When a project calls for sanding, one must confirm the correct materials are being used. Reason being is due to the different sizing, backing and grit of the sandpaper. But, how can we identify what type of sandpaper is best? Subjected to the work needed for your project, grit size will come into play. Thus, we must make note that sandpaper is measured by its grit size while others are measured by both the grit and grade of the backing. When buying your sandpaper, check the item to confirm it states the pressure sensitive adhesive (PSA) or the grit and size number. This will help when deciding which one is best for the project at hand.
Sandpaper Grit Sizing: If you are looking to remove a previous material such as gelcoat; begin sanding your surface with a 150 grit or lower. A low grit number determines the coarseness of the sandpaper which will give you the ability to remove materials and coatings. Sandpaper with a grit number in the 200’s and higher would be great for finishes such as buffing, polishing or the removal of small scratches. A high grit number is equivalent to how small the grains are which will allow you to smooth the surface.
Sandpaper Weight Grade: One may see grade letters ranging from A-E which represents the durability of the sandpaper, where E is the strongest. For example, (based on the figure above) the red Mirka Royal 40 grit disc would be ranked as the most durable, next the Mirka Bulldog 120 grit Gold, followed by the gray Mirka Bulldog 400 grit Gold .
Here is a great tip!
If you are looking to conduct a wet or dry sanding, the sandpaper coating must be waterproof. An abrasive that is waterproof will last you longer with end results you’re aiming for in a wet/dry process.
Gelcoat is a big part of our business here at FGCI. When looking at gelcoat, there is a wealth of options to choose from. The most obvious first choice is the color of the gelcoat; we have a vast array of over 25 stock colors with the ability to color match to a sample you provide. Once you have the color figured out, comes whether you want to brush the gelcoat or spray it, as we have the ability to do either. Lastly, however, is the option many people have a question about; interior or exterior. Let’s look at both options so you know which you will want for your job.
Exterior Gelcoat is our tried and true standard. If our gelcoat doesn’t specify interior or exterior, then the answer is automatically exterior gelcoat. It doesn’t mean that the gelcoat is only good for external use, or the outside of a boat, it means, simply that it does NOT have wax or Sanding Aid mixed in. This means that the lack of Sanding Aid will result in a tacky finish. If you want to avoid the tacky finish, you will want to add something like Sanding Aid, Patch Booster or Duratec to the mixture. This is mainly used as your primary coat or coats as you do not have to sand between coats, given you don’t wait too long.
Interior Gelcoat doesn’t mean the gelcoat can only be applied inside, it means it has Sanding Aid or Wax mixed in. Interior Gelcoat is used as a final coat, due to the Sanding Aid allowing it to dry tack-free, it will give a nice finish. You will not want to add Duratec or Sanding Aid to this product. If you use this product as your primary coat and look to add another coat, you will need to sand it first.
Now that you know which product you need, you can buy your gelcoat with confidence. And as always, remember that we are here to help with any questions you have!
Here at FGCI, we look to make common problems easy to solve and make difficult projects doable for the do-it-yourselfer. With that being said, we are introducing an easy solution to a very common question we get; “how do I fix spider-cracks?”
Let me introduce our Spider-Crack Repair Kit, including everything you need to fix those pesky cracks:
- 1 – Cordless two-speed dremel tool, complete with bits to bore out the cracks
- 1 – ½ pint of Gelcoat Putty to fill in the bored out cracks
- 1 – 1 oz MEKP bottle to catalyze the putty (see catalyst chart for amounts)
- 1 – 9” x 11” sheet of 80 grit sandpaper to sand down the repaired area to a smooth finish
Now your spider-cracks are fixed and the surface is ready for the matching gelcoat (not included) to make your repair un-noticeable and the area look like new.
Now, before you simply fix them, you want to make sure the reason the cracks are there isn’t because something is just broken underneath the fiberglass, causing flexing. Make sure you inspect the surrounding area for softness to ensure it’s not flexing too much, causing further cracking.