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Understanding calcium nodules

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In this video, the National Plasterers Council presents their current-held positions on the cause of calcium nodules (mineral growths) that sometimes occur on the surface of a plastered swimming pool or spa.

Hi i’m allen smith with the national plasterers council and thank you for joining us today today we’d like to talk about a special phenomenon and a pool plastering called calcium nodules the two types of calcium nodules found in many regions of the us and their methods of determining their causes are fairly straightforward other types of nodules or other

Potential causes of nodule growth have been reported but are not covered in this video so let’s define the two basic different types of calcium nodules that we see in the field that have plagued the pool finish industry for years the first nodule we’ll talk about also known as delaminating or nonbonding areas delamination means that a gap is caused by the base

Of the plaster being separated from the substrate it was originally applied to the secondary deposit that forms in the gap may or may not be calcium hydroxide it could be intra guy calcium carbonate gypsum or any other number of secondary deposits that are usually salts of calcium of which calcium hydroxide really isn’t assault by chemists definition so it’s

A little bit different either way it’s being dissolved and brought to the surface the second type of nodule is coming right out of well bonded or what we call intact plaster or any other type of cementitious pool finish that was applied the plaster is basically filled with what we call microstructure cracks or micro cracks that is the very basic dna of cement

Compounds and when the water can get into these microstructure cracks and then starts to transform these soluble salts products to the surface is when you get your calcium nodule today in studio we have john danjel who is the research director for pebble technologies in the past chairman for aci which is american concrete institute plaster committee now i’d like

To have john come in and weigh in on this and give some more details too the cement hydration process and how this all comes into play first most cement isha’s products are comprised of basically three materials a binder and aggregate and water hydraulic cements are typically made from hard rock and other mineral materials that are crushed and calcite to remove

The chemically bonded water and carbon then the material is ground to an ultrafine powder when we mix the cement powder with water we are converting the material back into a rock like hard matrix form but we make cement isha’s materials about 50% of the mix water we add isn’t needed for the cement powder hydration reaction about 50% is water of convenience this

Means that about 50% of the volume of water ultimately has to leave the system this represents about 8 to 10% of overall volume loss based on the raw material volume that we are mixing together thicker materials like concrete shotcrete and precast are able to store this water or hold most of it within themselves but actual shrinkage related to the volume loss after

The placement of a thin layer material such as plaster or mortar translates to a 0.2% overall loss in volume due to evaporation and absorption within just the first three hours fortunately cement relieves the internal strain from shrinkage by fracturing or micro cracking throughout the system these micro cracks develop in an order of one to three micro cracks per

Millimeter meaning in that 20 foot span of plaster micro cracks would be expected to transverse the span each helping to offset the half inch of overall volume loss of course these micro cracks are not visible to the naked eye without the aid of a powerful microscope and these cracks quickly seal themselves with ongoing cement reaction products in other words they

Pose no issue however about every 2 to 4 inches larger shrinkage micro cracks typically develop these relate to what alan was talking about earlier these micro cracks are much wider typically about 5 to 10 microns and where and these generally take several days to several weeks to fill shut with cement hydration compounds during this time any aggressive water

Such as low calcium low carbonate alkalinity or low ph can attack these larger micro cracks that haven’t fully sealed shut this scenario can allow for the second type of nozzle problem to occur where hundreds of small calcium carbonate growths can occur on areas across the finish we’re open micro cracks exist the same aggressive water that has removed the cement

Reaction compounds from the micro cracks can continue to leach soluble cement compounds from the interior of the plaster or what is known as the sub boundary layer through a process called dissolution from a solid to a soluble ion form and diffusion transport of the soluble ions and then deposit these as a mineral salt on the surface which creates the nodule

Deposit consisting mainly of a calcium carbonate d bonded areas can lead to flexural cracks they can also lead to nodule deposits even without aggressive water as pool water can circulate in and out of these hollow areas and transport soluble salts that then deposit on the surface these can often be repaired whereas this second type of knowledge of formation is

Much harder if not impossible to repair now that we heard that water balance is a major player with this calcium nodule phenomenon let’s hear from david hodge national chairman for its independent pollster postman’s association way on on this subject the national plasterers council teaches right out of the ipps a basic training manual that was so very well done

It was written by have said specifically bob lowry and we teach about water chemistry and balance and how it interacts with pool surfaces if it gets too aggressive on the saturation index as it’s so properly teaches it can start dissolving and pulling calcium or plating calcium out on pool surfaces and we just want your opinion on weighing and make sure that we’re

Properly you know diagnosing this in concordance with your basic training manual sure and thank you for using our training manual i think bob lowry says it’s it’s the best book that nobody knows about so we need to get that out and get that information out there and a big part of our job in the service industry is balancing the water and the video very plainly

Shows what can happen when we have aggressive water in a pool and the ramifications of that and so we’re hoping that the video as well as the rest of your programs continue to help us as service technicians keep the water balance to keep it where it’s supposed to be so that we can have a nice swimming environment and likewise all your terrific education ifs is

Put out over the years is shared by our plastering association as far as educating customers and other service in and pull plasters themselves in conclusion what we’ve learned from this video today is that there’s two basic types of calcium nodules that originate from two different sources the first one where you’ll see multiple nodules within a pool surface

Comes directly out of the plaster surface itself through micro cracks and micro structures filled with calcium hydroxide pool water that needs calcium to buffer it will simply pull them out of these micro structures and cracks and form little nodules on the surface as you can see in this core sample that we’re pulling out these nodules come out of plaster that

Is firmly attached to the gunite substrate there’s no delamination whatsoever with these the second type of nodule we see is the nodules being pulled out of an area where there is separation between the plaster and the gunite substrate in this very thin structure between the plaster and the gunite we have calcium hydroxide building up in a large reservoir so if

The water can get to it it pulls it out and develops a much larger nodule as you can see in this core sample in this picture as we pull it out there is a clear separation between the plaster and the gunite and you see a much larger nodule on top a simple coring of the nodule will tell you the whole story whether it’s delamination or write out the plaster we hope

This video has been educational and informative to explain the calcium nodule phenomenon

Transcribed from video
Understanding calcium nodules By National Plasterers Council