Browse Forums DIY, Home Maintenance & Repair 1 Jun 04, 2010 9:31 am A general question about waterproofing and concrete...If you are putting a topping over existing concrete that is affected by dampness...what is the best additive to use? someone recently said a product called silasec (silicon based) followed by a surface membrane...others stand by bondcrete.... Onc if you're around....any suggestions? thanks heaps PS: I think this topic is in the wrong forum so I've moved to paving and concreting Re: Concreting question 3Jun 07, 2010 12:39 pm I'm not an expert, but two solutins come to mind. The first is 200 um (0.2 mm) polyethylene sheets. This is what they put beneath on-ground slabs to provide a moiste barrier. Cheap, easy to apply and easy to get right. The second solution is waterproof concrete. This is done by adding an admixture such as Xypex. Or maybe go for both. Silasec looks like a surface coating, which means that the polyethylene sheet would be cheaper and just as good. If using a polyetheylene sheet, I'd put a very thin sand layer (5 mm woudl do) to make sure there are not too many puncture poitns forthe sheet. Some are OK. Demolition August 2009, Construction Started September 2009, Completed December 2010 Re: Concreting question 4Jun 07, 2010 10:53 pm Thanks Casa for your reply...the floor will have a topping of about 40mm on top of the existing slab so it will need to be 'keyed' in...does this mean that the plastic membrane will not allow the topping to bond to the slab? I've never heard of xpex but will investigate this product. cheers Re: Concreting question 5Jun 08, 2010 9:41 pm Having the slab keyed in means that the plastic sheet can't be used, at least not beneath the new slab. Sounds like a concrete waterproofing admixture is the way to go. Probably wouldn't hurt to provide back-up protection with either a plastic sheet on top of the slab or a waterproofing coating. Demolition August 2009, Construction Started September 2009, Completed December 2010 Re: Concreting question 6Jun 09, 2010 12:37 pm Thanks casa, sounds like it will have to be an admixture like the one you mentioned....I just wondered if anyone else had used these products and what was the result? I know a flexible membrane will be needed over the top of the slab before tiling...the house has rising damp problem so I need to get the waterproofing right...(I'm guessing the original slab didn't have a membrane but I really don't want to have to jack hammer the slab if I can avoid it. Re: Concreting question 7Jun 26, 2010 11:19 am Oops sorry I missed this one. Hmmm a 40mm topping is going to be a tough one to get to 'bond'. Silasec is cement based. What you need is a primer, but I would expect that with even a primer the topping would have a lot of tension and will most likely 'pop' off. Rising damp is a problem, I think I would go the added expense and remove the offending slab and replace with the membrane as should have been done in the first place. An admix will only help waterproof the topping, if you have moisture as an issue then the hydrostatic pressure will not allow the 'primer' (bonding agent) to cure.... well unless you go for a high tech epoxy, which in the end will cost about the same to replace the slab rising damp will most likely lever the topping off. Does that help? Where you are coming from is where you are going to... Re: Concreting question 9Jun 26, 2010 11:58 am If it is only 6 sq mtrs then I'd remove/replace it. The epoxy primer i was talking about wouldn't be a membrane more of a barrier to stop moisture transuding into the topping. Where you are coming from is where you are going to... It will be neat but you won't have much freeboard. At least they are not weep holes. Are you in a high intensity rainfall region? The regulatory slope is only required… 3 8366 We've had decent weather for last 7 weeks and now the drvieway has been cut out we had an evening of 50mm of rain including all the water from half the street, ground is… 0 4490 Just get as close as you can without hitting the posts. Once you are close to the edge of the path the chance of cracking is minimised. 7 9221 |