Waterproof sealant for garage base.

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Hi,
After some advice/ criticism! I've just finished building a timber garage on a fresh concrete base. There is some water seepage under the garage walls when it rains. I used builders mastic around the structure where the concrete meets the wood, but the water has gotten under it.

I'd cleaned the concrete and it was dry when I applied it. Was my prep just not good enough, or is there a better product for this task?

Thanks.
 
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Is the water getting through the frame or through the frame/base junction?

If the latter, how have you detailed and sealed the junction?
 
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It's coming in where the wooden base meets the concrete base. Would appear to be lifting the mastic and getting underneath the seal.
My prep was ensuring everything was dry, then using a stiff brush to ensure the concrete was dust and dirt free.
 
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This would normally be designed with a mastic seal between the sole plate and the base and this will compress to seal the joint. Retrospectively, it will need a bead of mastic at the joint, but water should not be allowed to run down the frame and over the joint, nor should it be allowed to sit on the base against the joint.

So there should be a drip formed above the base of the frame behind the cladding, and the base (if flat) sloped away from the frame, or the with frame protruding over the base edge.

If you can't design the problem out, it's very difficult to get a seal.
 
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Ah yes, I should have had mastic between the frame and the concrete. That would have done it..
So yes I've tried the bead around the edge and it's not working.
 
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How much bigger is the concrete that the timber? If it isn’t much you could put flashing under/over it like you would on a dormer wall.
 
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How much bigger is the concrete that the timber? If it isn’t much you could put flashing under/over it like you would on a dormer wall.
It varies. 1m on the one side and next to nothing on the other side.
Is there some kind of rubberised paint I could use along the 2 faces? Only other thing I can think of is making some waterproof cement and building up a fillet.
 
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A fillet will help. But remember that the timber will flex and expand/contract seasonally - which could form and open joint. So the most important thing would be to prevent water getting to it in the first place.
 
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Ah yes, I should have had mastic between the frame and the concrete. That would have done it..
So yes I've tried the bead around the edge and it's not working.
Polysulphide mastic ?
 
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Got some Everbuild Weathermate on order. Going to strip back all the mastic and try starting again.
 
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