# Forum Home Renovation Concreting  sealing concrete slab for rising damp

## Wallaby

Hi guys, 
We are renovating an old shack/shed which has a concrete floor (only to be used as holiday home) and we will be building the floor up off the concrete on a new wooden base which should help warm the place up a bit. 
But before we do that, we think there is some rising damp in the concrete already - our builder has suggested that we seal it before he builds up the new floor with a two part epoxy based sealer.  
Wondering if there are any suggestions as to what kinds of products (names etc) would do the job here?  
Would a simple bondcrete work for this purpose (I think not, but someone else is trying to tell me it would work just as well as the two part epoxy) - I have seen the Gripset Betta product called Damp Stop which I think sounds easier to use. 
Any thoughts or suggestions??

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## d00biez

gday mate 
i dont really have any answers but have researching this subject myself for a similar reason. 
things ive learnt so far: 
from what ive heard, you cant completely stop damp rising thru the concrete after its been laid. you may be able to minimise it but it will still come up as concrete sucks up moisture from below and it has to go somewhere. 
most bondcrete concrete sealers are alkaline based and from what i know, are meant to mixed into the concrete prior to pouring. if you apply it over the top of the slab, it reduces back to a milky white liquid once water starts coming into contact with it. i spent $50 on two buckets of it for my slab and it did @@@@ all. 
if you are building a floor over the slab, make sure you put down moisture barrier film. big B has it in two grades, go for the thicker one, its 200u or something (that may be wrong but you'll see the one i mean). its pretty cheap too. 
sorry thats about all and as i say its just what ive heard so may not be factual but i'll be checking back to see what the wiser heads have to say. 
good luck

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## Master Splinter

There's at least one product that I know of available off the shelf in the local Bunnies - $75ish for two litres. 
Other Crommelin stuff for creating a damp proof membrane:  http://www.crommelin.com.au/displayProduct.php?id=%2063  http://www.crommelin.com.au/displayProduct.php?id=%2022 
Or see what is recommended by the people who put down those engineered timber floors. 
However if you are putting a timber floor on joists over it, I'd just lay black plastic and be done!

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## Wallaby

I have been recommended not to put the moisture film down as it will simply cause the existing slab to sweat and pool with water. 
I found a product called Gripset Betta Damp Stop (which is the same as a two pack epoxy paint) but all mixed into 1 tin already, available at Bunnings for $190 for 4 litres (24m2 for 1 coat) - should do 2 coats. But I think I might give this a go with just one coat (kinda compromise as I don't want to spend $500 doing the job 100%, as it really is a quick and nasty fix for a few years for us. 
Thanks for the ideas though - it definately put me in the right direction!!!

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## Moondog55

it may be better to use proper dampcourse material but only under the bearers themselves and make sure there is plenty of ventilation to allow the water vapour to vent out and away, also to use H4 treated  pine as the bearer

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## Black Cat

Yes I would second Moondog's recommendation. If the slab is damp, any sealant you place on it will float off over time due to the moisture that is still wicking up from underneath. Better to treat the floor as a new structure and do the damp-proofing there and provide the ventilation to remove the damp coming up through the concrete.

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