Internal lime plastering
Having spent several months of summer 2020 plastering the outside of our house, I began the inside around the end of September. Maria – when she recovered from her ankle injury – focussed on completing the internal studwork, soundproofing and insulating our internal walls.
For our internal lime plastering we decided to apply two coats only, as we wanted the plaster to broadly follow the contours of the straw bales. This decision was informed by aesthetics and also by economics. Even though we had straightened the bales and given them a ‘hair-cut’, they were not uniform, although plumb. To impose a uniform finish would use a considerable amount of plaster, which would also not reflect the natural ‘feel’ of the straw walls. We decided to apply two coats as the third or ‘straightening’ coat seemed to be unnecessary, given our decision on aesthetics.
I used NHL 2.0 with the same 5mm down aggregate used on the outside. Internal lime plastering in the Autumn/Winter months has advantages as the plaster takes much longer to dry, giving you more time to sort out any issues before it sets, and possibly cracks. As the windows and doors were installed, we didn’t have to worry about local weather conditions. One of the disadvantages about the slow drying time is that there was a lot of moisture from the drying plaster, and it caused rust to form on some of the screws we used to fix the plasterboard. We treated all the screws with a primer so that the rust would not affect any subsequent paint.
Our window reveals (internal and external) are rounded rather than the usual right-angle. There are several reasons for this; a) rounded reveals allow in more light than square ones, b) the straw bales which are notched around the window posts (2 lengths of timber (4″ x 2″) in the centre of the wall which holds the windows) are irregular, and, c) rounded reveals compliment an irregular wall surface and enhance the natural look.
The reveals were built up in several passes and utilised a fibreglass mesh for structure, strength and support (see photo below). I shaped the reveals with my hands, using the back to smooth out the shape. It’s good practice to add mesh at 45 degree angles to each corner of window and door openings as this is where plaster is more likely to crack. Depending on the size of the crack, they were fixed either by an application of limewash (for hairline cracks) mixture or were opened up and filled with additional plaster.
External lime plastering: Top Coat
Due to the rather cool overnight temperatures in May, we decided to postpone plastering the top coat until later in the Summer, and, eventually began plastering in mid-July. There was a lot of preparation before the final coat could be applied. Maria worked on sealing all the windows and doors with airtightness tape, and shaping the XPS render board to provide a curved substrate at window reveals, as well as making drip-moulding for the top of the window to ensure rainfall is directed away from the wall. The moulding was made from Douglas Fir heartwood which we got from the local timber yard. The reveals were then built up in several passes and reinforced with fibreglass mesh before the top coat was applied. The blue XPS render board will help protect the wood window frame from any moisture ingress.
Applying the top coat of plaster is a really enjoyable job. The really heavy slog of applying the first two coats is replaced by a far more subtle and creative one. The top coat layer is between 3 and 5mm, and is applied with a hawk and trowel. The mix ratio for this coat is 2.5 buckets of aggregate to 1 of lime, with some fibres added to strengthen the plaster. As with all lime plaster careful wetting before and after the job is important.
As the substrate is not uniform like a block wall, it was not possible to load the trowel fully and apply. It needs to be applied in smaller quantities particularly if you want to accentuate the walls’ natural shape. This inevitably caused the job to be more time-consuming, however, the results make this additional detailing worthwhile. It’s great covering up, what is quite a rough uneven surface, with a thin layer of top coat, and, giving the walls their final shape.
Overall this job took about a month to finish. We kept a tarpaulin protection up for about three weeks after the plastering was finished, so that the top coat would not dry out too quickly. I then applied five coats of limewash to the walls. Limewash is fairly quick to apply as its texture is similar to milk. The fifth coat had some linseed oil added to form a soapy coating to increase rain run-off.
Limewash has a dual refractive index which means that it can appear really bright under blue skies with lots of sunshine. When it is cloudier the house appears to be more off-white in colour. The house truly reflects the brightness of the day. The walls have a lot of character and texture. It’s noticeable that people generally want to feel the walls when they see it.
As with a lot of tasks on our build about 75% is relatively straightforward and the remaining 25% is awkward and challenging. To complete the dry-lining Maria had to cut lots of plasterboard to fit around rafters and braces. Plasterboard is not really manufactured for this purpose and can be quite brittle to work with when cut into irregular shapes. A major problem with this task was that a lot of the work was at height or difficult to access.
Soundproof and insulate internal walls
We had several sheets of insulation and wood fibre board left over from previous jobs which we used to insulate and soundproof the internal walls. Maria completed this task following the first fix by our electrician. Wood fibre board is an excellent noise insulator and has a high heat attenuation value, as well as acting as a fire retardant. We are looking forward to experiencing really good acoustics in the finished house. As our main living room/kitchen is over 70 metres squared, with an above-average ceiling height we wanted to avoid the room having poor sound quality or an echo.
