Membrane for verandah decking

[AlexS]

Have an open verandah decked in old 1/2" hardiplank, about 35 years old. The joints were sealed with silicon mastic, but have leaked. I've repaired the damage underneath, but to prevent it happening again, I'm looking at topping it with a waterproof membrane.
Membranes seem to come in three types - sheets that you roll out, and one or two-packs that you paint on. I haven't looked at comparitive prices yet.

Does anyone have any experience with these, and recommendations for one versus the other. Any good advice will be much appreciated.

[Bleedin Thumb]

Hi Alex,

Hardies or some other similar co. make a mastic specifically for their fiber cement products. I used it on a small deck at my place and I dont think it leaks after 5 years - but its a non critical storage area so not sure.

Usually with waterproofing membranes I would always go for a roll out type to a paint on one, the trouble is you then have to protecting the membrane, so for this application you may be better of with a flexible paint on type. I think a 2pac will fail as it will be too ridgid.

I'm not an expert in this field mind.(not mind field)

[bitingmidge]

Alex,

A membrane type WILL outperform a paint-on under any circumstance, which is why they are used in all the critical locations, below the water table and in jobs where hydrostatic pressure is going to be a problem.

Next down the line, although I haven't seen too many of late, is the paint-on with fibreglass reinforcing. We used to insist on the reinforcing in the early days of paint-ons because it was a sure way of guaranteeing coating thickness.

Then the paint-ons, which create a a rich tapestry of the price and performance matrix.

A couple of things to watch for:

Make sure if you are going to tile or stick something over the top, that you use compatible product. Most membrane products are formulated to match glues from the same manufacturer, and I've seen LOTS breakdown when a different (non recommended) glue is used over the top.

Make sure you protect the coating from UV. Don't worry, it usually only breaks down over the cracks, so you won't have much to repair!

It needs to be flexible, as the joints are going to move. I would still prefer something with a reinforcing over these areas - a glass mat would be fine.

Avoid the rigid polyester type systems such as those used for bathrooms and wet area sealing, UNLESS they are specifically formulated for outdoor use. As Bleedin says, rigid = BAD.

Any reputable brand will do, but make sure you've got enough coating thickness, and the more you spend the longer it's likely to last.

Don't try to fix it from underneath. It won't work in the long haul. There's a reason that you wear a raincoat over all your clothes rather than under 'em!

Cheers,

P

[AlexS]

Thanks BT & Midge. I was inclining towards the roll-out, although one of the paint-ons with reinforcing also looked good. Will have to check the specs for roll-outs re UV. They say they are suitable for outdoor use, but this will be in direct sunlight. Will have to think about some sort of covering.