GrantMcscott Posted November 11, 2021 Share Posted November 11, 2021 Hi I am going to lay my floor insulation 190mm in total made up off 150mm PIR and 40mm PIR Is it better to put the thinner PIR down first? Do you butt it up against each other or does it need expansion gaps or should be tight fitted? thanks Link to comment Share on other sites More sharing options...
Dudda Posted November 11, 2021 Share Posted November 11, 2021 Get whatever services you need put down, eg pipes to a kitchen island or trunking to allow you pull cables later to the island. A gas or electrical feed if you've a free standing fireplace wall, etc. Then you can put the 40mm PIR down and cut around the pipes. Hopefully the insulated pipes will be about the same thickness making it very easy for you. Then the 150mm with fit nicely on top of everything. 1 Link to comment Share on other sites More sharing options...
Onoff Posted November 11, 2021 Share Posted November 11, 2021 Thick over thin I did...I think. Butt tight. Overlap the joints. Foil tape the joints. 1 Link to comment Share on other sites More sharing options...
Onoff Posted November 11, 2021 Share Posted November 11, 2021 Whoops! Looking back and I did thin over thick. It was a bit springy. Thick over thin would have been better. There's also 25mm EPS under the 100mm. 1 Link to comment Share on other sites More sharing options...
GrantMcscott Posted November 11, 2021 Author Share Posted November 11, 2021 1 hour ago, Onoff said: Whoops! Looking back and I did thin over thick. It was a bit springy. Thick over thin would have been better. There's also 25mm EPS under the 100mm. Looks like you have no upstands on that for the screed Link to comment Share on other sites More sharing options...
Onoff Posted November 11, 2021 Share Posted November 11, 2021 14 minutes ago, GrantMcscott said: Looks like you have no upstands on that for the screed I did later... Link to comment Share on other sites More sharing options...
Gus Potter Posted November 11, 2021 Share Posted November 11, 2021 If you have any DPM left pop another bit over the insulation as it can provide a slip membrane for the screed to shrink, helps reduce the risk of getting cracks in the middle for example. Maybe you are going / have done this anyway. Link to comment Share on other sites More sharing options...
Onoff Posted November 11, 2021 Share Posted November 11, 2021 I used Polypipe trays rather than a slip membrane. Makes for a lighter, castellated, slab. Think the tray inside the biscuit tin at Christmas! It doesn't "ring" quite as dense as a solid, full depth slab does but it's strengthened by A142 mesh Thank God I put the mesh in as I forgot to add the fibres in when I mixed the concrete. I used wet concrete btw, not screed. Tamped level using screed rails attached to the stud walls. 1 Link to comment Share on other sites More sharing options...
Gus Potter Posted November 11, 2021 Share Posted November 11, 2021 Good photos onoff! For all. Screeds and concrete shrinks. It cost pennies to do but where you have an internal corner just drop in diagonal bar, even if it is a poured self levelling screed or a screed with fibres. Even with fibres (plastic firbre ones definitley, steel fibres a bit less) you can still get crack development.. and this can cause you to worry that you have stretched your UF heating pipes. 1 Link to comment Share on other sites More sharing options...
JohnMo Posted November 11, 2021 Share Posted November 11, 2021 If you aluminium covered PIR insulation, you need to separate from concrete, as it forms it forms harmful gases. Aluminum reacts with the alkalis (OH) found in portland cement concrete. When these two chemicals are combined, the reaction produces hydrogen gas. This is why, when the reaction occurs in wet concrete, you'll notice tiny bubbles coming to the surface of a slab. Use a thin DPM to separate. 1 Link to comment Share on other sites More sharing options...
Onoff Posted November 11, 2021 Share Posted November 11, 2021 48 minutes ago, Gus Potter said: Good photos onoff! For all. Screeds and concrete shrinks. It cost pennies to do but where you have an internal corner just drop in diagonal bar, even if it is a poured self levelling screed or a screed with fibres. Even with fibres (plastic firbre ones definitley, steel fibres a bit less) you can still get crack development.. and this can cause you to worry that you have stretched your UF heating pipes. Should that be a piece of actual re-bar? Link to comment Share on other sites More sharing options...
Polish Builder Posted November 11, 2021 Share Posted November 11, 2021 Make sure you keep your Windows closed. Do not let your screed dry fast. Keep this floor in high humidity. Sorry for language-polish builder 1 Link to comment Share on other sites More sharing options...
Gus Potter Posted November 11, 2021 Share Posted November 11, 2021 16 minutes ago, Onoff said: Should that be a piece of actual re-bar? Yes. Link to comment Share on other sites More sharing options...
GrantMcscott Posted November 12, 2021 Author Share Posted November 12, 2021 The company that is going to do the screed for mw has given me 2 options GYPSOL Calcium Sulfate based flowing Floor Screed CA-C25-F5 or CEMFLOOR Cement based flowing Floor Screed CT-C25-F5 Not sure what one is better to use Link to comment Share on other sites More sharing options...
saveasteading Posted November 12, 2021 Share Posted November 12, 2021 12 hours ago, Gus Potter said: 13 hours ago, Onoff said: Should that be a piece of actual re-bar? Yes. And tied with wire to the mesh, so that it stays tight to the mesh, and doesn't get displaced or even lost. This is really important to avoid big cracks from a corner to the nearest edge. 1 Link to comment Share on other sites More sharing options...
GrantMcscott Posted November 12, 2021 Author Share Posted November 12, 2021 (edited) 9 minutes ago, saveasteading said: And tied with wire to the mesh, so that it stays tight to the mesh, and doesn't get displaced or even lost. This is really important to avoid big cracks from a corner to the nearest edge. I was not planning on putting any re-bar in my floor as did not think it needed it and the underfloor heating pipes would give the screed the support the biggest area we have is 70 m2 I will be using GYPSOL Calcium Sulfate based flowing Floor Screed CA-C25-F5 or CEMFLOOR Cement based flowing Floor Screed CT-C25-F5 Edited November 12, 2021 by GrantMcscott Link to comment Share on other sites More sharing options...
saveasteading Posted November 12, 2021 Share Posted November 12, 2021 No problem: the discussion has grown towards general theory. Ask your supplier how they avoid shrinkage cracks at box-outs. Perhaps it doesn't shrink? Or they add fibre? 1 Link to comment Share on other sites More sharing options...
Polish Builder Posted November 17, 2021 Share Posted November 17, 2021 On 12/11/2021 at 08:52, GrantMcscott said: The company that is going to do the screed for mw has given me 2 options GYPSOL Calcium Sulfate based flowing Floor Screed CA-C25-F5 or CEMFLOOR Cement based flowing Floor Screed CT-C25-F5 Not sure what one is better to use Second option sounds better 4 me 1 Link to comment Share on other sites More sharing options...
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