Suspended timber floor insulation + floorboard restoration questions

[prodical]

In about 3 weeks I will be lifting up all the existing pine floorboards in order to add insulation between the joists (using the system devised by ecological building systems). So this is a great opportunity to restore & repair the existing pine flooring which is looking rather crap. Photos don't do it the misjustice it deserves.






My initial plan was to run all the lengths through a thicknesser/planer. BUT, I lifted 2 boards this week and measured their thickness, they are only 15mm (ish). If I was to plane or sand these it would make them even thinner. In fact, if I put all my weight on some boards they flex in between the joists.

Question 1: Are these boards a total no go and need full replacement? What is the minimum thickness before I start restoration so I know which are no good?

Question 2: I would have liked to place all the boards back down with zero gap between them, but despite their age this is probably a bad idea. Would a 3mm gap between boards be sufficient for seasonal expansion contraction?

Question 3: Screw recommendations! Ive decided to go with screws, but I don't like the famous SPAX flooring screws as they are silver and their head is rather wide. Would Tongue-tite TX screws be suitable? Would they have enough purchase on the soft pine? I like how their heads are narrower so can be burried/ hidden easier.

Question 3a: Would screwing through existing nail holes be a no go?

 

[Toby Newell]

Question 1: Are these boards a total no go and need full replacement? What is the minimum thickness before I start restoration so I know which are no good?

It's up to you. Personally I never sand 15mm floors with a walk around belt sander. You can sand with a hand sander but you have worm and the iron stains indicate your floor has been very damp at some point. The fact that your boards feel springy means I would not sand this floor. The only 15mm floors I do start from Georgian wide board ones where I often strengthen them by lifting and glueing 6mm or 9mm ply to the back. You can do this to any age. I also bridge weak boards with ply accross to adjacent boards or fit noggins.

Question 2: I would have liked to place all the boards back down with zero gap between them, but despite their age this is probably a bad idea. Would a 3mm gap between boards be sufficient for seasonal expansion contraction?

Why is it a bad idea? You don't need individual expansion gaps, just cumulative ones at walls. If you are doing the work now boards will be at maxima so you would have the reverse problem, ie shrinkage gaps in winter (especially if you have central heating) If you are doing work in winter with CH full on and you don't intend filling then you can leave 1.5mm gaps for summer expansion.

Question 3: Screw recommendations! Ive decided to go with screws, but I don't like the famous SPAX flooring screws as they are silver and their head is rather wide. Would Tongue-tite TX screws be suitable? Would they have enough purchase on the soft pine? I like how their heads are narrower so can be burried/ hidden easier.

I've used tens of thousands of tongue tite, Spax do the same screws that are better, Spax Wirox 3.5 x 55mm T10, plus you get a free T star plus bit. I am probably up to 100k with these screw types now, being an early adopter, they are fine on sound wood and have equal or better holding power than a 2 inch cut floor nail. You will still need to use some bigger screws in places if you have rot / worm. I go 3.5mm, then Spax 4.5x60mm decking screws with minimised head, then Spax 4.5 x something with larger head. The 4.5x60 flooring screws are ok for board damage but if you have weak areas in your joist you may need to go up to 70, 80 or 90mm.

Question 3a: Would screwing through existing nail holes be a no go?

Yes. Unless you used massive 8mm sized screws, the 3.5mm's will simply go straight through!

My initial plan was to run all the lengths through a thicknesser/planer

Would not work anyway, you would be left with terrible planer marks which would need sanding afterwards and planing would take more off compared to sanding alone.

 

[prodical]

Why is it a bad idea? You don't need individual expansion gaps, just cumulative ones at walls. If you are doing the work now boards will be at maxima so you would have the reverse problem, ie shrinkage gaps in winter (especially if you have central heating) If you are doing work in winter with CH full on and you don't intend filling then you can leave 1.5mm gaps for summer expansion.

I figured leaving zero gap could cause tenting/ protruding. But I will indeed be doing this job in summer and I refer to the look of minimal or no gap so will just leave sufficient gap at the walls. Thanks

I've used tens of thousands of tongue tite, Spax do the same screws that are better, Spax Wirox 3.5 x 55mm T10, plus you get a free T star plus bit. I am probably up to 100k with these screw types now, being an early adopter, they are fine on sound wood and have equal or better holding power than a 2 inch cut floor nail. You will still need to use some bigger screws in places if you have rot / worm. I go 3.5mm, then Spax 4.5x60mm decking screws with minimised head, then Spax 4.5 x something with larger head. The 4.5x60 flooring screws are ok for board damage but if you have weak areas in your joist you may need to go up to 70, 80 or 90mm.

