Surface preperation for Alexseal Topcoat 501 | Guide | Baltic Sails - Progresss through Research
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Surface preperation for Alexseal Topcoat 501 | Guide

Baltic Sails - Progresss through Research
Published by Yannic-Tim Noack in boatworks · 24 March 2021
Tags: refit2021guidepaintalexseal
The three levels of surface prep
Lets open up a concept that I hav ejust decided to come up with for the sake of this entry.
There are three levels of surface preparation:
  1. Bumps, dents and repairs
  2. pinholes and reworking
  3. surface guide
1. Bumps, dents and repairs
This is the first and least work intense part of the process.
It is generally about fixing damage, dents and bumps that accumulated over the year(s). This is also the phase where I will be repairing the wing screw terminals.
The material I will use throughout this whole process is the West System 105 System and the different additives or combinations thereof for different purposes. (I will write an article on those later)
We will be using 407 additive for the majority of the filling in low-stress areas such as the deck and rounded edges along the rail.

You want to progress fast in this phase so you are best off using 80 grit paper for the first works and 120 grit in the final steps of your filling.

But let me tell you, this is only the tip of the iceberg.

Quick Tip: Use a metal ruler and hold it on the surface of the deckto identify high and low spots. Shine a light from the back and you will see the surface proifile by looking at the shadows created.

2. pinholes and reworking
Now - you will, from step 1. above but also from factory, have pinholes.
There is no way you don't have pinholes.

Pinholes by sight
The first step you could take is look at the surface closely, identify small textured spots (open glass is typically a good place to start) and using the same 407 additive we used before, but fairly thin in consistency, fill up the areas that you can already see. Take your time with this step.

Sand after every fairing you did and look at the surface profile. Repeat if necessary.

Using a primer to find pinholes
The previous step was there to take some work off of your shoulders for this step.

Its time for the first layer of paint. But don't see it as that. See it as a small helper to help you nail the surface prep.
Apply one coat of primer of your choice. We always use the Alexseal Epoxy Primer system. This will help you to see all imperfections more clearly because of the more uniform color and surface.

If you start using a primer you could still carry on using the West System fillers but we recommend you use a fairing compound that was developed alongsides your primer. This ensures optimal adhesion and workability later on. Also, if you should accidentally sand through on your final faint job, you won't run the risk of getting any kind of bubbling, this is especially important if you are using Vinyl/Polyester resins.
What to do with the new surface information
You can start off by using a pencil and circle all spots that you can already see. Pinholes and bigger dents should be fixed by filling, bumps should be sanded flat, even if it means sanding through the primer. Remeber to repeat the filling untill there are no pinholes left. We know this takes ages but it is the only way you can achieve perfection in the end.
No more spots? Use a dry guide coat.
Dry guide coat is a form of black graphite powder that will enable you to see any little inperfection on the surface. This may help you, especially if you have bad eyes or work in a badly lit situation.
Be careful with repairs
If your deck/wing has a repair or reenforcement, this may create a natural bulge at the area. Its better to taper that bump off smoothly and and create a flatter contour than sanding the reenforcement flat, as it obviously reenforces something below. (We will soon publish an article on working with carbon and polyester laminates.

Rinse & repeat
This step can be repeated as often as necessary, until you are happy with the results. Always consider that you will be seeing any imperfeection later on the surface of the finished paint, especially if you are using glossy paint and no non-skid.

3. Surface guide
Great! You've flattened out your yurface and fixed any imperfections of it. From now on, we will no longer need 80 grit paper. Only 120 grit and 320 grit will be used from this point onwards.

If your primer is covering all of the surface and no dark spots are shining through more than 50% you are good to continue to the next step. If not, read Finnishing primer:
Finnishing primer
The finnishing primer is the final coat(s) of primer that we are going to paint on. For the primer, it is important that the underlying surface is sanded enturely with 120 grit or residual 80 grit spots. This is just so that it adheres perfectly.
The aim of the finishing primer is to 1. create a sterile surface away from fairing compounds, glass and even coring material for the paint to adhere and flow on and 2. cover any discoloration of the underlying surface and thus, make the final color shine with more depth and contrast.

You can apply up to three more coats of primer but remember to balance weight and quality of the paint job. (meaning try to limit the amount of layers you paint.) If you should find any more imperfections in the surface I recommend you revert to the previous step and fix those first before you carry on.
Surface Prep
Onc you are happy with the way your final surface looks (should be flat and evenly coloured), you are ready for the final paint process.
What you may have observed is that the primer does not leave a smnooth surface but rather a bumpy, textured surface from the roller. The only way to get rid of that is more sanding. Yay!
Using the dry guide coat and 320 grit (or 120 grit if it is a very rough texture, make sure to end with 320 grit though),
sand the surafe perfectly flat, no scratch marks from 80 or 120 grit should be visible. Do that on all surfaces of the are or the paint will not adhere later on and create a water droplet on glass efect because the surface is not keyed enough.

Thats the final countdown.
We have been using paint for two main reasons: weight and repairability/workability.
If you are using gelcoat, you have my full respect. We didn't want to bother with though and we also didn't have the material at hand.

Make sure you clean the surface thouroughly, also removing any debris of the dry guide coat with soapy water and wet sandpaper. Finally go over it again with a surface cleaning solution like the West System 850 cleaner.

The area around you should be entirely dustfree and airflow should be kept at a minimum for the first 90 minutes after putting paint down to reduce duste setteling on the painted surface.
Top tip: If you hang the surface vertically, you will get less dust accumulation on the surface. However, runs are more likely to occurr this way.

The finnishing coat
The finishing coat will be the last step of your project. Its is also the most important.
Paint thin layers and slowly, this ensures a minimum of bubbles enter your paint.

This guide is a very brief, but it is a start.

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