Woodworm and very old beams

[Tigger]

I purchased a cottage in Dec ‘23 and unfortunately woodworm has shown up in multiple places in a house full of wood. The house was actually only built in the late 1950s but was designed to look much older and has some reclaimed oak (I assume) beams that are clearly very old, hence asking here.

We have 14 old beams installed in the house. A couple that are structural and much more sound/regular shaped and some that we’re fairly sure are decorative. To keep the character of the cottage we’d like to keep the beams but have been advised that the stain/varnish needs to be removed to allow woodworm treatment to be applied. How on earth do you go about getting varnish/stain/oil off beams that look like this? (Note, the house is fully decorated and lived in).

Prior to us buying it it was fairly unused for a number of years and with very primitive heating controls (no thermostat) so I suspect got cold and damp in the winter (going by the slug trails we saw on carpets on our second viewing!)

We have replaced some of the windows/doors, upgraded radiators, heating controls and added loft insulation. The house is quite draughty still but I guess that can be a good thing!





We also have lots of more modern wood that needs prepping in a similar way - I’m assuming we’ll sand that but advice always welcome. Unfortunately the modern wood has sap wood areas which are the areas being attacked.

 

[Matt Green]

No treatment needs to be applied to those beams, there are no furniture beetle in there. All the sapwood was eaten decades ago.

I suggest filling the holes in the modern sapwood with wax and waiting for two years before doing anything else, at worst you will only need to remove the varnish from the modern sapwood sections to brush treat the affected areas fill the flight holes and re-varnish. That's a decision you don't need to make now. See where the activity is, if any, after you have lived in the house for a while.

 

[Flyfisher]

Exactly. There's a big difference between historic woodworm and active woodworm! Our house C16 timber frame house has plenty of signs of historic woodworm but is still standing after about 450 years so I'm not about to start spraying toxic chemicals all over the place.

Follow Matt's expert advice (as a new member, Tigger may not be aware that Matt is a professional scientist in this field), relax into the house and stop worrying.

 

[Tigger]

Thanks both. There’s definitely active woodworm in some of the modern bits as you can see holes that have come through the paint colour we used 15 months ago!

And this beam appears to be active as you can see from the dust on the wardrobe below.





This one I think is active too as all of the beams were oiled 15 months ago.




Brilliant to have Matt on here - thank you for your advice.

 

[Matt Green]

The second photograph is really interesting.

Timber tends to oxidise under UV light in that the surface becomes darker. Remove the surface layer with a plane and you se the natural colour of the wood again. The frass in the second photo is very dark, and frass is just timber that has been through a beetle, and I don't think it's active, I think it's fallen out of existing tunnels.

Furniture beetle emergence April-June. I wood vacuum up and wait until the end of June before making any decision. I would bet that you will dislodge more dust than that before then.

M.

 

[Cubist]

Whoever slathered those old beams with varnish or shellac has done you no favours and the coating of varnish, I'm assuming, on the newer timbers too is far from helpful. Not least because those coatings limit the efficacy of any anti woodworm treatments you might apply now or in the future whilst also limiting the ability of those timbers too breathe effectively and therefore shed any acquired moisture to the atmosphere. As @Matt Green would advise, and I would surmise that your prior research has already shown, the wood munchers like to inhabit and are somehow drawn to damp/moist timber and presently the now vacant holes and galleries created by the old larvae populations is a potential magnet for any airborne moisture produced in those rooms. As a consequence, and though the risk may be small, a new prospective mother beetle may find some of these old exit holes quite attractive. Also, depending on how much sustenance may remain in the timber some elements of the old larvae population may not have left home yet.

It's a personal opinion but my attitude to the risk in this situation is predicated on 'better safe than sorry'. There is though a limit to what you can reasonably do. In identical straits with varnished/coated timbers I have employed a hypodermic syringe to inject a permethrin based woodworm killer directly into the galleries using the exit holes as a means of entry - masks and eye coverings are essential as too much pressure on the plunger can get a 'blow back' on occasion. Once dry, the holes can then be filled using a hard wax applied with a suitable cloth.

Belt and braces perhaps but then it does come down to your personal attitude to risk.

 

[Tigger]

I have quite a low tolerance to risk on things with long term potential impact.

Currently I’ve been advised by a large nationwide company to sand down both affected old beams and a couple of entire doorframes and at least one complete window.

This beam is said to be active





And this window sill and window are def active. They have advised stripping the whole window frame internally for treatment.







There is also some active woodworm in the eaves cupboard next to this room, so that needs the insulation removing and to have rafters and floor treated. Likewise the floor in the room and so it continues.

 

[Tigger]

I have treated to some extent the window bottom rail and sill with a DIY product which is why the holes look less fresh.

