Original floorboard sealing ?

Poppy9

Sanding back original floorboards on 1930s house.  How can I stop draughts coming up from underneath.  

Ebe_Scrooge

You can't :-)

I'm assuming you're wanting the floorboards to remain exposed?  There's a limit to what you can do without spoiling the look, unfortunately.  The simplest option is to put down a rug to cover the largest gaps.  An alternative is to stuff the gaps with damp newspaper, leaving it slightly below the level of the boards.  Then mix up some PVA wood glue and sawdust, use that to finish off the gaps.  The problem is, you'll never get a perfect colour match.  It's usually a trade-off between retaining the original look, or stopping the draughts - you can't have both.

It's worth checking underneath, see if you can reduce the amount of draughts coming in in the first place.  But you can't completely seal it all off, you need some airflow to stop damp and mould.

FreeBear

Ebe_Scrooge said: An alternative is to stuff the gaps with damp newspaper, leaving it slightly below the level of the boards.  Then mix up some PVA wood glue and sawdust, use that to finish off the gaps. 

String, plumbers hemp/flax, or draught excluder foam would all do the trick. But first, check that the boards aren't tongue & groove - Building regs (such as they were back then) had been specifying T&G boards on the ground floor in many areas.

It is also worth plugging the gap between skirting board and floorboards - If your house is anything like mine, that is (was) the main source of draughts coming up through the floor.

Rural_Puppy

How feasible is it to insulate under the floorboards? We had a similar age of house, and there was a sufficient crawl space under the floor to install insulation between the joists. Not a pleasant job though!

FreeBear

Rural_Puppy said: How feasible is it to insulate under the floorboards? We had a similar age of house, and there was a sufficient crawl space under the floor to install insulation between the joists. Not a pleasant job though!

To do the job properly without missing bits, the floorboards should really be lifted. Realistically, that means skirting boards off, and major hassle around the stairs. You also have to be very careful not to block air flow over any dwarf walls or air bricks. Whilst it may appear easy to crawl around under the floor, you'll quickly find it isn't.

If it is anything like my 1929 built house, the most you could get in the way of insulation would be 25mm of Celotex/Kingspan - 3x2 joists, 25mm of insulation, and battens nailed to the joists to stop the insulation from dropping. That would leave 50mm for air to circulate over any dwarf walls. But 25mm of insulation would only give you half the required thermal performance needed for building regulation compliance. Going to 50mm would get you much closer, but would restrict the air flow under the floor.

Plugging the draughts is a low cost fix that will save energy. Insulating under the floor is expensive and disruptive - Whilst it would seal the draughts (if done right) and save a bit more on heating costs, the pay back time will be considerably longer.

Jeepers_Creepers

Hi Poppy.

Will the 'boards receive clear varnish or a stain? 

I did this job in our last house and we finished the floors with a mid-oak stain. I first used brown frame sealant to seal the gaps... This stuff is very cheap and I cut the nozzle to leave a neat concave bead that was below 'board surface level. When the whole floor was subsequently stained/varnished, the floor looked as you'd expect it to with slightly darker T&G groove - the use of sealant wasn't noticeable (unless you planted your nose on the floor and looked that closely). 

Probably not a solution if ta clear finish will be used. 

Poppy9

The floorboards will not be stained or varnished.  We will use this https://osmouk.com/product/polyx-oil-original/.  I put this on my solid oak wood block floor 15 years ago and it's fantastic.  (I have 1950s house with solid woodblock floors throughout so no draughts .  My daughters bought the 1930s house with suspended wooden floors downstairs that will look stunning stripped back but might be too cold as my daughter a freezer and the two living rooms have large bay windows which might  only be single under the bays though the square one becoming patio doors with new insulation but front round bay staying with the curved radiator under bay ).   Wine , food etc been spilt on my wood floors protected with this hard wax  is only now showing some slight marks from dining table chairs constantly moving on it (felt pads need replacing).  It's so easy to apply no need to be precise with brush strokes .