vala Posted September 25, 2021 Share Posted September 25, 2021 Hi all, what's the rough length of time I should allow before laying a ply T&G sub floor down over 25mm pug mix (8:1)? no wet trades have occurred and UFH being installed as part of a first floor refurb with no occupants. Link to comment Share on other sites More sharing options...
saveasteading Posted September 25, 2021 Share Posted September 25, 2021 25mm can dry quickly, but depends on the conditions, (especially if it was a dry mix., as a lot of the water disappears in chemical reaction) . How warm and dry is it? Link to comment Share on other sites More sharing options...
LA3222 Posted September 25, 2021 Share Posted September 25, 2021 I waited a few weeks with mine, I got a dehumidifier in aswell to help and monitored humidity levels. You'll be surprised how much moisture is in it - I did a dry mix but the sand still holds a hell of a lot of water in it. Link to comment Share on other sites More sharing options...
vala Posted September 25, 2021 Author Share Posted September 25, 2021 Thanks for the quick replies. @saveasteading although the heating is off in the house it's surprisingly warm. New windows and plenty of insulation has been installed so that's helping. House is very dry. I'll take some temperature readings during the day tomorrow when I'm back installing my pipe runs. Would it help if I had a fan heater on the first floor whilst installing the pug mix? I was initially thinking I could wait 1-2 days before starting to lay the plywood T&G flooring. Link to comment Share on other sites More sharing options...
saveasteading Posted September 26, 2021 Share Posted September 26, 2021 23 hours ago, vala said: fan heater on the first floor whilst installing the pug mix? No not really. In fact the mix should be kept damp for a few days to harden properly, with the chemical reaction before drying. Leave it as long as you can before laying flooring, and I would say 2 weeks minimum. Air through is good, so leave windows open in daytime. Link to comment Share on other sites More sharing options...
vala Posted September 27, 2021 Author Share Posted September 27, 2021 6 hours ago, saveasteading said: No not really. In fact the mix should be kept damp for a few days to harden properly, with the chemical reaction before drying. Leave it as long as you can before laying flooring, and I would say 2 weeks minimum. Air through is good, so leave windows open in daytime. The mix is done dry, no water added. I guess it's just the natural moisture from the sand you're referring to? Link to comment Share on other sites More sharing options...
saveasteading Posted September 27, 2021 Share Posted September 27, 2021 Cement in a mortar mix needs water or it doesn't perform the chemical reaction that you absolutely need. There may have been enough water in the sand but that sounds rather approximate. If there was the perfect amount then the water will have disppeared chemically into the screed and therefore be absolutely dry already. if you were light on water then it wont be fully hard. All I can suggest is banging with a hammer and you will know if it is hard, or a bit on the soft side. If the former, and you really added no water and had a very dry mix, then your are probably good to go. If it is soft the spray with water and it should harden up. Link to comment Share on other sites More sharing options...
vala Posted September 27, 2021 Author Share Posted September 27, 2021 @saveasteading the mix is definitely done dry. it's not there for any structural benefit, rather it's there as a thermal store for the UFH. it doesn't go hard, and is also known as a biscuit mix as that supposedly is the texture of it. Here's the blurb from Wunda and Continal http://wundagroup.com/wp-content/uploads/2017/02/F05T-Pug-Screed-System.pdf https://www.ufh.co.uk/system/pug-dry-mix @LA3222 Looks like I'll have to leave it a couple of weeks before laying the ply T&G flooring. What did you use to test the humidity levels? I've found this on Screwfix https://www.screwfix.com/p/htc-1-thermometer-hygrometer/2806x any good? Also what reading where you aiming for? Today was a wet day and house was very dry with the inside temp being 19-20° according to the little UFH manifold temperature gauges I left in a couple of rooms that had already had their pipe laid. Link to comment Share on other sites More sharing options...
saveasteading Posted September 27, 2021 Share Posted September 27, 2021 ok, I had not understood the context. So your floor will bear on the joists and does not sit on the screed. The screed mix was dry and is basically sand. You can put your floor down any time. I had no idea a hygrometer was £15. In my experience they are a closed box, sealed to the floor, and costs hundreds. Play with it if it if you wish: could be fun. Link to comment Share on other sites More sharing options...
LA3222 Posted September 27, 2021 Share Posted September 27, 2021 1 hour ago, vala said: @saveasteading the mix is definitely done dry. it's not there for any structural benefit, rather it's there as a thermal store for the UFH. it doesn't go hard, and is also known as a biscuit mix as that supposedly is the texture of it. Here's the blurb from Wunda and Continal http://wundagroup.com/wp-content/uploads/2017/02/F05T-Pug-Screed-System.pdf https://www.ufh.co.uk/system/pug-dry-mix @LA3222 Looks like I'll have to leave it a couple of weeks before laying the ply T&G flooring. What did you use to test the humidity levels? I've found this on Screwfix https://www.screwfix.com/p/htc-1-thermometer-hygrometer/2806x any good? Also what reading where you aiming for? Today was a wet day and house was very dry with the inside temp being 19-20° according to the little UFH manifold temperature gauges I left in a couple of rooms that had already had their pipe laid. That's similar to what I have. My house was sat around 50% humidity iirc for a long time, went up to 60s/70s soni just ran the dehumidifiers for a couple of weeks until it dropped back down to the 50s. It looked dry after couple of days. The colour change over the course of a couple of weeks showed it wasn't truly dry. If you put a moisture resistant surface down on top the last thing you want to do is trap any residual moisture in between. I had plenty of stuff to do somleaving that for a couple of weeks didn't bother me - I felt better err on the side of caution. 1 Link to comment Share on other sites More sharing options...
vala Posted September 27, 2021 Author Share Posted September 27, 2021 @saveasteading thats exactly it. Near enough all sand. It's mixed 8:1 and tbh I don't know exactly what the cement actually does in this mix. @LA3222 I'll get that hydrometer in the morning and see what the readings are. Plan is to install the pug mix from Weds so I'll keep an eye as to what there doing and just wait till it gets back to what the reading is tomorrow. Link to comment Share on other sites More sharing options...
LA3222 Posted September 28, 2021 Share Posted September 28, 2021 You'll be surprised how hard it goes. I did exactly the same mix, builders sand in a bulk bag has shit loads of moisture in it. Even at that week a mix the floor goes rock hard. Link to comment Share on other sites More sharing options...
vala Posted September 28, 2021 Author Share Posted September 28, 2021 @LA3222 interesting to know. I got that hydrometer this morning and have left it on the landing and currently for the last few hours it's saying 16° and 60% humidity. Sand got delivered this morning and I'll start laying it from tomorrow. I'll keep an eye on the hydrometer and take note of how much it rises and when it falls. Link to comment Share on other sites More sharing options...
saveasteading Posted September 28, 2021 Share Posted September 28, 2021 14 hours ago, vala said: what the cement actually does in this mix. Keeps the sand manageable and not running through gaps like an egg-timer to the room below. Links the grains of sand and heat transfer will be much better, ie absorbs more heat to release later, and spreads it better. Fills between the grains and gives you extra density. All important things. Link to comment Share on other sites More sharing options...
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