# Any tips for plastering a pool?



## Tscarborough (Feb 25, 2006)

Do you know what they use as the aggregate in Thoroseal? That's right, marble dust.


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## Fancis Casini (Jan 31, 2013)

JBM said:


> The coating on my bro in laws pool was white under the paint and it didnt feel like a cement with sand, marble dust is how I would describe it yes.


Jb you said it.....painted! The stucco gets dirty and needs a smoother slick finish a a paint or plastic ane even fiber glass. I neve said sand, I said sea sand meaning silica! The marble imo is weaker.

here I googled this ....

The plastering trade tends to be very secretive about their techniques. In my area the contract for a plastering job is typically made by a well-dressed, well-paid salesman, who produces volumes of endorsements, referrals, recommendations, and photos of splendidly perfect past jobs, whereupon after signing you discover that the crew actually doing the work consists of very skilled and polite, but not English-speaking, laborers who have been hired as independent subcontractors from some other part of the world where swimming pools are non-existent. Once you realize that plaster as a building material is still used in less-developed countries, you understand that perhaps this is a good thing for your concerns. You don't see the Anglo boss except when he collects payment (if you were tough enough to hold out for payable-on-completion). This all adds to the mystery of how it is done. The tradesmen don't seem to care if you watch, and I did watch a few jobs done for my neighbors this way. But there just isn't anything like a textbook description of all the tips and tricks to doing this work, at least not that I could find, and they certainly aren't giving you a running narrative of their every deft, cat-like move, not least because they are so well-practiced at it that they don't have to think about it that much. But watching a few professional runs did equip me with a knowledge of what tools and materials were appropriate, and how things work in general and on what pace. Some tools, like stepping boards, must be improvised yourself.

Pool plaster is nothing more than a kind of concrete, that is, a mix of portland cement, aggregate, and additives. Despite what the contractor's salesmen want you to believe, it is not a mysterious material containing diamonds or secret ingredients. While the aggregate in common concrete (such as is used to pour slabs and sidewalks) is stone gravel in a blend of sizes, in pool plaster the aggregate is fine quartz sand (also called silica sand, quartz being also called silica) or very fine marble dust. These days it is fashionable to use quartz sand which has been dyed with pretty colors, and while the dyeing process involves some impressive chemistry, the plaster itself is not otherwise different in application. Certain chemicals such as calcium chloride (accelerator), gypsum (calcium sulfate, retarder), or lime (calcium oxide, retarder) may be added to improve workability (rheological factors such as plasticity and thixotropy) and to slow or accelerate setting time. The hydration and consequent setting of portland cement is a very complex chain of chemical reactions, which is why the full strength takes many days to develop, and why accelerators and retarders can have profound effects.

Your placement and troweling techniques will be better if you understand how portland cement paste hardens with an "initial set" and a "final set". The initial set occurs within an hour or two of mixing (depending on the accelerators or retarders), and prevents any further handling or placement.

ASTM standard cements are designed to have an initial setting time of not less than 60 minutes, and a final setting time of not more than 10 hours. If you want to scientifically test a product for setting time, you can improvise your own Gillmore (ASTM C266) tester. You first form a pat of cement 3 inches in diameter by 1/2 inch thick on a glass plate (a scrap tile will do). For the Gillmore test, you apply a pin of 1/12 inch diameter weighing 1/4 lb, which will not indent the pat when the initial set has occured, and likewise 1/24 inch and 1 lb when the final set has occured. The pin pressures are 46 psi and 733 psi respectively. The Vicat test (ASTM 191, British standard BS12) is a similar method. Note that this test is specified for the cement paste alone, not the mix of cement and aggregate. Note that the specified pressure for initial set would permit an 250 lb worker to walk on new plaster with only 4 or 5 square inches of footprint.

When working plaster, do not be confused with "false set" or "flash set". This is a stiffening that happens soon after mixing or placement. For example, a bucket of wet plaster will take a false set in a matter of minutes of sitting undisturbed. A bit of agitation (stirring or shaking the bucket) will loosen the mix, and restore a workable product.

