Guys I've coated a polystyrene cave with 3 coated of cement mix but when dry it just crumbles off.

Has anyone that has made a DIY background or the like, had this problem.

What am I doing wrong, is it the mix ratio (sand to cement) or do I just have to seal it when it's dry.


Mark

Hi mate,
not something i experenced personally but have you tried adding pva to the mix or something similar.

I've a question do what fish will you have, would the cement not leach into the tank and effect the water?

Mickey

Well Mickey,

My plan was (if I get it to stick) to leave it in a bucket of salt water and keep doing water changes until it stops affecting the ph of the water. Then bung it into the tank.
Well thats what I've read.?

Hi mate
That is interesting! will you keep us up date on how you get on. I am sorry i can't be more help.

i have a link saved on my other pc which maybe of help about glues but it is sick at the moment and gone for repais when i get it back i will read through it again and if it will help i will pm you. just give me a nudge to remind me next week

Mickey

Mark,
I think that, if the PVA doesn't work your next plan of action would be to consider using a fine mesh to help 'bind' the concrete, perhaps something like the stuff which plasterers use to bind their work in awkward spots, it's almost like a plastic string-formed mesh with square holes about 1/8".
Sorry if this sounds a little vague but the plasterer working on my house used it and I snaffled some of the offcuts.

Alternatively you could let it dry then paint it with non-toxic polyurethane paint/varnish, that should help restrain it against crumbling.
Somewhere on the Forum there are posts from people who have made concrete backgrounds for their tanks - there are suggestions therein on coating the concrete.
One last thought...there is a 'concrete sealing paint' which is sold for people who make ponds from concrete, I would think this would solve not only your 'crumbling' problem but would also seal the whole assembly against leakage of lime or whatever else will leach out...

All this reminds me that when making concrete ponds years before plastic liners became available the pond would be filled up with clean water and then dosed with Potassium Permangenate, changing it daily, but this is no longer available anyhow, I think it has been declared as being carcenogenic.
Just a few thoughts...
John

Thank you men,

@mickey.....if I remember myself I'll give you a nudge

@john.....yea I know the stuff ur on about. The way it is now if I was to seal it with non-toxic polyurethane paint/varnish the brush would knock off most of the cement.

So I'm going to make a mix & slap it on with my hand good and thick to see if it makes any difference. Reason being (i think) is the paint brush is holding onto most of the sand & coating the cave with mostly cement.?? I'll report back later 2day.

Mark,
Here are some links to backgrounds posted by Seamus:

www.irishfishkeepers.com/cms/component/o...w/id,29028/catid,41/

I know that's for backgrounds but the principle could be of assistance?

Also Avonmore did a thread in 'DIY' section about his own work making backgrounds as well, could be worth a look..

I wonder if you made your mix with less sand might that be better? - When I used concrete to coat some Earthenware flower pots years ago (to try to make them look a little more 'natural' I put it on by hand and set stones into it too, but they ended up looking 'less than natural' and broken up for pot drainage - but all my attempts at DIY end up this way, I'm not a DIY person!!!

John

some links on making caves hope these help and i've tried some of them to great effect the first link deals with making aquarium rocks using concrete i think this might be what your looking for?? the second is on using pvc pipes as caves but the third is a cave network background that i personally think looks wicked
www.fishinthe.net/html/section-viewarticle-52.html

aquarium.shuru.com/DIY%20Aquarium%20Cave%20Page%201.

this one looks superb think i'll try this myself soon


www.duboisi.com/diy/BNdiygrotto/bndiygrotto.htm

pm sent zale

also try making a mould from polyst. then burning the polyst. out and recoat the inside. there WILL be more info on this subject soon. matt