Hempel Epoxy Primer Undercoat / Light Primer

Delivery from MBFibreglass was next day and entirely reliable.

The Light Primer can be tricky to get a good finish. It is sensitive to humidity and you'll need a good scraper (and bank balance) if you use this in a humid environment. The results when used at above 70% relative humidity are horrible.

The resin component is heavy and on opening the tin it needed a good stir. Allow time to do this - it's important to getting the best out of the product. When you think you've stirred it enough - spend another few minutes stirring – perhaps more than a few.

When mixing with the hardener there’s more important stirring to be done – more active and over a shorter period of time. Once mixed there’s a limited pot life so time is crucial. There’s only one way I found to do this successfully – by mixing small batches (less than 200ml – I found 150ml about right). Larger batches don’t mix properly in the limited time – the heavier resin will sit at the bottom of the tub.

Drying/hardening is sensitive to temperature and keeping ambient temperature above 15C seems to work fine. In Northern Ireland 15C+ can be rare and artificial heat may be needed. Do not use direct heat on to the surface – just focus on the ambient temperature. Using an IR lamp is not advised – it produced disastrous results for me.

There may be a better way of getting the best out of this product and I’d be interested in hearing about it. This primer is not forgiving of errors – when it goes wrong it goes badly wrong – sanding is unlikely to fix it.

Used properly this primer is great. A few basic rules; avoid high humidity, stir well, use small batches, keep the temperature at 15C or above and don’t use direct heat.