Balintore Castle Restoration Project: Underfloor Heating: The Pour

I have put a short video of the start of the screed pour at the end of this blog entry, so if you are the impatient sort, you can jump right there!

To say I was having kittens this morning is an understatement: there were so many ways today's screeding of the kitchen wing floor could go wrong.

I had followed the company's guidelines on arranging the sub-floor construction for a minimum screed depth of 50mm. However, I discovered on the company's costing spreadsheet just last night that they were only going to supply 40 mm! Their area estimate of 111 m² gave in consequence their volume estimate of 4.4 m³. The company were only bringing 4.75 m³, so their tolerances were already very tight.

In last night's panic I did my own calculations using multiple depth measurements to get an average screed depth for each room. The kitchen in particular introduces huge uncertainty as the floor height is all over the place because it is above basement vaulting. The sub-floors of all the other rooms in the kitchen wing were installed at different depths so nothing was standard. This was despite me emailing plans to try to ensure consistency! :-) Anyhow, my own calculations gave a figure of 4.5 m³, and I breathed a sigh of relief as I was in the company's window. However, I had a niggling doubt that the screeding would run out because of the previously mentioned discrepancy, and dashed off an email to the company about the inconsistent depths in their documentation. I hoped this would cover my back.

Gregor and Andrew arrived early to hold my hand, which was very kind of them. However, when the workmen arrived from the screeding company, Andrew and Gregor headed off to do some landscape gardening in the grounds of the castle. No-one else wanted to take responsibility for the screeding so I had to be on site myself. Indeed supervising the screeding was the principal reason for my current stay at the castle, and I had known for years that no-one else wanted to do it. This is as it should be of course – I was paying the money – but it didn't make it any less nerve-racking.

I showed the workmen the room layout, the finished level I wanted and explained the existing irregularities in levels e.g. stone slabs at opposite ends of rooms which you would assume were at the same level, were out by up to 13mm. I even started miming with a slate tile, assuming that gesture and show would remove any ambiguity in what I was saying. One of the workmen must have picked-up my nervousness, as he said “We do this every day, we know what we are doing.”. I had no doubt they knew what they were doing, but was concerned they were doing it with my money :-) and that I had not communicated properly the non-standard requirements of the castle's restoration.

Before any pouring, the workmen placed a large number of small metal tripods in each room. Using a laser level the workmen screwed down a circular plate built into the tripod, to the final floor level. The pour would be complete when it reached the level of these circular plates. Using the measurements obtained the workmen came up with a figure of 5 m³. I was warned that, in consequence, they might need to fetch another lorry-load of screed and that this would cost me an arm and a leg. My panic increased!

The workmen wanted me to tape a few bits of pipe and a few lengths of expansion strip down to ensure they would not float during the pour. I was eager to oblige as I just didn't want anything to go wrong. During the pour, they said that by going just 2 millimetres lower in each room, that they thought they could manage with 4.75 m³. I readily agreed! There was another panic in the former scullery, as they had to go higher than the requested floor level to ensure some pipes would be properly covered - but would this cause the screed to run out?

So yes, I was on hand to make some quick real-time decisions – again as it should but my adrenalin was definitely on high! My mouth was going dry, and when your body responds, you know you are giving birth to kittens. :-)

There was a hump in one part of the kitchen floor, isolating a low area which I had identified as problematic. One of the workmen found this and asked if I wanted him to kick some screed in there. My response: “Yes, please!”

At one stage, I could see some pipes in the kitchen rising slightly above the surface of the screed. This is called “crowning” and I was trying to assess how bad it would be. However, the workmen do a second pass where they spray the screed with a hardener and tamp the surface with a T-shaped tool. Thankfully the crowning disappeared after this.

The whole pour only took about 30 minutes – much quicker than the preparations and indeed much quicker than the subsequent cleaning up. As the pumping finished in the last room with the workmen running out of screed, it looked to a first approximation that there had just been enough screed and that the levels were about right. I deliberately did not look too closely as what had been done was now a fait-accompli and I could check things over accurately once the screed had dried. I was too worried about falling into the liquid screed, and spoiling the good judgement and care which had accompanied the pour.

I was asked if they could pump out the remaining contents of the wide bore pipe on the grass. I asked “Well how much is in there?” as I didn't want to pollute the castle grounds. It turned out there would be quite a lot, so I asked if they could fill some containers instead and I could use this to fill voids in the entrance hall floor. We had cleared out the entrance hall just in case there was any remaining screed. In the end we managed to get a couple of full barrow loads on the entrance hall floor. This was some last minute running around I was not expecting – and yes I was panicing! :-)

The most important thing, I guess, is that the membrane Andrew installed did not leak – hurrah! We had gone round this a number of times taping any holes or places where leaks might occur.

In fact the screeding is such a major and long anticipated landmark that I cannot believe it has actually happened. Acceptance may take some time, perhaps after 48 hours when one can actually walk on it? I will do another blog entry with the "after pour" pictures.

Huge thanks to Danny and Norbert of East-West Flooring for bringing their professional and good-humoured charm to a stressed-out castle laird!