Fiberglass lined pool cracking

[youngstructural]

Hello All;

I have a client with a pool which has been cracking through the fiberglass lining. The cracks in the fiberglass are approximately 1.0mm wide, with the mirroring cracks in the concrete below being fine hairline cracks ranging from 0.2mm to 0.5mm.

The pool construction is a cast insitu concrete base, reinforced masonry block walls, and the fiberglass lining already mentioned. It was cast 14 months ago, and used as a warm water pool over winter. There was little delay between construction and fiberglass lining.

The pools is an irregular, approximately 1/3 as wide as it is long, with four cracks occuring where the pool walls are closest to each other, as well as at a difference in slab thickness. The pool is roughly 15 meters long (approx 49') by 5meters (16'), and was constructed without the saw cut joints (control) that were called for.

The concrete cracks are clearly shrinkage cracks, but what about the fiberglass lining? The thickness seems very low, sometimes under 1mm, occasionally down to 0.5mm. The lining was sprayed, and the owner wants to know if the concrete or fiberglass is more likely the cause.

Now, please don't concentrate on concrete shrinkage, slab restraint, etc, etc. I know and understand the concrete shrinkage, but know next to nothing about fiberglass. I presume that the tolerance to cracking is based on thickness, but very much want any guidance and tips anyone might be able to offer. I'm doing my own research, but would greatly appreciate any input that may be offered.

Thanks all,

YS

B.Eng (Carleton)
Working in New Zealand, thinking of my snow covered home...

 

[youngstructural]

So if anyone is curious, it seems that although there is no industry standard on pool liner thickness, the normal thickness ranges from 4.0mm +/- 0.5mm to 8.0mm, with thicker areas being used where cracking is expected in the concrete to which the fiberglass is being applied.

This varies by product and with the proportion of resin, but apparently not down to 1.0mm or less.

I'll post again when I know more, but it looks like the fiberglass is significantly thinner than required.

Cheers,

YS

B.Eng (Carleton)
Working in New Zealand, thinking of my snow covered home...

 

[hokie66]

YS,

If the lining is only 1 mm thick, it really is just resin in those areas. Not much room for the glass reinforcing. Fibreglass lined concrete pools are new to me. As far as I know, pool liners in Australia are welded vinyl. Sounds like the lining was definitely not fit for the purpose.

 

[youngstructural]

Hello Hokie;

Just on annual leave and away from PCs for a healthy break, so my appologies for the long delay in my reply.

Thanks for the opinion; It does coincide with what I have found in my research and looking into the matter... Definately not structural.

Also, your opinion regarding resin content was also correct; The layer is highly resin rich with a low fiber content. Completely non-structural. No surprise at all that it failed.

Cheers,

YS

B.Eng (Carleton)
Working in New Zealand, thinking of my snow covered home...