Just to confirm, are these the same Spax Wirox 3.5x45? You also mentioned 55mm was it a typo? I just felt the gold/ brass colour of the tongue tite would hide better against the wood colour. But if sunk below the surface I guess it wont be a concern.

Yes. Unless you used massive 8mm sized screws, the 3.5mm's will simply go straight through!

So in this case if you had boards with old nail holes, would you put your screws right next to them or would you put them as far away as possible? Far away may make the board look too busy with holes. Right next to them might again look too messy.. hmmm.



Thanks for the detailed reply! It sounds like most if not all of my boards will not be suitable and I will probably be purchasing all "new" reclaimed boards. And I'll ditch the planer idea then

 

[Toby Newell]

Never any need to leave individual gaps if your floor is acclimatised, just leave 15mm at each edge, you only need 5mm or less at each end, expansion is lateral.

Your boards don't seem overly wonderful but then 'new' reclaimed boards of similar age, albeit 20mm thick, will cost you about £80 sqm, plus delivery, plus wastage and they might have worm, rot or heavy iron staining. If some of your boards feel firm then leave those, the wormy or otherwise springy ones just bridge underneath with quality ply, 6mm or 9mm. I use MS hybrid adhesive, Everbuild (Sika) Multi Stick, 3C Max Bond cartridges or Wakol MS262 foil sausages, you should be able to save pretty much your entire floor. It might be more work but cheaper and you will retain originality.

The 45mms I was using on a reclaimed floor fit with ply underneath, I normally use the 55mm as standard but not much in it, just a little extra purchase. But yes, the link is correct, just get the 50 or 55mm ones if you can.

Neither. I screw next to the nail holes. You won't see much of the head, you should sink them 3mm below the surface and fill them.

I can post a photo tmoro, Im going back to the reclaimed pine floor I just fitted using about 1300 of the 45mm's.

I will fill it after the painters have been before I do final sanding.

 

[prodical]

Your boards don't seem overly wonderful but then 'new' reclaimed boards of similar age, albeit 20mm thick, will cost you about £80 sqm, plus delivery, plus wastage and they might have worm, rot or heavy iron staining. If some of your boards feel firm then leave those, the wormy or otherwise springy ones just bridge underneath with quality ply, 6mm or 9mm. I use MS hybrid adhesive, Everbuild (Sika) Multi Stick, 3C Max Bond cartridges or Wakol MS262 foil sausages, you should be able to save pretty much your entire floor. It might be more work but cheaper and you will retain originality.

I have 2 local places doing 145mm x 18mm pine or spruce floorboards, one is £35 the other is £45 per square metre. They are de-nailed and ends trimmed but will need sanding obviously. I am planning a trip to each site to look at their stock and might opt for wider boards depending on price. But I also like the original look of 145mm width. I will for sure be keeping as many of my original boards as I can but many have worm or are too thin. I'm also up against the clock, I've booked off 2 weeks to get the insulation and flooring done across 30m2 and I'll be working alone for majority. I'll likely opt for new boards for speed, over re-enforcing old thin ones.

Neither. I screw next to the nail holes. You won't see much of the head, you should sink them 3mm below the surface and fill them.

Do you fill them with a polyurethane glue + saw dust, or do you use an off the shelf product?

 

[Toby Newell]

£35 sqm, reclaimed floorboards? Interesting. Normally only ex scaffold planks at that price. Two weeks? Good luck! Be careful removing the boards and nails.

Guide to Wood Floor Sanding - NEWELL FLOOR SANDING & WOOD RESTORATION

“You should take the approach that you are wrong. Your goal is to be less wrong” Elon Musk These DIY guides were originally written in 2006 and are amended when I get the chance. These pages remain by far my most visited. As mainly a one man operation I do not have the funds to ... Read more

newellwoodworks.co.uk

^^^ The most detailed guide to sanding wooden floors, includes lifting, filling etc. Mmm never glue boards, will restrict movement. I use Lecol 7500 and clean sieved sawdust.

 

[prodical]

£35 sqm, reclaimed floorboards? Interesting. Normally only ex scaffold planks at that price. Two weeks? Good luck! Be careful removing the boards and nails.

