Deep Dive: How to DIY my own underwater hydraulic plaster patch?


New member
Jan 16, 2016
allen, tx
I'm new to actually posting on forums, this is the best place I could find for this topic... hope it's okay.

Pool Patch (edit: name of product) is too expensive, and E-Z Patch is even worse. How do I make my own fast-acting underwater patching compound? Some hydraulic cement products such as carried by Lowes are cheap but I think would turn out grey; I need a white to match existing plaster.

Also patching new plaster onto old it appears has some requirements, like minimum 1/4" thickness.
In my current case i have some small parts flaking off, seems delamination, very thin material like a credit card. only by the waterfall, rest of pool is fine except for some roughening on some parts causing spots of black algae to be there that I couldn't get off last year with steel brush and decent amounts of chlorine. Pool build '93, not sure if ever replastered. Seriously dreading that and want to do as much diy patching as possible + good chemistry to extend the plaster life.
Could the community discuss or confirm the following issues:
- use pneumatic diamond grinder to cut rectangle or polygonal shape around the bad area, to get the 1/4" thickness.
- light chiseling to discover and pop off the weak plaster spots?
- troweling techniques, is there one document containing all the essentials so i can start practicing?
- Joint: Feathering to somehow join the old and new plaster? I read it doesn't work, it sounds like difficulties are there but can somehow be done it seems? This part is a bit mysterious
- flexible high grit diamond pads for smoothening after the patch hardens,

I've mixed self leveling concrete for floor leveling, so I have a feel of slowly adding powder to water on a slow-setting product.

For roughness, would flex pads also be good for smoothing the (mildly) rough spots that attract the black algae? (north TX, typically high calcium hardness in water, i can post my pool strips results here.
I've read about smoothing temporarily working but rough problems coming back soon after. If chemistry is maintained well would such a problem come back? Not sure if roughness is due to CH or to plaster aging.

Thanks for all the help.

Not sure if my signature is active. 1993 pool, 14,500 gal, filtersize is average, 1.5HP main pump, .5HP(?) booster pump w/polaris 280, with strips the CYA used to be typically a bit high like 80 but now appears around 20-40. Backwashing and rain is my best guess for this. No noticeable leaks or waterlevel going down over time.

Getting a proper test kit sounds cool but if the reagents expire/useless after a year.... starts to get expensive . Not sure how dead-on exact I have to be with that to extend plasterlife.