BoatManCave
08-21-2009, 12:56 AM
Perhaps someone there could explain why the gel coat did not stick to the hull.
The hull was prepped with Duratec VE gray primer* and sanded with 220 using a random orbital sander. I then rinsed the hull with a garden hose and large sponge. A week later I blew the hull off with compressed air and gave it a solvent wash with acetone and let it flash off for about ½ an hour. I sprayed gel coat* only on the transom (for a test) using a compressor HVLP gravity feed gun with a 2.3mm tip.
This was the schedule:
Batch Gel coat Duratec clear gloss additive* MekP thinner
1 4oz none 2.5cc none
2 4oz none 2.5cc none
3 4oz none 2.5cc none
4 8oz none 5cc none
5 6oz 2oz 5cc none
6 4oz 4oz 5cc none
_________________
Total Gel mix=36oz
I would guess that each 4oz took two or three coats on the 10 square foot transom. I cleaned the gun with acetone between each batch. The next day I dry sanded the transom down to 1200grit - it looked like a fine piece of white porcelain - I was happy. The total dry thickness was between 22-24 mils (I measured with a micrometer after it peeled off). - I was unhappy.
Before I knew that the gel coat on the transom could be peeled off with a putty knife, and about a week after I did the transom, I sprayed the starboard side of the hull (100 square feet). The prep was the same, and I used up about 2 ½ gallons of gel coat mix. The first 1 ½ gallons was a 4:1mix of gel coat/clear additive (4 parts gel coat to 1 part Duratec clear additive). The remaining gallon was a 50/50 mix. The batches were all 16 oz. The first couple of batches started to kick off in the gun as it was a very hot day and a slow spray - somewhat less than you would get from a spray can of paint, so in the following batches I reduced the MekP to between 1 and 1 ½% and added about 20% acetone (big mistake) to thin it - it sprayed wonderful.
The next day I went to admire the beautiful job and noticed that I missed removing a small piece of tape by the waterline. As I picked this tape off, I noticed that some of the gel coat seemed to be lifting from the hull. With my fingernails I could start removing pieces of gel coat which lifted easily from the hull. I then used a putty knife and could easily slip it under the gel coat removing larger pieces. The next half hour or so, I was using a 12 inch sheetrock blade and removing the gel coat in sheets as large as newspaper pages - it came off easier than any wallpaper I’ve removed from walls. It was when I got to the back of the boat that I tried to see how well the gel coat held to the transom. It held somewhat better, but I was still able to remove it all with a 3” blade.
The back of the gel coat was pure white; the hull was pure gray; little adhesion took place and there was no transfer of primer to gel coat or visa versa.
The hull was prepped with Duratec VE gray primer* and sanded with 220 using a random orbital sander. I then rinsed the hull with a garden hose and large sponge. A week later I blew the hull off with compressed air and gave it a solvent wash with acetone and let it flash off for about ½ an hour. I sprayed gel coat* only on the transom (for a test) using a compressor HVLP gravity feed gun with a 2.3mm tip.
This was the schedule:
Batch Gel coat Duratec clear gloss additive* MekP thinner
1 4oz none 2.5cc none
2 4oz none 2.5cc none
3 4oz none 2.5cc none
4 8oz none 5cc none
5 6oz 2oz 5cc none
6 4oz 4oz 5cc none
_________________
Total Gel mix=36oz
I would guess that each 4oz took two or three coats on the 10 square foot transom. I cleaned the gun with acetone between each batch. The next day I dry sanded the transom down to 1200grit - it looked like a fine piece of white porcelain - I was happy. The total dry thickness was between 22-24 mils (I measured with a micrometer after it peeled off). - I was unhappy.
Before I knew that the gel coat on the transom could be peeled off with a putty knife, and about a week after I did the transom, I sprayed the starboard side of the hull (100 square feet). The prep was the same, and I used up about 2 ½ gallons of gel coat mix. The first 1 ½ gallons was a 4:1mix of gel coat/clear additive (4 parts gel coat to 1 part Duratec clear additive). The remaining gallon was a 50/50 mix. The batches were all 16 oz. The first couple of batches started to kick off in the gun as it was a very hot day and a slow spray - somewhat less than you would get from a spray can of paint, so in the following batches I reduced the MekP to between 1 and 1 ½% and added about 20% acetone (big mistake) to thin it - it sprayed wonderful.
The next day I went to admire the beautiful job and noticed that I missed removing a small piece of tape by the waterline. As I picked this tape off, I noticed that some of the gel coat seemed to be lifting from the hull. With my fingernails I could start removing pieces of gel coat which lifted easily from the hull. I then used a putty knife and could easily slip it under the gel coat removing larger pieces. The next half hour or so, I was using a 12 inch sheetrock blade and removing the gel coat in sheets as large as newspaper pages - it came off easier than any wallpaper I’ve removed from walls. It was when I got to the back of the boat that I tried to see how well the gel coat held to the transom. It held somewhat better, but I was still able to remove it all with a 3” blade.
The back of the gel coat was pure white; the hull was pure gray; little adhesion took place and there was no transfer of primer to gel coat or visa versa.