Yeah £35 per m2 from Monkswood flooring, his ebay listing here. If I bought from him I would be asking to look through his stock so I can pick good boards. The other place selling for £45m2 was recommended to me by the local wood recycling centre who are very good guys.

Does it seem dodgy?

I also just got a quote of £900 for sanding and finishing 27m2. That was higher than expected haha. Your guide looks fantastic and I will be studying that if I decide to try this part myself.

 

[fernicarry]

using the system devised by ecological building systems).

That’s a pretty decent guide. Particularly the focus on airtightness around the perimeter. Only thing I’d do differently is change the top layer to a breather membrane instead of a VCL.

I’ve just done a mini version of this in a room where I had to remove some of the skirtings and boards. Membrane on top of the joists, lapped up onto the wall secured with air tight tape.

A few practical things to consider. Where ever a board goes under an internal wall you’ll need to cut it and that could leave the wall with little or no support. Some boards here were replaced when the joist ends were repaired leaving a few wall studs floating in thin air. Predictably that’s allowed movement with gaps opening up where the internal walls meet external. Another consideration is that your joist spacings probably aren’t all perfectly equal so unless a board goes back in exactly the same position the nail holes won’t line up any more. Similarly reclaimed boards unless they were secret nailed.

If you have the access to do the work from below that’s preferred. It’s not a pleasant task but you’ll cause far less damage.

 

[Toby Newell]

Yeah £35 per m2 from Monkswood flooring, his ebay listing here. If I bought from him I would be asking to look through his stock so I can pick good boards. The other place selling for £45m2 was recommended to me by the local wood recycling centre who are very good guys.

Does it seem dodgy?

I also just got a quote of £900 for sanding and finishing 27m2. That was higher than expected haha. Your guide looks fantastic and I will be studying that if I decide to try this part myself.

Mmm, mix of scaffold planks and resawn beams, not many actual 'floor boards' in the photos. Last time I bought period pine boards for £35 was over a decade ago, so yea, kinda dodgy as per 95% of business listings for the same on ebay. FYI you don't 'trim the ends' unless you are selling scaffold planks, you can see in one photo where they left the end, there is a rowof nails where the tin protector strip was fixed.

mmm, £30 sqm, well, that was my price 25 years ago. Depending on the amount of filling, repairs, staining, colour matching etc that's minimum 3 to 6 days for me. Assuming you fitted 15mm shims to your existing to match your 30mm scaffold planks, then probably about £2,500 to £3,000 for me, as probably quite a lot of colour matching.

£900 would just about cover my overheads and materials. But then I do a colour matched 4 or 5 coat process with double filling, 4 or 5 days. Your £900 dudes will be in and out in 2 days, probs one and a half and will probably quote 2 coats of Osmo oil or similar. My quote would normally be 1x / 2x shellac coats, tinted as required + 2x lacquer, Junckers Strong, Bona Mega, Loba Viva or Traffic HD (with extra Primer UX coat - extra cost)

£900 is low end so I would set your expectations accordingly, expect filler loss and visible sanding marks, I advise clear coat only as the possibility of them staining or colour matching at that price is roughly zero.

 

[prodical]

That’s a pretty decent guide. Particularly the focus on airtightness around the perimeter. Only thing I’d do differently is change the top layer to a breather membrane instead of a VCL.

I think the idea of the VCL layer on top is it lets the insulation breathe via the suspended timber floor, and prevents moisture from reaching the floorboards. I guess its good to have the entire system be breathable, afterall thats how the victorians designed the suspended floor. But with the use of a breathable natural insulation that moisture element can be contained to below with the breathable insulation+ the breathable membrane. In all honesty, I think both methods would be perfectly ok!

A few practical things to consider. Where ever a board goes under an internal wall you’ll need to cut it and that could leave the wall with little or no support. Some boards here were replaced when the joist ends were repaired leaving a few wall studs floating in thin air. Predictably that’s allowed movement with gaps opening up where the internal walls meet external. Another consideration is that your joist spacings probably aren’t all perfectly equal so unless a board goes back in exactly the same position the nail holes won’t line up any more. Similarly reclaimed boards unless they were secret nailed.

This is a slight concern of mine. Also the stairs, currently sitting on floorboards and I believe partially over a sleeper wall. The joist spacing is all over the shop yeah, variances of up to 6cm which would mean screwing into new areas and filling the old holes.

