Help with old floorboards

[Anna Kettle]

Happy new year to you all...

I have an old oak floor which I want to extend and have bought some old oak floorboards to do this with. The extension floorboards will be purely decorative, the structural floor is already in place and made of plywood. My problem is that the plywood floor is not flat at all - it curves downwards about 10cm towards one corner of the room whereas the floorboards are reasonably flat, so somehow I need to combine the two. Ideas I have had are ...

- Wet the boards before fixing

- Fix the dry boards in place using long screws and tighten them a little more each day

- Shave the back of the boards to make them thinner and so more flexible. I dont like this idea because it is abusing nice old half inch thick boards, but if needs must ...

- Pack out the plywood floor to fit the boards. I dont like this idea at all because the plywood floor is 'right' in that it follows the shape of the timber frame

Suggestions and experiences welcome please Anna ~ ~ Anna Kettle, Suffolk, England |""""| ~ Lime plaster repair and conservation / ^^ \ // Freehand modelling in lime: overmantles, pargeting etc |____|

[dom]

10cm !!! ? You really have a floor that is meant to be flat that varies by 4 inches (in old money)?

I would go for this one. Cut up say 6mm ply into strips and use stacks of these as packings as necessary (I'm assuming that figure above is wrong). The other methods sound like recipes to make a floor that springs and bounces as you walk on it.

If you really must make the new boards follow the line of the old - then saw kerfing across the back should create some flexibility (i.e. set the depth on a circular saw appropriately and cut across the backs of the boards at regular spacings).

Another (somewhat involved) alternative is steam bending, if you're willing to build a suitable steamer and steam box:

you really must

[Owain]

Do you mean 4" in height difference, or level until 4" from the wall?

How about packing between the plywood and the boards so that the boards are level, but leaving a gap at the sinking end so the floor is visually 'floating' separate from the timber frame?

Owain

[Roger Mills]

As someone else has said, 10cm is a *hell* of a lot of unflatness!

Would it help if you laid the boards at right angles to your originally intended direction - so that the curve is across the joints rather than along the length of the boards? [Or maybe it's as broad as is it long, so to speak?]

[Anna Kettle]

Yes. Thats one of the joys of a 500 year old timber frame house

What spacing and how deep a cut?

diyfaq says that it is possible to oversteam. I am imagining the outside oversteamed and the interior untouched. I've never done any steaming though so I could be wrong

Anna

[Anna Kettle]

4" in height difference

Am thinking about that idea ... not sure yet if I like it

Anna

[Anna Kettle]

That doesnt help unfortunately. The dip is in a corner

Anna

[dom]

Experiment on a scrap piece.

Obviously the deeper the cut and the closer together the cuts, the greater the flexibility. Lots of shallower cuts is better than a few deep. And you only need to kerf the boards in the region where you need flex.

Try on a piece of scrap cutting 3/4 of the way through at 1 inch spacings and see if that will flex around the most difficult part of the floor.

Remember though that you're removing most of the structural strength of the boards in the region of the kerf cuts and relying on plywood below.

Again experiment with the least good board you have. Steam it for an hour and see what results you get. I was taught how to do this for boatbuilding, but I've only done it with relatively light boards on dinghies. To be honest it would be complete overkill for domestic floorlaying - but you sound like a maniac that might be persuaded to try.

[Roger Mills]

In that case, if you're not relying on the boards for structural strength ('cos that's provided by the ply) could you achieve the necessary curvature by using a lot of short boards (effectively in straight line segments) and then sanding them into a curve where they join? [You could cut the boards at a slight angle so that they contact each other at the top surface.]

This method would help in the other dimension too because, from what you say, long boards would have to twist as well as bend.

[The Natural Philosopher]

If you *want* a wonky floor, do that. Wood is flexible and the pressure a screw can exert is massive.

NEVER WET OAK. it stains terribly.

I'd simply screw it down and plug he holes with oak plugs.

Half inch is very flexible.

.

Your choice..

[mail]

Dear Anna GOOD FOR YOU! You understand how to respect an old building. I have never done this but working from first principles and knowing just how you lost the 4" in the first place, I would use the same phenomenon to acheive your desired effect.

My advice is to use a phenomenon called "duration of load effect". It is best done if the wood is (steamed or ) wet and I do note other advice about staining so you will have to decide between the two evils. Personally I would wet it and on the tensile part of the bend and only selectively steam it if the system I proposed does not work quickly enough for you. So - fix the boards down where you want them and it is relatively flat and where they cantilever over you 100mm yawning gap put a decent old load on it at the point where you want it to go down - say a few rolls of Code 8 lead! Go on holiday - start another project in another part of the house - whatever but be patient and record the deformation (proprtional creep) with time. If it looks like it will be next year rather than say next Feb - then apply the steamer. Use a sponge or the like on the tension zone to put in some water and ease its change of shape, (wood at the FSP will creep up to 7 x faster than "dry" wood.

Please let me know how /IF ? this worked.

Chris

[Anna Kettle]

Hello Chris I was hoping you would reply :-)

Thankyou, I do like old buildings which is just as well really as I work with them and this one is my hobby. But sssshhh!!! SPAB would not approve of my using old floorboards :-) Who knows what glorious old building has been ripped apart to provide them for me

That makes sense

I found TNP's comment very interesting. TNP has a new timber framed house and water does indeed stain badly on new oak. A while ago I went to visit another rather wonderful (dragon beams etc) new timber framed house and I was horrified to see that the client had the timber sandblasted, completely losing the fine surface. I couldnt think why the client would have done this, but it could well have been because of water staining

In complete contrast, my floors have been washed down so many times in the last 500 years that there is nothing but stain, so that isnt a problem :-)

I have put in a request for the loan of some stonkingly heavy lead weights. As my dad says "parents come in handy sometimes"

The are plenty of other things to do ...

I like this idea. You are not in favour of cutting the timber in any way? Because that is another possibility (thinning it or slotting it) to help it relax. I'm concerned that such old timber wont be very flexible at all

I will let you know how it goes

Anna

[mail]

Dear Anna The first principle is to make any change reversible cutting the underside (kerf) in lots of slots is a good way of dealing with furniture or non-structural timbers to conform to a shape but I personally would not do this with floorboards. Chris

[Roger Mills]

WHY? Says who?

Virtually everything you make from raw materials involves cutting things to size which is - by definition - non-reversible since you can't stick the bits you've cut off back on again. For starters, wood would have to be left on the tree!

[Anna Kettle]

Its a principle of conservation and not a principle to be applied to every situation in life!

The idea is that presented with an old (building, in this case) all the repairs and alterations that are made should be reversible just in case it is later discovered that the alteration is harming the building or a better way of doing the repair is developed

So for example I will fix my floorboards in place with screws rather than nails so the floor can be easily dismantled if necessary

Anna

[Roger Mills]

Fair enough - but notching the underside of the boards still qualifies, 'cos you can reverse the repair by removing the boards altogether.

[mail]

It is a SPAB principle posed by Ruskin Morris et al over 130 years ago and is as true today as then. Your comment is dead right fwith respect to r the building but I was thinking of the floorboards which, once cut with multiple cuts, would not be reusable in that unlikely event. They would also be stronger as solid against any ravages of point loads such as stilletto heels. Chris