Grouting loose plaster and ideas for plastering over timber

[inwood]

Has anyone grouted behind loose plaster to stabilise it. I have various areas of old plaster which have loose edges which need to be stabilised before I patch repair the remaining wall. Any advice on the process and best mix to use?

I also have a timber beam - it's about 4 metres in length and 100mm deep which I need to plaster. The building recorder suspects the building was originally single story and cruck framed so this may be an old sole plate for the original roof. The old plaster along this beam fell off when I sneezed upstairs :lol: and I clearly need to repair back to the plaster above and below it. My problem is that I don't have enough depth for cross lathing so need alternative suggestions to stop the new plaster falling off as easily as the old. My initial thought was running a strip of expamet along it's length, good idea?

 

[Ian Bond]

If it's just a bit loose at the edges, the new plaster should consolidate it somewhat. It may crack a bit at the join, but limewash should sort it out.

Depends how loose it all is. A technique I've heard about (but not used myself) involves using a big syringe. Water is squirted behind the loose plaster to clean out debris, followed by runny lime to 'glue' the plaster back to the substrate. Probably a lot more involved and tricky than my description would make it seem. For very precious, historic plaster you'd be leaving this to a skilled conservator, rather than having a DIY go!

I've used expamet in places, but prefer to give timber a darn good hacking to provide a key.

 

[Ian Bond]

Found this article on t'web - looks to be very interesting at first glance. Lots of info about plaster conservation, including the syringe job.

http://www.mendip.gov.uk/Documents/Regeneration/Heritage Conservation/Heritage Matters/Iss10.pdf

Also says DON'T use hessian and plaster poured onto the ceiling from above as a fix, and explains why.

I've saved myself a copy for future reference!

 

[Ian Bond]

Extract:

However, not all hollow plaster must be removed; sometimes it can be re-secured by grouting (injecting a liquid lime plaster into the void). Holes are drilled through the plaster and, after flushing out the void with a solution of water and alcohol, the grout is introduced by syringe.

For large voids the plaster surface should be supported first, to withstand the grout pressure. Once the plaster has been stabilised, cracks can be cut out, dovetailed inwards, consolidated and filled with haired lime plaster for major cracks, or scrim and casting plaster for smaller fissures.

 

[inwood]

Thanks Ian,

Grouting is only really required around the edges. The background (daub), appears to be well adhered but the finish coat (lime) is where the separation is. Where I've lost both background and finish coats the finish on the remaining section is flapping around in places. Since it's a haired finish coat I can peel it back carefully to grout behind.

Thanks for the link the the syringe info. I also had a search and found a wealth of detailed conservation info on the following site:
http://www.archnet.org

Go to the library section.

This document (download link at the bottom of the page) is particularly interesting:
http://www.archnet.org/library/documents/one-document.jsp?document_id=9483
and describes grouting behind blown render in Stone Town, Zanzibar. Not sure of their use of PVA during the grouting but the description of the process (p.117 onwards) makes for interesting reading. This is of particular interest for me as this is where my wife and I spent part of our honeymoon. A fabulous place, packed full of historical architecture.

 

[Ian Bond]

Ta for the link Daron - that looks like a very interesting resource you've found.

I see what you mean about the PVA. Mind you, I'm near Bradford in West Yorks, about as far from the sea as you can get in UK, so obtaining seaweed for 'seaweed water' may be a problem!!!!!

 

[Ian Bond]

That was well worth reading, and keeping for future reference, thanks Daron!

A lot of the methods and materials used are very familiar. Brick dust added to the grout as a pozzolan. Galleting with small bits of stone when dubbing out etc.

Not so familiar - slivers of bone to pin the grouted plaster, and using boiled seaweed. Although in some place in the UK, bone was used for roof tile pegs, and probably a lot else too.

A low-tech yet sophisticated approach to the conservation and repair - very impressive. I only spotted the use of an electric drill once, fitted with a piece of bent wire in order to whisk the grout for TWENTY minutes!!!! Maybe that would work for limewash? Another use for wire coat hangers!!!

 

[inwood]

Talking of slivers of bone, just found an almost impossibly thin bone button when preparing the area under one of the windows inside for refitting window board (lovely ash boards about 600mm wide - reclaimed 'sarking' board from an old barn).

Also found a pile of old pins and a coin from 1750 under another old window board that had to be replaced. I just imagined someone sitting there looking out the window doing their embroidery when they spilt the tin of pins down between then window board and the window.

 

[Ian Bond]

Keep it all for your museum!

It's great to find things like that - and know you're the first person to see them for a couple of hundred years.

Under floors is another favourite place. Children in particular love to 'post' things through the gaps.

Perhaps you should stuff something under the window for future generations to find. Something that would be best hidden for a couple of centuries...

Mika CDs perhaps?! .....

 

[inwood]

Not sure about CD's, I think they're already on the endangered list - especially Mika's :wink:

I had a guy in helping me with the external stonework last summer. He dropped a stone on his wrist smashing his rather nice watch. He gave it to me to plaster into one of the internal walls which I did last week into the scratch coat. Should be a nice little surprise when the plaster is repaired/replaced - hopefully if my plastering is any good in a couple of hundred years.

 

[charlie-ia]

we too found buttons under the windowsill, an old broken thin one, a more normal looking bone/shell one, and some fairly modern ones, including a nearly new pressstud. the wood unfortunately has rotted to dust, but im tempted to leave a small gap for more generations of lost buttons in the new window.

under the same window i found an old rosary too. wonder if it was put there to scare away the button faerie?