[r-man]

I've heard people go on about resining up the rock to make slightly friable or crumbly holds more solid. How effective is it? What resin do you use? Is it expensive?

Just how the devil does it all work?

[Bonjoy]

This subject pops up on a regular basis. Usually most people agree that the sparing use of some sort of fixative on loose crumbly holds is a good idea and then nobody does anything about it. I have seen evidence of 'stuff' being used at the Bridstones (looks like a thick resin was used leaving a thick slippery coating over holds), Bowden and Southern Sandstone (looked like a thin liquid was used which permeated between the grains, leaving some staining but only a minor loss of friction). However no-one ever pipes up who knows what has actually been used so its hard to say what does and doesn't work.

[Bubba]

al has done some work along these lines, as have some of the county crew I believe - apparantly it's costly and difficult, one of the main problems getting a realistic finish in terms of colour and texture.

Somebody did recently tell me exactly what stuff can be used - was it you Fatboy?

I really wish some official guidelines on this could be drawn up before things get any worse in the badly affected areas.

[dave]

i think when used in the context of rock repairing the word "resin" isn't exclusivley used to mean "pine resin":

res·in  
n.

   1. Any of numerous clear to translucent yellow or brown, solid or semisolid, viscous substances of plant origin, such as copal, rosin, and amber, used principally in lacquers, varnishes, inks, adhesives, synthetic plastics, and pharmaceuticals.
   2. Any of numerous physically similar polymerized synthetics or chemically modified natural resins including thermoplastic materials such as polyvinyl, polystyrene, and polyethylene and thermosetting materials such as polyesters, epoxies, and silicones that are used with fillers, stabilizers, pigments, and other components to form plastics.

[fatboySlimfast]

resins in industry covers a whole multitude of sins.
With regard to rock repair, what als done before is to fill in chips with the stuff used for making climbing holds, skillfully blending natural products in with it to make good some dumbshits vandalsim.
What they use on rock to bind(soft sandstone types, footholds on vienna etc) it is the same stuff used to stop erosion on important buildings. Houses of parliament for example. The problem is that it has to permeate into the rock before setting, if you use epoxy for instance it will just form a skin and break very quickly because its only binded to the surface layers. I cant remember the formulation used but it is expensive. Joe Piccali has got a phd in this kind of shit, ill ring him later to get some info

[Bonjoy]

Found a good article on the subject (Sandstone consolidants). Lots of interesting points on the subject.
http://www2.rgu.ac.uk/schools/mcrg/miconsol.htm
 Concludes:

For consolidant treatments, there is agreement that treatments confined to the outer surface are dangerous since they can result in spalling of the stone but there is no agreement on what would be an appropriate depth of treatment beyond the fact that it is obviously necessary to treat the stone deeply enough to consolidate the full thickness of the decayed zone. Some stone consolidants also have water repellent properties. Since it is dangerous to confine consolidation to the near surface this makes the use of a combined water repellent-consolidant problematic if it is considered best to confine water repellency characteristics to the outer surface.

The ideal polymer for use in stone consolidation would be one which can reverse the degradation of a stone, returning it as nearly as possible to its original condition. In order to achieve this the treated stone should mimic sound stone in as many characteristics as possible. Some characteristics are, however, more important than others. The most important include strength, porosity, permeability, thermal dilation and colour. Of all the polymers tested, silanes seem to hold out the most promise although they may not be suitable in every situation. The theoretical end product of polymerisation of the simplest silanes is silica which is present as a cementing mineral in many sandstones and may mimic the behaviour of a natural cement more closely than many other polymers.

 So maybe a Silane (silicone based) consolidant is the one to go for.

[Bonjoy]

Another similar article - http://www.buildingconservation.com/articles/stoneconsol/stoneconsol.htm
 Has a bit more detail on silane consolidants:

Silane-based materials
Silane-based materials are generally organosilicon compounds which polymerise inside the stone. Some water is needed to aid the reaction, but the amount is critical; a high humidity means the reaction may take place too quickly and too much water leaves no space for the polymer to form. The end product of polymerisation is silica, similar to the natural silica deposits which bind many sandstones. Penetration can be quite deep but this depends greatly on the product used and the conditions in which it is applied.

By the production of silica there is a definite consolidating effect and many silane-based products seem to increase the strength (flexural, compressive, tensile etc) of damaged stone. Unfortunately, there is some colour change with most types of silanes, although studies show that this usually lessens after about 18 months. Porosity, water absorption and pore size distribution have shown to be affected by the treatment, a little in some cases and a lot in others. This influences resistance to salt crystallisation and freeze/thaw action. Where there is a new area of stabilised decayed material, moisture evaporation has to take place within the stone and this may lead to salt crystallisation at the boundary between treated and non-treated stone.
These are the main silane-based products and their main features:

    * tetraalkoxysilanes - have little water repellency;
    * alkyl trialkoxysilanes (such as brethane) - less consolidation, but good water repellency;
    * polysiloxanes - flexibility and more water repellency;
    * silicon hydrides - use presents many health and safety problems;
    * halogen bearing silanes - generate damaging acids, so thought to be too dangerous to use in conservation.

[clm]

colour change would be good if it darkens as worn patches usually are raw and sandy.

[Sloper]

I think Martin Veale is the man to ask (from memory he reapired the slab at RHS chipped by th egomaniac moron)

[SA Chris]

i think when used in the context of rock repairing the word "resin" isn't exclusivley used to mean "pine resin":

res·in  
n.

   1. Any of numerous clear to translucent yellow or brown, solid or semisolid, viscous substances of plant origin, such as copal, rosin, and amber, used principally in lacquers, varnishes, inks, adhesives, synthetic plastics, and pharmaceuticals.

The pine resin we think of when people speak of resin is actually the "rosin" referred to above.