a recent visit to a newly built school they had the same problem. All the drip beads had failed and had 'blown' the cement render. So it is not just old buildings where care needs to be taken with regard to material selection and combinations thereof.