Help! GRP roof is bubbling 6 months on?

[sattira]

Guys I decided to embark on a DIY bay window GRP roof....never again.

Anyway it looked fine and more importantly it's been waterproof ever since. Fast forward 6 months, I have just noticed bubbling on one side? I have no idea why and hope you guys can help.

Will it be fine? No water leaking as I speak.

Secondly, can I sand the bubbles and add another top coat? or Even sand down and add a roll on rubber paint roof?

Was happy with it but now I've seen the bubbles I'm expecting a leak.

Picture attached and guys thanks so much for taking the time to answer.

 

[Rufus Raintight]

Strange one could be a contamination of something, either with the catalyst or the topcoat, strange it's in one spot which may point to a problem with a particular mix or something landing on the topcoat when curing, not sure.

The topcoat layer is to protect the main glass fibre laminate underneath so if this is still intact then the roof should be fine, just sand back the affected area and re-apply a new layer of topcoat.

 

[sattira]

Thanks so much for replying. I did wonder whether it's because of the sun? As in it withstood the worst rain here in Manchester and we had the hottest day on record, what are your thoughts?

As for Sanding..are we talking a very light sand and then a couple of coats of top coat? I don't want to sand too much.

Thanks

 

[^woody^]

Blistering is typically due to air or water - heated by the sun and the pockets expand. This may just stretch the coating a little, or it can stretch it too much to crack it.

It may be the top or base coats, and if the base coat and adhesion is lost, then that will need to be re-done too.

Looking at that image, there seems to be a distinct pattern from the bottom left corner to the top right - looks like water has run and ponded. Are you sure that no water is or has got beneath and ran under the coating?

 

[sattira]

Woody, sorry to sound simple but is there way to check? Pushing it or poking it? I ask because there are no visible leaks inside. I will get my ladder up and take better photos, is there something I should be looking for?

Thanks for your help.

 

[^woody^]

Is there any way or sign that water could be running down the house wall, behind flashing/ upstand and then under the roof in the area of those blisters - or did so before you coated it?

 

[sattira]

Woody I guess there is a chance that water has got in against the wall. I did seal it but I'm going to get up when it's dry and get more pictures.I replaced with a new deck etc so I don't think anything before would affect it.

The roof angles down a lot to that affected area, pools slightly and there is a roof drain in that corner to the left. For a first GRP roof is was complicated. The larger blisters in the bottom corner are against the wall side. I guess from your comments I need to A. try and find a place it's getting in and B. push the bubbles and hope they are soft and only the top coat is affected? Am I right?