strip water proofing membrane

[havabeer69]

so, to cut a long story short I haven't applied an undertile water proofing membrane correctly and as such I need to remove it so I can do the proper prep

the product is crommellins pro-500 WP. I applied it onto some 35mm fibre cement sheets with the idea of tiling a deck (there's no dwelling under the deck but I still don't want water dripping through). but I didn't prime the sheets like I should so the adhesion hasn't been great and its also been sun exposed for a number of months and started cracking/orange peeling.
https://www.crommelin.com.au/product...pid-undertile/



the part that was most sun and weather exposed has come up fairly easy just using hand tools to scrape it up, how ever the last 3rd that is some what protected is proving to be MUCH hard to get up.

i've currently got to hand scraper/jointing knifes and can JUST get under it if i'm lucky
i'm trying xylene to soften it but it just softens the top skin and doesn't help really get the full thickness
acetone does the same as xylene
i've bought a scraper blade for my recipro, this doesn't do too much better on the really stuck down parts and then kicks back and jams the blade into the sheet a few times leaving some decent nicks. it also struggles to "get under" the water proofing. in the poorer adhered it does pretty dam well though.


basically the main thing I've haven't tried is a proper concrete grinder, I'm just concerned as the sheets are quiet soft and i'm worried about digging into them, especially having never used one before (walk behind or hand held)

its not a huge area... the deck is only 18m2 ish with the last 3rd that actually needs more oomf



so is there some magical chemical I can pour on it to soften enough to scrape it up? the xylene appears that you have to just really let it soak in for it to do anything


20250827_161230.jpg

20250827_161224.jpg

20250827_162233.jpg

[r3nov8or]

Given it's so very hard to get off, you might consider priming the area which did come up, and recoating the whole lot?

[ErrolFlynn]

Sandpaper, perhaps. There's an amazing range of wheels available for your angle grinder. Certainly, many are designed to be used against steel, but there might be something softer. Possibly a polishing. A buff type attachment might work. A piece of cloth spinning at high revs will probably cut quite well. You might be able to make up an abrasive wheel yourself. So long as you can run it at a moderate speed. You could try cardboard, canvas, or plastic. It's only paint. You won't have to lean hard at all.

[havabeer69]

Given it's so very hard to get off, you might consider priming the area which did come up, and recoating the whole lot?

this isn't the worst idea though it would probably commit me to using the same brand again


I wonder if I can't use something more like a rapid strip disc and get a whole heap of spots back to FC and prime the lot and go over it again.



might even take Mr flynns suggestion below and use the belt sander on 40 or 60 grit just to scuff up the surface a bit of the existing coat.

[r3nov8or]

I've been frustrated trying to sand some substances. The heat can cause them to soften and clog the sheet pretty quickly. Worth a try with various types of spinning things as suggested by ErrolFlynn