Looking for advice on underlay please

I'm having a carpet fitted next week and I've decided to fit my own underlay to save cash. To be honest I'm a bit confused over the choice of construction and I'm trying to find out the pros and cons of 'traditional' rubber waffle, compared to the newer PU products.
I can find both products in the same thickness with very similar tog and impact sound reduction values, so given this fact what else is there to consider? (Apart from price as the PU products appear cheaper on a like for like basis).
Thanks
http://www.tradepriced.co.uk/tredaire_carpet_underlay.html
http://www.tradepriced.co.uk/tredaireapt_carpet_underlay.html
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IMNSHO PU any day of the week.
I fitted 12mm PU recently and it was perhaps over thick so the 8mm you linked to appears ideal.
I got ours from the site you linked to based on price and was very happy with the service. Get the grippers there too, we got a bulk box cheaply from their special offers section and they're fine but now have to store the excess which appears enough to fully carpet all the houses in our extended family.
Grippers go half an inch from the skirting, then lay the underlay inside. I used plenty of long staples from a staple gun to secure the underlay and gaffa taped the seams just to be sure, a very straightforward job.
Make sure you have plenty new sharp trimming (stanley) knife blades for cutting the underlay, they don't stay sharp long.
--
fred
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All the existing rubber waffle underlay in my house is 'loose laid', ie not stuck or stapled down. Why is PU different? If I understand you correctly PU has to be fixed down?

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I didn't say it had to be fixed down but I think it is better practice. If you are moving heavy furniture around [1] it means that the underlay will stay put without risk of it walking under the carpet. The risk is slight but it would be a PITA fix if it did happen and the extra effort is minimal.
[1] or have kids running wild around the around the house
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fred
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PU underlay does suffer compression set as with all polyurethane foams, probably 25%. So the extra thickness does tend to diminish a little over time (weight of carpet is not inconsiderable).
The only real downside with thick PU underlay is the "bounce" with furniture that has large load spreading feet. In this instance the furniture will "rock" on the underlay as it is not rigid. With furniture that has small feet it will show deep pressure indents. Rubber underlay has better recovery than PU and lower compression set, so does not suffer these downsides.
The benefit of PU is actually thermal insulation, last time I looked the really thick stuff was about 30-50% higher TOG rating which can be really beneficial if you have solid uninsulated floors (or uninsulated ventilated wooden floors with a howling gale blowing under them). It can stop the "aching calves" from cold in older houses etc.
Some say use the thickest PU for bedrooms, thinner for elsewhere. The thickest PU can lift carpet away from the grippers, but proper stretching overcomes this - PU does soon drop back a bit after a few months.
Rubber waffle & crumb do perish and breakup over time, rubber crumb CAN suffer compression set with high load - it basically turns into a "depression" which is unpleasant to walk on and somewhat hard. So it is not true that they outlast the carpet where someone "sits in the same place or walks a corridor in the carpet".
Never nail wooden backed carpet grippers into asphalt covered floors, it breaks up the surface which is often your only damp course. Not so much a problem re damp usually, it is just a mess that is time consuming to fix. Instead use a polyurethane spray adhesive, gripfill or such like. Not much will stick to asphalt so you can still get them up eventually.
PU underlay comes in "quiet" (no paper) and standard versions. Last I used was Tredaire Dreamwalk for my mother's and it made a bitterly cold floor tolerable, no "calf ache" and it gets all the cold air "traffic" to a radiant gas fire. To reduce the drawing cold air through the entire house (and thus chilling the floors) a colleague is "piloting" a baffled-vent with external pre-heater. Really need a 2008 winter to test it properly though.
If your floors are cold, getting the highest TOG does help. I'm surprised we haven't done a closed-cell polyethylene based carpet underlay, that feels noticeably warmer to the touch than polyurethane, not checked their thermal conductivity figures or compression set.
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On Wed, 09 Dec 2009 17:54:24 +0000, BodgeIt wrote:

This is a bit of an FAQ, is it in the FAQ or Wiki?
http://www.diyfaq.org.uk http://wiki.diyfaq.org.uk
Most people in here prefer the PU products. I'm very happy with the bedrooms I've done with 10mm (I think) Cloud 9. I've cleaned up enough times after the rubber crumb stuff has turned to black dust to not want to fit the stuff myself.
--
Cheers
Dave.




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