Waterproofing of Swimming Pools
PREFACE
When it comes to the waterproofing of swimming pools, constant hydrostatic pressure combined with rigid and porous structure of concrete pose serious challenges for an effective and lasting job.
All water containing and water retaining structures should meet the strictest specifications from the conception to the design and finally the materialization of the project.
THE CONCRETE
Cracks number and width is controlled from sufficient and properly placed steel reinforcement.
Aim for a water/cement ratio W/C: 0,45. Try PCE superplasticizers.
Concrete synthesis, placement as well as curing practices should conform to the local regulations of concrete technology for water resisting concrete.
WATER RESISTING ADMIXTURES
The first successful movement is to use a PCE superplasticizer. This should reduce size, number and continuity of pores.
Pore blockers as silica fume can be used or hydrophobic materials to line the concrete pores and thus reduce capillary absorption by altering the intermolecular forces in the system concrete – air – water.
LEVELING MORTAR
Depending on the smoothness of concrete substrate a leveling mortar layer should be used.
Usually these leveling mortars are quite thin (less than 6mm thick). To reinforce them and increase their adhesion an SBR LATEX is usually used.
A common formula :
Portland cement: 1 part
Moist, sharp sand: 3 parts
SBR Latex: 0,2-0,25 parts
Clean water: as required to achieve desirable consistency.
CONSTRUCTION JOINTS
All not movable joints e.g. new to aged concrete, floor to wall joints, casting interruption joints should be preventively sealed with bentonite waterstops. The same is valid for all through-wall penetrations.
WATERPROOFING OPTIONS
A. FINAL LAYER: CERAMIC TILES
A1. Waterproofing can be effected with one component, cementitious products. In this case they should be gauged with at least 2Kg/sac of 25Kg polymer dispersion (SBR latex or styrene acrylic or polyacrylate).
An SBR latex will:
- Improve the adhesion of the waterproofing layer.
- Help with the curing procedure because it highly increases water retention of the fresh layer.
- Enhance flexural strength and durability.
A2. A much more preferable and safe from a waterproofing point of view solution is the use of flexible, two-component cementitious products. Flexible systems can – unreinforced – bridge cracks of 1,5-2mm. A suitable reinforcement can further enhance this impressive performance.
Reinforcements usually used for such applications are:
- alkali resistant fiberglass mesh fabrics. Indicative type: 60gr/m2 – 4x4mm.
- spunbond, isotropic, polyester reinforcements of various weights.
The former kind of reinforcement is also used with rigid, one–component cementitious products.
Needless to say that use of reinforcement is one-way when substraters are old and with extensive cracking. Reinforced flexible materials can really induce miraculous results in such cases.
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The tile adhesive you will use should be of the appropriate type. Grout the tiles properly using a two-component epoxy, antimold grout.
FINAL LAYER: PAINT
The waterproofing procedure for swimming pools to be painted doesn’t change at all. Everything mentioned in the 2nd part of this trilogy is valid.
Though to get a smoother surface – if desirable at all – one could use a smoothing trowel to finish the final coat of the waterproofing layer.
Any considerations before I apply the paint?
1) First of all check compatibility with the substrate! For example solvent based paint are not generally compatible with flexible cementitious products.
2) It’s time to remember: have you used a vapor barrier? If not, there is a real danger for adhesion reduction and flaking due to the build up of water vapor pressure. Maybe you should seek a solution like a water vapor permeable paint or a special primer to harness water vapor migration.
3) You should respect the minimum time recommended before waterproofing layer is applied (e.g. on a highly alkaline substrate).
4) Just think how many stressing factors your swimming pool paint has to endure! Alkaline substrates, water pressure, various chemicals, mechanical abuse, solar radiation, UVs etc. The paint should be waterproof, resistant to mildew and discoloration and if possible water vapor permeable. It should be both functional and aesthetically appealing!
What paint shall I use?
In the case of new swimming pools there are many options. There are solvent based products or water based products.
There are many kinds of epoxies, acrylic based products and those based on chlorinated rubber. Think carefully what best suits your needs. In case of already painted surfaces check for compatibility.
In a future entry we will see into this matter in detail. For the moment just keep in mind the following:
Some notes on surface preparation
Impeccable preparation of substrates is a must for this kind of applications! Surfaces should be free of dirt, contaminants, foreign matters, biological agents, salt deposits, laitance etc. There are no short cuts, no miracle products!
Cracks, holes and other defects should be remedied with appropriate patching materials.
Depending on the substrate, the following methods of cleaning might be used:
-water blasting
-wet sand blasting
-scrubbing with trisodium phosphate
-etching with a muriatic acid solution
-biocide cleaning
Some tips on paint application
1) Use the right equipment: rolls, brushes, spray mechanisms.
2) Avoid, if possible, summer season. Best seasons are spring and fall. In Greece preparations of hotels take place in spring. Thus end–March to April are maybe the best options.
3) Never work during hot hours and under a blazing sun! Hot surfaces will give blisters! Improperly cleaned surfaces will give blisters. Finally thick layers of paint will also give blisters.
4) Best hours for painting are late morning, after night dew has evaporated. Take care, this is vital! You should stop round 11am and restart after hot hours. The paint should be quite dry before sunset because dampness is lurking in the dark!
5) Always work between 10-30oC.
6) Never work under elevated humidity or if rain is eminent!
7) Play with the sun! Seek shaded surfaces. Usually you can work on east and south sides during morning hours and on the north and west in the afternoon.
Caution: The paint film should be chemically resistant before filling with water. This means that depending on the paint you should wait for 3-5 days.
9) And last but not least! Don’t let many old coats build up! You mortgage the future of the paint! Every now and then do remove all paint layers to reach bare substrate!
Chris Strogilis
http://maconwaterproofing.blogspot.com
About the Author
Civil engineer with postgraduate studies in MBA and Marketing
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