Taping and Jointing of internal walls
When we completed all the plasterboard work we decided to tape and joint the internal walls, rather than cover them with a skim of plaster, which is a more common choice in Ireland. Taping and jointing covers the joins in the plasterboard, thereby providing a smooth finish for painting. Plasterboards are tapered along their longest edges to allow for this. We used both paper and some mesh in combination with joint filler. Paper works better for internal corners, as it can be folded and placed easily. The whole process normally takes two passes and is then sanded when hard for a really smooth finish. It’s important to ‘feather’ out the edges either side of the join to keep the surface as smooth as possible.
For an amateur, taping and jointing works quite well. Once you get used to using a trowel, and setting times, it is relatively straightforward. This benefit of this approach is that is uses a lot less material than skimming, and it is much faster. As plasterboard is already a flat surface it makes sense to just focus on the joins, rather than on the entire surface of the wall, unless you can properly skim walls. As well as taping and jointing we had a lot of caulking to do, particularly around the rafters and where the plasterboard meets the ceiling.
When we had completed the above tasks, the walls were ready for painting. We applied five coats of white emulsion, which works really well against all the exposed wood. We experimented with a few off-white colours but brilliant white was the most complimentary colour to the house’s interiors.
We then applied two coats of lime wash to the internal straw bale walls. Overall we were really happy with the finish on the internal walls. The house was still shrouded with tarpaulin on the outside (as the final coat of external plaster had yet to be applied) so we don’t really know how the rooms are going to be – in terms of light – but we are getting closer.
For our flooring cover we used the we used the same 7mm laminate flooring throughout the house, on top of a 3mm underlay, designed for underfloor heating systems. This is a quite an easy job to do, and, relatively quick too. The underlay has good sound proofing qualities and the combined 10mm of flooring provides a really good floor surface.
Leaving an adequate expansion gap is important here. We did have to reduce some of the laminate along the edges later on as we hadn’t left enough space in some places. It’s surprising how the floor can expand in a short space of time. It’s worth leaving a bit of time between laying the floor and installing doors and skirting boards, to allow the floor to expand.
Second fix carpentry – doors, skirting and architrave
We decided to use natural or waney-edged architrave and shirting. Our local timber yard, Clonmore, supplied us with 3/4″ 16ft lengths of Spruce, which we air-dried for about 9 months. We ran each length through a neighbour’s thicknesser and belt-sander, which prepared them for oiling. We used boiled linseed oil and applied three coats, sanding each length after each coat had dried. The linseed oil really highlights the grain and other features of the wood, and transforms what is white knotty wood into something which is richer and more colourful. When all the lengths had dried they were moved inside to acclimatise to the house for a few months before being used.
We experienced delays with our door order, which took about two months to be supplied. In construction global supply chains have been experiencing problems with many items and prices have also increased, as the global economy rebounds from the pandemic. We consider ourselves lucky that we are towards the end of our build a lot of building supplies have increased by 30% + over the last six months.
For the skirting and architrave I cut the lengths down to about 150mm and 100mm respectively, this 2/3 proportionality seems to work quite well visually. When they were cut to size they often needed to be trimmed and planed further to make them align with the door frames. I quite enjoyed the challenge of this job. When hanging a door everything has to be correct or the door simply wont open and close correctly.
When all the architrave and skirting was finished, we were really happy with the finish. There was a sense of flow to these features of the house. The natural curves and shapes in the wood used here provides a unique and beautiful delineation of the doorways, and the intersection between the walls and floor.
In late April we had some really nice sunny weather so we decided to complete some outside tasks. We had lots of galvanised mesh sheets which we made up into rectangular gabion boxes. We filled these with rocks and stones unearthed during the groundwork phase of the build. We assembled the gabions at the entrance to our site. Each gabion contains about 2/3 of a tonne of material and is a fairly simple way of utilising lots of surplus rocks and stone. It also acts as a retaining wall. We backfilled the gabions with clay and and planted some wildflower seeds.
We are getting closer to the finish line! In the final stage of the build achieving a quality finish is really important, and can make some jobs seem longer. However, the stage of the build we are at now is all about the quality of the finished work, so attention to detail and precision are vital.
I read a very useful summary about building projects from Sigi Koko, which is an excellent summation of the challenges of project management; “In any construction project, you can only have two of these working in your favour: cost, time, quality. That means if you are on a budget and you need to finish quickly, quality will suffer. If you are on a budget and everything is completed with quality, it will take longer to complete. And if you need your construction project completed quickly and with high quality, it will cost more. So choose the 2 that are most important to you for any construction project. This is true whether you are building naturally or conventionally”.