Best way of fixing into stone

[Feltwell]

In the midst of repairing my lounge bay, the saga of which I'll post up at some point. I have a need to fix a replacement wooden sub-cill onto the stone cill below, which is sandstone. Don't want use screws and plugs, as I'm worried about the expansive force within the stone. I reckon one of the screws that cuts it's own thread into masonry, like to the Multi-Monti below, will be best - you are supposed to be able to use these close to the edge of masonry as it puts so little expansive force on the masonry.

http://www.screwfix.com/p/multi-monti-t-star-countersunk-head-bolts-6-x-50mm-pack-of-50/91817

Any comments? I was also thinking of bedding the (hardwood) cill on linseed putty on the stone. Once it's all in I'll seal the front joint with a fillet of burnt sand mastic.

 

[plasticpigeon]

Hello. I have two thoughts. Do you need to fix the wooden sill to the sandstone one? Can it not just sit on it if it is held in place with the rest of the woodwork? My bay is only fixed to the front wall and just rests on the front masonry. Also were the windows ever bedded into anything anyway? I know quality windows had a water bar but I'm sure mine just sit on the stone and had a mastic seal at the front, there is no evidence of a bedding material. Also if you really need to make a solid fixing, you could fix into the stone using anchorfix adhesive, the only problem is that it would make any future repair difficult as it would be very permanent.

 

[88v8]

Expansion... longditudinallally [can't spel it] would be OK presumably, so I would select a plug that has two legs rather than four and align it accordingly, and then use a screw thickness towards the bottom end of the plug capacity.

Or, a resin fixing perhaps?
http://www.toolstation.com/shop/p11337?utm_source=feed&utm_medium=googleshopping&utm_campaign=googleshopping&mkwid=10V1Bpqy&pcrid=26798336183&gclid=CIDY9bK-078CFQHlwgodO4sA0Q

Ivor

 

[DJH]

You could use the old trick of forming a dovetail hole in the stone and putting a screw in the corresponding position under the wooden cill, fill the hole with a cement like material ( :shock: ) and press the board down on to the stone cill. Bingo, a concealed fixing...

Doug

PS Leave some weights on the board until while it (the cement!) cures below.

 

[billybuntus]

Having just removed a fillet of render from a reveal that had a bead of mastic along it I can vouch for its strength. It has been in situe for around 15 years and needed some extreme force and cutting to remove it. It was only 1/4.

I would personally drill a whole and resin a fixing it. I wouldn't use an expanding or cutter bolt/screw.

 

[Flyfisher]

I had to fit a temporary hopper and downpipe into a chalk block wall and had the same concerns about breaking the chalk apart using expanding fixings.

I was recommended to use coachbolts and a resin fixing and was assured they would be able to be removed when necessary.

Despite my scepticism I tried it and, sure enough, a week later I was able to unscrew the coachbolts. I haven't tried it but I guess I could also screw them securely back in as well.

 

[CliffordPope]

If you are worried about expansion forces within the stone, you could drill larger holes and use wooden pegs, epoxied/glued to the stone/wood.

 

[a twig]

If you are worried about expansion forces within the stone, you could drill larger holes and use wooden pegs, epoxied/glued to the stone/wood.

Second the above with a slight variation, drill a larger hole, wooden "plug" into that, and then screw into the wooden plug - a rustic rawl plug if you will - that's the method that was used to fix the original iron downpipes to the bath stone walls in our house when it was first built.

 

[DJH]

Hmm...my way means the fixings are concealed which has both advantages and disadvantages but it's a shame to have fixings showing through the face of timber cills/shelves etc.

Doug

 

[Andrew Bodenham]

Feltwell,

Multi-monti screws are very good - I use them a lot. But they do rust in time - and eventually that rusting will create its own expansive force which will be more than capable of cracking stone.

A stainless screw or coach bolt into a nylon plug exerts some expansive force, but not a huge amount if the fixing, hole and plug are well matched.

Stainless threaded rod set in a resin such as Rawl R-Kem+ or the Fischer equivalent exerts no expansive force and will not suffer future corrosion.

You might consider whether your cills need just a dowel type fixing to ensure lateral location, or if they actually need to be held down as well - this may inluence your choice of fixing.

As for sealing to the stone I would avoid linseed putty as it will dry out and crack in time, and is not really either adhesive or flexible. I would use a polyurethane or polysulphide sealant - these are far more tenacious than linseed. To ensure a good thickness of sealant bedding I would pack the cill off the stone using 3 or 5mm plastic horseshoe packers in strategic locations, then apply a very generous bead of sealant maybe 10 - 20mm back from the weather edge before lowering the cill into place. In this way the cill is well supported and you obtain a suitable 'body' of sealant to accomodate future movement. A common cause of sealant failure is creating a tight joint containing a thin film of sealant which soon fails by shearing off one surface.
You can then finish along the visible egde with burnt sand mastic for appearance and to provide a first layer of protection to the more 'engineered' solution behind.
Finally, if you're concerned about fixing close to a masonry edge then take care drilling - in such situations I avoid using my SDS drill and go with a non-percussive masonry bit (e.g. Bosch Multi-material drill bit) to avoid splitting the stone. Takes longer, but causes less damage.

 

[Feltwell]

Thanks everyone, very useful.

I *may* be able to get away without fixing it into the stone - looks like I can get at enough of the supporting frame of the bay to make a decent joint. Will still need to seal to the cill though, so thanks for the tips. I was making good progress until my multitool decided to die They really are invaluable - especially for jobs involving cutting timber in-situ like window repairs. New one collected today.......