If you have the access to do the work from below that’s preferred. It’s not a pleasant task but you’ll cause far less damage.

I cut a hole and did a reccy at the weekend to inspect the joists... screw doing that job from underneath!! would be night on impossible haha.

 

[prodical]

Mmm, mix of scaffold planks and resawn beams, not many actual 'floor boards' in the photos. Last time I bought period pine boards for £35 was over a decade ago, so yea, kinda dodgy as per 95% of business listings for the same on ebay. FYI you don't 'trim the ends' unless you are selling scaffold planks, you can see in one photo where they left the end, there is a rowof nails where the tin protector strip was fixed.

mmm, £30 sqm, well, that was my price 25 years ago. Depending on the amount of filling, repairs, staining, colour matching etc that's minimum 3 to 6 days for me. Assuming you fitted 15mm shims to your existing to match your 30mm scaffold planks, then probably about £2,500 to £3,000 for me, as probably quite a lot of colour matching.

£900 would just about cover my overheads and materials. But then I do a colour matched 4 or 5 coat process with double filling, 4 or 5 days. Your £900 dudes will be in and out in 2 days, probs one and a half and will probably quote 2 coats of Osmo oil or similar. My quote would normally be 1x / 2x shellac coats, tinted as required + 2x lacquer, Junckers Strong, Bona Mega, Loba Viva or Traffic HD (with extra Primer UX coat - extra cost)

£900 is low end so I would set your expectations accordingly, expect filler loss and visible sanding marks, I advise clear coat only as the possibility of them staining or colour matching at that price is roughly zero.

Yeah, you've got me rightly doubting the entire thing now lol. And I don't feel comfortable doing the sanding and finishing work myself, just far too many ways I can cock it up. But yeah I need to reset my expectations. Ive got 2 or 3 more quotes incoming so I'm interested to see what they say.

May yet end up taking an entirely different direction on this!

 

[Toby Newell]

Yeah, you've got me rightly doubting the entire thing now lol. And I don't feel comfortable doing the sanding and finishing work myself, just far too many ways I can cock it up. But yeah I need to reset my expectations. Ive got 2 or 3 more quotes incoming so I'm interested to see what they say.

May yet end up taking an entirely different direction on this!

All the quotes will be similar. Especially since the Bulgarian who owns Floor 'Something' Experts had 22 websites, at my last count, and floods the top google places Ask me (ex position 1 and 2 in the world for 'Floor Sanding' and 'Floor Sanding London') how I know...

If you have just two weeks to do what you said, I would struggle to do that in that time and I have a few decades headstart.

But to be honest, unless you are a total gorilla, if you follow my guides I am almost certain you would cock it up less than 99% of the floor sanding industry and I would fully expect you to do a better job.

 

[Toby Newell]

^^^ primarily because you would have more dilligence and 99% of the industry don't give two craps.

 

[fernicarry]

I think the idea of the VCL layer on top is it lets the insulation breathe via the suspended timber floor, and prevents moisture from reaching the floorboards. I guess its good to have the entire system be breathable, afterall thats how the victorians designed the suspended floor.

The VCL is borrowed from modern methods where you try to make the habitable space moisture tight to avoid any migration of moisture from inside into the fabric of the building where it could cause interstitial condensation due to the high level of insulation. Moisture is instead removed using some sort of planned ventilation.

Traditional buildings rely much more on unplanned ventilation through gaps in the fabric as well as the fabric itself being vapour open and not having much insulation value. We try not to upset that too much with our interventions. Deliberately using a material that blocks vapour seems to go against that and could have unintended consequences down the line but really depends on how far towards a modern build up you intend going.

I think at the end of the day the air tightness is the biggest benefit from this exercise. I’ve partially insulated my ground floor from below but mostly I’ve just stapled a breather membrane under the floorboards and that’s made a noticeable difference. Obviously if you are going to the trouble of lifting the floor then you might as well put insulation in too.

 

[Toby Newell]

VCL is an over complication the main issue with suspended floors is the force nine gale coming up between the gaps, filling them vastly increases heat retention. The actual insulation doesn't do that much as wood is quite a poor conductor. Putting metal foil on the underside reduces the emission as wood is a great emitter, but then any foil is a condensation magnet. In general draught control increases thermal comfort on ground floors and insulation works more efficiently the higher up you go. If you want to test this, pop up to your loft or attic right now. Its prolly quite a bit warmer than downstairs.