Besides setting time, other mechanical properties of cement of interest to the craftsman include porosity and permeability. Porosity measures the size and proportion of volume of pores, which are microscopic voids in the material, and which will typically fill with water under immersion, like a sponge. Porosity is related to water absorption, the volume proportion of water which a sample will hold. Final strength is believed by many authorities to have a negative exponential dependence on porosity (a porous product will be weak, non-porous strong). Porosity ranges from 12 to 38 percent in Type 1 portland cement, corresponding to corresponding compressive strengths of 12 to 4 Kpsi. Porosity should not be confused with voids due to incomplete compaction, and air entrainment from frostproofing admixtures. Permeability measures how quickly water under pressure diffuses through the cement, which for practical purposes in pool plaster is always slowly enough that it doesn't matter. See Analytical Technicques in Concrete Science and Technology, Ramachandran and Beaudoin, 2001, and Concrete Admixtures Handbook, Ramachandran, 1995.

The only ingredients in today's pool plaster that are not of ancient practice are the polymers (fancy name for plastics) which are nowadays added to improve bonding, curing requirements, strength, and chemical resistance. Modern paints contain the same components. These can be present in a dry form as part of the dry mix product, or added as a liquid emulsion as part of the on-site mixing. During curing, the polymer elements polymerize into a surface coating, and in the bulk areas, they form a cross-linked polymer matrix, not unlike paint.

Common portland cement is gray in color, and this accounts for the grey color of fresh concrete slabs. The gray type is cheaper than the white, and thus is used when the finished color is not important. The portland cement used in pool plaster is a white variety, which is slightly more expensive, being made from minerals which are slightly less economical to process. This type is used not only in plaster, but in grouts and colored concrete where the white background is necessary to achieve a decorative color by the addition of mineral pigments.

No too long ago, asbestos fibers were also included in pool plaster to improve the spreadability and final strength, but this has not been allowed in the US since the mid-1970s. However, one should be aware of a possible asbestos hazard if you are grinding and chipping old plaster out of a pool dating back to the era when asbestos was quaintly considered the "wonder material" of modern times.

As an aggregate, marble dust makes plaster that is easier to work than quartz sand, but not as durable. Marble is a soft stone and subject to chemical attack, while quartz is very hard and utterly impervious to pool chemistry. So unless you're a contractor aiming for a quick and cheap job that looks good just long enough to escape responsibility, you want to use the durable quartz sand instead of marble dust.


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## Tscarborough (Feb 25, 2006)

You must have gotten that from a quartz manufacturers website. Finished correctly marble dust is extremely hard and durable.

(not to say that quartz is not a good aggregate, it is, but mostly for looks)


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## superseal (Feb 4, 2009)

I've used Thoroseal with a bit of white sand mixed in...3:1 acryl and steel trowel smooth as a babies you know what.

Sponge float ain't gonna cut it - too abrasive.


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## superseal (Feb 4, 2009)

If your looking for quartz based, try diamond brite

http://www.diamondbritepoolplaster.com/


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## NYCB (Sep 20, 2010)

Well that was a pain right the balls.

I am pretty sure all my knowledge of stucco finishing can be thrown right out the window when dealing with a pool mix.

I screwed around this morning with a few different designs. I settled with basically what internet told me earlier. 1:2 Portland:Sand, I used an acrylic modifier at a low percentage and about a pound of lime per batch because I could not get anything workable without it.

I have no idea how those guys fight off crazing all day, I was battling the entire time to keep it from shrinking, and actually one spot will require a patch in the morning because dad mixed it too wet and I was dumb enough to actually put it on the wall.

I ended up giving it a sanded finish because he is pretty adamant about painting, he doesn't seem to mind the fact that he will be repainting it every other year.

I will let the pool plaster guys stick to pools, and I will stick to a nice fluffy lime mix for houses.


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## hdavis (Feb 14, 2012)

sitdwnandhngon said:


> I screwed around this morning with a few different designs. I settled with basically what internet told me earlier. 1:2 Portland:Sand, I used an acrylic modifier at a low percentage and about a pound of lime per batch because I could not get anything workable without it.


I would have just put more modifier in to get the workability.


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## hdavis (Feb 14, 2012)

Fancis Casini said:


> here I googled this ....


Link was already posted.:whistling


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## NYCB (Sep 20, 2010)

hdavis said:


> I would have just put more modifier in to get the workability.


