Tips for barrier coating with Interprotect?
So my boat has been out of the water since last October. Upon hauling her last fall, I noticed a band of thousands of little (BB to #2 pencil eraser sized) blisters to about 30'' below the water line. I removed all of the bottom paint, and the gelcoat to fiberglass in the area of the blisters. The bottom is dry (verified with moisture meter) and I would like to barrier coat soon. I have read Interlux's Interprotect instruction manual, but does anyone have any additional tips/advice? Has the interprotect been "kicking off" too quickly on 90 degree days? Would rolling on a coat of low viscosity resin (MAS or similar) help seal the fiberglass, or would this be a wasted step?
Some photos of the bottom ready for barrier coat:
You don't want to try applying interprotect if the temps are much above 75˚ or so.... it kicks way too quickly to make applying it properly feasible. I wrote a post on applying it a while back, which I'll repost here:
Lots of ways to go
West has a material Barrier Coat additive (422) you add to there epoxy and roll on and of course they feel its the best :)
The big item i have seen is they all need to be built up to thickness X (say 20 mils) or they dont work as well
Here's a hint to arrive at a 'smooth' layer of Interprotect. If you ROLL it all on it will have the surface finish equivalent of someone who has a severe skin disease - rough, cratered, uneven - a surface that will create a lot of drag in the water and a surface that will promote uneven bottom paint.
1. Calculate the residual/cured thickness of the barrier - buy that amount plus 15%+. You will need the 'application tech sheet' from Interlux to do this. This will ensure that you will ultimately build up the RECOMMENDED thickness of barrier. Its easy when rolling to develop hills and valleys .... and the valleys may be less than the recommended thickness; leading to premature failure of the coating. Apply less can result in failure of the Interprotect to 'protect'.
2. Roll on the first layer to be sure that all the surface is covered.
3. When the first layer starts to 'kick', take a large polyethylene trowel and with light pressure and with the trowel held at a very shallow angle 'knock down' the tops of the hills, spreading them into the valleys caused by the roller fabric.
4. Roll on additional coats but immediately use a trowel to fill the valleys and 'clear' the now flattened hills. Continue until the surface is FLAT and smooth as a babies ass. (This is how one lays up gel coat on a male plug mold)
Note: the above steps will prevent a lot of needless 'sanding' to remove the surface roughness
5. Allow to 'kick', then immediately begin to apply bottom paint in the same manner ---- first is a roll coat, the following coats are troweled. Called 'hot coating' and will form a better bond between the paint and the barrier. Use a different color on the first application of bottom paint .... later (months) when you see the 'indicator color' coming through in contrast to the subsequently applied different color .... you know that its time to apply more paint - and you dont have to guess about if or not you need to reapply more ablative. Thick layers of accumulated ablative bottom paint ultimately begin to lose adhesion and you get HUGE 'flakes' when the 'previous' layers begin to 'go'. This allow the minimum of (now quite expensive) ablative to be applied to 'do the proper job'.
Advantages: smooth bottom with uniform thickness barrier and uniform thickness bottom paint. Especially if you use an ablative bottom paint you will have more consistent 'ablation', better 'polishing' due to consistent water flow next to the hull, longer life of the bottom paint, less growth and slime, much FASTER BOAT, etc. Caution - this application process has a high learning curve.
Caution: the above barrier application should be a 'continuous' application to allow proper 'chemical bond' between the 'layers'. Typically I lay-up for 2 hours and sleep for 1 hour until 'done' ... sometimes taking more than 24 hours to do a large boat.
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