Dead wood

[Athers1971]

In an earlier post that I hijacked @Toby Newell suggested to go carefully with friable material on old beams.

I’m now at the point where I actually need to take some action, rather just trying to think of all my problems.

The oak purlins (300-400) years old in the roof have many sections of friable material on the ‘top edge’ where I guess condensation etc has settled there in prior years.

The roof covering and rafters are not original and in many places shims have been used between the rafter and purlin in places where there has been previous damage.

I’ve removed the old insulation and am about to replace, but before I hide some of the purlins ‘forever’ I want to make sure they are in sound condition.

In places I can just pick chunks of soft wood away and then if I rub with my fingers I get a lot of dust.

Is there a tool better than my fingers to use to get rid of the damaged wood? Should I use a wire brush? Drill with wire brush attachment? Orbital sander?

I want to finish the beams now as part of them will remain visible when the room is insulated (wood fibre) and lime plastered. I’ve added some lap vents and so hopefully the attic rooms will have good ventilation and remain dry.

Thank you.

 

[Toby Newell]

In an earlier post that I hijacked @Toby Newell suggested to go carefully with friable material on old beams.

I’m now at the point where I actually need to take some action, rather just trying to think of all my problems.

The oak purlins (300-400) years old in the roof have many sections of friable material on the ‘top edge’ where I guess condensation etc has settled there in prior years.

The roof covering and rafters are not original and in many places shims have been used between the rafter and purlin in places where there has been previous damage.

I’ve removed the old insulation and am about to replace, but before I hide some of the purlins ‘forever’ I want to make sure they are in sound condition.

In places I can just pick chunks of soft wood away and then if I rub with my fingers I get a lot of dust.

Is there a tool better than my fingers to use to get rid of the damaged wood? Should I use a wire brush? Drill with wire brush attachment? Orbital sander?

I want to finish the beams now as part of them will remain visible when the room is insulated (wood fibre) and lime plastered. I’ve added some lap vents and so hopefully the attic rooms will have good ventilation and remain dry.

Thank you.

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*takes off Somali pirate costume*

EDIT: Puts glasses on. Oh, YOU hijacked. And tbh you can be pretty heavy handed when cleaning 400 yr old oak. I was only advising that doing nothing is the safest. You will be very lucky to remove 0.5mm from the heartwood, unless you use something insane like industrial zirconia-alumina sanding discs.

Be creative. You can be quite hard if you want to remove the rotted sapwood. The heartwood will be amusingly tough. So you can use wire brushes, nylon brushes, chisels, WC scrapers (tungsten carbide)

Spinny things on drills are normally amusingly bad on wood, yet perfectly reasonable on old beams, the nylon ones will help clean.

The heartwood will laugh apoplectically at a cheap, orbital sander, so unless you have a very, very good sander, doing it ny hand is just as good, with very good abrasives (Festool Granat, 3M 947a / 950u / 245, Sia 1950 etc)

 

[Toby Newell]

In general any blasting method is quite destructive. Most of the friable areas are sapwood, if you want to retain as much sapwood as possible then be careful, the heartwood is literally 100x as hard.

Personally I use my antique chisels to remove and dress the friable areas / filler / plaster etc. Then I use carbide scrapers ( all the scrapers, Bahco 625, 650, 655, 50mm tungsten carbide scrapers and cats paws, pincers, punches etc to deal with any fixings.

I then sand with one or more of Festool RO150, RO90, ETSEC150, you can start with P40, P60, P80, after P80 the heartwood will just start laughing so you can skip straight to P150. You can work up to P320 or P500. You won't take much visible wood off but you will burnish it. From P100 you won't really be moving much material and cheaper abrasives will last less than 20 or 30 seconds on a machine. Even the best abrasives, which can be several times as efficient only last for 1 or 2 mins before they dull. It really is amusingly hard. The density of the heartwood will be up to 1.2, which is on the level of ebony and lignum vitae.

I finish mainly in shellac then beeswax and carnauba.