I didn't want it to flash set on me, it was pretty warm today.


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## hdavis (Feb 14, 2012)

Tscarborough said:


> You must have gotten that from a quartz manufacturers website. Finished correctly marble dust is extremely hard and durable.
> 
> (not to say that quartz is not a good aggregate, it is, but mostly for looks)


It was a DIYer site.

I prefer marble dust for two reasons - workability, and similar erosion rate to cement under normal pool chemistry conditions and no modifier added. The pool surface stays somewhat smooth as it gets etched away. 

For maximum life, use silica aggregate and as much acrylic modifier as it can handle.


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## hdavis (Feb 14, 2012)

sitdwnandhngon said:


> I have no idea how those guys fight off crazing all day, I was battling the entire time to keep it from shrinking, and actually one spot will require a patch in the morning because dad mixed it too wet and I was dumb enough to actually put it on the wall.


They work really fast. A 25000 gallon pool would be less than a half day for applying and tooling the plaster. As soon as the plaster has set up enough to not get messed up by the fill, they start filling it. Garden hose with something like a sock at the end to diffuse the water stream. Fill it too slow and it's hosed. 

When it gets too hot, you don't do pool plastering:laughing:


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## Fancis Casini (Jan 31, 2013)

Tscarborough said:


> You must have gotten that from a quartz manufacturers website. Finished correctly marble dust is extremely hard and durable.
> 
> (not to say that quartz is not a good aggregate, it is, but mostly for looks)


Anyone who plays with rocks knows which is harder, marble or silica. Both are not the wateproofing ingrediant rather it is the portland...."internet is littered with verifcation'' 
Yes aggregate is important and in my saying this,I'd pick the hardest of the two. Pozzalone and or fly ash is key also in stoping salt crystalization...chlorine! 
And as far as the diy site I got the paragraph from I also noted many others that said similar"before I pasted it" ..ie it was on the top of the list and the guy did his homework!

It wasn't me whom started the testosterone contest.....and you should learn to respect those whom are more than just artistic with their hands and not be so quick to correct what one "didnt" say!


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## hdavis (Feb 14, 2012)

Fancis Casini said:


> And as far as the diy site I got the paragraph from I also noted many others that said similar"before I pasted it" ..ie it was on the top of the list and the guy did his homework!


That was the best part of it - he clearly did a lot of research before starting his plastering project.


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## Tscarborough (Feb 25, 2006)

I have great respect for both your skill and your experience, Mr. Casini. I also know many times when experienced masons do a thing for either the wrong reason or just do it wrong, simply on the basis of "I have been doing it this way for 30 years".

I am also willing to admit when I am wrong and learn from it, since I am also getting to the age where I "do things because I have been doing it that way for 30 years".

At any rate, I had my tools out to make some samples so I decided to test it. All I had was some colored PCL type S masonry cement, but it should work fine for this test. 

I mixed 2 samples, one with PCL and C144 masonry sand at 2-1 and the other with PCL and marble dust, also 2 to one. I plastered them 3/8" thick on some old window panes. I will let them cure out for a couple of three days and then drip water onto them. If it is waterproof, no moisture should be visible on the glass side, right?


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## Inner10 (Mar 12, 2009)

T you been hanging out with JohnFWhipple? :laughing:


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## NYCB (Sep 20, 2010)

I started a debate thread...Neat.


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## hdavis (Feb 14, 2012)

I don't think that it's waterproof in the sense that water won't pass through it - it does, slowly. Sand should slow it a *little* compared to marble. Acrylic modifier slows that down even more.

Let's see if I'm going to unlearn something from the test.


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## NYCB (Sep 20, 2010)

hdavis said:


> I don't think that it's waterproof in the sense that water won't pass through it - it does, slowly. Sand should slow it a *little* compared to marble. Acrylic modifier slows that down even more.
> 
> Let's see if I'm going to unlearn something from the test.


I imagine the area will make a difference too. Up here there is almost always water in the ground, so you might get an equalization effect, some water will migrate through the plaster and concrete, but won't really have anywhere to go when it hits moist earth.


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## hdavis (Feb 14, 2012)

...


