My tent groundsheet is damp under my sleeping pad, dry pitch but rained at night. Don’t think it’s condensation. Is it just the case that groundsheet needs reproofed?
If so what with?
Do you mean "groundsheet" to mean "tent floor" or "independent sheet that goes under the tent to protect tent floor"?
Sounds like your weight effectively increased the hydrostatic head on the water pushing it though. Is it a lighteweight? Personally I always take a section of thin pvc type plastic (last bit was some of the packaging from a mattress) to lay as a footprint to protect the door on my (lightweight) tent.
Yes tent floor and not super lightweight. Vango Mirage so 70D I think
I would expect that to be condensation.
Most probably condensation; the sleeping mat effectively isolates that bit of the ground sheet and so condensation collects there.
I had in a 3 man tent in Scotland in the winter using a hot air heater; the bit under my sleeping mat was wet because it stayed cold.
Maybe not mega lightweight but not a family camping or festival camping tent was more my point.
Personally I have never had the problem described. Not sure I am in agreement unless the sleeping mat was already wet of the op is an exceptionally sweaty sleeper.
I’m not convinced it was condensation as this was the only place it happened.
Happened under the kids mats as well not just mine!
It will be condensation. I get it sometimes in my tent and other times it will stay completely dry.
Mine does it sometimes, depends on atmospheric conditions. It's condensation.
Not sure how condensation would occur under a sleeping mat in close contact with the groundsheet. There is no air circulating there for the water to come from.
Most likely the groundsheet failing. Anyway, easy to test. Pitch on properly damp ground and go in on your hands and knees. You'll soon find out if the groundsheet leaks with weight on it.
As suggested above I use lightweight plastic roughly 7ftx3ft under my tent.
I've never had condensation under the mat, but I found that no tent floor lasts more than 2 seasons, even those that say they resist 5m of hydraulic head.
Not sure how condensation would occur under a sleeping mat in close contact with the groundsheet. There is no air circulating there for the water to come from.
There is air there, and it's in contact with the cold ground under the groundsheet. The air in the tent is saturated with moisture from people breathing, sweating, damp clothing and maybe cooking. If you cool that air condensation will occur therefore you get wet bits where it's coolest...like under mats.
I've run a heater in a tent in December in Glencoe; hot air blowing through the tent. Everywhere in the tent was warm and dry despite a wee chill(!) in the air outside. The floor of the tent was wet under my bags and under the mat because condensation...
My hunch is water forced through ground sheet by pressure. It slowly got worse in my Hilleburg then stopped when they replaced the ground sheet.
Why would condensation form in one of the warmest spots on the ground sheet?
I'm not sure it is one of the warmest spots. Maybe the pressure of a person on top pushes the groundsheet down into the cold earth making it colder than the rest of the groundsheet?
I've had it a few times and I've always thought it was condensation, pretty sure it's not a leaky groundsheet as I've camped in quite wet conditions and not had it happen.
Ok so I put tent up in the garden last night, I’m in NI so was around 20 degrees in the evening and dropped to about 13 overnight.
I left a normal roll mat and a self inflating in the tent overnight, I didn’t sleep in it, and both were damp underneath.
Also when I kneeled directly on groundsheet it was definitely damp inside on the area under pressure. So do I need to proof the groundsheet or do I need a replacement?
As above. Thin plastic sheet. A cheap shower curtain cut to size works.
I've read of people using this stuff but can't comment from personal experience.
https://www.amazon.co.uk/Plasti-Dip-Multi-Purpose-Rubber-Coating/dp/B0006SU3QW
Proofing doesn't usually restore the hydrostatic head. It just help water run off. I'd cut out a water proof sheet as above