Here’s a photo of the sill taken before - with frass in some of the holes.

Pity our level 3 RICS survey decided that these weren’t active 22 months ago after I specifically asked!

 

[Cubist]

Just how does the supplier propose to treat the wood? Stripping the extant finishes, particularly that window frame, strikes me as bolting the stable door so I'm thinking they want to paint, or maybe spray, the raw wood with permethrin as their easiest approach. In my opinion that would be wasteful and largely pointless as no doubt you would want to apply a new varnish finish to the window and door frames after they are treated?. I'm not at all sure @Matt Green would agree with me but as far as the window and door frames are concerned I would be considering drilling some new small holes in strategic locations to then inject some worm killer before then closing and sealing those I'd drilled and those excavated by the wood munchers. As far as the old heavy beams are concerned I might consider stripping the finish off them but only with the aim of increasing the surface area exposed to atmosphere to aid drying. In any event these larger timbers should be less prone to significant worm damage.

 

[Tigger]

Just how does the supplier propose to treat the wood? Stripping the extant finishes, particularly that window frame, strikes me as bolting the stable door so I'm thinking they want to paint, or maybe spray, the raw wood with permethrin as their easiest approach. In my opinion that would be wasteful and largely pointless as no doubt you would want to apply a new varnish finish to the window and door frames after they are treated?. I'm not at all sure @Matt Green would agree with me but as far as the window and door frames are concerned I would be considering drilling some new small holes in strategic locations to then inject some worm killer before then closing and sealing those I'd drilled and those excavated by the wood munchers. As far as the old heavy beams are concerned I might consider stripping the finish off them but only with the aim of increasing the surface area exposed to atmosphere to aid drying. In any event these larger timbers should be less prone to significant worm damage.

Thanks for your thoughts @Cubist


Yes, the supplier wants to paint or spray on a treatment, I assume one that contains permethrin. They then won’t guarantee them as they don’t guarantee things that have one side outside and also won’t treat the outside. He didn’t mention injecting anything, which I’ve asked about.

Yes, we would refinish to match existing. I wasn’t planning on filling the holes but considering them as “character”.

Not sure what we’d do with the beams if they were stripped. When we bought the house we wanted to make them lighter but it was prohibitively expensive and we thought it wrong to paint them.

 

[Cubist]

I removed a coat of black wax from all the interior timbers here shortly after we moved in. All done manually with no special kit or materials to get the colour back to something near enough natural - to my eye at least. Since then, 15 years ago, they have been given one thinned coat of linseed oil and an occasional brush down with a soft bristled brush to get rid of accumulated dust. The hard finish on your beams may not be as easy but they do look like a chemical stripper and some judicious elbow grease would do the job.

 

[Tigger]

Something like this? https://priorypolishes.co.uk/product/nitromors/

 

[IHateDamp]

The trouble with nationwide companies is that they are often peddling their own products

Is there a timber expert who espouses a more holistic approach in the round that you can ask for a survey, who just makes their money for a survey and is not taking kickbacks?

 

[Tigger]

The trouble with nationwide companies is that they are often peddling their own products

Is there a timber expert who espouses a more holistic approach in the round that you can ask for a survey, who just makes their money for a survey and is not taking kickbacks?

I’ve been looking and can’t find one closer than Manchester ish requiring about £150 in travel expenses on top of the survey fee. I’m in Windermere, Cumbria so if anyone has suggestions I’m all ears.

I’ve also gone back to the surveyor who said it was historic and he’s engaging his insurer which will inevitably lead to more faff but hopefully some financial help.

 

[Cubist]

Something like this? https://priorypolishes.co.uk/product/nitromors/

I've used that product successfully on paints in the past - notably here recently for an old plank and ledger door that ultimately became two pairs of internal shutters - but never to remove varnish. Its always worth testing a small, unobtrusive patch first.

 

[a twig]

If you really want to use permethrin it would probably be more effective if injected into the holes with a syringe - with the added bonus that it would save you the hassle of stripping and refinishing

 

[Kearn]

I can’t really personally buy into the chemical approach for many reasons. I find it analogous to fighting the symptoms of moisture in walls etc by covering them rather with modern snake oil, instead of finding, and fixing the cause.

However, for you to have guests, the timber is attractive, moist and tasty. Its moisture level is too high. Which will cause other issues too.

Why is it damp? Is it just the horrid impervious coatings trapping moisture from the living environment? Are there leaks somewhere? Condensation?

Cleaning the surface coverings off will no doubt help, so I’d be doing that first.

Find the source and fix it, then wait for the timber timbers to dry out, below 12% moisture content the little buggers will vacate…