Laminate on top of Celotex

[Daniel123]

I am going to replace an old carpet with laminate downstairs. The plan is to put some insulation under the laminate as otherwise the floor will be really cold. I will end up with the following layers:

Laminate 10 or 12mm thick
Celotex TB4025 insulation -- 25mm thick (would love to have more but can't sacrifice too much ceiling height and don't want to change external doors)
Damp Proof Membrane
Concrete floor

endecotp advised me in another thread that that one is supposed to put tongue and groove chipboard over Celotex, but my hope is that good thick laminate is strong enough to distribute the load. My very informal reasoning is as follows. Celotex has compression strength >120kPa. If my laminate can distribute a point load across 200x200mm square (just an assumption) then it will hold 4800 N -- probably enough for domestic use. At this load, 25mm Celotex will compress by 10%, i.e. 2.5mm which is OK for laminate.

Do you think this makes sense? Also, is Celotex designed to be compressed regularly (as opposed to being compressed once and stay like that forever)? I found that XPS boards are significantly stronger but they are more expensive and have higher thermal conductivity.

Any thoughts would be appreciated!

 

[cjard]

In my experience, celotex doesn't exactly compress regularly. Regards is some elastic deformation but also some plastic.. try it for yourself in BnQ; get a sheet off the shelf and stand on it. You'll see the shoe mark retained. Other brands are less affected, but all in this shouldn't affect your plans. I too reason that a thick locked-together laminate will bear onto celotex adequately. I would probably go for engineeed wood though, slightly thicker and not much of a price jump

 

[Dan Robinson]

Wouldn't try it personally.

 

[Daniel123]

In my experience, celotex doesn't exactly compress regularly. Regards is some elastic deformation but also some plastic.. try it for yourself in BnQ; get a sheet off the shelf and stand on it. You'll see the shoe mark retained. Other brands are less affected, but all in this shouldn't affect your plans.

Thank you cjard, what other brands would you recommend that have smaller elastic deformation?

I am not worried that Celotex will shrink after the first attempt to compress it (indeed, laminate will massively reduce the pressure), but I am not sure what will happen after 10000 attempts... Not something I can easily check in B&Q

Engineered wood is an option, though I am going to have it in the kitchen too, and I guess good laminate is more water resistant.

 

[Tigercubrider]

could you fit thin ply or mdf over the celotex before the laminate?

my worry would be cracks forming along the weak points of the laminate joins. The thin material might mitigate that?
I helped build a floating floor on 1" (maybe 2") rock wool and used flooring chipboard that we glued together as we went.

 

[dazlight]

Have a look on the QA Products underlay website. Might help.

 

[Daniel123]

could you fit thin ply or mdf over the celotex before the laminate?

my worry would be cracks forming along the weak points of the laminate joins. The thin material might mitigate that?
I helped build a floating floor on 1" (maybe 2") rock wool and used flooring chipboard that we glued together as we went.

Thank you Tigercubrider, I see your point, and thin ply would help indeed. I am still worried though about plaster deformation. I went to B&Q as cjard suggested to see how Celotex feels; it will probably hold enough load if distributed well but I am afraid that it will compress after numerous applications of weight.

Have a look on the QA Products underlay website. Might help.

Thank you dazlight, I checked various underlays. I like the idea because these materials are designed to be placed under laminate. Most of the fibreboard underlays however are only 5mm thick; I could potentially put three layers but then the overall compression might be too high?

I found Warmup Insulation Boards (details here) which is designed for underfloor heating but is placed above subfloor so does not need any further load distribution. Its compressive strength is 300 kPa -- much stronger than Celotex. Thermal conductivity is higher but better than nothing. The only problem with it is the price; the cheapest I found so far is about £23.5 per sq. m.! Are you aware of any cheaper alternatives?

 

[Tigercubrider]

I know that there's are discount places that sell damaged or part order insulation ?
Maybe a way to find a cheaper solution

 

[bobsuerita]

just go for real wood or egineered flooring with therma foil under lay wood is alot warmer than laminate

 

[endecotp]

I found Warmup Insulation Boards (details here) which is designed for underfloor heating but is placed above subfloor so does not need any further load distribution. Its compressive strength is 300 kPa -- much stronger than Celotex. Thermal conductivity is higher but better than nothing. The only problem with it is the price; the cheapest I found so far is about £23.5 per sq. m.! Are you aware of any cheaper alternatives?

That's similar to Marmox Multiboard, which one online retailer is selling for £43 for six 600x1250 boards, plus delivery.

 

[Daniel123]

I know that there's are discount places that sell damaged or part order insulation ?
Maybe a way to find a cheaper solution

Will definitely try once I converge to some solution.

just go for real wood or egineered flooring with therma foil under lay wood is alot warmer than laminate

As far as I understand, the flooring itself (laminate, wood, etc.) gives virtually no thermal insulation. Hence it's all up to the underlay, and 5-7mm underlay cannot give any reasonable insulation.

That's similar to Marmox Multiboard, which one online retailer is selling for £43 for six 600x1250 boards, plus delivery.

Thank you, this sounds like a good solution. However, the best price I found for 20mm was £49 for 5 boards (3.5 sq. m.) which is a bit too much for me...


I found out that a few products designed as laminate underlays have compressive strength around 100-150kPa, i.e. quite modest (Celotex is 120kPa). They don't even specify how thick the laminate has to be, hence they don't see this as a problem. From this I conclude that even if my insulation will be considerably thicker (15 or 25mm), 12mm laminate might be able to cope with this. The two more reliable options I am considering are:

1. 5.5 or 9mm plywood over Celotex (or some other insulation board), and then 8mm laminate. This should provide the necessary support to the joins.

2. Three layers of some relatively cheap laminate underlay, 5-7mm thick each layer.

Any thoughts?

 

[endecotp]

I found out that a few products designed as laminate underlays have compressive strength around 100-150kPa, i.e. quite modest (Celotex is 120kPa)

The other factor is the thickness of the material.
I think that those deformation pressures are normally specified for 10% deformation.
10% of a 5mm underlay board is half a mm which the laminate will cope with, but 10% of 100mm of celotex is 1cm, which it won't. I don't know how far I'd be happy to go between those extremes.

 

[Daniel123]

The other factor is the thickness of the material.
I think that those deformation pressures are normally specified for 10% deformation.
10% of a 5mm underlay board is half a mm which the laminate will cope with, but 10% of 100mm of celotex is 1cm, which it won't. I don't know how far I'd be happy to go between those extremes.

It is indeed at 10% deformation, which is why I am worried, and which is why I am thinking of some stronger laminate. And it is exactly my problem that I don't know how much does the thicker laminate compensate for reduced support.

 

[Daniel123]

Thank you again for all your advice. I decided not to risk and ordered 7mm fibreboard underlay and 10mm laminate. I understand this will not be very warm but at least I am not going against standard practices.

 

[Doggit]

Actually, the problem isn't the underlay, it's going to be the laminate. If you put 5mm fibreboard on a concrete floor, you'll find you can stand on it quite happily. Laminate on the other hand, is always going to be cold, as although it's made of MDF, the top is plastic, and is always cold to the feet, and a room with laminate, always takes longer to warm up.

But I'm surprised you feel the XPS boards are expensive; if you check them on ebay, they're quite cheap.

But you can pick up 14mm engineered wood on ebay for about £25 a sqm, and as wood is warm, you can get away with a cheap underlay.