Sounds like a prep problem causing coating failure. Some additional information regarding what you did might be helpful in diagnosing what the issue is. Some sample questions to answer:
- Were these spot repairs
to existing varnished teak, or did you take all the varnish off down to the bare wood on each piece?
- How did you remove the varnish? Chemicals? Heat gun? Sanding
- How did you prep the wood for the thinnned epoxy
sealer other than sanding
- How long did you leave the wood after final cleaning
before applying the sealer? What were the weather
conditions and what time of day did you apply the sealant
- What did you apply the sealer with?
- What did you do between coats of varnish?
A few general pointers:
- It's all about prep. The cleaner and dryer the wood when you begin application, the better. This is one reason why using a heat gun, if possible, to strip most of the varnish has advantages. It helps to dry out the wood in the process.
- The weather
when you apply varnish is critical. It should be warm and dry, and you need to be careful to apply the varnish with adequate time for it to fully dry before the temperature drops below the dew point at the end of the day. At the same time, avoid applying varnish during the hottest part of the day in warmer weather.
- Thinning varnish to match weather conditions is also critical. If it's hot and sunny out, add more thinner so that the varnish does not wrinkle from the top of the layer drying more quickly than the bottom.
- Put 12 coats on when completely refinishing. Then you can topcoat it every year or as required and get a longer service
life before you need to strip and refinish again.
As far as how to repair what you have, that is going to depend somewhat on what caused the failure.