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## fjn (Aug 17, 2011)

sitdwnandhngon said:


> I imagine the area will make a difference too. Up here there is almost always water in the ground, so you might get an equalization effect, some water will migrate through the plaster and concrete, but won't really have anywhere to go when it hits moist earth.





Just for clarification,is the purpose of the pool plaster / stucco strictly for aesthetics or waterproofing or both ?


If it is for waterproofing could that have been accomplished easier with a integral waterproofer in the concrete ?


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## Tscarborough (Feb 25, 2006)

It is to waterproof the concrete, which is not waterproof alone.


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## fjn (Aug 17, 2011)

Tscarborough said:


> It is to waterproof the concrete, which is not waterproof alone.





Thank you ! That is what I thought. That said,would an integral waterproofing add mixture make life simpler ? The plaster would be more like window dressing as opposed to a primary line of defense.
Also,in conjunction with the add mix,the plaster would provide the "belt and suspender" approach. 


http://www.waterproofmag.com/back_issues/201004/integral.php


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## Inner10 (Mar 12, 2009)

fjn said:


> Thank you ! That is what I thought. That said,would an integral waterproofing add mixture make life simpler ? The plaster would be more like window dressing as opposed to a primary line of defense.
> Also,in conjunction with the add mix,the plaster would provide the "belt and suspender" approach.
> 
> 
> http://www.waterproofmag.com/back_issues/201004/integral.php


I have a job I'm working on right now, although I'm just automating the pool controller and the powered spa/pool cover.

The pool builder used TEC liquid waterproofing and crack prevention membrane on the entire custom built hot tub, then laid tile over it.

I'm guessing doing an entire pool with a membrane would be vastly more expensive than blasting portland/sand mix then troweling flat.


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## Tscarborough (Feb 25, 2006)

Putting the waterproofing behind the concrete is asking for trouble. It will work, but when it doesn't then what do you do? Integral concrete waterproofers certainly work, but then you have to finish the gunite or build formwork that is perfect.

The current method of gunite/forming, then waterproof plaster is the best all around solution.


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## fjn (Aug 17, 2011)

Inner10 said:


> I'm guessing doing an entire pool with a membrane would be vastly more expensive than blasting portland/sand mix then troweling flat.




The integral waterproofer is a different animal from an applied membrane. It is apart of the concrete design mix.


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## Tscarborough (Feb 25, 2006)

Here is your answer: Neither one is waterproof at all. I dribbled a little on the top of each, the sand one soaked in instantly, it took a few seconds for the marble dust (that is why it ran), but not long.


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## Tscarborough (Feb 25, 2006)

Here is my fingernail running across both. Note that I was not able to hard trowel or burnish either, which would have been done in a pool. The sand is very much softer, probably having to do with the larger aggregate size of the marble dust (1/4 to fines) VS the C-144 sand.


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## hdavis (Feb 14, 2012)

My prediction was completely wrong - cool, I learned something new:thumbsup:

Thanks for the test results:clap:


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## hdavis (Feb 14, 2012)

So you're thinking the wider range of sizes in the marble aggregate gives a better packing density, so a slower water movement through the plaster?


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## Tscarborough (Feb 25, 2006)

Next weekend will do 2 more batches and do half of each with each mix. Now that there is a substrate other than glass, I will be able to hard trowel/burnish them, which certainly makes a difference.


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## Tscarborough (Feb 25, 2006)

No, it just makes for a harder mix.

I will also water cure both samples this time.


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## natural1 (Aug 30, 2007)

I have waterproofed several concrete water features. I went to the local pool warehouse and bought a product called mulasticoat. It is membrane type product that brushes on. 

http://multicoat.com/documents/pdf/Instructions/Instructions_Mulasticoat.pdf

The first step is to apply a thuroseal type product then the mulasticoat. The mulasticoat is blue so if you want a different color you can apply another coat of thuroseal or other mortar based material like plaster.

I would be concerned you will have leaking where the walls meet the bottom slab. I assume they were poured separately. Without a membrane I think plaster may crack in this area.

Typically for gunite pools the walls and floors are poured together with a lot of rebar and 6"-8" thick. Also with a psi of 8000 which is close to waterproof (i think).


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