James Newport Posted August 16, 2021 Share Posted August 16, 2021 I found that cheapy wood jigsaw blades works well for STS construction boards, which are also fibre cement. They only manage a few cuts before they blunt and become useless, but at a pound or so per blade it worked out better value than buying the magic circular saw blade the manufacturer recommends. Lots of dust though! 1 Link to comment Share on other sites More sharing options...
MortarThePoint Posted August 16, 2021 Author Share Posted August 16, 2021 CompacFoam appears to be an option when you have a thicker slab rather than just a screed. Included here for anyone who's interested. https://www.greenbuildingstore.co.uk/products/compacfoam-200/#prettyPhoto Link to comment Share on other sites More sharing options...
MortarThePoint Posted August 16, 2021 Author Share Posted August 16, 2021 Reconsidering slate as I have some on site: Rearranging the equation for Flexural Strength, the fracture force is F = (2 * width * thickness^2 * flexural_strength) / (3 * span). Popping some numbers in: thickness = 0.005m (roofing slate is 5 - 7 mm thick) width = 100mm = 0.1m (complicated this as there is obviously more to the side of the loaded the area, but if there is load spreading under a point load...) span = 100mm = 0.1m flexural strength = 50MPa (various sources state a range of 50 - 80MPa, link, link) This gives a fracture force of F = 833N = 83kgf. Almost identical. Thermally, the thermal conductivity of slate looks to be around 1.6W/mK so 10x more conductive then HardieBacker and being half as thick it will be 5x overall. That's a shame. Despite the worse thermal properties I am tempted by slate as I expect it is stiffer and probably more usual to find in this sort of position. I know that it behaves well with mortar too. Link to comment Share on other sites More sharing options...
MortarThePoint Posted August 16, 2021 Author Share Posted August 16, 2021 In the spirit of over engineering. I could use both. The slate would serve well to spread the load as well as adding stiffness. I'd need something thin and compressively strong between the slate and the HardieBacker. I wonder though if this concentrates the stress on the screed at the end of the slate? Would it want to crack between the two Es of SCREED? Not is there's no movement going on I suppose. Should convince the wife that a slate floor would look nice. ? 1 Link to comment Share on other sites More sharing options...
sean1933 Posted November 22, 2021 Share Posted November 22, 2021 (edited) On 16/08/2021 at 12:18, MortarThePoint said: CompacFoam appears to be an option when you have a thicker slab rather than just a screed. Included here for anyone who's interested. https://www.greenbuildingstore.co.uk/products/compacfoam-200/#prettyPhoto I plan to use this detail as I have heavy sliders but one thing bugs me about this. If dense EPS is used in the cavity so load bearing, why is the inside skin blockwork breaching the insulation to create a thermal bridge... is this really necessary, why can't the insulation just carry through as with a normal block and beam!? Edited November 22, 2021 by sean1933 1 Link to comment Share on other sites More sharing options...
MortarThePoint Posted December 31, 2021 Author Share Posted December 31, 2021 On 16/08/2021 at 15:09, MortarThePoint said: Reconsidering slate as I have some on site: Rearranging the equation for Flexural Strength, the fracture force is F = (2 * width * thickness^2 * flexural_strength) / (3 * span). Popping some numbers in: thickness = 0.005m (roofing slate is 5 - 7 mm thick) width = 100mm = 0.1m (complicated this as there is obviously more to the side of the loaded the area, but if there is load spreading under a point load...) span = 100mm = 0.1m flexural strength = 50MPa (various sources state a range of 50 - 80MPa, link, link) This gives a fracture force of F = 833N = 83kgf. Almost identical. Thermally, the thermal conductivity of slate looks to be around 1.6W/mK so 10x more conductive then HardieBacker and being half as thick it will be 5x overall. That's a shame. Despite the worse thermal properties I am tempted by slate as I expect it is stiffer and probably more usual to find in this sort of position. I know that it behaves well with mortar too. k=1.6W/mK with an average dT=13C, an area of A=0.005*2.4=0.012m2 and a 'thickness' of around t=0.070m makes for a heat flow of k*A*dT / t = 3.6W. COP of 300% makes that 1.2W of electricity so pretty small (about 1kWh/month so <£1/yr based on 6months heating). Link to comment Share on other sites More sharing options...
Iceverge Posted December 31, 2021 Share Posted December 31, 2021 I bought some secondhand GRP grating from ebay and laid it across the cavity, level with the top of the floor. It's proper stuff. Really tough but can be cut with a wood circular saw and suitable dust extractor. This is the detail that ended up being built. A bit messy but works fine in the end. The holes in the GRP covered mesh are filled by the EPS beads. K value of GRP ends up at about 0.065 W/m/K. Below is what I wanted to do. Simpler to construct and better thermally. I was talked out of it by various disbelievers. Early on in the build wasn't belligerent enough to insist I knew better. 1 Link to comment Share on other sites More sharing options...
MortarThePoint Posted January 2, 2022 Author Share Posted January 2, 2022 Interesting, they look good. This whole area is a bit under detailed. Link to comment Share on other sites More sharing options...
MortarThePoint Posted January 2, 2022 Author Share Posted January 2, 2022 I was just thinking about perimeter insulation and it's about 10mm thick with maybe 0.03W/mK so if 75mm high the PSI is 0.03*0.075/0.010=0.225W/mK. Doesn't normally have outside temperature on the other side but I have seen drawings with it between screed and concrete door step which are both good thermal conductors so step would be near outside temp. 7mm slate detail is 1.6*0.007/0.070=0.16W/mK. I think I'll only be able to achieve 35mm 'thickness' with slightly thinner slate so more like 0.25W/mK. These figures are indicative of the elements only rather than the build up which is far more complicated to work out. Link to comment Share on other sites More sharing options...
MortarThePoint Posted January 2, 2022 Author Share Posted January 2, 2022 On 31/12/2021 at 23:00, Iceverge said: I bought some secondhand GRP grating from ebay and laid it across the cavity, level with the top of the floor. It's proper stuff. Really tough but can be cut with a wood circular saw and suitable dust extractor. This is the detail that ended up being built. A bit messy but works fine in the end. The holes in the GRP covered mesh are filled by the EPS beads. K value of GRP ends up at about 0.065 W/m/K. Below is what I wanted to do. Simpler to construct and better thermally. I was talked out of it by various disbelievers. Early on in the build wasn't belligerent enough to insist I knew better. What level is the ground outside? It looks like your DPM is about 4 brick courses under floor level, so is the ground level with the top of your foundation? Link to comment Share on other sites More sharing options...
Iceverge Posted January 2, 2022 Share Posted January 2, 2022 No thats the radon barrier. There's a seperate DPC 150mm above ground level in the outer leaf. Ground level is 150mm below floor level. We also have a substantial gravel filled French drain all around the perimeter. 1 Link to comment Share on other sites More sharing options...
mac the knife Posted February 16, 2022 Share Posted February 16, 2022 just jumping in here. would anyone have a detail for how to the base of a door with wheelchair accessible saddle? thanks Link to comment Share on other sites More sharing options...
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