The following is a long email with transcripts of inadvertent back-channel conversation between Nick Micros and david west which grew out of an earlier thread on patch shrinkage.
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Aug 20, 1999 [on list]
"Patches vs Indents (previously Patch Shrinkage)"
Good to get a user's evaluation of the patching compounds ... maybe others could add to these?
On a slightly different tack, what are your cost comparisons for a 6 x 6 x 1 inch patch?
That is, what difference in cost for a patch compared to an indent?
Do you guys reinforce your patches - our current spec requires stainless steel pins and stainless steel wire reinforcing ....
Would be good to get a response on this, maybe from a few of the hands-on contractors ... but no bias just because you like doing indents more than you do patches please!
Cheers
david
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Sept 17, 1999 [off list]
"Re: Patches vs Indents (previously Patch Shrinkage)"
Dear David,
Sorry for the late reply.
Do you hail from a strange and far away land?
"Indent", is this perhaps a "dutchman" repair? A repair with an
identical or matching natural stone?
In answer to your question, an indent is more like the "Cadillac" of
stone repair, patching is the "Honda Civic". A well executed indent is forever.
Patching, 6x6x1":
1.Obtain matching patch material, ? hours.
2.Cut out stone, 1 hour.
3.Mix material, apply (no stainless pins needed for this size patch), 1 hour.
4.Depending on weather, wait aprox. 1 hour, dress patch, 1 hour.
5.Mist patch at least once a day for the next 3 days. if very hot, more frequently. .25 hour.
Indent.6x6x3"
Indents should be cut in 3-4 inches below the surface of the stone, to keep pins and epoxy well below the surface.
1.Obtain identical or matching stone, ? hours.
2.Cut out stone, 2.5 hours.
3.Cut and fit stone indent, joints should be aprox. 1/16", 2 hours.
4.Drill for pins, epoxy indent in place. .5 hour.
5.Wait 1 hour, perform any surface carving and texturing. Time spent depends on specific detailing needed. Aprox. 1 hour.
6.Grout joints with color matched grout, .25 hour.
Patch: Aprox. 3.25 hours
Indent: Aprox. 6.25 hours
Indents take longer because there is much more fitting and stonecutting involved. Patches though are no pushovers, they require much care and finesse. Atmospheric conditions play a bigger role and adequate misting for days after can not be underestimated.
I don't have much faith in patches over 6x6x1". Manufacturers recommend stainless pins and wire generally for large and thick patches or in projection from the building surface. Architects usually follow the manufac. specs.
Indents become a part of the masonry fabric. At Cooper Union in NYC I have seen original indents from 1859, looking strong, just in need of a little grout.
I relate patches to pointing, meaning they are sacrificial. They need to be redone when a building comes up for re-pointing. They are very effective for small repairs, when you don't want to excessively remove stone to make a repair.
The color of patches is a sensitive issue. Matching substrates is
difficult. The amount of water used, air temp. and humidity, batch
variations and old material create many variables.
I like the Keim mineral coatings to stain and faux patches after the
fact. Thats a little trade secret between BPers.
Indent, yeah, I like that word,
Respectfully,
Nick Micros
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Sept 18, 1999 [off list]
"Re: Patches vs Indents (previously Patch Shrinkage)"
Nick
Thanks for your thoughtful response on patches vs indents (dutchmen).
Not only do I hail from a strange and faraway land where the animals hop around on their rear legs, but I'm writing this response whilst at 30,000 feet over Vietnam en-route from Bangkok to Hong Kong.
An indent is indeed a dutchman repair.
I agree that a well-executed indent will last much longer than a patch, although well-executed patches should be able to perform for many years.
My personal preference, as a specifier, is to use indents wherever I can get good stone and where the repair will be visible. Unless the programme of repairs is only intended as an interim measure, in which case I will contemplate patching.
I have been happy using indents as small as 6 x 2 x 1.5 inches, with small diameter stainless steel pins, and epoxy in the hairline joint. I always specify hairline joints, but reluctantly accept them up to 2mm in width (1/12") on the job. My basis for such small indents is indeed the work of past master masons - having seen lots of little touch up jobs on buildings where stones were a bit short .... and these original dutchman repairs were still going strong, even given the relative simplicity of the adhesives used at the time.
I do not like patches with large surface area. I will go to 1 square foot, but no more. I will do longer patches on mouldings, but don't like to go more than 2 feet without a break. I insist that all patches bigger than about 3" diameter have some form of stainless steel reinforcement, even if it is only 1.5mm (1/16") diameter wire.
I have seen too many old patches debond due to differential movement and/or deterioration behind the patch.
One of the biggest problems with both patches and indents is when the specifier or owner has failed to understand the driving mechanism for the stone deterioration. If this is water moving through the stone masonry, then unless the water is stopped, the deterioration continues. Consequently, whether an indent or a patch is installed, the problem will continue.
We are doing a lot of metal weathering to flat exposed surfaces on cornices, string courses and mouldings, because these are the primary points of deterioration in our sandstones. Where there is a lead weathering going over the top, I am generally happy to patch the upper surface of the sandstone ... because nobody is going to see the damn thing anyway!!
I reckon that for smaller patches, where the indent is not so thick (and sorry, but I am generally comfortable with a 2" thick indent .... if my stone is only 3-4'' thick in the first place, I don't think there is a lot of point in chopping in all out), and with the installation of reinforcement as I specify, then the time differential probably looks more like:
Patch: Approx. 3.75 hours
Indent: Approx. 5.25 hours
and maybe even less of a difference.
I like your secret technique of Keim coatings to stain and faux patches ... how do you feel about using them to colour match stone where you can't get the original material or anything reasonably similar in colour?
Can I appropriate your technique? Any hints for the newcomers to Keim coatings? Will the supplier support this use - or is this part of the secret tradition?
Cheers
david west
PS Your message was off the list, and so is my reply. I wonder whether we should share this conversation with everybody else ...
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Sept 25, 1999
Dear David,
I enjoyed your reply a great deal.
I didn't mean to go back channel, I am computer confused! Please feel free to put our past dialogs on Bullamanka if you know how ( I don't).
Keim supports the technique of coating patches, especially their patch material.
They support the coating of natural stone (especially stones with high silica content), providing the substrate is sound and clean. I have used this technique to stain new looking dutchman to blend with adjacent aged stone. Also to integrate stains that just won't come out of the stone and the client doesn't want yo see it.
Jahn makes a stain for their patch material. Prosoco makes stains and breathable paints for masonry.
Regards,
Nick Micros
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