How to turn a lovley old house with solid walls into a warm efficient home




I had done all the research I could and had come up with what I considered to be the best solution.My earlier article on the site discussed the issues, pros and cons of insulating solid walls, and how the use of internal insulation could lead to future problems.

I planned to install Magnaline Superslim from Enviroform Solutions.

I Laid DPM and insulation over the subfloor, ensuring the boards fitted tightly together. I also laid a thin 1200 gauge polythene over the insulation before laying the ufh pipes. People often dont bother with this polythene if thtey are plannign to use a sand/cement screed. However, I spoke with Kingspan and Celotex and they both recomend the use of a thin polythene membrane over the insulation as it is possible for the cement within the screed to react with the metal surface of the insulation boards.

underfloor heating pipes, insulation, screed, flexidry, eco, green dealThough you can buy special trays into which to lay the UFH pipes I chose to use pipe clips that simply hook over the pipe and into the insulation. They are not very strong but it seemed a cheaper and easier option and they do hold the pipe in place.

Two types of screeds are available - traditional sand/cement of modern flowing screeds. The suppliers of each system claims theres is better, of course.I did my best research to decide which I thought was most appropriate. Flowing screeds do sound attractive. Being very liquid the screed finds its own level. Suppliers of this kind of screed also claim that because of its consisntency there is no rick of voids around pipes and that this ensures good conductivity for the UFH to work efficiently. Flowing screeds can also be laid thinner than traditional screeds, so the heat up time for the floor should be less.

The potential downside to a flowing screed is cost. The screed is pumped and most of the work and cost is about set up. This system, therefore, becomes most efficient when very large area are being screeded. Though I was doing around 46 sqaure meters, this was considered a small area. Some companies said it was not worth even quoting, other did quote but it was costy.

A Traditional sand/cement screed would certainly be cheaper, and was something that I could do myself. However, the idea of mixing 6 or so tons of sand cement and barrowing it around my house and in through the back door was not very appealing. I was also aware that mixing screeds in a traditional tumble cement mixer produces a poorly mixed screed. Screeds should always be mixed in a forced action or pan mixer to enure a good mix. Hiring such a mixer would add quite a bit off cost. A solution I considered, therefore, was to use readymix screed. Much like readymix concrete, there are a growing number of companies that will deliver readymix screed, often with an additive to slow the curing which means you may have up to 12 hours working time - great if you are not very experienced at screeding. Unfortunately, because my house is raised above road level I would still have the issue of getting the readymix screed from the truck to my floor - 6 tons of screed via a wheelbarrow through my workshop and in through the back door did not sound very appealing.

screed mixing, flexidry, eco, green renovationTraitional screed, being made up of sharp sand, can produce a floor that actually has many many very tiny voids where the sand is not fully compacted together. It is these tiny voids that might account for why the thermal conductivity of a traditional screed is considered inferior to a flowing screed by the flowing screed companies.

I came across a product called Flexi-Dry. This is a liquid additive for traditional screed mixes. The claim is that it drys out screeds much more quickly - only 7 days! The additive reacts with the water within the screed mix and crytalises. This means that the voids or filled and that the whole slab set evenly throughout its thickness rather than relying on surface evaporation.

Flexi Dry's claim, therefore is that a traditinoal screed with their additive dries evenly and quickly so there is no chance of curling,a nd because of the crystalisation it improves thermal conductivity so that it is better than flowing screed.

Judging and verifying company claims for a product is not alway easy. However, tables show that cement is a better thermal conductor than gypsum (the constituent of flowing screeds). Rightly or wrongly I was quite impressed with Flexi Dry's approach, and when I phoned them they did sound like people who knew what they were talking about.

I was planning to lay Vinyl over the screed, so it was important to me to get a very good, flat and level screed. As the additino of Flexi Dry reduces working time I chose to get Flexi Dry's sister company to come and lay my screed.

screeding, flexidry, eco, home renovationTwo guys turned up with a forced action mixer and screed pump which pumped the mixed screed into the house. Flexi Dry was added along with fibres to help strengthen the screed.

Inside the house the pump delivered the well mixed screed pretty efficiently.

The guy laid the screed mix in traditional manner, using a straight edge to compact and level the screed.

screeding, home renovation, eco houseThe guys worked quickly and the final screed was to a very high standard. The screed was nicely finished and, as promised by Flexi Dry, the surface did not dust up in a way screeds often do. When pressing my hand to the surface it came away clean rather than dusty. I was very impressed so far.





© Christopher Thompson