Shrinkage cracks

[Keithj]

The extensive repair and extension work on our (Tudor) house was finished in early September, and we have the house back. (See copious earlier correspondence on here).

The builder and his foreman came to look at remaining snags last week. Most were straightforward - thin plaster skim separating from the nailheads that hold the plasterboard to the wall, for example. Those he will deal with.

All the sole plates, and about 10% of the studs, were replaced with green oak (it had to be green, apparently, because those are the rules). The new wood has now shrunk, and there are gaps through which one can see daylight (and feel the gentle breeze when it's blowing hard outside). There is no problem with the old timber and the new plaster/lime render.

"No problem", said the foreman, "I'll just fill those cracks with decorator's caulk".

My immediate reaction was "No, you won't", basically because decorator's caulk wasn't a normal Tudor material. I'm going to have to redecorate after this exercise anyway, and I'd prefer to do it neatly myself rather than have apprentice builder number three spread the stuff around the place. They used caulk to fill gaps in the original repairs at one side of the kitchen, and that's cracked and separated where the oak has shrunk, crazing the plaster in a way that a straight wood join wouldn't have done. I'll remove and fix that properly.

My instinct is to pack the cracks with wool (we have large quantities of "builder's wool" which was used to lag the walls), and then fill with lime putty outside, plaster inside. But before I go off and do the wrong thing ... what would be the team's view on the right way to fix these shrinkage cracks?

 

[middi]

Traditionally all shrinkage gaps were filled with sheep ' s wool soaked in thick limewash and finished off with lime putty or lime plaster. ( as you suggested). That is the good news.
The bad news ?. You keep repeating the process untill the green oak timbers have seasoned and the shrinkage has stabilised.

There is no short cut I am afraid.

Middi

 

[Penners]

All the sole plates, and about 10% of the studs, were replaced with green oak (it had to be green, apparently, because those are the rules).

I'm not sure that green oak is "the rules", but it may well be that, if your house is listed, new oak was required by the CO (as opposed to re-using old oak beams). This is a normal requirement, in order to show an "honest", modern repair of the old frame.

It may have been permissable to use dry new oak, as opposed to green, but carpenters will invariably favour green oak because it's much easier to work, and because the drying/shrinking process is beneficial to certain types of joint. So this is what is usually used.

Middi's answer to your crack filling question is authoritative. He's an expert.

Incidentally, as time passes you may find your green oak members themselves developing cracks. Don't worry about this - it won't affect their strength to any significant degree and is a perfectly normal part of the drying out process. You can fill the cracks with your wool/lime putty formula or leave them open - just as you wish.

 

[MdB]

Middi's answer to your crack filling question is authoritative. He's an expert.

Incidentally, as time passes you may find your green oak members themselves developing cracks. Don't worry about this - it won't affect their strength to any significant degree and is a perfectly normal part of the drying out process. You can fill the cracks with your wool/lime putty formula or leave them open - just as you wish.

I'm sorry, but in my experience Middi is wrong, the standard method for dealing with cracks in oak is to fill them with spiders. You see this method used all over the place if you look carefully.

 

[Penners]

Keith - ignore MdB's advice. Spiders are excellent as crack-fillers provided they're all dead. But given the life-span of the house spider can be several years, it's not really worth the wait.

Anyway, it takes a-g-e-s to train them all to die with their legs interlocked.

 

[Keithj]

Yerst, well, I have a goodly stock of wool (walls for the filling of with), and a pot of lime putty as well as a couple of buckets of limewash (one Suffolk pink, one magnolia - the statutory colour for all indoor walls where we used to live in Essex). There is also a surprisingly rich vein of spiderhood around the place, but herding spiders seems to be harder than herding cats, so I prefer the limey wool filler approach. The new vacuum cleaner seems very effective at removing spiders.

The green oak is indeed acquiring some very artistic shakes in certain places, which add to the vintage feel of the place. There are a couple of large ones in the sole plate outside, facing upwards so prone to collecting rain (we had some of that, a month or so back). The collected rain seems to percolate through the oak and make tea-stains down the limewash indoors, so I'll probably fill those ones with the limey wool, too.

The advice is very welcome, and thank you all.

 

[biffvernon]

the sole plate outside, facing upwards so prone to collecting rain

I wonder whether there's a bit of a design flaw here.

 

[Keithj]

I reckon so. There wasn't much choice this time around, given the way the place was built. I blame those Tudor chappies. I have a cunning plan...

 

[CumbriaSteve]

Traditionally all shrinkage gaps were filled with sheep ' s wool soaked in thick limewash and finished off with lime putty or lime plaster. ( as you suggested). That is the good news.
The bad news ?. You keep repeating the process untill the green oak timbers have seasoned and the shrinkage has stabilised.

There is no short cut I am afraid.

Middi

I’m new to this. We have installed a considerable amount of new green oak in this Cumbrian farmhouse ove the past 12 years. It has shrunk back considerably, leaving gaps up to 1.5cm between the timber and the plasterboard. I have a quantity of sheeps wool insulation which I plan to use filling thes gaps. A couple of questions; why soak the wool in lime wash and how to make a suitable mix? Sounds messy as hell. Necessary to use plaster to finish or will anything else do? Any tips for application technique? It all internal. I’m guessing that with underfloor heating and wood burners the timbers have done most of their drying by now...

 

[Penners]

Steve - if you've used plasterboard for your interior linings, I think you're making a rod for your own back if you try filling the gaps between it and the studs/joists with sheep's wool and lime. This wouldn't really have any beneficial effect on the building.

Have you skimmed the plasterboard with a gypsum plaster? If so, I should just fill your gaps with Polyfilla or similar (if the cracks are very deep, maybe pack them with some newspaper or similar first). Whatever filler you use, you'll almost certainly be repeating the process in the future, possibly several times, until the moisture content of the oak reaches equilibrium with the ambient air in your house.

You could substitute lime putty for the Polyfilla - it will be a little more plastic. But in the long term I don't think it will make much difference.