Best type of Celotex to use under hardwood sheets

**Pondlife** · 6 October 2014, 10:19

We had some oak flooring fitted a while back. You need a damp proof membrane if it's ground floor. We then used this. You get a roll of this black rubber which is sticky on one side. You put it in place and peel the protective film off as you lay the wood. Our builder reckoned it was a right PITA but since I didn't want to run batons to screw the floor to, we didn't have much choice.

Very happy with the result. YMMV

**OwlHoot** · 6 October 2014, 10:49

Originally posted by Pondlife View Post

We had some oak flooring fitted a while back. You need a damp proof membrane if it's ground floor. We then used this. You get a roll of this black rubber which is sticky on one side. You put it in place and peel the protective film off as you lay the wood. Our builder reckoned it was a right PITA but since I didn't want to run batons to screw the floor to, we didn't have much choice.

Very happy with the result. YMMV

Many thanks Pondy.

I'll certainly make a note of that for the wooden floor I plan in another room; but the builder insists that this Celotex is the best/only stuff to use under large hardwood sheets on a concrete floor.

Also, that Fast Fit Peel and Stick underlay page says "Must not be used with products over 150mm Wide". So I guess it would be more suitable for smaller wood tiles or narrow planks. (The hardwood sheets are monstrous great unwieldy things, about 8 by 4 feet as I recall, or possibly even larger.)

**Pondlife** · 6 October 2014, 11:00

Originally posted by OwlHoot View Post

Many thanks Pondy.

I'll certainly make a note of that for the wooden floor I plan in another room; but the builder insists that this Celotex is the best/only stuff to use under large hardwood sheets on a concrete floor.

Also, that Fast Fit Peel and Stick underlay page says "Must not be used with products over 150mm Wide". So I guess it would be more suitable for smaller wood tiles or narrow planks. (The hardwood sheets are monstrous great unwieldy things, about 8 by 4 feet as I recall, or possibly even larger.)

No probs. The flooring we had was your typical 6 inch wide stuff and so not the type you're looking at.

**vetran** · 6 October 2014, 13:11

the Celotex is to provide insulation, maybe there is a grant out there you can get?

Celotex - UK PIR Thermal Insulation Manufacturers

I would imagine there is a maximum load you can put on it (Celotex is expanded foam with sometimes foil on) so if you are moving in a grand piano you might want to check first.

**FiveTimes** · 6 October 2014, 13:32

As vetran mentioned the Celotex is being used as insulation - you can get it with a membrane on also. Another product to look at is Kingspan.

Its really easy to fit and you can cut it with a hand saw.

**OwlHoot** · 6 October 2014, 15:55

Seems there are quite a few - I also found some others, including Marmox, Alveolit, and Timbermate

But although the heat insulation is a nice to have, my main aims are a completely damp proof membrane and a rigid incompressible texture. Anything even slightly crumbly (for example that "easy to cut" stuff) or squidgy won't support the snooker table I plan to fit, or possibly even the 25 mm hardwood boards that will be overlying it.

edit: The Stego Wrap 15mm vapor barrier looks the bees knees. But it is a US product, and I can't find any reference to a UK distributor.

**jamiecelotex** · 6 October 2014, 15:56

Originally posted by OwlHoot View Post

I had a builder round on friday (not a euphemism - one really did visit) to check a dodgy partition wall that is supporting a couple tons of roof on a rotting wood frame and needs replacing by an RSJ.

Anyway, on seeing the large expanse of floor (over 1000 square feet) that I planned to screed (c.f. discussion here a couple of weeks ago Laying Smooth Concrete Floor), he reckoned I would be much better off laying something called Celotex and fitting tongue and groove 2.5cm hardwood sheets over that.

Sounds much more manageable, although I know from experience that those huge, thick sheets of hardwood are monsters to lift and carry around! So not looking forward to that aspect.

Anyone done anything like this? What kind of Celotex would be the best to use under hardwood? I imagined Celotex would be just be of one type, like Sellotape, but there seem to be literally dozens of Celotex products!

Dear OwlHoot,

Celotex can be used in your floor construction to provide an improved insulation value.

Celotex can be laid upon your concrete slab and a chipboard floating floor can be installed on top.

A damp proof membrane should be used under the insulation board. If there is already a damp proof membrane under the existing slab then you do not need to provide another one.

A 1000 gauge polythene vapour control layer should be laid on top of the insulation boards.

A minimum 18mm tongue and groove chipboard floating floor can be installed directly on to the insulation and vapour control layer. All joints should be wood glued and a 10-12 mm expansion gap should be left around the edges. Floor boards, laminate flooring or other floor covering can then be installed on top of the chipboard.

In terms of floor loadings, the boards are suitable for all domestic uses. As was pointed out, if you have any extreme loads in mind then you may need to chat to a structural engineer.

With regards to the specific Celotex products, we would recommend Celotex TB4000, Celotex GA4000 and Celotex XR4000. These are our standard multi-purpose boards and the different codes relate to the different thickness ranges available.

Celotex TB4000 12 – 45mm
Celotex GA4000 50 – 100mm
Celotex XR4000 110 – 200mm

Full details of using Celotex in this application can be found in our Specification Guide for floors, which is available from our website here: Floor insulation from Celotex

Good luck with your project!

Best wishes
Jamie

Celotex Technical Centre

**OwlHoot** · 6 October 2014, 16:29

Wow! Many thanks for your detailed reply Jamie.

Best type of Celotex to use under hardwood sheets